IVERSITY Ll RAF" 11111111111111111111111 3 00885 0111 This is to certify that the dissertation entitled EFFECTS OF NITROGEN MANAGEMENT ON POTATO YIELD, FERTILIZER NITROGEN UPTAKE EFFICIENCY, AND NITROGEN MOVEMENT IN SOIL presented by Brad Christopher Joern has been accepted towards fulfillment of the requirements for Ph.D. degreein Crop & Soil Science-- Environmental Toxicology MW fl fizz/mu Major professor Date March 13, 1991 MS U it an Affirrmm'w Action/Eq ual Opportunity Institution 0- 12771 PLACE IN RETURN BOX to remove this checkout from your record. TO AVOID FINES return on or before date due. II DATE DUE DATE DUE DATE DUE _1 MSU Is An Affirmative Action/Equal Opportunity Institution omens-9.1 EFFECTS OF NITROGIN’IINIGININT’ON POTATO YIELD. FIRTILIZIR.NITROGIN UPTAKE EFFICIENCY. AND NITROGINIIOVIKINT IN SOIL BY Brad Christopher Joern A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1991 ABSTRACT EFFECTS OF’NITROGFN MANAGEMENT 08 POTATO YIELD, FERTILIXFR.NITROGIN UPTAKF EFFICIENCY, AND NITROGEN MOVEMENT IN SOIL BY Brad Christopher Joern Maximizing fertilizer nitrogen (N) uptake efficiency, while maintaining crop productivity may reduce potential nitrate contamination of groundwater. A two year field ' investigation was conducted to evaluate the effects of applied N on yield, fertilizer N uptake efficiency, and N levels in soil during potato (Solanum tuberosum L. var. Russet Burbank) production on irrigated sandy soils in Michigan. Nitrogen was applied as 15N depleted ammonium sulfate [(Nnazsou at rates of 0, 56, 112, and 168 kg N ha’1 in a single application at planting or in split applications during the growing season. Total tuber yield was maximized with 112 kg N ha“1 and the highest marketable yield was obtained when this rate was split evenly between planting and tuber initiation. Fertilizer uptake efficiency was relatively unaffected by the N treatments. An average of 55 percent of the total fertilizer N applied was measured in whole plant samples taken at onset of senescence, but only about 65 percent of this N was detected in the tubers at harvest. An additional 28 percent of the applied N was found in the soil to a depth of 120 cm, and only 20 percent of this N was found in the 61-120 cm depth. Over 90 percent of the fertilzer N recovered in the soil was in the organic form. Total 1 M potassium chloride (KCl) extractable N measured in the soil to a depth of 120 cm only increased by approximately 11 percent in the treated plots compared to the control. Data collected from soil and petiole samples taken during the growing season indicate that both samples have potential for assessing N sufficiency of potato during the growing season. One M KCl extractable soil N taken to a depth of 60 cm in mid June can detect differences in fertilizer N applied at planting of about 56 kg N ha”, while petiole N may detect differences in applied N as low as 28 kg N ha”. monsoon-rs There are many people responsible for helping me complete my Ph.D. at Michigan State University. Drs. Dick Chase, Boyd Ellis, and Matt Zabik, the members of my guidance committee have all been extremely helpful in sharing their expertise with me in all aspects of my research, as well as giving me the confidence and experience to become a better scientist. I would also like to thank Dr. Maury Vitosh, my major professor, for giving me the opportunity to conduct my research at MSU, and for instilling upon me the virtues of timeliness and organization when conducting research. I would be remiss if I did not express my sincere appreciation to Dallas Hyde, for without his help, knowledge, and experience, I would still be out standing in the field. I would also like to thank Ben Darling and Dennis Duncan, my other cohorts in the field and laboratory. To my beautiful and loving wife Sandra, I could not have done this without you. iv TABLE OF CONTENTS LIST OF TABLES CNAPTER.ONE: INFLUENCE OF APPLIED NITROGEN ON YIELD, QUALITY. AND NITROGEN UPTAKE OF RUSSET EURDANE POTATO ABSTRACT INTRODUCTION MATERIALS AND METHODS General Tuber Yield and Quality Plant Tissue Analyses Soil Analyses RESULTS AND DISCUSSION Tuber Yield and Quality Dry Matter Production Tissue Nitrogen Concentration Tissue Nitrogen Uptake REFERENCES CNAPTER.TNO: INFLUENCE OF APPLIED NITROGEN ON FERTILIZER.UPTREE EFFICIENCY OF RUSSET DUREANN POTATO ABSTRACT INTRODUCTION MATERIALS AND METHODS General Plant Tissue Analyses Soil Analyses PAGE 11 11 12 12 12 16 20 23 28 31 33 36 36 38 39 RESULTS AND DISCUSSION Plant Tissue Fertilizer Nitrogen Uptake Isotope method Difference method Plant Tissue Fertilizer Nitrogen Uptake Efficiency Fertilizer Nitrogen Recovery in Soil Total Fertilizer Nitrogen Recovery REFERENCES CHAPTER THREE: INFLUENCE OF.APPLIID.NITROGEN'ON FALL FERTILIZER.NITROGEN RECOVER! AND PARTITIONING IN SOIL FOLLOWING POTATO ABSTRACT INTRODUCTION MATERIALS AND METHODS General Soil Analyses RESULTS AND DISCUSSION REFERENCES CHAPTER FOUR: POTENTIAL.OF SOILMAND TISSUE SAMPLE ANALTSES AS INDICATORS OF NITROGEN SUFFICIENC! IN RUSSET BURBANK POTATO ABSTRACT INTRODUCTION MATERIALS AND METHODS General Soil Analyses Petiole Analyses RESULTS AND DISCUSSION Soil Analyses Petiole Analyses Total Nitrogen Analyses Nitrate Nitrogen Analyses REFERENCES vi 40 4O 4O 44 46 52 55 58 61 63 65 65 67 69 84 86 88 9O 9O 92 93 93 93 110 110 119 124 TABLE 1.1. 1.3. 1.4. LIST’OF’TABLES TITLE PAGE Initial soil test data from four sites 6 used to evaluate the influence of applied nitrogen on tuber yield and fertilizer uptake efficiency of Russet Burbank potato. 1 M KCl extractable nitrate and ammonium, 7 levels of soil samples taken to a depth of 60 cm prior to planting of Russet Burbank potato. Nitrogen fertilizer treatments used in the 8 experiment. Mean monthly precipitation, irrigation, and 10 air temperature data for the experimental sites. ‘ Effect of N rate and application time on 13 tuber yield and quality of Russet Burbank potato. Effect of N rate and application time on 18 dry matter production of Russet Burbank potato at onset of senescence and harvest. Effect of N rate and application time on 21 percent N in tissue of Russet Burbank potato at onset of senescence and harvest. Effect of N rate and application time on 24 total N uptake of Russet Burbank potato at onset of senescence and harvest. Effect of N rate and application time on 41 fertilizer N uptake of Russet Burbank potato at onset of senescence and harvest by isotope method. vii 3.4. Effect of N rate and application time on fertilizer N uptake of Russet Burbank potato at onset of senescence and harvest by difference method. Effect of N rate and application time on fertilizer N uptake efficiency of Russet Burbank potato at onset of senescence and harvest by isotope method. Effect of N rate and application time on fertilizer N uptake efficiency of Russet Burbank potato at onset of senescence and harvest by difference method. Effect of N rate and application time on fertilizer N and percent fertilizer N applied to Russet Burbank potato found in soil samples taken after harvest. Effect of N rate and application time on fertilizer N and percent fertilizer N applied to Russet Burbank potato recovered in tubers at harvest and soil samples taken to 120 cm after harvest. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the inorganic, organic, and total N pools in soil samples taken after harvest at Montcalm, 1988. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the inorganic, organic, and total N pools in soil samples taken after harvest at Montcalm, 1988. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the total N pool of soil samples taken after harvest. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the organic N pool of soil samples taken after harvest. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the inorganic N pool of soil samples taken after harvest. viii 42 47 48 54 56 7O 71 72 75 76 4.4. 4.5. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the total N pool in soil samples taken after harvest. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the organic N pool in soil samples taken after harvest. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the inorganic N pool in soil samples taken after harvest. Effect of N rate and application time on 1 M KCl extractable N found in soil samples taken after harvest of Russet Burbank potato. 1 M KCl extractable N (as nitrate) concentration of soil samples taken prior to planting of Russet Burbank potato. 1 M KCl extractable N (as ammonium) concentration of soil samples taken prior to planting Russet Burbank potato. 1 M KCl extractable N (nitrate and ammonium) concentration of soil samples taken prior to planting Russet Burbank potato. Effect of N rate and application time on 1 M KCl extractable N (as nitrate) concentration of soil samples taken in mid June. Effect of N rate and application time on 1 M KCl extractable N (as ammonium) concentration of soil samples taken in mid June. Effect of N rate and application time on 1 M KCl extractable N (nitrate and ammonium) concentration of soil samples taken in mid June. ix 78 79 80 82 95 96 97 98 99 100 4.7. 4.10. 4.11. 4.12. 4.13. 4.14. 4.15. Effect of N rate and application time on 1 M KCl extractable N (as nitrate) concentration of soil samples taken in mid August. Effect of N rate and application time on 1 M KCl extractable N (as ammonium) concentration of soil samples taken in mid August. Effect of N rate and application time on 1 M KCl extractable N (nitrate and ammonium) concentration of soil samples taken in mid August. Effect of N rate and application time on 1 M KCl extractable N (as nitrate) concentration of soil samples taken after harvest of Russet Burbank potato. Effect of N rate and application time on 1 M KCl extractable N (as ammonium) concentration of soil samples taken after harvest of Russet Burbank potato. Effect of N rate and application time on 1 M RC1 extractable N (nitrate and ammonium) concentration of soil samples taken after harvest.of Russet Burbank potato. Effect of N rate and application time on total N concentration of Russet Burbank potato petioles. Effect of N rate and application time on percent total N derived from fertilizer in Russet Burbank potato petioles. Effect of N rate and application time on petiole nitrate N concentration of Russet Burbank potato. 104 105 106 107 108 109 111 115 120 CRAPTER.ONE INFLUENCE OF.APPLIED NITROGEN ON YIELD, OUALITT, AND NITROGEN UPTAKE OF RUSSET BURBANNZPOTATO ABSTRACT Fertilizer nitrogen (N) may be managed to increase crop production and profitability while reducing nitrate contamination of groundwater. A two year field .investigation was conducted to evaluate the effects of applied N on tuber yield and quality, dry matter production, and N uptake of potato (Solanum tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. Nitrogen was applied as ammonium sulfate [(NH‘)ZSO‘] at rates of O, 56, 112, and 168 kg ha'1 in a single application at planting or in split applications during the growing season. -Total tuber yield was maximized with 112 kg N ha” and the highest marketable yield was obtained when this rate was split evenly between planting and tuber initiation. Tuber specific gravity was not affected by N rate. Nitrogen rates of 112-168 kg N ha'1 maximized dry matter production and N concentration of the plant tissue at onset of maturity and harvest. The N concentration of the tubers at harvest ranged from 1.3-1.7 percent in three of the four experiments conducted. Values for the fourth experiment were 1.0-1.3 percent N. Total N uptake by whole crop at onset of senescence averaged 92 and 169 kg N ha'1 for the 0 and 168 kg N ha‘1 treatments, 2 respectively. An average of 75 percent of this N was found in tubers at harvest. These results indicate that optimum tuber yield can be obtained with lower N rates than those currently used by most producers, with the potential for minimizing net loss of N from the soil. 3 INTRODUCTION During the past ten years, an average of 20,300 he have been planted to potato (Splanum tuberosum L.) in Michigan, with an average yield of 27.6 Mg ha'1 (Michigan Department of Agricultural Statistics, 1990). Much of the crop is grown in the west central region on coarse-textured soils under irrigation. The liberal application of fertilizer nitrogen (N) and irrigation water when producing the potato crop may be contributing to increased groundwater contamination in the region. There is a need to develop N management strategies for potato that will improve N use efficiency and reduce the nitrate leaching potential of the crop. Previous N studies with Russet Burbank potato in Michigan have produced mixed results. Some research (Vitosh, 1985; Vitosh et al. 1989a; and 1989b) has shown tuber yield increases with N application rates from 225-270 kg N ha”. Other investigations have shown little response in tuber yield to N rates exceeding 134 kg N ha’1 (Vitosh, 1971; Vitosh et al., 1980; Leep, 1988). In Wisconsin Saffigna et a1. (1977) found an increase in marketable yield with a reduction in N and irrigation water from 260 kg N ha'1 and 45 cm to 170 kg N ha"1 and 27 cm, respectively. Leaching through the soil profile was also reduced by nearly 50 percent with the reduced N and irrigation inputs. Establishing optimum N rates and application times for 4 potato is a difficult task. Three to four weeks may be required for crop emergence. During this time, little or no N is takenup by the crop (Lauer, 1985), but if fertilizer N applications are delayed until tuber initiation, yields may be depressed due to poor tuber set (Roberts et al., 1982). Conversely, excessive early season N applications may result in excessive vine growth and delay tuber initiation and the onset of tuber bulking by seven to ten days (Allen and Scott, 1980). Excessive N applications during tuber bulking can promote late season vegetative growth and delay tuber maturity (Ojala et al., 1990). High N during mid season can also promote secondary growth of tubers (Roberts and Cheng, 1985) and reduce tuber specific gravity (Lauer, 1986 and Ojala et al., 1990). Splitting N applications may be an effective management strategy some research has shown that sidedress N applications may be taken up more efficiently than preplant N (Westermann et al. 1988). Split applications may however, induce secondary tuber growth if not managed properly (Roberts et al., 1982). The major objectives of this research were to evaluate the effects of several N management strategies with reduced N inputs on (1) tuber yield, (2) tuber specific gravity, (3) dry matter production, and (4) total N uptake of Russet Burbank potato grown on irrigated sandy soils in Michigan. 5 MATERIALS AND METHODS This study was conducted at two sites during the 1988 and 1989 growing seasons. 'Russet Burbank' potato was planted in a three-year crop rotation of corn - rye cover - potato at the Michigan State University Montcalm Research Farm, Entrican, Michigan in both 1988 and 1989. The second site for the 1988 growing season was located in a farmer's field approximately 5 km southwest of the Montcalm Research Farm, in Stanton, Michigan. The previous crop at this location was cucumber. Both sites were mapped as a Montcalm-McBride sandy loam complex (Eutric Glossoboralfs-Alfic Fragiorthods). The second site for the 1989 growing season was the Michigan State University Soils Research Farm, East Lansing, Michigan on a Spinks-Riddles sandy loam complex (Psammentic Mapludalfs-Typic Hapludalfs) planted to corn in 1988. General soil test data for each site are presented in Table 1.1, and data for preplant 1 M_KCl extractable N are located in Table 1.2. The experimental design was a randomized complete block with four replications of six N treatments selected for the study (Table 1.3). Each plot consisted of four rows 0.86 m wide and 15 m long, except for the second site in 1988 where plots were three rows 18 m long. The crop was planted as whole seed or seed pieces weighing approximately 100 g placed 25 cm apart. Aldicarb {2-methy-2- (methylthio)propanal-O-[(methylamino)carbonyl]oxime} was 6 Table 1.1. Initial soil test data from four sites used to evaluate the influence of applied nitrogen on tuber yield and fertilizer uptake efficiency of Russet Burbank potato. Bray-1 --Exchangeable-- Organic _Ia::___L9£a§ign______nfll., P E___r1§e_____fln___flattsz C -----kg ha" ------ -§- cmol ’ kg"r 1988 Montcalm 5.6 672 332 806 120 1.9 6 1988 Stanton 5.7 1064 296 734 131 1.4 6 1989 Montcalm 6.2 597 305 853 151 1.7 5 1282 flag; Lagging 1.1 221 2§Q 1365 233 1.6 4 .amxz a.ceucso uh auuaansooum uo Ao>oa mo.o on» as accumumqo addendumqueun uoc ou03 heaved case on» an oesoHHOH aos~e> Ca” IIImm4maIIIlnuqqmuunlnqaqmanlrnnqu.o us.~ «6.8 u~.m mo.~ ma.~ a oo.on om.v eH.eH o«.m no.“ oq.m em.m ed.“ ee.e m em.e~ ofl.e ae.m~ «H.6H an.~ em.” ov.e ao.~ no.m v un.os no.6 an.~u ao.oH um.n no.e oe.e «H.~ en.m n o~.os o¢.m om.oa on.HH on.e no.9 em.e u~.~ no.n « us.su no.m ca.~a an.o as.“ ad.o em.o aa.~ «6.6 H Amuuqawaumamsauqimaquqqqnmumu as.e~ eo.m~ an.oH am.HH an.o no.m a~.«~ ae.s em.e o on.o~ ov.m «a.» uo.a no.¢ a¢.e an.e no.n am.n m um.ou uo.m om.m oe.m u~.o no.m em.o em.» um.n e no.o~ «H.HH um.a ca.o no.4 am.m «p.6H as.» no.n n as.nu ue.n~ «5.6 an.«« «8.8 no.» an.o «6.6 up.“ A am.mfl no.6 am.o ao.a ao.e no.m em.o no." am.n H 4aowmquluuamaququaauuuamm an.mp uo.¢fl an.ao as.m~ an.m am.os an.om ee.o em.ne o us.oo ae.ma u¢.oe «H.«~ um.m no.6” ao.on e~.o um.mu m um.~o no.4” an.ev on.e~ no.m am.os ao.en a«.m ao.ma e no.mm «p.6H no.6m ue.m~ no.8 us.mfl am.on ue.o n~.Hn n co.ep e~.mH ao.om nu.e~ «H.o «H.- no.6. ¢H.m «p.5n a no.mu u~.nfl no.«m am.«~ uH.m ue.e~ an.ne a«.o eu.mn a 4unwoaumuuaamaququqmuqquu um.on ae.na a~.m« em.en no.5 am.oa «H.H« no.6 «p.4H o em.co ao.ms em.mu no.e~ no.6 au.ss ae.«a ev.o «n.4H m am.«e «H.mH ae.eu em.o~ an.e a«.HH no.4“ no.» «n.6n c no.«e aa.vn ae.ea em.ms an.» ca.- an.«« no.6 am.mu n oe.on no.«~ ea.m~ am.pu am.6 no.as no.6" an.o em.vn « ee.mn oe.e~ oe.va no.pn an.e em.o~ a6.«« «4.5 au.¢n H 4uuquqqluuaaaauqleaqmucqa .u: z ox - H38. «unilaouIJj .ofl sauce : usurnuuuu oouo ritual--- unruuuuun oouan ruins--- unnnuuuuu o no nurtuuuuu nausea-u» an nonunouuou nudes added. soon a mo sumac e on case» madness Adam «0 cameoH asacoaae one avenues odoeuoeuuxe Hon x n .N.H canes 8 Table 1.3. Nitrogen fertilizer treatments used in the experiment. N application time N N fertilization rate fertilizer At Tuber TI+ TI+ Total _IIleImanL___D1anIin9__iniIieIi2n_iIIl__%iT§e¥§__2§_Q§¥§ N kg N ha' 1 -— -- -- -— 00 2 56 -- -- -- 56 3 112 -- -- -- 112 4 56 56 -- - 112 5 56 56 56 -- 168 _____§, 28 433 28 28 112 9 applied at planting (3.36 kg active ingredient ha”) for insect and nematode control. weeds were controlled with pre-emergent applications of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2- methoxy-1-methylethyl)acetamide] and metribuzin [(4-amino-6- (1,1-dimethylethyl)~3-methylthio)-1,2,4-triazin-5(4H)-one] at 2.24 and 0.56 kg active ingredient ha”, respectively. All plots received approximately 50 kg P and 90 kg K ha‘1 in a band approximately 5 cm below and 5 cm to the side of the seed piece at planting. Foliar applications of fungicides and insecticides were made as needed at all sites. Irrigation was applied based on precipitation and evapotransipiration according to Vitosh (1984) (Table 1.4). Ammonium sulfate [(NHQZSO‘] was the fertilizer N source applied to the crop. In 1988, approximately one third of each plot received natural abundance (NH‘) 280‘ fertilizer while the remaining two thirds of each plot received 1sN depleted (0.005 atom a "10 (1:3,) 2so . In 1989, each plot received only 1sN depleted (0.005 atom % 1sN) (NH‘)ZSO,.. The 15N depleted fertilizer was applied as a 40 percent by weight (NI-1‘) 280‘ aqueous solution with a backpack sprayer regulated to 4.35 kPa with a (202 tank. Nitrogen at planting was applied in a band 5 cm on each side of the seed piece and lightly incorporated. Nitrogen applied at tuber initiation was banded to the side of the plant and irrigated, while the final two fertilizer applications were 10 Table 1.4. Mean monthly precipitation, irrigation, and air temperature data for the experimental sites. Rainfall Irrigation Temperature ._Lesatien_______flsnth mm °c Jim 15.198: 1298mm 19.6.8 1mm Montcalm April 46 68 -- 5 7 May 13 66 -- 16 13 June 14 79 114 20 18 July 62 59 133 23 21 August 87 107 70 23 19 September 136 119 -- 16 15 TOTAL. 358 498 311 Stanton April 48 68 - 5 7 May 15 66 -- 16 13 June 10 79 126 20 18 July 38 59 62 23 21 August 130 107 38 23 19 September 126 119 -- 16 15 TOTAL 367 498 226 Lensztenm L289:§££m 1282mm 1282 1282mm Montcalm April 62 68 - 7 7 May 68 66 -- 12 13 June 123 79 -- 19 18 July 21 59 112 22 21 August 140 107 36 19 19 September 34 119 - 14 15 TOTAL 448 498 148 East Lansing April 41 73 -- 7 8 May 163 65 -- 14 14 June 83 89 -- 19 19 July 31 71 114 22 22 August 171 77 - 21 21 September 87 65 -- 16 17 11 topdressed along each row and immediately irrigated. Tuber Yield and Quality: The center rows of each plot were harvested in mid September at each site both years. Tubers were graded into oversize (>281 g), 'A' grade (114-281 g), oversize + 'A' grade, (U.S. number one), 'B' grade (<114 g), and offtype (secondary growth, soft rot, etc.). Tuber specific gravity was measured by the weight in air/weight in water method (Gould and Plimpton, 1985). Plant Tissue Analyses: The tops and tubers of three consecutive hills (0.76 cm of row) within the harvest rows were taken in mid August approximately 80 days after emergence for total N analysis. The samples were taken when the plants began to show signs of senescence. Previous research has shown that total N uptake is generally maximized between 80 and 100 days after emergence (Jackson and Haddock, 1959; Saffigna and Keeney, 1977). These samples were separated into tops and tubers, cut to facilitate drying, and dried in a forced air dryer at 55-60°C. The dried samples were then weighed and ground to pass through a 1 mm mesh screen. 'A random sample of 20 tubers within the harvest row was taken at harvest for total N analysis. These samples were also cut, dried at 55-60%:, weighed, and ground to pass through a 1 mm mesh screen. A subsample of each tissue sample was ground to < 250 um, and 12 analyzed for total N using the method of Harris and Paul (1989). Dry matter production, tissue N concentrations and total N uptake by the whole crop, tops, and tubers, at onset of senescence, and tubers at harvest were determined from these values. Soil Analyses: Soil samples (3-5 cores 5 cm in diameter) were taken to a_ depth of 120 cm from each plot prior to planting. These ' samples were separated into 0-30 and 31-60 cm increments. Soil samples were air dried, ground, and stored in cardboard boxes until analysis. Each sample was extracted with a 1:4 mass:volume (m:v) soil:1 M KCl aqueous solution for inorganic N (N03 and N11,) using a shaking time of 60 minutes. The extract was filtered through Whatman No. 2 filter paper that had been prewashed with 10 mls of the extracting solution and analyzed using a flow injection autoanalyzer (Anonymous, 1988). RESULTS AND DISCUSSION Tuber Yield and Quality: Tuber yield, size distribution, and specific gravity data for all experiments are presented in Table 1.5. In 1988, no significant increase in total tuber yield was observed beyond 56 kg N ha'1 (Treatment two) at the Montcalm Research Farm. However, 112 kg N ha” applied in an evenly split application between planting and tuber initiation (Treatment 13 Table 1.5. Effect of N rate and application time on tuber yield and quality of Russet Burbank potato. Fresh weight of tubers N Tuber size distribution fertilizer Over A 0.8. 8 Off Specific WWW OUIOUNH OM‘UNH (BUI5UNH M‘UNH 30.8 c 34.8ab 34.6ab 36.0a 34.5ab 33.3 b 43.4a 45.7a 50.7a 53.1a 51.2a 56.8a 20.0 c 28.6 b 37.1a 35.6a 36.3a 30.0 b 24.3 38.7 c 43.6 bc 50.2ab 52.2a 18.7a 20.8a 20.7a 21.8a 19.9a 19.4a 24.5a 23.9a 24.0a 26.5a 24.5a 24.8a 10.4 c 16.8 b 26.0a 25.1a 24.6a 17.6 b 17.9 c 27.0 b 32.4ab 36.8a 37.2a 18.1 28.6 c 34.3 bc 40.3ab 41.9a 6.0a 6.9a 6.4a 6.6a 7.1a 6.8a 4.9a 4.4a 5.4a 5.7a 4.5a 5.5a d 3.8a 4.6a 4.9a 4.5a 4.6a 6.0a 6.7a 6.9a 6.9a 6.7a 6.5a 13.4a 15.8a 19.8a 18.1a 18.7a 22.0a 0.8a 1.2a 1.7a 2.1a 2.1a 1.8a 2.4a 5.5a 4.4a 5.5a 5.7a 1.068a 1.070a 1.070a 1.067a 1.067a 1.068a 1.072a 1.075a 1.076a 1.077a 1.073a 1.073a 1.079a 1.080a 1.081a 1.079a 1.077a 1.079a 1.081a 1.083a 1.083a 1.084a 1.083a Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 14 four) resulted in a significantly higher total tuber yield than treatment six, where 112 kg N ha” fertilizer N was "spoon fed" to the crop. Marketable tuber yield (U.S. number one) was not significantly increased by any of the treatments, but oversize tuber yield was significantly greater for the 112-168 kg N ha'1 treatments when compared to the control (Treatment one). No significant response in tuber yield to fertilizer N was observed at the Stanton site in 1988, but yields at this location were much higher than at the Mentcalm site. In 1989, tuber yields were more responsive to the N treatments. At the Montcalm site, total and U.S number one tuber yield was significantly increased with N rates up to 112 kg N ha”, with the exception that treatment six had a lower yield than treatment four, or treatment three, when all of the N was applied at planting. No significant increase in tuber yield was observed with the 168 kg N ha'1 treatment (Treatment five), except for a slight increase in oversize tuber yield. Treatment four had the lowest B grade tuber yield, resulting in the highest percentage of U.S number one tubers (75 percent). "Spoon feeding" the fertilizer N to the crop (treatment six) produced significantly lower total and U.S. number one tuber yield than the other 112 kg N ha'1 treatments. At the East Lansing site, total and U.S number one tuber yield was significantly higher for treatment five than 15 all treatments except treatment four. Treatment four produced yields similar to treatment five, but treatment five had a slightly larger oversize tuber yield. Tuber specific gravity was not influenced by the N treatments at any of the locations, but specific gravity measurements in 1988 appeared to be slightly lower than in 1989. In 1988, preplant soil inorganic N levels were much higher than 1989 (Table 1.2). These elevated soil N levels, coupled with the lower than average rainfall and higher than average temperatures may all have contributed to a lack of tuber yield response to the fertilizer N treatments, particularly at the Stanton site. The warm, dry growing season may have promoted organic matter mineralization which released inorganic N without subsequent leaching of this N below the root zone. An extremely wet fall following the 1988 growing season may have been partially responsible for the lower inorganic N levels in the spring of 1989, as much of the inorganic N may have been leached during the fall rains and the spring thaw. Hill (1986) found that 50 percent of the N loss in soil can occur during the winter and early spring period. The higher yield of the control plots in 1988 compared to 1989 supports the idea that initial inorganic N levels and early season precipitation may have a significant influence on whether yield response to fertilizer N is likely. 16 In the experiments where a response to fertilizer N was evident, treatment four generally produced maximum total and U.S. number one tuber yield. Other researchers have found Russet Burbank yield response to fertilizer N from 134-340 kg N ha” (Bundy et al., 1986; Carter and Bosma, 1974; Gardner and Jones, 1975; Lauer, 1985; Roberts and Cheng, 1985; Saffigna et al., 1977; and White and Sanderson, 1983). The benefits of split applications were particularly evident in 1989. The higher rainfall, especially in May and June, may have contributed to significant N leaching beyond the root zone of the crop prior to canopy establishment and the onset of net negative evapotranspiration. "Spoon feeding" N to the crop (Treatment 6) does not appear to be an acceptable strategy for potato production in Michigan. Previous research has produced similar results regarding timing of N applications. Hansel and Locascio (1987) found two thirds of the N should be applied at planting for . maximum.yields. Vitosh (1971, 1985) concluded 67 kg N ha‘1 applied at planting followed by 134-202 kg N ha'1 at billing maximized Russet Burbank yield, but 134 kg N he“1 at planting produced near maximum yield in Michigan. Dry Matter Production: Date for dry matter production of whole crop, tops, and tubers at onset of senesence and tubers at harvest are presented in Table 1.6. For the 1988 growing season, the N 17 management treatments had very minimal effects on dry matter production. A significant increase in vine yield at onset of senescence was evident up to the 112 kg N ha'1 rate at the Montcalm site. Since whole crop dry matter production was not significantly different between the treatments, these differences may be attributed to a higher partitioning of the dry matter to the tubers in treatments one and two. Visual inspection of the plants at the time of sample collection revealed that the vines of these two treatments were slightly more senescenced than the other treatments in the study. Dry matter production of the tubers at harvest was higher for all N rates when compared to treatment one at the Montcalm site, but no significant differences between the N rates were observed. These data are supported by the lower fresh weight total tuber yield of treatment one when compared to the other treatments at this location. No significant differences in dry matter production were observed at the Stanton site. In 1989, the fertilizer N treatments had a much greater influence on dry matter production. For the Montcalm site, treatments three and five had a significantly higher whole crop dry matter production at onset of senescence than treatments one and two. Splitting the fertilizer applications at the 112 kg N ha'1 rate (Treatments four and six) resulted in intermediate dry matter production. These differences in whole crop dry matter uptake were due to vine 18 {Table 1.6. Effect of N rate and application time on dry matter production of Russet Burbank potato at onset of senescence and harvest. Dry matter production N Time of sample collection fertilizer -----Onset of senescence ------- Harvest g plant"d 207.4a 243.4a 250.5a 211.6a 237.5a 224.7a 183.5a 212.3a 213.5a 181.3a 175.9a 197.4a 165.4 b 160.7 b 215.8a 198.9ab 223.4a 185.5ab 153.1 d 185.2 cd 250.9ab 253.1ab 279.2a LUIQUNH GillfiUNH GMbUMH OMhNNH 31.9 c 53.8 b 82.3a 67.5ab 76.3a 64.6ab 46.5a 66.4a 74.0a 66.8a 69.8a 74.7a 31.6 c 30.9 c 49.6ab 44.2 b 58.3a 47.6ab 175.5a 189.6a 168.2a 144.1a 161.2a 160.1a 137.0a 145.9a 139.5a 114.5a 106.1a 122.7a 133.8a 129.8a 166.2a 154.7a 165.1a 137.9a 124.7 c 154.1 bc 203.3a 208.1a 214.8a 129.8 b 149.1a 148.7a 150.6a 146.1a 141.1a 181.9a 193.1a 233.8a 244.9a 230508 254.6a 87.9 c 125.6 b 162.7a 156.4a 160.2a 131.5a 107.3 d 169.5 c 191.3 bc 220.3ab 228.8a WW Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 19 growth as tuber dry matter production was not affected by the N treatments at this sampling date. Treatments one and two, which again showed visual symptoms of slightly more advanced senescence than the other treatments, had the lowest vine dry matter yield at this sample date. At N rates greater than 56 kg N ha”, no significant differences were observed, with the exception that treatment five had a significantly higher vine dry matter yield than treatment four. For the tubers at harvest, treatment two had a significantly higher dry matter production than treatment one, but lower than the other treatments. No significant difference in dry matter production of the tubers at harvest was found between the 112-168 kg N ha'1 rates at the Mentcalm site. At the East Lansing location, dry matter production was very responsive to the N treatments. Whole crop dry matter production at onset of senescence was increased up to the 112 kg N ha“, but there was some evidence that treatment six was not as effective in producing dry matter as treatments three and four. Vine dry matter production was maximized with treatment five. No significant differences in tuber dry matter production at onset of senescence were observed beyond 112 kg N ha”, regardless of application strategy. Tuber dry matter production at harvest was maximized with treatments four and five. The other 112 kg N ha'1 treatments showed some evidence that they were not as 20 effective as treatment four in producing tuber dry matter. This same trend was also observed in the total fresh weight tuber yields (Table 1.5). Tissue dry matter production was lower than found by Saffigna and Keeney (1977). The average dry matter production values combined over all experiments for treatment five at onset of senescence (168 kg N ha'1 in three splits) were compared to the average dry matter values for 77 and 85 days after emergence for the "improved” (170 kg N ha'1 in numerous splits) treatment of Saffigna and Keeney. Dry matter values for the vines and tubers were 70 and 79 percent of those found by Saffigna and Keeney. The tubers at harvest were also approximately 70 percent of their values. Tissue Nitrogen Concentration: Tissue N concentration data for all experiments are presented in Table 1.7. The percent N in the tissue of Russet Burbank potato was significantly influenced by the N treatments in three of the four experiments. In 1988, at the Mentcalm location, vine N concentration was maximized at the 112-168 kg N ha’1 rates, but treatment six had a significantly lower vine N concentration than treatments three and five. No differences in tuber N concentration were observed at the onset of senescence. At harvest, the N treatments with split applications had Table 21 1.7. Effect of N rate and application time on percent N in tissue of Russet Burbank potato at onset of senescence and harvest. Total N N -----Time of sample collection ----- fertilizer Onset of senescence Harvest __§reatmant V1831 Tubers Tubg;§____ l 1.27 d 1.44a 1.53 b 2 1.92 c 1.52a 1.54 b 3 2.88a 1.52a 1.60 b 4 2.65ab 1.61a 1.75a 5 2.87a 1.51a 1.75a 6 2.47 b 1.57a 1.76s 1 1.66 b 1.01 c 1.19 b 2 1.88 b 1.18 bc 1.43ab 3 2.29a 1.28ab 1.55a 4 2.36a 1.26ab 1.50a 5 2.63a 1.45a 1.50s 6 2.40a 1.27ab 1.48a W12”. 1 1.13 d 1.53 b 1.32 c 2 1.38 cd 1.54 b 1.32 c 3 1.58 bcd 1.67ab 1.39 c 4 1.83 bc 1.60 b 1.45 bc 5 2.41a 1.83a 1.66a 6 2.13ab 1.78a 1.57ab 1 1.35a 0.92a 1.03a 2 1.33a 0.90a 0.95a 3 1.29a 1.07a 1.03a 4 1.29a 1.07a 1.07a 5 1.62a 1.15a 1.29a 1. 1,17 __1 M a— Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 22 significantly higher tuber N concentrations than treatments where all of the N was applied at planting. For the Stanton experiment, vine N concentration also increased up to the 112 kg N ha’1 rate, but no significant differences between application strategies were observed. For the tubers at onset of senscence, no significant differences in N concentrations were detected between treatments two and the 112 kg N ha” treatments, or treatment five and the 112 kg N ha'1 treatments, but the N concentration was significantly greater for treatment five than treatment two. Tuber N concentration at harvest was not significantly increased beyond the 56 kg N ha'1 rate in this experiment. In 1989, vine N concentrations at the Montcalm site were maximized at the 168 kg N ha'1 rate. For the 112 kg N ha'1 treatments, split applications appeared to increase N concentrations of the vines, which is in contrast to the same location in 1988, where split applications showed a trend towards lower vine N concentrations. Tuber N concentrations at onset of senescence were maximized at the 112-168 kg N ha” rates, but treatment four had a significantly lower tuber N concentration than treatments five or six. At harvest, a trend similar to that observed in 1988 was evident, as the treatments with split applications generally produced tubers with higher N concentrations than the other treatments. No significant 23 differences in any of the measured tissue N concentrations were observed between treatments at the East Lansing location in 1989, and the actual N concentrations of the various tissues were significantly lower at this site than at the other locations. Tuber N concentrations at harvest were about 1.3-1.7 percent with the exception of the East Lansing experiment in 1989, and the control treatment at Mentcalm in 1988, where the values were much lower and ranged from approximately 1.0-1.3 percent. Other researchers have found tuber N concentrations at harvest from 1.2-1.5 percent (Liegel and Welsh, 1976; Saffigna and Keeney, 1977). Tissue Nitrogen Uptake: Data for N uptake of the plant tissue samples collected for the investigation are presented in Table 1.8. Tissue N uptake was signifcantly influenced by the N management treatments in all experiments. At the Mentcalm site in 1988, whole crop N uptake was significantly higher for treatments two through six than for treatment one. Treatment three had a greater N uptake than treatment two, but no significant differences in N uptake were observed between these treatments and the other treatments receiving N. As with the dry matter production data, these differences in N uptake are due to the vines, because no differences in tuber N uptake at onset of Table 24 1.8. Effect of N rate and application time on total N uptake of Russet Burbank potato at onset of senescence and harvest. Fertilizer LMfiUNH OMDUNH OMbUNH OMhUNH Total N uptake Time of sample collection ----- -Onset of senescence------- WWW—Aban— HWOSU 133.8 c 18.8 115.0a 90.6 c 180.6 b 47.7 d 132.9a 105.3 b 226.1a 108.9a 117.2a 108.3ab 186.9ab 81.3 bc 105.6a 120.4a 210.3ab 99.6ab 110.7a 116.5a 187.6ab 73.0 c 114.6a 113.5ab 97.3a 34.9 b 62.4a 98.3 c 135.1a 55.9ab 79.2a 124.2 bc 156.8a 76.0a 80.8a 164.4ab 136.8a 72.1a 64.7a 163.7ab 154.4a 85.5a 68.9a 155.1ab 155.4a 84.2a 71.2a 171.5a 110.2 c 15.8 c 94.4a 53.6 d 110.8 c 20.4 c 90.4a 75.2 c 162.8 b 36.2 b 126.6a 102.9 b 149.2 b 36.5 b 112.7a 102.9 b 199.4a 63.3a 136.1a 121.4a 157.8 b 46.8 b 111.0a 93.9 b 46.4 c 12.4 c 34.0 b 46.1 d 58.9 c 12.1 c 46.8 b 61.5 c 89.7 b 19.7 b 70.0a 85.0 b 86.8 b 17.8 bc 69.0a 82.4 b 111.0a 33.6a 77.4a 104.9a §§‘§_h 19.2 b §§,§a 79.9 b Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 25 senescence were observed at either location in 1988. The lower dry matter and tissue N concentrations of the vines for treatments one and two are reflected in their 'substantially lower N uptakes than the other treatments. Treatment three had the highest vine N uptake at onset of senescence for the Montcalm experiment. At Stanton, no difference in N uptake for the whole crop at onset of senescence between treatments was observed, and only a slight increase in vine N uptake was evident beyond the 56 kg N ha'1 rate. At both locations in 1988, N uptake by the tubers at harvest was influenced by the N treatments. This N uptake was maximized with 112-168 kg N ha”, and it is these values that reflect N removed from the system at harvest. In 1988, treatment five at the Montcalm site was the only case where N applications exceeded N removal by more than 50 kg N ha“. In 1989, the relative response in tissue N uptake to the N treatments was virtually identical for both experiments, but actual N uptake for the East Lansing location was much lower than any of the other experiments in 1988 or 1989. Whole crop N uptake at onset of senesence was maximized with 168 kg N ha”, and all of the 112 kg N ha"1 treatments were significantly higher than treatments one and two in both experiments. This same trend was observed for the vines except in the East Lansing experiment, treatment four did not have*a significantly greater N yield than treatments 26 one and two. No statistically significant differences were found for N uptake by the tubers at onset of senescence at the Montcalm experiment. At the East Lansing location, no increase in N uptake was detected at N rates greater than 56 kg N ha”. Tuber N uptake at harvest was very responsive to the N treatments at both locations. Increases in N uptake were observed for each increase in N applied, but no differences between the 112 kg N ha'1 treatments were observed. As in 1988, only treatment five appeared to have N applications that were substantially higher than N removal. This was even true for the East Lansing experiment where total N uptake was substantially lower than the other experiments. From the N uptake by the tubers at harvest and the total fresh weight tuber yield, approximately 29 kg N are required for 10 Mg of tuber yield. This value was computed excluding the East Lansing location in 1989, as the values for percent N in tissue and total N uptake are so low as to be questionable (only 18 kg N would be required per 10 Mg of tuber yield at this location). Kunkel et. a1 (1973), and Saffigna et. al (1977) found values of 30 and 28 kg N per 10 Mg, respectively. From these data, maximum total and U.S. number one tuber yield of Russet Burbank potato can be obtained with 112 kg N be”. This rate is much lower than those currently used by most producers in Michigan. The yield of U.S. number one 27 tubers may be increased by split applications even at these lower N rates. "Spoon feeding" low levels of N to the potato crop throughout the growing season does not appear to be an advantageous N management strategy in Michigan. c F.1d E 2 pr HCl TO ED... LET US...“ 28 REFERENCES Allen, E.J., and R.K. Scott. 1980. An analysis of the potato crop. J. Agric. Sci. Camb. 94:583-606. Anonymous. 1988. Quikchem methods 12-107-06-2-A and 12-107- 04-1-A. Lachat Instruments, Milwaukee, WI. Bundy, L.G., R.P. welkowski, and 6.8. Weis. 1986. Nitrogen source evaluation for potato production on irrigated sandy soils. Am. Potato J. 63:385-397. Carter, J.N., and S.M. Bosma. 1974. Effect of fertilizer and irrigation on nitrate-nitrogen and total nitrogen in potato tubers. Agron. J. 66:263-266. Gardner, B.R., and J.P. Jones. 1975. Petiole analysis and the nitrogen fertilization of Russet Burbank potatoes. Am. Potato J. 52:195-200. Gould, W.A., and S. Plimpton. 1985. Quality evaluation of potato cultivars for processing. N. Cent. Reg. Res. Pub. 305. Harris, D., and E. A. Paul. 1989. Automated analysis of 15N and ‘C in biological samples. Comm. Soil Sci. Plant Anal. 20: 935-947. Hensel, D.R., and S.J. Locascio. 1987. Effect of rates, form, and application date of nitrogen on growth of potatoes. Proc. Fla. State Hort. Soc. 100:203-205. Hill, A.R. 1986. Nitrate and chloride balance under continuous potato cropping. Agric. Ecosystems Environ. 15:267-280. Jackson, R.D., and J.L. Haddock. 1959. Growth and nutrient uptake of Russet Burbank potatoes. Am. Potato J. 36:22-28. Kunkel, R., N. Holstad, and T.S. Russel. 1973. Mineral element content of potato plants and tubers vs. yields. Am. Potato J. 50:275-282. Lauer, D.A. 1985. Nitrogen uptake patterns of potatoes with high-frequency sprinkler-applied N fertilizer. Agron. J. 77:193-197. Lauer, D.A. 1986. Russet Burbank yield response to sprinkler-applied nitrogen fertilizer. Am. Potato J. 63:61- 69. 29 Leep, R.H. 1988. Effect of increasing nitrogen rates upon production of Russet Burbank potatoes in the upper peninsula 1988. 1988 Michigan Potato Res. Rep. 20:68-69. Liegel, E.A. and L.M. Walsh. 1976. Evaluation of sulfur- coated urea (SCU) applied to irrigated potatoes (Solanum tuberosum L.) and corn (Zea mays L.). Agron. J. 68:457-463. Ojala, J.C., J.C. Stark, and G.E. Kleinkopf. 1990. Influence of irrigation and nitrogen management of potato yield and Roberts, 8., and H.H. Cheng. 1985. Advances in nitrogen management for Russet Burbank potatoes. Proc. Wash. Potato Conf. and Trade Fair. pp 41-47. Roberts, 8., W.H. Weaver, and J.P. Phelps. 1982. Effect of rate and time of fertilization on nitrogen and yield of Russet Burbank potatoes under center pivot irrigation. Am. Potato J. 59:77-86. Saffigna, P.G., and D.R. Keeney. 1977. Nitrogen and chloride uptake by irrigated Russet Burbank potatoes. Agron. J. 69:258-264. Saffigna, P.G., D.R. Keeney, and C.B. Tanner. 1977. Nitrogen, chloride, and water balance with irrigated Russet Burbank potatoes in a sandy soil. Agron. J. 69:251-257. Vitosh, M.L. 1971. Fertilizer studies with irrigated potatoes. Research report No. 142, Mich. State. Univ. A.E.S. 11 pp. Vitosh, M.L. 1984. Irrigation scheduling for potatoes in Michigan. Am. Potato J. 61:205-213. Vitosh, M.L. 1985. Nitrogen management strategies for potato producers. Mich. State. Univ. Ext. Bull. W009. 4 pp. Vitosh, M.L., J.W. Noling, G.W. Bird, and R.W. Chase. 1980. The joint action of nitrogen and nematicides on Pratylenchus penetrans and potato yield. Am. Potato J. 57:101-111. Vitosh, M.L., D.B. Campbell, D.A. Hyde, and B.P. Darling. 1989a. Nitrogen management studies on potatoes: Sandyland Farms. 1989 Michigan Potato Res. Rep. 21:81-85. Vitosh, M.L., D.B. Campbell, D.A. Hyde, and B.P. Darling. 1989b. Nitrogen management studies on potatoes: Anderson Bros. 1989 Michigan Potato Res. Rep. 21:86-90. 30 Westermann, D.T., G.E. Kleinkopf, and L.M. Porter. 1988. Nitrogen fertilizer efficiencies on potatoes. Am. Potato J. 65:377-386. White, R.P., and J.B. Sanderson. 1983. Effect of planting' date, nitrogen rate, and plant spacing on potatoes grown for processing in Prince Edward Island. Am. Potato J. 60:115- 126. CHAPTER.TNO INFLUENCE OF APPLIED NITROGEN ON FERTILIEER.UTTAEE EFFICIENCY OF RUSSET BURBANE POTATO nsmc'r ‘ Maximizing fertilizer nitrogen (N) uptake efficiency, while maintaining crop productivity may reduce potential nitrate contamination of groundwater. A two year field investigation was conducted to evaluate the effects of ‘applied N on fertilizer N uptake, uptake efficiency, and total fertilizer N recovery of potato (Solanum tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. Nitrogen was applied as 15N depleted ammonium sulfate [(NHQZSO‘] at rates of 0, '56, 112, and 168 kg ha"1 in a single application at planting or in split applications during the growing season. Fertilizer N uptake efficiency was relatively unaffected by any of the N treatments. Fertilizer N uptake efficiencies using the isotope and difference method for the whole crop at onset of senescence were 55 and 49 percent, respectively, while values calculated for the tubers at harvest were 36 and 35 percent. An average of 28 percent of the applied N was present in the soil to a depth of 120 cm after harvest, and only about five percent of this N was found in the 60-120 cm depth. Total fertilizer N recovery (tubers and soil) averaged 65 percent. Though no significant increase in fertilizer N uptake or recovery was obtained by splitting the N applications at 31 32 these rates, marketable tuber yield was maximized by evenly splitting 112 kg N ha'1 between planting and tuber initiation (See Chapter one). 33 INTRODUCTION Nitrate contamination of groundwater from non-point sources has developed into a serious and well publicized environmental issue. The current potato production system in Michigan is quite susceptible to nitrate leaching because much of the crop is grown on coarse-textured soils under irrigation. The relatively high economic value of potato has historically led to large inputs of fertilizer nitrogen (N) and irrigation water, which further contributes to the nitrate leaching potential of the potato production system. Fertilizer N and irrigation management are the two most important factors under man's control that influence nitrate leaching during potato production. By limiting irrigation water and fertilizer N the potential for nitrate leaching will be minimized. The incorporation of these strategies into a production program that will also obtain maximum profitable yield, will help insure that environmentally sustainable potato production in Michigan continues to develop. Maximum.yield of Russet Burbank potato has generally been achieved when the soil moisture regime of the root zone has been maintained at or above 65 percent of the available water holding capacity of the soil (Ojala et al., 1990; Vitosh, 1984). Proper irrigation management must limit irrigation to less than 100 percent of water holding capacity to minimize nitrate leaching. Once the soil is 34 saturated, each additional 2.5 cm of irrigation (or rainfall), can move nitrate 15 to 20 cm day'1 in sandy soils (Endelman et al., 1974). Minimizing the movement of nitrate during potato production is vital as over 90 percent of the root length is in the surface 25 cm of the soil profile (Lesczynski and Tanner, 1976). The results of N studies with Russet Burbank potato in Michigan have been variable depending upon the year and location of the the research. Some studies (Vitosh, 1985; Vitosh et al. 1989a; and 1989b) have shown tuber yield increases with N application rates from 225-270 kg N ha”. Other research has shown little response in tuber yield to N rates exceeding 134 kg N ha'1 (Vitosh, 1971; Vitosh et al., 1980; Leep, 1988). One potential reason for the inconsistent response to applied N is that N rates exceeding 200 kg N ha’1 have been shown to reduce yields in growing seasons under 130 days because the N in the vines was not translocated to the tubers (Clutterbuck and Simpson, 1978). This delay in maturity is potentially very important as early frosts are not uncommon in the west central region of Michigan where much of the potato crop is grown. The current Michigan N recommendation for Russet Burbank potato with a yield goal of 45 Mg ha”, following a non-legume is 246 kg N ha" (Vitosh, 1990) . Many studies utilizing isotopically labeled N in the western U.S. have shown that fertilizer N uptake efficiency 35 of potato may be enhanced by splitting the N applications. sidedress N applications may be taken up more efficiently than preplant N (Westermann et a1. 1988), but some N at planting or emergence is needed to stimulate tuber initiation because fertilizer N applications delayed until after tuber initiation generally result in low yields (Roberts et al., 1982). The timing of the split application is crucial as N applied later in the growing season (August) may remain in the vines, while N applications made earlier are in the season are generally translocated to the tubers (Roberts and Cheng, 1982). Heavy N applications made during midseason can also induce secondary tuber growth and substantially reduce the percentage of marketable (U.S. number one) tubers (Roberts and Cheng, 1985). The actual percent recovery of applied N for potato has been determined in washington and California. Fertilizer N uptake efficiency of Russet Burbank tops and tubers in mid August was found to be approximately 50 percent for a 336 kg N ha'1 N rate in washington (Roberts and Cheng, 1983). Tyler et a1. (1983) found N uptake efficiency of White Rose potato tubers in California to be about 57 percent at N rates up to about 200 kg N ha”, but only 39 percent at the 270 kg N ha'1 rate. Studies involving both N rate and irrigation scheduling have shown that high tuber yields can be obtained with lower 36 inputs of N and irrigation water if properly managed. In Wisconsin, Saffigna et al. (1977) found an increase in marketable yield with a reduction in N and irrigation water from 260 kg N ha'1 with 45 cm of water to 170 kg N ha'1 with 27 cm. Nitrate leaching through the soil profile was also reduced by nearly 50 percent with these reduced N and irrigation inputs. Vitosh (1971) found that 134 kg N ha‘1 applied at planting produced near maximum yield of Russet Burbank potato in Michigan when proper irrigation management was implemented, but 168 kg N ha’1 was required to produce the same yield when excessive irrigation was used. The major objectives of this research were to evaluate the effects of several N management strategies with reduced N inputs and optimum irrigation on (1) fertilizer N uptake, (2) fertilizer N uptake efficiency, and (3) total fertilizer N balance between plant and soil after harvest for Russet Burbank potato grown on sandy soils in Michigan. MATERIALS AND METHODS General: This study was conducted at two sites during the 1988 and 1989 growing seasons. Complete information regarding location, soil classification, and field history of each site can be found in Chapter one. Soil test data for each site are presented in Tables 1.1 and 1.2. The experimental design was a randomized complete block 37 with four replications of six N treatments ranging from 0 to 168 kg N ha“1 applied in single or split applications (Table 1.3). Each plot consisted of four rows 0.86 m wide and 15 m long, except for the second site in 1988 where plots were three rows 18 m long. Russet Burbank potato was planted as whole seed or seed pieces weighing approximately 100 g placed 25 cm apart. Aldicarb {2-methy-2- (methylthio)propanal-O-[(methylamino)carbonyl]oxime} was applied at planting (3.36 kg active ingredient ha”) for insect and nematode control. weeds were controlled with pre-emergent applications of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2- methoxy-l-methylethyl)acetamide] and metribuzin [(4-amino-6- (1,1-dimethylethyl)-3-methylthio)-1,2,4-triazin-5(4H)-one] at 2.24 and 0.56 kg active ingredient ha”, respectively. All plots received approximately 50 kg P and 90 kg K ha'1 in a band approximately 5 cm below and 5 cm to the side of the seed piece at planting. Fungicides and insecticides were applied as needed at all sites. Irrigation was applied based on precipitation and evapotransipiration according to Vitosh (1984) (Table 1.4). Ammonium sulfate ((NH‘)ZSO,) was the fertilizer N source applied to the crop. Some fertilizer N source evaluation studies have concluded (NH,) ZSO‘ is superior to other N sources for potato production (Bundy et al., 1986 and Lorenz et al., 1974), although Vitosh (1971) found no source 38 differences in Michigan. In 1988, approximately one third of each plot received natural abundance (NH‘)2SO‘ fertilizer while the remaining two thirds of each plot received 1sN depleted (0.005 atom a: 15m (NH‘)2SO . In 1989, each plot received only 1sN depleted (0.005 atom % 15N) (NI-1,.)ZSO . The 15N depleted fertilizer was applied as a 40 percent by weight (NH‘) 280‘ aqueous solution with a backpack sprayer regulated to 4.35 kPa with a C02 tank. Nitrogen at planting was applied in a band 5‘cm on each side of the seed piece and lightly incorporated. Nitrogen applied at tuber initiation was banded to the side of the plant and irrigated, while the final two fertilizer applications were topdressed along each row and immediately irrigated. Banded N at planting and sidedress N applications at billing have been shown to be superior to broadcast N applications in potato production in Michigan (Vitosh, 1985). Plant Tissue Analyses: The tops and tubers of three consecutive hills (0.76 cm of row) within the center rows of the 15N depleted area were harvested in mid August for total N and 15N analyses. The samples were taken when the plants began to show signs of senescence. Previous research has shown that total N uptake is generally maximized between 80 and 100 days after emergence (Jackson and Haddock, 1959; Saffigna and Keeney, 1977). These samples were separated.into tops and tubers, 39 cut to facilitate drying, and dried in a forced air dryer at 55-60°C. The dried samples were then weighed and ground to pass through a 1 mm mesh screen. A random sample of 20 tubers from the 15N depleted area was taken at harvest for total N and 15N analysis of the tubers at harvest. These samples were also cut, dried at 55-60°C, weighed, and ground to pass through a 1 mm mesh screen. A subsample of each collected tissue sample was ground to < 250 um, and analyzed for total N and 15N analysis using the method of Harris and Paul (1989). Fertilizer N uptake and uptake efficiency of the whole crop, tops, and tubers, at onset of senescence, and tubers at harvest was determined from these values. Soil Analyses: Soil samples (3-5 cores 5 cm in diameter) were taken across the hill of a center row within the 15N depleted area of each plot to a depth of 120 cm after harvest for total ”N analysis. These samples were separated into 0-60 and 61-120 cm depths, air dried, ground, and stored in cardboard boxes prior to analysis. Soil samples were ground to < 250 um in glass jars (Qorpak #2143, Fisher Scientific) containing 5-8 stainless steel bars (3 x 50 mm). The jars were rotated on a roller mill or conveyer belt system driven at approximately 120 rpm for 2-12 hours. The ground samples were stored in sealed polyethylene bags prior to analysis. Total soil 15N was analyzed according to Harris and Paul 40 (1989). Fertilizer N remaining in the soil after harvest was determined from these samples. RESULTS AND DISCUSSION Plant Tissue Pertiliser Nitrogen Uptake: Fertilizer N uptake in the plant tissue was measured using both the isotope and difference methods to determine the utility of the latter method as it does not require the use of 15N fertilizers or a mass spectrometer. Unlike the isotope method, the difference method is an indirect method of determining fertilizer N uptake using the following formula: C I B - A where C, B, and A are fertilizer N uptake, mass of N in fertilized plots, and mass of N in control plots, respectively (Broadbent and Carlton, 1980). Data showing fertilizer N uptake by the whole crop, vines, and tubers at onset of senescence, and tubers at harvest using the isotope and difference methods are presented in Tables 2.1 and 2.2, respectively. In general, fertilizer N uptake was directly related to the N fertilization rate for both methods. Isotope Method: In 1988, whole crop and vine fertilizer N uptake was maximized at the 168 kg N ha'1 rate (treatment five), but no significant difference between this rate and 112 kg N ha'1 41 Table 2.1. Effect of N rate and application time on fertilizer N uptake of Russet Burbank potato at onset of senescence and harvest by isotope method. Fertilizer N uptake N Time of sample collection fertilizer ------Onset of senescence -------- Harvest kg ha"" W 1 m --- u- 2 37.8 c 9.0 c 28.8a 3 82.1a 36.7a . 45.4a 4 59.3 b 24.6 b 34.7a 5 82.6a 38.4a 44.2a 6 61.6 b 23.4 b 38.2a W 1 m _-- --- 2 30.3 c 11.1 c 19.2 b 3 64.0ab 30.0ab 34.0a 4 45.0 bc 22.3 bc 22.7 b 5 70.9a 38.1a 32.8a 6 54.7eb 28.8ab 25.9ab W 1 --- -.. --- 2 33.1 c 5.4 c 27.7 c 3 70.8 b 14.9 b 55.9 b 4 70.6 b 15.5 b 55.1 b 5 114.5a 33.7a 80.8a 6 68.7 b 19.6 b 49.1 b W 1 ..- ... --- 2 16.0 c 2.9 d ' 13.1 c 3 41.6 b 8.1 be 33.5 b 4 39.6 b 6.8 c 32.8 b 5 64.1a 17.8a 46.3a 4 9.5 b 20.8 c 36.0 b 35.3 b 46.4a 34.6 b 25.4 b 60.5a 53.4a 57.9a 56.6a 21.2 d 40.3 c 48.3 b 67.1a 43.5 c 16.1 c 39.3 b 37.4 b 57.6a __.§ LL}: ELLE—JILL Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 42 Table 2.2. Effect of N rate and application time on fertilizer N uptake of Russet Burbank potato at onset of senescence and harvest by difference method. N fertilizer OthNH OtUlfiUNH OMDUNH ”lbw”.- 46.8a 92.1a 53.2a 76.4a 53.8a 37.7a 59.6a 39.7a 57.0a 58.2a 0.6 c 52.5 b 39.0 b 89.2a 47.5 b 12.5 c 43.3 b 40.3 b 64.5a Fertilizer N uptake Time of sample collection -----Onset of senescence -------- Harvest kg ha" W 28.9 c 17.9a 14.7a 90.0a 2.1a 17.7a 80.8ab -4.4a 25.9a W 20.9a 16.8a 25.9a 41.2a 18.4a 66.1a 37.3a 2.4a 65.4a 50.5a 6.5a 56.8a 49.4a 8.8a 73.1a N9ntsalm.12§2 4.6 C “4.0 C 21e6 C 20.4 bc 32.1ab 49.3 b 20.7 bc 18.3 b 49.4 b 47.5a 41.7a 67.9a 30.9ab 16.6 be 40.2 b W 7.3 b 36.0a 38.9 b 5.4 bc 34.9a 36.3 b 21.2a 43.3a 58.8a __L WM.— Values followed by the same letter were not statistically different at the .05 level of probability (0mm). 43 applied at planting (Treatment three) was found at either location. At the Stanton site, the 112 kg N ha'1 treatment, where N was "spoon fed" to the crop throughout the growing season (Treatment six), also had a fertilizer N uptake similar to treatments three and five. The 56 kg N ha‘1 rate (Treatment two) had the lowest fertilizer N uptake of all treatments. The control (Treatment one) was not included in the statistical analyses. No significant differences in tuber fertilizer N uptake at onset of senescence were detected at the Montcalm location, but at the Stanton site, treatments three and five had a higher fertilizer N uptake than treatment two, or treatment four, where 112 kg N ha'1 was split evenly between planting and tuber initiation. At the Montcalm experiment, fertilizer N uptake of the tubers at harvest responded to N application rates, but not the timing of the applications. Treatment five had the highest fertilizer N uptake, and treatment two the lowest, while treatments three, four, and six had intermediate fertilizer N uptakes. At the Stanton site, no increase in fertilizer N uptake was detected beyond the 56 kg N ha‘1 rate. In 1989, the trend in fertilizer N uptake at onset of senescence paralleled the amount of N applied, but was not affected by the time of application. Treatment five resulted in the highest measured fertilizer N uptake, followed by treatments three, four, and six (which were not 44 statistically different from each other), and finally treatment two, which had the lowest fertilizer N uptake. This was also true for both tubers and vines except at the East Lansing location. In this experiment, some differences in fertilizer N uptake by vines were observed between the 112 kg N ha'1 treatments, but the actual differences were small (<3 kg N ha“). It should be noted that the actual amount of fertilizer N found in the tissue at onset of senescence at the East Lansing location was about 50 percent lower than the values measured in the Montcalm experiment. This is due to the lower percent N measured in these samples compared to the Montcalm experiment (See Table 1.7). Fertilizer N uptake by the tubers at harvest followed the same general trend as tuber samples collected at onset of senescence. The only real difference was that, in the Mentcalm experiment, treatment four had a significantly greater fertilizer uptake than the other 112 kg N ha‘1 treatments. Difference Method: In 1988, no significant differences in fertilizer N uptake between treatments were detected in any of the tissue samples using the difference method except for the vines collected at the onset of senescence at the Montcalm site. Fertilizer N uptake in these vines was maximized with treatment three, but no significant differences were 45 observed between treatments three, four, and five. Treatment two had the lowest fertilizer N uptake. In 1989, the response in fertilizer N uptake to the treatments for tissue samples at onset of senescence using the difference method were closer to those found with the isotope method. The whole crop sample fertilizer N uptake values were lowest for treatment two, highest for treatment five, and intermediate for treatments three, four, and six at both locations. Vine fertilizer N uptake between treatments exhibited the same general trends as in the whole crop, but some differences were apparent. At the Montcalm site, though no differences in vine N uptake between the 112 kg N ha'1 treatments were observed, treatment six was not significantly lower than treatment five and treatments three and four were not significantly higher than treatment two. At the East Lansing location, fertilizer N in the vines of treatments two, three, and four were not significantly different from each other. Tuber fertilizer N uptake at onset of senescence at this location was also influenced by the N treatments. Again treatment five had the highest fertilizer N uptake and treatment two the lowest, but within the 112 kg N ha‘1 rate, a trend towards lower N accumulation in the tubers at onset of senescence was apparent with split applications. At the East Lansing location, no significant differences in tuber N uptake at onset of senescence were 46 detected beyond the 56 kg N ha'1 rate. The fertilizer N uptake of the tubers at harvest followed the same trends as the whole crop at onset of senescence in both experiments. In general, the isotope and difference methods gave similar results for fertilizer N uptake of the whole crop at onset of senescence and the tubers at harvest, but this relationship was qualitative, not quantitative. very poor agreement between the two methods was observed between the vines and tubers at onset of senescence. The lack of significant differences detected with the difference method, espeCially in 1988, suggests a higher degree of variability when using this method compared to the isotope method. Plant Tissue Fertiliser N Uptake Efficiency: Plant tissue fertilizer uptake efficiency in this investigation is defined as the percent of applied fertilizer N that is recovered in the plant tissue samples. Fertilizer N uptake efficiency was also determined using both the isotope and difference methods. The data are presented.in Tables 2.3 and 2.4 for the isotope and difference methods, respectively. Isotope Method: In 1988, fertilizer uptake efficiency for the whole crop at onset of senescence was maximized with treatment three at the Montcalm experiment. All other treatments except 47 Table 2.3. Effect of N rate and application time on fertilizer N uptake efficiency of Russet Burbank potato at onset of senescence and harvest by isotope method. --------- Fertilizer uptake efficiency-------- N Time of sample collection fertilizer ----Onset of senescence -------- Harvest 1 -- -.- --- _—- 2 63.4ab 15.0 b 48.4a 35.1a 3 69.1a 30.9a 38.2ab 30.3a 4 49.9 b 20.7 b 29.2 b 29.6a 5 46.4 b 21.6 b 24.8 b 26.0a 6 51.8 b 19.7 b 32.1 b 29.1a W 1 -.. ... --.. -.... 2 50.9a 18.7a 32.2a 42.7a 3 53.8a 25.2a 28.6ab 50.8a 4 37.9a 18.7a 19.2 c 44.9a 5 39.8a 21.4a 18.4 c 32.5a 6 46.0a 24.2a 21.8 bc 47.5a W 1 --- .... -..- --... 2 58.6a 9.5 b 49.1a 37.5a 3 62.8a 13.2ab 49.6a 35.8a 4 62.6a 13.7ab 48.9a 42.9a 5 67.8a 20.0a 47.8a 39.7a 6 60.9a 17.4a 43.5a 38.5a East_Lansins_12§2 1 ... ... --- --- 2 28.5a 5.2 23.3a 28.7a 3 36.9a 7.2 bc 29.7a 34.8a 4 35.3a 6.1 c 29.2a 33.2a 5 37.9a 10.6a 27.3a 34.1a 4, 4 b ___L 3.11.9.4___3.2...2.a__ Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 48 Table 2.4., Effect of N rate and application time on fertilizer N uptake efficiency of Russet Burbank potato at onset of senescence and harvest by difference method. ---- Fertilizer uptake efficiency -------- N Time of sample collection fertilizer -----Onset of senescence -------- Harvest E i 1 -- “- --— -_- 2 78.7a 48.6a 30.1a 24.6a 3 77.5a 75.7a 1.8a 14.9a 4 44.7a 52.6a -7.9a 25.1a 6 45.2a 45.6a -0.4a 19.3a W 1 -u --- --- --- 2 63.5a 35.3a 28.2a 43.5a 3 50.0a 34.6a 15.4a 55.6a 4 33.3a 31.3a 2.0a 55.0a 5 31.9a 28.3a 3.6a 31.8a 6 49.0a 41.5a 7.5a 61.5a W 1 a. --- -..- —-.. 3 46.6a . 18.1a 28.5a 43.7a 4 34.6a 18.4a 16.2a 43.8a 5 52.8a 28.1a 24.7a 40.1a 6 42.2a 27.5a 14.7a 35.7a W932 1 -.... --- --- --.. 2 22.0a -0.6a 22.6a 27.2a 3 38.3a 6.4a 31.9a 34.5a 4 35.8a 4.8a 31.0a 32.2a 5 38.2a 12.5a 25.7a 34.8a __§ W29...”— Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 49 treatment two had significantly lower uptake effficiencies. No significant differences in fertilizer N uptake efficiencies were found for the whole crop at onset of senescence at the Stanton study. Treatment three had the greatest percent fertilizer N in the vines at the Mentcalm site, but no significant differences were found between the other treatments at this location or any of the treatments at the Stanton site. The percent fertilizer N found in the tubers at onset of senescence was greatest for treatments two and three at both locations in 1988. These higher values may have been due to the more advanced senescence of these treatments at the time the samples were collected. Since these samples were more senesced, a greater proportion of the N would have been translocated to the tubers compared to the other treatments. For the tubers at harvest, no significant differences in fertilizer N uptake efficiencies between treatments were observed at either location in 1988. The Stanton site had a much higher average fertilizer N uptake efficiency by the tubers at harvest compared to the Montcalm location (44 percent vs. 30 percent). This is in direct contrast to the fertilizer N uptake efficiencies of the whole crop at onset of maturity. This discrepancy may be due to the fact that the whole crop N uptake samples at the Stanton location may have been taken before maximum N accumulation had been attained, as total N uptake by tubers at harvest was 50 actually greater than total N uptake measured in the whole crop at onset of senescence (See Table 1.8). Since 1 M KCl extractable inorganic N levels to a depth of 30 on prior to planting were actually greater at Stanton than Montcalm (See Table 1.2), a greater fertilizer N uptake efficiency at the Montcalm site would be expected unless there was a larger quantity of crop residue present at the Montcalm site that could immobilize some of the fertilizer N. No measurements of crop residue were made at either location so this possibility can not be confirmed. Russet Burbank potato consistently yields lower than other potato cultivars at this location, so it is possible that some other factor is responsible for the lower yields at this location, resulting in lower fertilizer uptake efficiencies. I No significant differences in fertilizer uptake efficiencies of the whole crop or tubers at onset of senescence were observed between treatments at either location in 1989. Significant differences between treatments were found for the vines at onset of senescence. At the Montcalm site, treatment two had the lowest percent of applied fertilizer N in the vines and treatments five and six had the highest fertilizer uptake efficiencies. Treatments three and four were not significantly different from any of the other treatments at this location. For the East Lansing experiment, treatment five had the highest fertilizer uptake efficiency in the vines while treatment 51 two had the lowest. Some differences between the 112 kg N ha“1 treatments were also observed. More fertilizer N was found in the vines of treatments six than treatment four, while treatment three was not significantly different than either of the other two 112 kg N ha'1 treatments. No differences in fertilizer N uptake efficiencies of the tubers at harvest were detected between any of the treatments at either location in 1989. The average fertilizer N uptake efficiency at the Montcalm experiment was higher than at the East Lansing location (39 percent vs. 33 percent), but the lower tissue N concentrations measured at the East Lansing site compared to all other locations may have decreased fertilizer N uptake efficiency values at this location (See Table 1.7). If the data for all experiments except the East Lansing location in 1989 are combined, whole crop fertilizer N uptake efficiency is about 55 percent, and this value may be underestimated as it appears that maximum N accumulation had not been reached in all treatments for the Stanton location in 1988. This data would agree with Roberts and Cheng (1983), who found that 50-60 percent of the N applied was found between the tops and tubers in washington. Fertilizer N uptake efficiency of the tubers at harvest was not increased by splitting the fertilizer N applications at these N rates. The average fertilizer N uptake efficiency of the tubers at harvest in all experiments averaged about 52 36 percent using the isotope method. Difference Method: No significant differences in fertilizer N uptake efficiency were found for any tissue samples collected using the difference method. This was true for all experiments. The average N uptake efficiency of the whole crop at onset of senescence for all experiments except the East Lansing experiment in 1989 was 49 percent using the difference method compared to 55 percent with the isotope method. The average fertilizer N uptake efficiency for the tubers at harvest was 35 percent; much closer to the value found using the isotope method (36 percent). From these data, the difference method appears to have some utility in making general inferences about fertilizer N uptake efficiencies, but the lack of statistical resolution may make this method inappropriate for research purposes. In addition, the difference method is of little value when determining fertilizer N partitioning within the plant, and is useless for quantifying fertilizer N values in soil. Fertilizer N uptake efficiency was not influenced by the different N application rates in this investigation. At these lower N rates, splitting fertilizer N applications may not enhance fertilizer N uptake efficiency of potato in Michigan. Split applications may, however, increase marketable tuber yield if the N is applied before the onset 53 z of tuber bulking (See Chapter One). Fertiliser Nitrogen Recovery In Boil: Soil samples taken after harvest were analyzed for total fertilizer N in the 0-60 and 61-120 cm depths. As in the fertilizer uptake of the tissue samples, the control treatment was not included in the statistical analysis. Soil fertilizer N recovery and percent fertilizer N recovery data for all experiments are located in Table 2.5. From the extremely small fertilizer N recoveries in treatments three, four, and six, it is obvious that some error occured during the soil analysis of the Montcalm experiment. No further' discussion of the soil data from this experiment will follow. At the Stanton location in 1988, 25 to 36 kg fertilizer N he” was detected in the soil to a depth of 120 cm, but no significant differences were found between the N treatments. Most of this N was recovered in the surface 60 cm. In 1989, some differences in total fertilizer N recovery between treatments were apparent. At the MOntcalm site, more fertilizer N was measured in the soil from treatment five than treatment two in the 0-60 cm depth. Treatment five also had a higher total N recovery to 120 than the other treatments. Significant differences between treatments were also found in the 0-60 cm depth at the East Lansing location, where treatment five had a higher N Table 54 2.5. Effect of N rate and application time on fertilizer N and percent fertilizer N applied to Russet Burbank potato found in soil samples taken after harvest. N fertilizer Soil sample depth cm 1 2 3 4 s 6 1 2 3 4 s 6 1 2 3 4 s 6 1 2 3 4 s __5 13.2a 1.3a 14.5a 22.3a 2.3a 24.6a 6.3a 4.0a 10.3a 5.2a 3.4a 8.6a Oeé‘ “0.38 0.38 006. -0e2‘ 0.4a 28.3a 0.5a 28.8a 15.9a 0.3a 16.2a 6.1a 2.6a 8.7a 5.2a 2.2a 7.4a W 25.9a 2.9a 28.8a 43.4a 4.9a 48.3a 24.3a 1.7a 26.0a 20.4a 1.4a 21.8a 23.0a 1.9a 24.9a 19.4a 1.6a 21.0a 31.1a 4.2a 35.3a 17.6a 2.4a 20.0a 32.3a 3.4a 35.7a 27.0a 3.1a 30.1a -W 20.8 b 0.6a 21.4 b 37.0a 1.0a 38.0a 31.8ab 0.3a 32.1 b 28.2a 0.3a 28.5a 31.7ab 0.3a 32.0 b 28.2a 0.3a 28.5a 48.2a 0.4a 48.6a 28.5a 0.2a 28.7a 32.4ab 0.3a 32.7 b 28.8a 0.3a 29.1a W 15.4 b 3.3a 18.7a 27.4a 5.8a 33.2a 27.0ab 1.9a 28.9a 24.0a 1.7a 25.7a 24.8ab 1.9a 26.7a 22.0a 1.7a 23.7a 35.5a 0.8a 36.3a 21.0a 0.5a 21.5a 19.6 p -1,23 18.53 17.5; -1.13 16.13 values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 55 recovery than treatments two or six. No significant differences in total soil fertilizer N recoveries to 120 cm, or any of the other measured depths were observed at the East Lansing experiment. As in 1988, very little fertilizer N was detected in the soil below 60 cm at either location. Soil fertilizer N levels expressed as a percentage of N applied were also examined. No significant differences in percent recovery of applied fertilizer N between treatments were evident in any of the experiments. Total percent recovery of fertilizer N in the soil to a depth of 120 cm was not affected by the N treatments in any of the experiments in this study. The average percent fertilizer N recovered in the soil to a depth of 120 cm was about 28 percent (excluding the Montcalm site in 1988). Only about five to six percent of the fertilizer N recovered was found in the 61-120 depth. Other researchers have found 25- 33 percent of applied N in the soil, with most of it in the surface 25 cm(Gerwing et al., 1979; and Westermann et al., 1988). Total Fertiliser N Recovery: By combining fertilizer N recovery in tubers at harvest (isotope method) and soil samples taken after harvest, a total fertilizer N recovery can be calculated. Data showing both total fertilizer N recovery and percent fertilizer N recovery are presented in Table 2.6. Due to the unreliable 56 Table 2.6. Effect of N rate and application time on fertilizer N and percent fertilizer N applied to Russet Burbank potato recovered in tubers at harvest and soil samples taken to 120 cm after harvest. N Total fertilizer N recovery fertilizer Soil -Crop- Soil -Crop- - 1 0-129 1393;: 19331 __SIIIEIIDL____9.129____I%§!§:Ffl7::£353;-_ = W 1 --- -.. --— -..-. -—- ..-.. 2 14.5a 20.8 c 35.3a 24.6a 35.1a 59.2a 3 10.3a 36.0 b 46.3a 8.6a 30.3a 38.9a 4 0.3a 35.3 b 35.6a 0.4a 29.6a 30.0a 5 28.8a 46.4a 75.2a 16.2a 26.0a 42.2a 6 8.7a 34.6 b 43.3a 7.4a 29.1a 36.5a Stanssn_12§§ 1 “- --.— —-- --- --- --- 2 28.8a 25.4 b 54.2 b 48.3a 42.7a 91.0a 3 27.7a 60.5a 88.2a 21.8a 50.8a 72.6a 4 24.9a 53.4a 78.3a 21.0a 44.9a 65.9a . 5 35.3a 57.9a 93.2a 20.0a 32.5a 52.5a 6 35.7a 56.6a 92.3a 30.1a 47.5a 77.6a W 1 -... ..... .... -... --... -.... 2 21.4a 21.2 d 42.6 c 38.0a 37.5a 75.5a 3 32.1a 40.3 c 72.4 b 28.5a 35.8a 64.3a 4 32.0a 48.3'b 80.3 b 28.5a 42.9a 71.4a 5 48.6a 67.1a 115.7a 28.7a 39.7a 68.4a 6 32.7a 43.5 c 76.2 b 29.1a 38.5a 67.6a W 1 -... --- -... -.... -.... --- 2 18.7a 16.1 c 34.8 c 33.2a 28.7a 61.9a 3 28.9a 39.3 b 68.2 b 25.7a 34.8a 60.5a 4 26.7a 37.4 b 64.1 b 23.7a 33.2a 56.9a 5 36.3a 57.6a 93.9a 21.5a 34.1a 55.6a __§..—1§.dA__2LLD_§§3§_h9__1.§.d.4—.12321__121§3_ Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 57 soil data, no discussion of the Montcalm.experiment in 1988 will be included. At the Stanton site in 1988, treatments three, four, five, and six had significantly greater total fertilizer N recoveries than treatment two, the 56 kg N ha‘1 treatment. Treatment four had an intermediate fertilizer N recovery and was not significantly different from any of the other N treatments at this experiment. In 1989, total fertilizer N recovery consistently reflected the amount of fertilizer N applied. At both locations the treatment five had the highest total N recovery, while treatment two had the lowest recovery of applied fertilizer N. The total fertilizer N recoveries of treatments three, four, and six were intermediate to those of treatments two and five. No consistant differences between these 112 kg N ha"1 treatments were observed, but treatment six did show a trend towards a lower total N recovery than treatments three and four at the East Lansing location. No significant differences in the total percent recovery of applied fertilizer N were observed between treatments at any of the locations during this study. The average total fertilizer N recovered in this investigation was about 65 percent. Approximately 35 percent of the applied fertilizer N remains unaccounted for and may be present in tubers and vines that were not harvested, or lost via runoff, leaching beyond 120 cm, or denitrification. 58 RIIIRINCBB Broadbent, F.E., and A.B. Carlton. 1980. Methodology for field trials with nitrogen-ls-depleted nitrogen. J. Environ. Qual. 9:236-242. Bundy, L.G., R.P. welkowski, and 6.6. Weis. 1986. Nitrogen source evaluation for potato production on irrigated sandy soils. Am. Potato J. 63:385-397. Clutterbuck, B.J., and K. Simpson. 1978. The interactions of water and fertilizer nitrogen in effects on growth pattern and yield of potatoes. J. Agric. Sci. 91:161-172. Endelman, P.J., D.R. Keeney, J.T. Gilmour, and P.G. Saffigna. 1974. Nitrate and chloride movement in the Plainfield loamy sand under intensive irrigation. J. Environ. Qual. 3:295-298. Gerwing, J.R., A.C. Caldwell, and L.L. Goodroad. 1979. Fertilizer nitrogen distribution under irrigation between soil, plant, and aquifer. J. Environ. Qual. 8:281-284. Harris, D., and E.A. Paul. 1989. Automated analysis of 15N and “C in biological samples. Comm. Soil Sci. Plant Anal. 20:935-947. Jackson, R.D., and J.L. Haddock. 1959. Growth and nutrient uptake of Russet Burbank potatoes. Am. Potato J. 36:22-28. Leep, R.H. 1988. Effect of increasing nitrogen rates upon production of Russet Burbank potatoes in the upper peninsula 1988. 1988 Michigan Potato Res. Rep. 20:68-69. Lesczynski, D.B., and C.B. Tanner. 1976. Seasonal variation of root distribution of irrigated, field-grown Russet Burbank potato. Am. Potato J. 53:69-78. Lorenz, O.A., B.L. Weir, and J.C. Bishop. 1974. Effect of sources of nitrogen on yield and nitrogen absorption of potatoes. Am. Potato J. 51:56-65. Ojala, J.C., J.C. Stark, and G.E. Kleinkopf. 1990. Influence of irrigation and nitrogen management of potato yield and quality. Am. Potato J. 67:29-43. Roberts, 8., and H.H. Cheng. 1982. 15N tracer studies on nitrogen uptake by Russet Burbank potatoes. Proc. Wash. Potato Conf. and Trade Fair. pp 69-73. 59 Roberts, 8., and H.H. Cheng. 1983. Additional results from 15N tracer studies on nitrogen uptake by Russet Burbank potatoes. Proc. Wash. Potato Conf. and Trade Fair. pp 69-72. Roberts, 8., and H.H. Cheng. 1985. Advances in nitrogen management for Russet Burbank potatoes. Proc. Wash. Potato Conf. and Trade Fair. pp 41-47. Roberts, 8., W.H. weaver, and J.P. Phelps. 1982. Effect of rate and time of fertilization on nitrogen and yield of Russet Burbank potatoes under center pivot irrigation. Am. Potato J. 59:77-86. Saffigna, P.G., and D.R. Keeney. 1977. Nitrogen and chloride uptake by irrigated Russet Burbank potatoes. Agron. J. 69:258-264. Saffigna, P.G., D.R. Keeney, and C.B. Tanner. 1977. Nitrogen, chloride, and water balance with irrigated Russet Burbank potatoes in a sandy soil. Agron. J. 69:251-257. Tyler, K.B., F.E. Broadbent, and J.C. Bishop. 1983. Efficiency of nitrogen uptake by potatoes. Am. Potato J. 60:261-269. Vitosh, M.L. 1971. Fertilizer studies with irrigated potatoes. Research report No. 142, Mich. State. Univ. A.E.S. 11 pp. Vitosh, M.L. 1984. Irrigation scheduling for potatoes in Michigan. Am. Potato J. 61:205-213. Vitosh, M.L. 1985. Nitrogen management strategies for potato producers. Mich. State Uhiv. Ext. Bull. W009. 4 pp. Vitosh, M.L. 1990. Potato fertilizer recommendations. Mich. State Univ. Ext. Bull. E2220. 8pp. Vitosh, M.L., J.W. Noling, G.W. Bird, and R.W. Chase. 1980. The joint action of nitrogen and nematicides on Pratylenchus penetrans and potato yield. Am. Potato J. 57:101-111. Vitosh, M.L., D.B. Campbell, D.A. Hyde, and B.P. Darling. 1989a. Nitrogen management studies on potatoes: Sandyland Farms. 1989 Michigan Potato Res. Rep. 21:81-85. Vitosh, M.L., D.B. Campbell, D.A. Hyde, and B.P. Darling. 1989b. Nitrogen management studies on potatoes: Anderson Bros. 1989 Michigan Potato Res. Rep. 21:86-90. 60 westermann, D.T., G.E. Kleinkopf, and L.K. Porter. 1988. Nitrogen fertilizer efficiencies on potatoes. Am. Potato J. 65:377-386. CBAPTIR.TEREE INILDINCI OF APPLIED NITROGIN'ON’BALL.FIRTILIZIR.NITROGEN RECOVER! AND PARTITIONING IN SOIL FOLLOWING»POTATO ABSTRACT Nitrate contamination of groundwater from agricultural fertilizers may be reduced by limiting nitrate leaching through proper irrigation management and supplying only as much N as is removed by the crop. Nitrogen was applied as 15N depleted ammonium sulfate [(NHJZSO‘] at rates of 0, 56, 112, and 168 kg ha'1 in a single application at planting or in split applications through the growing season to potato (selanum tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. The influence of these treatments on fertilizer N recovered in soil samples taken after harvest was measured. Fertilizer N recovery averaged 30 kg N ha'1 across all treatments. The percent recovery of applied N was 40 about percent for the 56 kg N ha'1 rate and 25 percent for the other treatments. Only six percent of the applied N was found at depths greater than 60 cm. Over 90 percent of the recovered N was in the organic form and the contribution of the inorganic fertilizer N to the total inorganic N averaged approximately 5 percent. Since total inorganic N levels measured in the treatments were only 11 percent higher than the control, the fertilizer inorganic N may account for 45-50 percent of this increase. In this investigation, total fertilizer N recovery in soils was 61 62 largely unaffected by the rate or timing of fertilizer N applications. 63 INTRODUCTION The potential negative impact of agricultural production on groundwater resources is receiving considerable attention in both agricultural and nonagricultural communities. Excessive and, or inefficient use of nitrogen (N) fertilizers may be contributing to increased nitrate levels in some rural groundwater supplies. The west central region of Michigan contains large areas of sandy soils overlaying unprotected aquifers, and much of this land is planted to potato. The high economic value of potato has historically led to high inputs of fertilizer N and irrigation water, so these inputs will not limit crop yield. Since over 90 percent of the root length of potato is in the surface 25 cm of the soil profile (Lesczynski and Tanner, 1976), the potential for substantial nitrate leaching beyond the root zone during the growing season exists. By minimizing nitrate leaching through proper irrigation management, and maximizing fertilizer N uptake by limiting N applications to about that removed by the crop, it may be possible to reduce potential nitrate contamination of groundwater from agricultural fertilizers. Maximum yield of Russet Burbank potato generally occurs when soil moisture in the root zone is maintained at approximately 65 percent of the available water holding capacity (Ojala et al., 1990; Vitosh, 1984). Proper irrigation management must limit irrigation to less than 100 64 percent of the water holding capacity because once the soil is saturated, each additional 2.5 cm of irrigation (or rainfall), can move nitrate 15 to 20 cm day'1 in sandy soils (Endelman et al., 1974). However, even short periods of moisture stress during the growing season may be associated with increased tuber deformation (Lesczynski and Tanner, 1976). The current N recommendation in Michigan for Russet Burbank potato with a yield goal of 50 Mg ha”, following a non-legume is 270 kg N ha'1 (Vitosh, 1990). A simple calculation using values of 20 percent tuber dry matter (Mackerron and waister, 1985) and 1.4 percent N in the tubers (Saffigna et al., 1977), only about 140 kg N ha” would be removed by the crop at harvest. Saffigna et al. (1977) found tuber N uptake values of 120-145 kg N ha‘1 in Wisconsin. At the recommended application rate of 270 kg N ha”, up to 130 kg N ha'1 may be susceptible to environmental losses such as runoff, volatilization, leaching, and . denitrification. Potato fertilization experiments using 15N techniques have not quantified total residual fertilizer N in the soil after harvest, though Tyler et al. (1983) did measure inorganic fertilizer N after harvest to a depth of 2.5 m. They found virtually no fertilizer N below 1 m. Studies involving other crops have shown that 25-33 percent of applied N remain in the soil after harvest (Gerwing et al., 1979; and 65 Westerman et al., 1972). Gerwing et al. (1979) also found that most of this N was in the surface 23 cm, regardless of whether the N (179 kg N ha”) was applied in single or split applications. No data showing the partitioning of total residual soil fertilizer N between the organic and inorganic N pools following potato has been found in the literature. In this investigation, Russet Burbank potato was grown on sandy soils using several N management strategies with reduced N inputs and optimum irrigation. The influence of these treatments on fertilizer N recovered in soil samples taken after harvest was measured. The specific objectives of this research were to (1) measure the fertilizer N recovered in the soil to a depth of 120 cm, (2) determine the distribution of this N through the soil profile, (3) quantify the partitioning of the fertilizer N between the organic and inorganic N pools, and (4) assess the contribution that fertilizer N may have on the total inorganic N that is susceptible to leaching at the end of the growing season in Michigan. IITIRIALB AID»IBTIDD8 General: I This study was conducted at two sites each year during the 1988 and 1989 growing seasons. Complete information regarding location, soil classification, and field history 66 of each site can be found in Chapter one. Soil test data for each site are presented in Tables 1.1 and 1.2. The experimental design was a randomized complete block with four replications of six N treatments ranging from 0 to 168 kg N ha'1 applied in single or split applications (Table 1.3). Each plot consisted of four rows 0.86 m wide and 15 m long, except for the second site in 1988 where plots were three rows 18 m long. Russet Burbank potato was planted as whole seed or seed pieces weighing approximately 100 g placed 25 cm apart. Aldicarb {2-methy-2- (methylthio)propanal-O-[(methylamino)carbonyl]oxime} was applied at planting (3.36 kg active ingredient ha”) for insect and nematode control. Weeds were controlled with preemergent applications of metolachlor [z-chloro-N-(2-ethyl-6-methylphenyl)-N-(2- methoxy-l-methylethyl)acetamide] and metribuzin [(4-amino-6- (1,1-dimethylethyl)-3-methylthio)-1,2,4-triazin-5(4H)-one] at 2.24 and 0.56 kg active ingredient ha”, respectively. All plots received approximately 50 kg P and 90 kg K ha'1 in a band approximately 5 cm below and 5 cm to the side of the seed piece at planting. Fungicides and insecticides were applied as needed at all sites. Irrigation was applied based on precipitation and evapotranspiration according to Vitosh, (1984) (Table 1.4). Ammonium sulfate ((NHJZSO‘) was the fertilizer N source applied to the crop. Some fertilizer leource evaluation 67 studies have concluded (NH‘) 280‘ is superior to other N sources for potato production (Bundy et al., 1986 and Lorenz et al., 1974), although Vitosh (1971) found no source differences in Michigan. In 1988, approximately one third of each plot received natural abundance (NH,)2S0‘ fertilizer while the remaining two thirds of each plot received 1sN depleted (0.005 atom 1: "m (N11,)zso . In 1989, each plot received only 1sN depleted (0.005 atom % 15N) (NI-1‘) 280,. The 15N depleted fertilizer was applied as a 40 percent by weight (NI-1,.) 280,. aqueous solution with a backpack sprayer regulated to 4.35 kPa with a C02 tank. Nitrogen at planting was applied in a band 5 cm on each side of the seed piece and lightly incorporated. Nitrogen applied at tuber initiation was banded to the side of the plant and irrigated, while the final two fertilizer applications were topdressed along each row and immediately irrigated. Banded . N at planting and sidress N applications at billing have been shown to be superior to broadcast N applications in potato production in Michigan (Vitosh, 1985). Soil Analyses: Soil samples (3-5 cores 5 cm in diameter) were taken across the hill of a center row within the 15N depleted area of each plot to a depth of 120 cm after harvest. These samples were separated into 0-15, 16-30, 31-60, 61-90, and 91-120 cm increments. Soil samples were air dried, ground, 68 and stored in cardboard boxes prior to laboratory analyses. These samples were analyzed for total soil N and 15N as well as 15N in the inorganic N pool. Soil samples to be analyzed for total N were ground to < 250 pm in glass jars (Qorpak #2143, Fisher Scientific) containing 5-8 stainless steel bars (3 x 50 mm). The jars were rotated on a roller mill or conveyer belt system driven at approximately 120 rpm for 2- 12 hours. The ground samples were stored in sealed polyethylene bags prior to analysis. Total soil 15N samples were analyzed according to Harris and Paul (1989). The ”N’ in the inorganic N pool was extracted with a 1:4 (m:v) soil:1 M KCl aqueous solution using a shaking time of 60 minutes. The extract was filtered through Whatman No. 2 filter paper that had been prewashed with 10 mls of the extracting solution and analyzed for 1 M KCl extractable nitrate (N03) and ammonium (NH‘) and for percent 15N in this inorganic N pool. Nitrate and NH, levels were analyzed with a flow injection autoanalyzer (Anonymous, 1988). The percent 15N of the extract was analyzed by volatilizing the N03 and NH, to NH3 and capturing the NH3 on an acid trap using the method developed by Brooks et al. (1989). The method of Harris and Paul (1989) was used for 15N analysis of the acid trap. Fertilizer N remaining in the soil after harvest and the partitioning of this N between organic and inorganic fractions was determined from these samples. 69 Results and Discussion Soil samples taken after harvest were analyzed for total, organic, and inorganic fertililizer N in 0-15, 16-30, 31-60, and 61-120 cm soil increments. Since no fertilizer N was applied to the control, it was not included in the statistical analyses. Data for the Montcalm experiment in 1988 are located in Tables 3.1 and 3.2. It is obvious that some error occured during this experiment because large negative fertilizer N values were measured in the organic soil fraction at the 31-60 cm depth. These data are only included for completeness and will not be included in any further discussion. Data showing fertilizer N recovery in the total N pool to a depth of 120 cm is presented in Table 3.3. At the Stanton location in 1988, 25 to 36 kg fertilizer N ha'1 was detected in the soil to a depth of 120 cm, but no significant ' differences were found between the N treatments. Approximately 90 percent of the fertilizer N recovered was in the surface 60 cm. Most of this recovered N was present in the surface 15 cm except in the 56 kg N ha'1 treatment (treatment two) and the 112 kg N ha'1 "spoon feeding" treatment (treatment six) where much of the fertilizer N was present in the 31-60 cm depth. In 1989, some differences in total fertilizer N recovery between treatments were apparent. At the Montcalm site, more fertilizer N was measured in the soil from the 168 kg N 70 Table 3.1. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the inorganic, organic, and total N pools in soil samples taken after harvest at Montcalm, 1988. Soil sample depth cm fertilizer tgggtmgnt 9-15 1 m 2 0.6a 3 0.5a 4 0.6a 5 1.4a 6 1.3a 1 --- 2 17.1a 3 13.3a 4 18.7a 5 22.8a 6 21.8a 1 m 2 17.7a 3 13.8a 4 19.3a 5 24.2a ___§____2.L.ls 16-30 3l-§9 61-129 Total kg ha" IHQIQIEIE_1!IILLLZIE_H 0.3a 0.6 b 0.7a 0.4a 1.6 b 1.7a 0.5& 1.2 b 0.9a 0.9a 2.8a 1.1a 1.3& 1.7lb 1.1. W]! -4s0‘ -1e4‘ 0.68 008‘ '10.33 203‘ Del“ '20.58 -1e2‘ 0.1a 0.3a -0.6a -3.2a -16.8a 1.5a 19§31_II£§11LZII_H -3e7. -008: lea‘ 1e2‘ -807. ‘eO‘ OeG‘ -19e3‘ -0e3‘ 1.0a 3.1a 0.5a -1.93 'JLB__Z;_§.I___L1|_ . Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 14.5a 10.3a 0.3a 28.8a 71 Table 3.2. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the inorganic, organic, and total N pools in soil samples taken after harvest at Montcalm, 1988. N Soil sample depth fertilizer cm SEIISEIBI 9-15 15-39 31-§Q 51-129 293.] .. "U "— 1W 1 -.. u- --- -c- “- 2 1.0a 0.6a 1.0a 1.2a 3.8a 3 0.4a 0.4a 1.3a 1.4a 3.5a 4 0.5a 0.5a 1.0a 0.8a 2.8a 5 1.8a 0.5a 1.5a 0.6a 3.4a 6 1.1a 1.1a 1.4a 1.0a 4.6a Mills” 1 ... ... ..- --- --- 2 28.8a -6.7a -2.4a 1.1a 20.8a 4 15.7a 0.1a -17.2a -1.0a -2.4a 5 12.8a 0.1a 0.2a -0.3a 12.8a 6 18.4a -2.7a -14.la 1.2a 2.8a W 1 m m --. --- --- 2 29.8a -6.1a -1.4a 2.3a 24.6a 5 14.6a 0.6a 1.7a 0.3a 16.2a ______§ 19-5: ‘1'§§_____:12&1§_______2L2! 7:43... values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 72 Table 3.3. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the total N pool of soil samples taken after harvest. N Soil sample depth fertilizer cm kg ha‘”’ W 1 m m “- -- u- 3 21.8a -0.4ab 2.9a 1.7a 26.0a 5 20.5a 1.9a 8.7a 4.2a 35.3a 6 15.8a -0.1ab 16.6a 3.4a 35.7a W 1 --.. ..- -.... --.. -..... 2 14.8 c 2.3a 3.7a 0.6a 21.4 b 3 22.9abc 5.7a 3.2a 0.3a 32.1 b 4 27.4ab 2.2a 2.1a 0.3a 32.0 b 5 34.2a 3.3a 10.7a 0.4a 48.6a 6 22.0 bc 5.9a 4.5a 0.3a 32.7 b W 1 ... ..- -_- --.. -..- 2 8.0 c1 3.6a 3.8a 3.3a 18.7a 3 17.8 b 6.5a 2.7a 1.9a 28.9a 4 19.2 b 3.4a 2.2a 1.9a 26.7a 5 28.7a 4.6a 2.2a 0.8a 36.3a ___i IbuMm—Ma—JZA—lfida— values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 73 ha’1 treatment (treatment five) than treatments two or six in the 0-15 cm depth. Treatment four, where 112 kg N ha'1 was evenly split between planting and tuber initiation, also had a greater fertilizer N recovery in the soil at this depth than treatment two. No differences were detected between treatments at the other soil depths analyzed, but total soil fertilizer N recovery to 120 cm was greater for treatment five than the other treatments at the Montcalm site. Total N recovery to 120 cm averaged approximately 21,‘ 32, and 49 kg N ha" for the 56, 112 and 168 kg N ha" treatments. Only about 1.5 percent of the recovered N was found below 60 cm at this location. At the East Lansing location, significant differences between treatments were also found in the 0-15 cm depth. Fertilizer N recovery was influenced by N application rates, but not the timing of the applications. Treatment five had the greatest fertilizer N recovery and treatment two had the lowest. The soil samples from the 112 kg N ha'1 treatments all contained 15-20 kg N ha‘1 in the 0-15 cm soil depth. No significant differences in total soil fertilizer N recoveries to 120 cm, or any of the other measured depths were observed at the East Lansing experiment, but the measured fertilizer N recovery for treatment six did appear to be lower than the other 112 kg N ha'1 treatments. As in the Montcalm experiment, very little fertilizer N was detected in the soil below 60 cm (about five percent). 74 Data showing the partitioning of the total fertilizer N recovered in the soil between the organic and inorganic fractions are presented in Tables 3.4 and 3.5, respectively. At the Stanton location in 1988, over 90 percent of the total N recovered was present in the organic form and more than 90 percent of this N was in the top 60 cm. The inorganic fertilizer N recovered in this experiment was less than ten percent of the total fertilizer N found in the soil. Over 85 percent of the inorganic N was measured in the top 60 cm as well. Though no significant differences in overall fertilizer N recovery were detected in either fraction, treatment five did have the highest N levels detected in the 16-30 and 31-60 cm depths for the inorganic fraction. Similar trends in the partitioning of fertilizer N between the organic and inorganic fractions were observed in 1989. An average of 85 and 90 percent of the total fertilizer N measured in the soil samples was organic N in the Montcalm and East Lansing locations, respectively. In both experiments virtually all of the fertilizer N recovered in the organic fraction was present in the surface 60 cm, and most of this was in the top 15 cm. More organic fertilizer N was recovered in the surface 15 cm under treatment five than treatments two or six at both locations. No significant differences were detected between treatments at other depths or for total organic fertilizer N recovery. 75 Table 3.4. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the organic N pool of soil samples taken after harvest. N Soil sample depth fertilizer cm mat—M 31-6 - kg ha.‘ WM 1 m m --- m -—- 5 18.8a 1.4a 8.0a 3.7a 31.9a 6 14.1a -0.5ab 16.3a 3.1a 33.0a W 1 m -- --- a- --- 2 14.1 c 2.0a 3.4a 0.2a 19.7a 4 25.8ab 1.7a 1.6a 0.0a 29.1a W 1 ...... --- .... ... ...- 2 7.6 c 3.4a 3.4a 3.0a 17.4a 3 16.5ab 6.0a 2.3a 0.9a 25.7a 4 17.8ab 3.0a 2.0a 1.5a 24.3a 5 25.3a 4.0a 2.0a 0.4a 31.7a 6 14e4 legal -1. values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 76 Table 3.5. Effect of N rate and application time on fertilizer N applied to Russet Burbank potato found in the inorganic N pool of soil samples taken after harvest. N Soil sample depth fertilizer cm “Mam 9-15 ”-39 “was - “-129 m“ W 1 -.... -.. I..- --- --- 2 1.0a 0.3 b 0.1 b 0.2a 1.6a 3 1.4a 0.4ab 0.1 b 0.5a 2.4a 4 1.5a 0.3 b 0.1 b 0.2a 2.1a 5 1.7a 0.5a 0.7a 0.5a 3.4a 6 1.7a 0.4ab 0.3 b 0.3a 2.7a WM 1 --- --- --- --.. --.. 2 0.7a 0.3a 0.3a 0.4a 1.7 b 3 2.5a 0.7a 1.1a 0.7a 5.0ab 4 1.6a 0.5a 0.5a 0.3a 2.9ab 5 4.4a 1.1a 1.5a 1.7a 8.7a 6 3.7a 1.8a 1.9a 1.3a 8.7a WM 1 ... --- -.. --- -.. 2 ‘ 0.4 b 0.2a 0.4a 0.3a 1.3 b 3 1.3 b 0.5a 0.4a 1.0a 3.2ab 4 1.4 b 0.4a 0.2a 0.4a 2.4ab 5 3.4a 0.6a 0.2a 0.4a 4.6a 1. 1.9 b __.L LL.__9...2.I___Q...3.L____9..Ae Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 77 Only about ten to 15 percent of the total fertilizer N recovered was in the inorganic form, only about 20 percent of this inorganic fertilizer N was found below 60 cm. Treatment five had the highest fertilizer N levels in the 0- 15 cm sample at the East Lansing location. Treatment five also had the highest total inorganic N levels measured to 120 cm in both experiments. The lowest inorganic fertilizer N measurements were made in treatment two. Intermediate fertilizer N levels were measured in the 112 kg N ha'1 treatments, except treatment six which was as high as treatment five at Montcalm and as low as treatment two at East Lansing. The soil fertilizer N levels expressed as a percentage of N applied found in the total, organic, and inorganic fractions are presented in Tables 3.6-3.8. No significant differences in percent recovery of applied fertilizer N between treatments were found for the total N fraction at the Stanton site in 1988. This was also true in the Montcalm experiment in 1989. The only significant difference detected was that treatment two had a higher percent recovery of fertilizer N in the 31-60 cm depth than the other treatments at the East Lansing location in 1989. Although no significant differences were detected between the treatments, the average percent recovery was higher for treatment two than the other treatments (40 percent vs. 25 percent). Table 3.6. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the total N pool in soil samples taken after harvest. 78 N fertilizer treatment 9.}: 15-39 31-§9 §J-]29 19s.] Soil sample depth ‘ ‘ W 1 .- “- a- -- -..- 2 14.9a -4.4 b 32.9a 4.9a 48.3a 3 18.3a -0.4a 2.5a 1.4a 21.8a 5 11.6a 1.1a 4.9a 2.4a 20.0a 6 13.2a -0.1a. 13.9a 3.1a 30.1a WW 1 a..- m -.. --- -- 2 26.3a 4.1a 6.6a 1.0a 38.0a 3 20.3a 5.1a 2.8a 0.3a 28.5a 4 24.4a 1.9a 1.9a 0.3a 28.5a 5 20.2a 1.9a 6.4a 0.2a 28.7a 6 19.5a 5.3a 4.0a 0.3a 29.1a W 1 m m -u..- “- "- 2 14.2a 6.5a 6.7a 5.8a 33.2a 3 15.8a 5.8a 2.4 b 1.7a 25.7a 4 17.0a 3.0a 2.0 b 1.7a 23.7a 5 16.9a 2.8a 1.3 b 0.5a 21.5a ______§ 13i1a_______la§a_______2a9_h_____:lila_______l§11a__ Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 79 Table 3.7. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the organic N pool in soil samples taken after harvest. the 0.05 level of probability (DNMRT). N Soil sample depth fertilizer cm W 31-59 GIL-Ml— W 1 -- -- '--- --- --- 3 17.1a -0.7a 2.4a 1.0a 19.8a 4 13.5a -0.7a 5.0a 1.4a 19.2a 5 10.6a 0.8a 4.5a 2.1a 18.0a 6 11.8a -0.4a 13.7a 2.8a 27.9a W 1 ... --- --- --- --- 2 25.0a 3.6a 6.0a 0.3a 34.9a 4 22.9a 1.5a 1.5a 0.0a 25.9a 5 17.6a 1.3a 5.5a -0.8a 23.6a WW 1 ..... ... -.. --.. -..- 2 13.4a 6.1a 6.0a 5.3a 30.8a 3 14.6a 5.3a 2.0 b 0.8a 22.7a 4 15.8a 2.7a 1.8 b ‘1.3a 21.6a 5 14.9a 2.5a 1.2 b 0.3a 18.9a 6 l.§g;i 1.7 b. ~115§ l4{§g__ Values followed by the same letter were not statistically different at 80 Table 3.8. Effect of N rate and application time on percent fertilizer N applied to Russet Burbank potato found in the inorganic N pool in soil samples taken after harvest. N Soil sample depth fertilizer cm Mat—.935 16-32 iii-W— W 1 “- -.... u- -—. m 2 1.6a 0.5a 0.1a 0.4a 2.6a 3 1.2a 0.3 b 0.1a 0.4a 2.0a 4 1.2a 0.3 b 0.1a 0.2a 1.8a 5 1.0a 0.3 b 0.4a 0.3a 2.0a 6 1.4a 0.3 b 0.2a 0.3a 2.2a W 1 ..- --- --- --- --- 2 1.3a 0.5a 0.6a 0.7a 3.1a 3 2.2a 0.6a 0.9a 0.6a 4.3a 4 1.5a 0.4a 0.4a 0.3a 2.6a 5 2.6a 0.6a 0.9a 1.0a 5.1a 6 '3e3‘ 1.58 1e7‘ 1.28 7.88 W 1 --- -.. --- --- --- 2 0.8a 0.4a 0.7a 0.5a 2.4a 3 1.2a 0.5a 0.4a 0.9a 3.0a 4 1.2a 0.3a 0.2a 0.4a 2.1a 5 2.0a 0.3a 0.1a 0.2a 2.6a the 0.05 level of probability (DNMRT). 0:4! ___i W 1.§;_ Values followed by the same letter were not statistically different at 81 The same trends were found for the organic fraction in all experiments. The only difference was that the percent recovery in this fraction averaged 37 percent for treatment two and 22 percent for all of the other treatments. Accordingly, only an average of 3 percent of the total fertilizer N applied was recovered as inorganic N. Total percent recovery of fertilizer N in the soil to a depth of 120 cm was not affected by the N treatments in any of the experiments in this study. The average percent fertilizer N recovered in the soil to a depth of 120 cm was about 28 percent (excluding the Montcalm site in 1988). Approximately 63 percent of this N was located in the surface 15 cm. An additional 31 percent of the fertilizer N found in the soil was in the 16-60 cm section, leaving only about six percent of the fertilizer N measured in the soil between 60 and 120 cm. Other researchers have found 25-33 percent of applied N in the soil, with most of it in the surface 25 cm (Gerwing et al., 1979; and Westerman et al., 1972). Only about 10 percent of the fertilizer N recovered in the soil after harvest of Russet Burbank potato was in the inorganic form. This represents only about 3 percent of the total N applied to the crop. Data showing the total 1 M KCl extractable N in the soil to a depth of 120 cm is presented in Table 3.9. Although no significant differences were detected, total inorganic N levels were 11 percent higher for treatments two through 82 Table 3.9. Effect of N rate and application time on 1 M ECl extractable N found in soil samples taken after harvest of Russet Burbank potato. N Soil sample depth fertilizer cm WWW}— values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 1 18.4a 19.8a 27.6a 46.4a 112.2a 2 17.7a 17.3a 27.2a 50.0a 112.2a 3 17.1a . 21.6a 33.9a 58.2a 130.8a 4 20.5a 22.7a 37.9a 50.4a 131.5a 5 18.4a 20.6a 32.0a 45.6a 116.6a 6 22.3a 23.5a 33.3a 55.2a 134.3a 1 21.9a 17.5 bc 24.0a 45.2a 108.6a 2 23.7a 20.7a 26.9a 54.2a 125.5a 3 22.7a 16.7 c 24.3a 48.6a 112.3a 4 22.6a 19.3abc 25.9a 51.3a 119.1a 5 23.0a 18.9abc 23.4a 56.3a 121.6a 6 25.3a 20.2ab 28.7a 48.7a 122.9a l 15.8a 10.8a ‘14.0a 24.0a 64.6a 2 15.8a 10.5a 14.2a 25.1a 65.6a 3 20.4a 12.9a 17.9a 25.6a 76.8a 4 14.9a 9.0a 13.3a 24.1a 61.3a 5 19.8a 11.8a 17.2a 30.5a 79.3a 6 19.9a 13.5a 15.9a 27.2a 76.5a ‘1 11.1 b 8.7a 13.9a 27.7a 61.4a 2 11.6 b 10.3a 18.3a 36.3a 76.5a 3 12.1 b 10.3a 13.9a 32.7a 69.0a 4 13.6 b 10.3a 14.9a 28.3a 67.1a 5 17.8a 9.5a 14.8a 31.4a 73.5a § 11.3 p 2.1; 15.1; 35.43 71.55____ 83 five compared to the control at all locations. It is evident that the contribution of inorganic fertilizer N (Table 3.3) to the total inorganic N in these soils is extremely small averaging only about two percent in 1988 and five percent in 1989. It should be noted that the fertilizer N bound to the organic fraction will be mineralized at a higher relative rate than the native N, but even if 20 percent of this fertilizer N was leached, this would only constitute about a five to ten percent additional increase in N loss from the soil to a depth of 120 cm. In this investigation, total fertilizer N recovery in soils was largely unaffected by the rate or timing of fertilizer N applications. At these N rates, total inorganic N levels at the end of the growing season only increased approximately 11 percent beyond the control and fertilizer N generally accounted for less than half of this increase. An average of 75 percent of the total inorganic N measured was in the nitrate form (data not presented). 84 REIIRIICIB Anonymous. 1988. Quikchem methods 12-107-06-2-A and 12-107- 04-1-A. Lachat Instruments, Milwaukee, WI. Brooks, P.D., J.M. Stark, B.B. McInteer, and T. Preston. 1989. A diffusion method to prepare soil extracts for automated nitrogen-15 analysis. Soil Sci. Soc. Am. J. 53:1707-1711. Bundy, L.G., R.P. Wolkowski, and G.G. Weis. 1986. Nitrogen source evaluation for potato production on irrigated sandy soils. Am. Potato J. 63:385-397. Endelman, F.J., D.R. Keeney, J.T. Gilmour, and P.G. Saffigna. 1974. Nitrate and chloride movement in the Plainfield loamy sand under intensive irrigation. J. Environ. Qual. 3:295-298. Harris, D., and E.A. Paul. 1989. Automated analysis of 15N and 1‘C in biological samples. Comm. Soil Sci. Plant Anal. 20:935-947. Gerwing, J.R., A.C. Caldwell, and L.L. Goodroad. 1979. Fertilizer nitrogen distribution under irrigation between soil, plant, and aquifer. J. Environ. Qual. 8:281-284. Lesczynski, D.B., and C.B. Tanner. 1976. Seasonal variation of root distribution of irrigated, field-grown Russet Burbank potato. Am. Potato J. 53:69-78. Lorenz, O.A., B.L. Weir, and J.C. Bishop. 1974. Effect of sources of nitrogen on yield and nitrogen absorption of potatoes. Am. Potato J. 51:56-65. MacKerron, D.R.L., and P.D. Waister. 1985. A simple model of potato growth and yield: part I. model development and sensitivity analysis. Agricultural and Forest Meteorology. 34:241-252. Ojala, J.C., J.C. Stark, and G.E. Kleinkopf. 1990. Influence, of irrigation and nitrogen management of potato yield and quality. An. Potato J. 67:29-43. Saffigna, P.G., D.R. Rooney, and C.B. Tanner. 1977. Nitrogen, chloride, and water balance with irrigated Russet Burbank potatoes in a sandy soil. Agron. J. 69:251-257. Tyler, K.B., F.E. Broadbent, and J.C. Bishop. 1983. Efficiency of nitrogen uptake by potatoes. Am. Potato J. 60:261-269. 85 Vitosh, M.L. 1971. Fertilizer studies with irrigated potatoes. Research report No. 142, Mich. State. Univ. A.E.S. 11 pp. Vitosh, M.L. 1984. Irrigation scheduling for potatoes in Michigan. Am. Potato J. 61:205-213. Vitosh, M.L. 1985. Nitrogen management strategies for potato producers. Mich. State. Univ. Ext. Bull. W009. 4 pp. Vitosh, M.L. 1990. Potato fertilizer recommendations. Mich. State Univ. Ext. Bull. E2220. 8pp. Westerman, B.L., L.T. Kurtz, and R.D. Hauck. 1972. Recovery of “N labeled fertilizers in field experiments. Soil Sci. SOC. Am. Proc. 36:82-86. CHAPTER FOUR POTENTIAL.OF SOIL.AND TISSUE SANPEBNANALKSIS AS INDICATORS OP NITROGEN SUFTICIINCY IR RDSSIT BURBANRIPOTATO ABSTRACT Assessing the supplemental N requirement of potato prior to tuber initiation could potentially optimize sidedress N applications, increase tuber yield and decrease N leaching. A two year field investigation was conducted to evaluate the potential of several soil and petiole N fractions for detecting differences in fertilizer N applications to potato (Sblanum tuberosum L. var. Russet Burbank) grown on irrigated sandy soils in Michigan. Nitrogen was applied as 15N depleted ammonium sulfate [(NHQZSO‘] at rates 0, 56, 112, and 168 kg ha'1 in a single application at planting or in split applications during the growing season. Preplant 1 M KCl extractable N levels were found to have some utility in predicting the N supplying capacity of soil. Soil samples taken at tuber initiation were shown to detect differences in fertilizer N applied at planting of about 56 kg N ha”. No benefit from sampling at depths greater than 60 cm were observed. The total petiole N concentration of the newest fully expanded leaf is very responsive to fertilizer N applications and may be able to detect differences in N applications to 28 kg N ha”. It appears that the current nitrate N sufficiency levels for mid and late season petiole 86 87 samples used in Michigan may be slightly higher than necessary for maximum yield of Russet Burbank potato. 8 8 INTRODUCTION Optimizing nitrogen (N) fertilization is probably the single most important management practice for maximizing potato tuber yield. Insufficient N can drastically reduce tuber yield, while excessive N rates may induce tuber malformations (Roberts and Cheng, 1985) and reduce tuber specific gravity (Lauer, 1986; Ojala et al., 1990). Applying large quantities of fertilizer N and irrigation water have also been shown to increase nitrate leaching through the soil profile (Saffigna et al., 1977). Currently, Michigan State University does not have a soil test for determining crop fertilizer N requirements (Vitosh, 1990). Michigan producers have historically applied liberal amounts of fertilizer N to potato because the potential economic risk of reduced tuber quality is not as great as a reduction in tuber yield. If N in the root zone could be' maintained at the minimum levels required for optimum.crop growth throughout the growing season, the potential for nitrate leaching could be reduced. Unfortunately, the availability of native soil N is not consistent from year to year, even within a particular soil type. Due to the dynamic nature of net soil N mineralization, the optimum fertilizer management program for one year could be inadequate, or even excessive in a subsequent year. Increases in tuber yield and fertilizer uptake efficiency often result from applying some fertilizer N at planting 89 with the balance sidedressed at tuber initiation (Westermann et al., 1988; MacMurdo et al., 1988). If a soil or plant tissue sample taken at tuber initiation could predict the N requirement of the crop for the remainder of the growing season, sidedress applications resulting in maximum tuber yield with minimal N leaching could be applied more consistently than with conventional fertilization practices. The nitrate concentration of the petioles of the most recent fully expanded leaf has been used as an indicator of N sufficiency throughout the growing season in Michigan (Vitosh, 1985). Similar tests have been used in Idaho (Westerman and Kleinkopf, 1985). However, Doll et al. (1971) found that petiole nitrate levels change too rapidly to be of much use unless the age of the plant is known precisely. They suggested that soil nitrate may be a more stable criterion of N needs during the growing season. Inorganic soil N levels taken prior to planting and after tuber initiation have also been used as a N monitor to some extent with potato and other crops. Muller and Beer (1986) found that a fertilizer credit of 10 kg N ha'1 could be A given for each 30 kg of total inorganic N ha‘1 above 75 kg N hafl in the surface 60 cm of soil prior to planting. Nestermann and Kleinkopf (1985) found the critical soil nitrate level in the top 45 cm to be 7.5 mg N kg'1 during tuber bulking. ' One objective of this study was to evaluate 1 M KCl 9O extractable soil nitrate, ammonium, and total inorganic N (nitrate and ammonium) samples taken at tuber initiation for their ability to detect differences in levels of fertilizer N applied at planting. The potential of petiole N (total N and 1 M KCl extractable nitrate) samples taken throughout the growing season for detecting differences in fertilizer N applications was also evaluated. NATERIALS AND METHODS General: This study was conducted at two sites each year during the 1988 and 1989 growing seasons. Complete information regarding location, soil classification, and field history of each site can be found in Chapter one. General soil test data for each site are presented in Table 1.1. The experimental design was a randomized complete block with four replications of six N treatments ranging from 0 to 168 kg N ha'1 applied in single or split applications (Table 1.3). Each plot consisted of four rows 0.86 m wide and 15 m long, except for the second site in 1988 where plots were three rows 18 m long. Russet Burbank potato was planted as whole seed or seed pieces weighing approximately 100 g - placed 25 cm apart. Aldicarb {z-methy-z- (methylthio)propanal-O-[(methylamino)carbonleoxime} was applied at planting (3.36 kg active ingredient ha”) for insect and nematode control. 91 weeds were controlled with preemergent applications of metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2- methoxy-l-methylethyl)acetamide] and metribuzin [(4-amino-6- (1,1-dimethylethyl)-3-methylthio)-1,2,4-triazin-5(4H)-one] at 2.24 and 0.56 kg active ingredient ha”, respectively. All plots received approximately 50 kg P and 90 kg K hafi in a band approximately 5 cm below and 5 cm to the side of the seed piece at planting. Fungicides and insecticides were applied as needed at all sites. Irrigation was applied based on precipitation and evapotransipiration according to Vitosh (1984) (Table 1.4). Ammonium sulfate ((NH‘)ZSO‘) was the fertilizer N source applied to the crop. Some fertilizer N source evaluation studies have concluded (NH‘) ZSO‘ is superior to other N sources for potato production (Bundy et al., 1986 and Lorenz et al., 1974), although Vitosh (1971) found no source differences in Michigan. In 1988, approximately one third of each plot received natural abundance (NHQZSO‘ fertilizer while the remaining two thirds of each plot received 1sN depleted (0.005 atom % "m (Nuazso . In 1989, each plot received only 1’N depleted (0.005 atom % 1sN) (NH,)ZSO‘. The ‘fiN depleted fertilizer was applied as a 40 percent by weight (NH‘) 280‘ aqueous solution with a backpack sprayer regulated to 4.35 kPa with a C02 tank. Nitrogen at planting was applied in a band 5 cm on each side of the seed piece and lightly incorporated. Nitrogen applied at tuber 92 initiation was banded to the side of the plant and irrigated, while the final two fertilizer applications were topdressed along each row and immediately irrigated. Banded N at planting and sidedress N applications at hilling time have been shown to be superior to broadcast N applications in potato production in Michigan (Vitosh, 1985). Soil Analyses: Soil samples (3-5 cores 5 cm in diameter) were taken from each plot to 120 cm prior to planting in late April or early May. After planting, a strip three m long by four rows wide was established within the 15N depleted area of each plot for the collection of all subsequent soil samples. These samples (3-4 cores 5 cm in diameter) were taken across the hill of one of the two center rows within each plot in mid June, mid August, and in late September following tuber harvest. All soil samples were separated into 0-15, 16-30, 31-45, 46-60 and 61-120 cm increments. Soil samples were stored at -15°C and then air dried, ground to < 2 mm, and stored in cardboard boxes prior to analysis in 1988 and immediately air dried, ground, and stored in cardboard boxes until analysis in 1989. Each sample was extracted with a 1:4 (m:v) soil:1 M KCl aqueous solution forinorganic N (NO3 and NH‘) using a shaking time of 60 minutes. The extract was filtered through Whatman No. 2 filter paper that had been prewashed with 10 mls of the 93 extracting solution and analyzed using a flow injection autoanalyzer (Anonymous, 1988). Petiole Analyses: Petiole samples were taken biweekly for six to eight weeks following tuber initiation. Approximately 25-30 petioles were taken from the newest fully expanded leaf (usually the fourth petiole from the top of the stem) from plants in the center rows of each plot. The petiole samples were dried at 60°C in a forced air drier, ground to < 250 um and stored in polyethylene bags at room temperature prior to analysis. Petiole N0; was determined using the same 1 M KCl extraction procedure as used for the soil with the following exceptions. A 1:500 (m:v) tissue:solution extraction was used and activated charcoal was added to the mixture prior to shaking to remove color impurities that could potentially interfere with the colorimetric analysis. Total petiole N and ”N of the petioles was determined with an automatic N and carbon analyzing mass spectrometer (Tracermass, Europa Scientific) using the procedure outlined by Harris and Paul (1989). RESULTS AND DISCUSSION Boil Analyses: Nitrate, ammonium, and total (nitrate and ammonium) 1 M KCl extractable N data for soil samples taken prior to 94 planting are presented in Tables 4.1, 4.2, and 4.3, respectively. The majority of the 1 M KCl extractable N was in the nitrate form. The only differences detected were in the nitrate and total KCl extractable N levels in the 0-15 cm depth for the East Lansing location in 1989. Since the greatest difference between any two treatments was less than 3.5 kg N ha”, these differences were of no practical significance. It should be noted that the values in 1988 were much higher than in 1989. This was especially true at the Stanton site in 1988. The warm and dry spring climatic conditions in 1988 compared to 1989 (Table 1.4.) may have stimulated N mineralization and reduced N leaching. In addition, soil samples at the Montcalm site in 1988 were taken much earlier than at the Stanton study (4/6 vs. 5/16). From analysis of the control plot tuber yield data in Chapter one (Table 1.5), it is apparent that preplant 1 M KCl extractable N levels may be an important factor in determining tuber yield potential from soil N sources and the relative utility of subsequent fertilizer N applications. Data for nitrate, ammonium, and total 1 M KCl extractable N found in soil samples taken in mid June are located in Tables 4.4, 4.5, and 4.6. These data should reflect differences between the amount of fertilizer N applied to the treatments at planting. No differences in nitrate levels were detected between Table 4.1. 1 M ECl extractable N (as nitrate) concentration of soil 95 samples taken prior to planting of Russet Burbank potato. N Soil sample depth fertiliser cm W5 0-§L___9_129___- kg N ha'1 1 8.0a 14.2a 20.0a 24.7a 44.6a 2 7.5a 14.5a 20.4a 26.0a 47.7a 3 8.2a 15.5a 22.1a 27.7a 49.2a 4 8.6a 16.2a 21.7a 27.5a 49.1a 5 8.3a 14.3a 19.8a 25.4a 45.8a 6 7.6a 14.7a 20.0a 25.2a 46.5a 1 23.7a 35.3a 43.8a 52.7a 104.3a 2 22.4a 37.7a 48.2a 58.9a 112.0a 3 17.9a 31.2a 41.1a 50.9a 101.2a 4 16.9a 28.8a 37.7a 47.3a 99.6a 5 17.2a 29.8a 38.1a 46.4a 95.8a 6 28.0a 41.5a 51.1a 61.4a 115.1a l 1.4a 3.9a 6.5a 8.8a 16.9a 2 0.7a 2.7a 6.5a 9.7a 23.1a 3 0.6a 3.6a 6.6a 9.5a 18.1a 4 1.1a 3.3a 5.4a 8.9a 18.8a 5 1.4a 3.5a 6.2a 7.9a 19.6a 6 1.6a 4.5a 7.4a 13.8a 24.7a l 3.6abc 6.0a 9.2a 12.1a 29.3a 2 1.8 c 3.8a 7.2a 10.8a 32.7a 3 2.1 bc 5.3a 8.9a 12.4a 27.5a 4 2.4abc 5.6a 9.5a 13.4a 29.2a 5 4.3a 7.7a 10.9a 14.2a 28.9a __§ 4-1lh 7.1. 9. values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 96 Table 4.2. 1 M ECl extractable N (as ammonium) concentration of soil samples taken prior to planting Russet Burbank potato. N Soil sample depth fertilizer cm Armament—JUN 9-45 9:69—41:29.— kg N ha'1 WW 1 3.7a 7.4a 11.7a 14.7a 26.8a 2 3.5a 6.3a 10.3a 12.9a 26.3a 3 3.6a 6.8a 11.2a 14.1a 26.7a 4 4.6a 7.8a 12.1a 15.1a 26.8a 5 4.1a 8.4a 12.5a 15.0a 27.6a 6 3.5a 6.4a 10.4a 13.4a 26.1a l 4.4a 8.1a 10.9a 13.1a 24.1a 2 4.5a 9.1a 12.5a 15.2a 25.8a 3 4.5a 8.7a 12.1a 14.7a 24.9a 4 4.2a 8.2a 11.5a 14.0a 25.2a 5 4.1a 8.2a 11.3a 13.7a 23.9a 6 4.8a 8.7a 11.7a 14.0a 25.3a l 1.2a 2.6a 4.5a 6.7a 15.2a 2 3.6a 6.6a 10.0a 13.4a 26.3a 3 4.2a 7.1a 8.6a 11.1a 20.6a 4 1.5a 5.5a 8.2a 9.6a 18.9a 5 1.9a 3.9a 6.4a 8.5a 17.8a l 0.9a 2.9a 4.1a 5.0a 10.7a 2 0.1a 1.1a 3.7a 5.4a 11.7a 3 0.5a 2.1a 4.7a 6.0a 9.4a 4 0.3a 1.8a 2.9a 4.1a 10.3a 5 0.4a 2.1a 3.8a 4.9a 8.0a Values followed by the same latter were not statistically different at the 0.05 level of probability (DNMRT). 97 Table 4.3. 1 M ECl extractable N (nitrate and ammonia) concentration of soil samples taken prior to planting Russet Burbank potato. N Soil sample depth fertilizer cm Wilt—9:19 9-4 - - kg N ha‘ 1 21.6a 31.7a 39.5a 71.6a 2 20.9a 30.8a 38.8a 73.9a 3 22.3a 33.4a 41.8a 76.0a 4 24.0a 33.8a 42.6a 75.9a 5 22.7a 32.3a 40.5a 73.6a 6 .2l.la 30.4a 38.6a 72.6a l 43.3a 54.6a 65.8a 128.4a 2 46.8a 60.7a 74.0a 137.7a 3 40.0a 53.2a 65.6a 126.2a 4 37.0a 49.2a 61.3a 124.8a 5 38.1a 49.3a 60.2a 119.8a 6 50.2a 62.8a 75.4a 140.4a l 6.5a 11.0a 15.5a 32.1a 2 9.3a 16.5a 23.1a 49.4a 3 10.7a 15.2a 20.7a 38.8a 4 8.8a 13.6a 18.5a 37.7a 5 7.4a 12.6a 16.4a 37.4a 6 12.2a 18.2a 24.2a 53.7a 1 8.8a 13.4a 17.0a 39.9a 2 4.9a 10.8a 16.2a 44.4a 3 7.4a 13.6a 18.4a 36.9a 4 7.4a 12.4a 17.4a 39. 4a 5 9.8a 14.7a 19. 0a 36. 8a ___L Ma 97J__1.L§.I___1Lil___3lnfil___ values followed by the same»letter were not statistically different at the 0.05 level of probability (DNMRT). Table 4.4. Effect of N rate and application time on 1 M ECl extractable N (as nitrate) concentration of soil samples taken in mid June. fertilizer “gm“; 9-15 9-3g kg “91.3; . 9-59 9.39 LUQUNH OU'IfiUNH OUI‘UNP 00'5“”.- Soil sample depth cm 40.2a 54.2a 62.5a 70.7a 100.9a 41.6a 59.7a 71.5a 80.5a 111.3a 40.6a 64.5a 78.5a 86.6a ll3.4a 59.6a 82.9a 93.8a 104.9a 136.4a 39.0a 55.1a 64.8a 71.2a 99.3a 37.9a 49.8a 59.0a 65.7a 94.4a 24.6a 47.8a 59.7a 70.8a 122.4a 28.7a 51.4a 65.5a 80.6a 133.7a 26.0a 47.5a 62.3a 76.0a 126.3a 33.5a 55.3a 68.7a 83.6a 135.9a 29.8a 51.4a 65.7a 80.5a 129.9a 28.0a 48.8a 66.0a 83.6a 137.3a 4.1 c 8.2 c 15.4 c 20.9 d 33.0 c 12.5 bc 23.4 be 33.4 bc 60.1ab 73.6 bc 38.4a 64.2a 78.2a 76.1a 89.7a 21.5 b 36.2 b 47.3 b 37.0 cd 49.9 b 17.1 b 31.0 b 41.1 b 49.8ab 65.2 b 15.3 bc 24.4 bc 32.4 be 37.1 be 52.6 be 4.5 c 10.1 15.6 d 20.9 d 43.8 12.5 b 33.7 b 48.2 b 60.1ab 95.4ab 30.0a 51.4a 66.0a 76.1a 118.2a 9.8 bc 21.8 c 30.1 cd 37.0 cd 60.6 cd 13.4 b 27.0 bc 39.4 bc 49.8ab 82.8 bc 11.6 is ,ZQ‘1__Qfl___ZQifl__2fl__31a1_h£————§1L2——§§——— Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 99 Table 4.5. Effect of N rate and application time on 1 M ECl extractable N (as ammonium) concentration of soil samples taken in mid June. N fertilizer ““3”“; 9-15 52-39 “gr-'9“: . 9-59 9-129 Soil sample depth cm 1 7.8a 12.4a 15.4 c 18.4 b 29.6a 2 11.2a. 15.6a 20.0ab 23.4a 34.0a 3 9.3a 15.2a 21.0a 24.9a 40.7a 4 8.4a 14.3a 18.5abc 21.9ab 33.7a 5 7.8a 12.7a 16.3 bc 19.2 b 29.7a 6 7.6a 12.3a 15.9 c 18.8 b 29.5a 1 5.7 b 9.0 b 12.8 b 16.3 b 30.0 b 2 9.5 b 14.9 b 19.1 b 24.4 b 40.7 b 3 44.7a 79.9a 102.2a 113.4a 143.5a 4 17.9 b 24.7 b 29.5 b 34.4 b 50.0 b 5 7.6 b 12.1 b 16.1 b 19.3 b 32.7 b 6 11.8 b 23.0 b 33.5 b 38.2 b 53.6 b l 8.7a 16.3 b 22.7 b 28.3 be 50.7 bc 2 13.8a 22.6ab 29.1ab 35.5abc 59.8 b 3 20.9a 33.8a 41.1a 47.2a 71.6a 4 14.6a 24.4ab , 31.7ab 37.0ab 59.7 b 5 9.8a 17.9 b 24.2 b 30.3 bc 52.1 bc 6 8.6a 14.9 b 19.4 b 24.3 c 44.2 c l 8.1a 13.8a 18.9a 23.8a 43.4a 2 8.4a 17.0a 24.1a 31.2a 64.6a 3 9.4a 16.0a 22.1a 27.6a 49.5a 4 7.6a 13.0a 18.1a 22.9a 47.5a 5 7.4a 13.9a 19.5a 25.6a 49.1a ______§ 7.0; 12.63 15.2; 22.1. 47.4: Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 100 Table 4.6. Effect of N rate and application time on 1 M ECl extractable N (nitrate and ammonia) concentration of soil samples taken in mid June. N Soil sample depth fertilizer cm 'l I I - - kg N-ha'1 - - LM.U”H OUI§UNH maneuver- 0.43540”!- Values followed by the same letter were not statistically different at 48.0a 52.8a 49.9a 68.0a 46.9a 45.5a 30.3 b 38.3 b 70.6a 51.4ab 37.3 b 39.8 b 66.6a 75.3a 79.6a 97.1a 67.8a 62.1a 56.8 b 66.3 b 127.4a 80.0 b 63.5 b 71.8 b 24.4 c 46.0 bc 98.0a 60.7 b 49.0 be 39.3 bc 23.9 d 50.7'b 67.3a 34.9 cd 40.9 bc 78.0a 91.5a 99.5a 112.3a 81.1a 74.9a 38.1 c 62.5 bc 119.3a 79.0 b 65.3 bc 51.8 bc 34.5 72.2 b 88.1a 89.1a 103.8a lll.6a 126.8a 90.4a 84.5a 49.1 c 74.6 bc 131.8a 92.0 b 78.5 be 62.8 bc 6 44.7 91.3ab 103.7a 130.5a 145.1a 154.3a 170.1a 129.1a 123.8a 149.0a 178.7a 272.5a 194.7a 174.9a 194.5a 83.6 c 112.4 bc 169.8a 127.6 b 115.7 b 98.1 bc 87.1 c 160.0a 167.7a 48.2 Cd 59.9 Cd 108.2 bc 58.9 be the 0.05 level of probability (13mm). 75.3 bc 131.8 b 101 the treatments in either experiment in 1988. In 1989, differences between treatments were observed. In both experiments, treatment three (112 kg N ha”) had the highest nitrate levels while treatment one (control) had the lowest. Treatments two, four, and five all received 56 kg N ha'1 and the nitrate levels of these treatments were between those of treatments one and three. Treatment six, which had 28 kg N ha“1 applied, generally showed nitrate levels between the control and the 56 kg N ha’1 applications. Significant differences in ammonium levels were detected between treatments in 1988 and 1989, but these differences were not present at all soil depths. At the Montcalm site in 1988, no significant differences were found in the surface 30 cm, and the differences detected at the lower depths had very little impact on the total 1 M KCl extractable N levels. In the Stanton study, a very large increase in the ammonium level was detected in treatment three. This increase in ammonium beyond that detected in the check is approximately equal to the total fertilizer N applied to this treatment. No differences were detected between the other treatments in this study. In 1989, significant increases in soil ammonium levels were detected below the surface 15 cm at the Montcalm site. These differences appeared to be related to the N treatments because the treatments that received higher N rates generally contained greater ammonium levels. No differences 102 in ammomium levels were found between treatments at the East Lansing location. Total 1 M KCl extractable N levels were not influenced by the N treatments in the Montcalm experiment in 1988. At the Stanton study, only treatment three had a higher N soil level than the other treatments, and this difference was not detected at depths greater than 45 cm. The differences in total 1 M KCl extractable N in the soil samples were more responsive to the N treatments in 1989. In both experiments, treatment three had the highest N levels and 'treatment one had the lowest. The other treatments contained intermediate soil N levels. 'Significant differences between treatment six, the control, and treatments receiving 56 kg N ha'1 at this time, were not found at the Montcalm site, but samples taken to 30-60 cm i were significantly different in the East Lansing experiment. Upon analysis of the data from the mid June soil samples, no benefit from sampling the 61-120 cm depth was evident. Taking soil samples to this sample depth on a routine basis would be impractical. The greatest mean separations were generally obtained when soil data from the surface to a depth of 45-60 cm was used, and soil samples could be taken to these depths on a routine basis. Since over 90 percent of the total root length in potato is present in the surface 25 cm (Lesczynski and Tanner, 1976), the merits of sampling below 30-45 cm is questionable. It appears that measuring 103 inorganic N in soil would allow for the detection of differences in fertilizer N applications of approximately 56 kg N ha”, so there may be some potential for using this information as part of a N management program. The data for soil samples taken in mid August and late September are presented in Tables 4.7-4.9, and 4.10-4.12, respectively. Since these samples are of no use in evaluating the need for supplemental fertilizer N during the growing season, they will not be discussed and are included only for completeness. 104 Table 4.7. Effect of N rate and application time on 1 M ECl extractable N (as nitrate) concentration of soil samples taken in mid August. N Soil sample depth fertilizer cm “um“, 9-15 9-39 "91:511.: 919 9.1252 1 29.1a 50.7a 63.7a 78.2a 127.4a 2 30.4a 55.2a 72.5a 88.1a 136.2a 3 29.4a 54.6a 72.5a 88.8a 141.8a 4 35.9a 59.5a 78.3a 96.3a 142.4a 5 30.0a 52.8a 73.7a 91.5a 145.9a 6 41.1a 68.6a 85.2a 99.9a 149.9a 1 21.7a 32.1a 39.9a 46.3a 86.4a 2 23.1a 35.9a 45.6a 53.7a 93.2a 3 19.9a 29.2a 37.5a 44.9a 86.7a 4 24.3a 36.6a 47.3a 56.1a 108.4a 5 31.9a 43.6a 55.4a 64.9a 112.8a 6 27.7a 39.5a 49.4a 59.3a 114.0a l 7.5a 11.8a 15.4a 19.2a 35.1a 2 4.4a 8.8a 11.4a 14.2a 28.6a 3 5.8a 10.8a 13.2a 16.8a 31.8a 4 5.0a 10.8a 13.9a 17.7a 33.5a 5 8.2a 13.6a 16.8a 20.6a 36.7a . 6 9.9a 14.6a 19.5a 24.4a 41.8a l 5.1a 11.4a 16.6a 21.8a 42.2a 2 3.4a 8.0a 12.3a 18.7a 45.2a 3 5.9a' 10.2a 15.4a 21.7a 53.0a 4 4.5a 9.7a 14.1a 18.1a 42.8a 5 9.6a 14.5a 19.7a 26.5a 48.7a ___§ WILL—im— values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 105 Table 4.8. Effect of N rate and application time on 1 M ECl extractable N (as ammonium) concentration of soil samples taken in mid August. N Soil sample depth fertilizer cm 9.99.9999; 9-, 9 9-99 kg91.9,“, . 9-99 9-, ,9 values followed by the same latter were not statistically different at the 0.05 level of probability (DNMRT). 1 5.4a 9.4a 13.3a 19.8a 41.3a 2 4.1a 7.6a 11.6a 18.4a 41.7a 3 3.9a 7.9a 12.9a 19.9a 42.0a 4 4.3a 9.0a 13.6a 21.2a 42.7a 5 4.1a 8.2a 12.5a 19.3a 42.0a 6 4.8a 9.6a 13.4a 19.4a 42.4a WW 1 2.6a 5.4a 7.3a 10.0a 22.0a 2 3.1a 5.6a 7.7a 10.5a 21.0a 3 2.6a 5.4a 7.5a 10.3a 21.2a 4 2.7a 5.6a 7.8a 10.6a 20.5a 5 2.8a 6.1a 8.5a 11.4a 22.0a 6 2.8a 5.6a 7.4a 10.5a 21.2a 1 5.0a 9.7a 14.1a 17.5a 33.0a 2 5.6a 10.3a 14.4a 17.6a 33.3a 3 5.1a 9.0a 13.6a 16.6a 35.4a 4 6.9a 11.1a 15.4a 18.8a 37.0a 5 10.9a 15.6a 20.2a 23.5a 40.3a 6 6.4a 10.7a 14.4a 18.0a 36.1a l 7.0a 13.1a 17.0a 20.5a 34.5a 2 7.6a 13.1a 17.2a 22.0a 43.5a 3 7.7a 13.2a 17.4a 21.7a 45.6a 4 8.1a 13.8a 17.8a 22.4a 44.4a 5 7.9a 14.1a 18.4a 23.1a 42.8a ______§ A1.9 106 Table 4.9. Effect of N rate and application time on 1 M ECl extractable N (nitrate and ammonia) concentration of soil samples taken in mid August. N Soil sample depth fertilizer cm IEIIIIIDI 9-15 9-39 9-95 . g-§9 9-129 kg N ha 1 34.4a 60.1a 77.0a 97.9a 168.6a 2 34.4a 62.8a 84.1a 106.5a 177.9a 3 33.3a 62.4a 85.3a 108.7a 183.7a 4 40.3a 68.5a 91.9a 117.6a 185.2a 5 34.0a 61.0a 86.2a 110.8a 187.9a 6 45.8a 78.2a 98.6a 119.3a 192.3a l 24.3a 37.5a 47.2a 56.4a 108.4a 2 26.2a 41.5a 53.4a 64.2a 114.2a 3 22.6a 34.6a 45.0a 55.2a 107.8a 4 27.0a 42.2a 55.1a 66.7a 128.8a 5 34.7a 49.7a 63.9a 76.3a 134.8a 6 30.5a 45.1a 56.9a 69.8a 135.2a 1 12.5a 21.4a 29.5a 36.8a 68.2a 2 9.9a 19.0a 25.8a 31.8a 62.0a 3 10.9a 19.7a 26.8a 33.4a 67.2a 4 12.0a 21.9a 29.3a 36.4a 70.3a 5 19.1a 29.2a 37.0a 44.1a 77.0a 6 16.3a 25.3a 33.9a 42.4a 77.9a 1 12.1a 24.6a 33.6a 42.4a 76.8a 2 11.1a 21.2a 29.5a 40.6a 88.6a 3 13.6a 23.4a 32.8a 43.4a 98.6a 4 12.6a 23.5a 31.9a 40.5a 87.2a § 14.2; 239§g 32,1; 59,3; 15,3; Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 107 Table 4.10. Effect of N rate and application time on 1 M ECl extractable N (as nitrate) concentration of soil samples taken after harvest of Russet Burbank potato. N Soil sample depth fertilizer cm “9,9999: 9-, 9 9-99 1.992353“: _ 9-99 9-, 99 l 13.7a 28.3a 38.4a 47.3a 83.2a 2 13.4a 26.4a 36.9a 45.8a 82.7a 3 12.7a 29.1a 42.7a 55.1a 99.2a 4 14.5a 30.7a 45.8a 58.2a 93.8a 5 13.7a 29.4a 42.5a 53.6a 88.4a 6 17.0a 34.6a 47.2a 58.8a 98.4a 1 10.4a 19.6a 27.44 34.0a 66.0a 2 13.1a 22.6a 31.7a 39.2a 76.3a 3 9.6a 17.9a 25.1a 32.1a 69.4a 4 10.2a 18.5a 25.4a 32.2a 68.2a 5 11.3a 20.3a 27.5a 33.8a 72.5a 6 12.2a 22.3a 30.8a 38.8a 70.5a 1 11.9a 20.1a 24.8a 28.8a 42.9a 2 12.9a 20.9a 25.6a 29.7a 45.2a 3 16.8a 26.9a 33.6a 38.3a 54.5a 4 11.9a 18.4a 23.5a 27.2a 41.0a 5 16.3a, 25.5a 32.0a 37.2a 53.9a 6 16.4a 27.5a 33.6a 38.6a 55.6a 1 9.1a 15.3a 18.6a 23.4a 43.0a 2 9.9a 17.9a 22.7a 29.2a 55.8a 3 10.1a 17.2a 20.3a 25.0a 49.0a 4 11.4a 19.2a 23.5a 28.2a 48.5a 5 12.5a 19.8a 23.2a 28.0a 51.9a ___§ tile—Law— values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 108 Table 4.11. Effect of N rate and application time on 1 M ECl extractable N (as ammonium) concentration of soil samples taken after harvest of Russet Burbank potato. N Soil sample depth fertilizer cm ' - - kg N ha" - - WM 4.7a 10.0a 15.1a 18.6a 29.1a 1 2 4.4a 8.6a 12.9a 16.4a 29.5a 3 4.4a 9.7a 13.7a 17.5a 31.5a 4 6.0a 12.6a 18.0a 23.0a 37.8a 6 5.4a 11.2a 16.2a 20.3a 35.8a W 1 11.4a 19.8a 25.2a 29.4a 42.6a 2 10.6a 21.8a 27.9a 32.2a 49.3a 3 13.1a 21.5a 25.7a 31.5a 42.8a 4 12.5a 23.5a - 31.2a 35.7a 51.0a 5 11.8a 21.6a 27.1a 31.5a 49.1a 6 13.1a 23.2a 30.0a 35.4a 52.4a W l 4.0a 6.6a 9.5a 11.9a 21.8a 2 2.9a 5.5a 8.1a 10.8a 20.4a 3 3.6a 6.5a 10.9a 12.9a 22.3a 4 3.0a 5.6a 7.7a 10.1a 20.4a 5 3.5a 6.1a 9.1a 11.6a 25.4a 6 3.5a 5.9a 8.2a 10.8a 21.0a WW 1 2.1 b 4.6a 8.3 b 10.5 b 18.9 b 2 1.7 b 4.0a 7.4 b 11.0 b 20.7ab 3 1.9 b 5.1a 8.8 b 11.2 b 19.9 b 4 2.1 b 4.7a 8.2 b 10.7 b 18.7 b 5 5.3a 7.5a 11.2a 14.1a 21.6a __5 M 7-Lb__19...9_b__J.§-.§_b___ Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 109 Table 4.12. Effect of N rate and application time on 1 M.ECl extractable N (nitrate and ammonia) concentration of soil samples taken after harvest of Russet Burbank potato. N Soil sample depth fertilizer cm Jaw-45 0-§9___.9;129____ kg N ha" 1 18.4a 38.3a 53.4a 65.8a 112.2a 2 17.7a 35.0a 49.8a 62.0a 112.0a 3 17.1a 38.7a 56.4a 72.6a 130.7a 4 20.5a 43.2a 63.8a 81.2a 131.5a 5 18.4a 39.0a 56.5a 71.1a 116.7a 6 22.4a 45.9a 63.3a 79.1a 134.2a l 21.9a 39.4a 52.7a 63.3a 108.5a 2 23.7a 44.5a 59.5a 71.4a 125.6a 3 22.7a 39.3a 50.9a 63.6a 112.2a 4 22.6a 42.0a 56.6a 67.9a 119.2a 5 23.0a 41.9a 54.7a 65.3a 121.6a 6 25.3a 45.5a 60.8a 74.2a 122.9a l 15.8a 26.7a 34.2a 40.7a A 64.7a 2 15.8a 26.3a 33.7a 40.5a 65.6a 3 20.4a 33.3a 44.5a 51.3a 76.9a 5 19.8a 31.6a 41.0a 48.8a 79.3a 6 19.9a 33.4a 41.9a 49.3a 76.5a 1 11.1 b 19.9a 26.9a 33.8a 61.5a 2 11.6 b 21.9a 30.1a 40.2a 76.5a 3 12.1 b 22.4a 29.2a 36.2a 68.9a 4 13.6 b 23.9a 31.7a 38.8a 67.1a 5 17.8a 27.3a 34.4a 42.1a 73.5a ____§ 11.3 p 21,93 29,53 3L1. 11,5. Values followed by the same letter were not statistically different at the 0.05 level of probability (DNMRT). 110 Petiole Analyses: Total Nitrogen Analyses: Total N data for petiole samples taken in all experiments is presented in Table 4.13. Petiole samples were taken just prior to any fertilizer N applications made at these dates. In 1988, no differences were detected between treatments for the petiole samples taken at tuber initiation. These values were only about 60 percent of the values found in the petiole samples taken at the same stage of growth in 1989. The lack of adequate moisture prior to the start of irrigation may have affected early season N uptake in 1988. In 1989, however, petiole N concentrations directly reflected the amount of fertilizer applied at planting in both experiments. Treatment three (112 kg N ha‘1 applied at planting) had the highest N concentration, followed by treatments two, four, and five, which all had 56 kg N ha'1 applied at planting. Only 28 kg N ha'1 was applied at planting in treatment six, and the petiole N concentration of this treatment was intermediate between the 56 kg N ha'1 treatments and the control. Significant differences in total N concentration were detected in the second petiole sample (tuber initiation + 14 days) in all experiments. These petiole samples should reflect fertilizer N applied at planting and tuber initiation. At the Mentcalm site in 1988, treatments three, four and five had the highest total N concentrations. All 111. Table 4.13. Effect of N rate and application time on total N concentration of Russet Burbank potato petioles. Petiole sample time N Tissue N concentration Fertilizer Tuber TI+ TI+ TI+ E: l 3.43a 3.10 c 3.59 e 2.32 c 2 3.53a 3.78 b 4.54 d 2.50 c 3 3.64a 4.44a 5.13 bc 3.18 b 4 3.60a 4.72a 5.27ab 3.39 b 5 3.63a 4.42a 5.57a 3.83a 6 3.51a- 3.91 b 4.87 c 3.39 b l 3.24a 3.30 b 2.95 d 2.13 d 2 3.37a 4.66a 4.15 c 2.71 c 3 3.24a 4.80a 4.63 b 3.14 c 4 3.26a 4.81a 4.94 b 3.32 bc 5 3.32a 4.73a 5.77a 4.10a 6 3.44a 4.53a 4.99 b 3.79ab W l 3.97 d 3.56 c 3.43 d 2.88 b 2 5.98 b 3.20 c 3.05 e 2.59 c 3 6.94a 4.35 b 4.02 c 2.90 b 4 6.12 b 4.83a 4.19 c 2.89 b 5 6.12 b 5.04a 5.21a 4.05a 6 5.15 c 4.23 b 4.56 3.98a l 3.85 2.85 c 2.38 e 2.16 c 2 5.74 b 3.44 bc 2.66 de 2.29 bc 3 6.59a 4.16a 3.26 bc 2.61 b 4 5.63 b 3.95ab 3.00 cd 2.64 b 5 5.76 b 4.15a 4.36a 3.81a ___§ we M 3 -§§.a_ Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 112 three treatments had received 112 kg N ha” by this time. Treatments two and six each had 56 kg N ha‘1 applied at this time and N concentrations were significantly lower than treatments three, four, and five, but significantly higher than the control (treatment one). At the Stanton location, all treatments receiving N had higher N concentrations than the control, but no differences between these treatments were detected. At the Montcalm site in 1989, benefits of split applications were apparent. Though all three treatments received 112 kg N ha'1 at this time, treatments four and five (55 kg N ha“ at planting and 56 kg N ha" at tuber initiation) had significantly higher total N concentrations than treatment three (112 kg N ha'1 at planting). The petiole N concentration of treatment six was similar to treatment three. Only 56 kg N ha'1 had been applied to treatment six at this time but the split application apparently increased the fertilizer uptake efficiency over applying all of the fertilizer N at planting. Similarly, treatment six had a significantly higher total N concentration than treatment two, where 56 kg N ha'1 had been applied at planting. No difference in total N concentration was detected between treatment two and the control at this sampling date. In the East Lansing experiment, benefits to split applications were not apparent. Total N concentrations in the petioles reflected N application rates only, not the timing of the 113 applications. The third petiole samples represented fertilizer applied at planting, tuber initiation, and tuber initiation plus 14 days. These petiole sample N concentrations were highly responsive to the N applied at all locations. Only treatments five and six received additional N after the second petiole sample collection. In all experiments, treatment five (168 kg N ha”) had the highest petiole N concentrations. In all experiments but the Montcalm site in 1988, the petiole N concentration of treatment six (84 kg N ha'1 applied by this petiole sample collection) was equal to or greater than teatments three and four, which had 112 kg N ha"1 applied at planting, or evenly split between planting and tuber initiation, respectively. No significant differences were detected between treatments three and four at any location. Treatment two and the control had the lowest total N concentrations in all experiments. The fourth petiole samples were taken 42 days after the initial petiole samples. By this time all fertilizer N had been applied to the treatments. Only treatment six had received fertilizer N since the third petiole sample was taken. In all experiments except the Montcalm site in 1988, treatments five and six had the highest petiole total N concentration. At the Montcalm site, the petiole N concentration of treatment five was significantly greater than in treatment six. In this experiment, treatments 114 three, four and six had similar petiole total N concentrations. At the Stanton site in 1988, a trend toward higher N concentrations with split fertilizer applications was apparent in the 112 kg N ha” treatments. The lowest fertilizer N concentrations were found in the control at both locations in 1988, though no differences between treatment two and the control was observed in the Montcalm experiment. No differences between treatments three and four were observed in 1989. At the Montcalm.site in 1989, the control actually had a higher total N concentration than treatment two. No significant difference was detected between treatment two and the control at the East Lansing location. From these data, it appears that total N concentration the petiole of the newest fully expanded leaf is very responsive to fertilizer N applications and may be able to detect differences in N applications of 28 kg N ha”. .The sufficiency level of total N 14 days after tuber initiation appears to be about 4.5 percent. The percent total N in the petiole samples derived from the fertilizer was also measured. These data are presented in Table 4.14. The percent fertilizer N detected in the petiole samples generally reflected the total fertilizer N applied. If the total N applied was equal between two treatments, the percent fertilizer N in the treatment with the most recent N application was usually as high or higher Table 4.14. 115 Effect of N rate and application time on percent total N derived from fertilizer in Russet Burbank potato petioles. N Fertilizer GMDUNH GalfiUNH GM§UNH M’NNH Petiole Sample Time Tissue N Concentration Tuber TI+ TI+ TI+ : N from fertilizer W 21.1 b 28.5 c 23.1 d 18.2 b 30.4a 42.2a 37.1 b 29.9a 18.1 bc 37.9 b 35.9 b 29.3a 15.4 c 30.5 c 41.8a 30.6a 9.0 d 27.3 c 32.1 c 36.4a fitsn§9n_12§§ 10.0 be 35.1 bc 29.5 c 22.4 b 15.0a 45.9a 44.1 b 38.4a 11.0ab 41.8ab 45.6 b 34.2a r 3.5 d 34.8 bc 53.3a 39.1a 5.8 cd 28.2 c 40.8 b 39.6a W 61.0 b 36.2 c 19.5 d 13.7 e 68.7a 49.0 b 35.3 c 24.6 d 61.9 b 61.0a 45.5 b 31.6 c 61.3 b 61.2a 57.0a 49.7a 46.2 c 46.2 b 43.3 b 43.3 b Esst_Lansins_12§2 53.9 b 45.8 b 37.6 c 28.5 c 70.2a 62.5a 51.8 b 41.7 b 57.3 b 56.7ab 52.1 b 39.9 b 59.0 b 65.5a 70.9a 59.7a 4 _§ Elf—ew— Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). 116 than the other treatments. These results were particularly evident in the 1989 experiments. The first petiole samples taken in 1988 had a lower total N concentration than those taken in 1989 (Table 4.13). The percent fertilizer N found in these petiole samples was also much lower than in 1989. This resulted in inconsistent fertilizer N uptake responses due to the treatments in the first petiole samples collected in 1988. Though treatment three had the highest percent fertilizer N and treatment six the lowest (control was excluded from the analysis), differences between treatments two, four, and five were detected even though all of these treatments received 56 kg N ha". The percent fertilizer N found in the first petiole samples collected in both experiments in 1989 directly reflected the amount of fertilizer N applied to the crop. The highest percent fertilizer N was found in treatment three, and the lowest in treatment six. Treatments two, four, and five all had intermediate fertilizer N values, and no differences were observed between these treatments in either experiment. In the second petiole sample, some differences between treatments that could not be attributed to N applied were still apparent in the 1988 experiments. At this time, treatments four and five had each received two applications of 56 kg N ha”, but the percent fertilizer N in treatment five was lower than treatment four in both experiments. The 117 percent fertilizer N in the other treatments was more closely related to the fertilizer N applications. In 1989, the percent fertilizer N in the second petiole samples was more responsive to N applications. At the Montcalm site, treatments four and five had the two highest N applications at tuber initiation. These two treatments also had the highest percent fertilizer N in the second petiole samples. Treatment six was the only other treatment to receive fertilizer N at tuber initiation. Though only a total of 56 kg N ha'1 had been applied in two equal applications, this treatment had the same percent fertilizer N as treatment three which had 112 kg N ha'1 applied at planting. Treatment six also had a higher percent fertilizer N in the petiole sample than treatment two. In the East Lansing experiment, no significant differences in percent fertilizer N were detected between treatments three through six. Treatment two had the lowest percent fertilizer N, but was not significantly lower than treatment six, or treatment four. Fertilizer N levels in the third petiole sample were closely related to the N treatments in all experiments. Treatment five had the highest percent fertilizer N, while treatment two had the lowest. No significant differences were detected between applying 112 kg N ha” at planting or evenly splitting the application between planting and tuber initiation, except in the Montcalm experiment in 1989, where 118 the split application did have a higher percent fertilizer N. Treatment six was significantly lower than the 112 kg N ha'1 treatments only at the Montcalm site in 1988. The fourth petiole sample was taken 14 days after the last fertilizer N application to treatment six and should represent all of the fertilizer N applied to the crop. In 1988, no significant increases in percent fertilizer N found in the petioles were detected beyond 56 kg N ha'1 in either experiment. This was not true in 1989. In the Mentcalm experiment, the percent fertilizer N found in the petioles was directly related to the rate and timing of the fertilizer N applications. The highest and lowest percent fertilizer N was found in treatment five, and treatment two, respectively. Among the the 112 kg N ha'1 treatments, percent fertilizer N detected increased with increased split applications. For the East Lansing location, the percent fertilizer N in treatments five and six were not significantly different. No differences in percent fertilizer N were found between treatments three and four, but both of these treatments were significantly lower than the other 112 kg N ha'1 treatment (treatment six). Again treatment two had the lowest percent fertilizer N in the petiole samples collected at this time. This data shows that the total N concentration in the petioles of the newest fully expanded leaves may indicate not only the overall N status of the crop, but also the 119 relative contribution of any particular fertilizer N application. This may prove to be a relatively inexpensive method of qualitatively measuring fertilizer uptake efficiency. Nitrate Nitrogen Analysis: The nitrate N concentration of the petiole samples was also analyzed in this experiment. These data are presented in Table 4.15. In the first petiole sample at the Mentcalm study in 1988, treatments one and six had the lowest nitrate concentrations, but no significant differences were detected between the other treatments. No significant differences were detected between any treatments for the first petiole sample at the Stanton site. In 1989, petiole nitrate concentrations were strongly influenced by the fertilizer N treatments. In both experiments, nitrate concentrations paralleled N applications. The highest nitrate concentrations were found in treatment three, followed by treatments two, four, and five (no differences between these treatments), treatment six, and treatment one, which had the lowest nitrate concentration. The adequate nitrate N range for petiole samples collected at this time is 18,000 - 22,000 mg N kg‘1 (Vitosh, 1985). Since early season fertilizer N uptake appeared to be limited in 1988 (Table 4.14), the treatments had a minimal affect on nitrate N concentrations in the first petiole samples. The relatively 12C) Table 4.15. Effect of N rate and application time on petiole nitrate N concentration of Russet Burbank potato. Petiole sample time N Tissue N concentration Fertilizer Tuber TI+ TI+ TI+ megi W 1 18600 b 7200a 5700 e --- 2 21300a 9100a 9500 d -- 3 21600a 13300a 13500 bc -- 4 20500ab 14300a 14500ab --- 5 19600ab 13000a 15900a --- 6 19000 b 9900a 12100 c -- W l 17200a 3800 b 2100 d 6600a 2 18200a 11000a 8500 c 2100a 3 l7700a l2400a 9500 bc 4600a 4 18700a 13200a 14500ab 5400a 5 17200a 12000a 15600a 8400a 6 18300a 12300a 16200a 7200a W 1 6200 d 3700 c 5400 c 3500 cd 2 15800 b 2500 c 3400 d 2700 d 3 24900a 6700 b 6300 c 3800 be 4 19000 b 10500a 8400 b 4500 b 5 18400 b 11300a 12700a 10400a 6 11900 c 6900 b 8800 b 10600a W l 6200 d 1400 d 400 d 300 b 2 18000 b 4200 cd 900 ed 400 b 3 24300a 9100a 2000 c 900 b 4 18100 b 7100abc 2000 c 1000 b 5 19500 b 7700ab 8300a 4700a ___.6 14W 4909:— Values followed by the same letter were not statistically different at the .05 level of probability (DNMRT). , 121 high preplant inorganic soil N levels in 1988 (Table 4.3) may explain why all treatments were within 800 mg N kg'1 of the adequate range. Only the control and treatment six were consistently below these levels in 1989. It would appear from the 1989 data that 112 kg N ha” applied at planting may be excessive. Nitrate levels for the second petiole samples were not influenced by any of the treatments at the Montcalm site in 1988, and no significant increases were detected beyond the control at the Stanton study. In 1989, the nitrate concentrations were more responsive to the treatments. Treatments one and two had the lowest nitrate concentrations at both locations. Among treatments three, four and five, where 112 kg N ha“ had been applied in single (treatment three) or split (treatments four and five) applications, the split applications had significantly higher nitrate concentrations in the Montcalm experiment. No significant differences between these treatments were detected at the East Lansing location. Splitting 56 kg N ha'1 between planting and tuber initiation (treatment six) resulted in higher nitrate concentrations than when all of the N was applied at planting, but the difference was statistically significant only at the Mentcalm study. Nitrate concentrations of 12,000 - 15,000 mg N kg'1 are considered adequate at this sampling time (Vitosh, 1985). In 1988, treatments one and two were below these levels in 122 both experiments. The nitrate concentration in treatment six was also inadequate in the Montcalm experiment. In 1989, all of the nitrate concentrations were below the sufficiency level at this stage of growth, but only treatments one and two were consistently in the deficient range according to Vitosh (1985). From the yield data in Chapter one (Table 1.5), the petiole nitrate sufficiency levels may be as low as 7000 ppm at this stage of growth. The third petiole samples were responsive to the N treatments both years. Treatment five had the highest nitrate concentration in all experiments (except Stanton in 1988), while the control had the lowest nitrate levels in all experiments but the Mentcalm site in 1989 where treatment two was actually lower than the control. Treatments three and four had similar nitrate concentrations, though a trend toward higher values was observed by splitting the N applications. This difference was statistically significant only at the Montcalm site in 1989. Nitrate concentrations for treatment six were variable depending on the year and location, but in general the N concentrations were as high or higher than treatment three. These samples were taken during the transition period between mid and late season (Vitosh, 1985). The actual nitrate concentrations were higher in the 1988 samples than those collected in 1989, especially at the East Lansing location. The lower nitrate concentrations in the 123 East Lansing experiment are consistent with the other tissue data collected at this location. All treatments except the control in 1988 had nitrate levels within the sufficiency range for late season petioles, and most were also sufficient for mid season petiole samples. At the Montcalm site in 1989, treatments one and two were below sufficient levels for late season petioles, while only treatment five had nitrate concentration values in the sufficient range for mid season petioles. In the East Lansing experiment, none of the treatments had sufficient nitrate levels for mid season petiole samples and only treatment five had sufficient levels using the late season ranges. No petiole samples were analyzed for nitrate in the Mentcalm experiment, as insufficient tissue was available for analysis. No significant differences were detected between treatments at the Stanton site in 1988. In 1989, treatments five and six had the two highest nitrate concentrations in both experiments. No differences between the other treatments were detected at the East Lansing location, but treatments three and four generally had higher nitrate concentrations than treatments one and two in the Montcalm experiment. Based on tuber yield data presented in Chapter one, the nitrate N sufficiency levels may be slightly higher than necessary for maximum yield for mid and late season petiole samples. If these levels are indeed too high, over 124 fertilization later in the growing season may contribute to higher residual N levels in the soil after harvest, and may lead to higher nitrate leaching through the soil profile in the fall and spring. 125 RNIERNNCES Anonymous. 1988. Quikchem methods 12-107-06-2-A and 12-107- 04-1-A. Lachat Instruments, Milwaukee, WI. Bundy, L.G., R.P. WOlkowski, and 6.6. Weis. 1986. Nitrogen source evaluation for potato production on irrigated sandy soils. Am. Potato J. 63:385-397. Doll, E.C., D.R. Christenson, and A.R. Wolcott. 1971. Potato yields as related to nitrate levels in petioles and soils. Harris, D., and E.A. Paul. 1989. Automated analysis of 15N and 1‘C in biological samples. Comm. Soil Sci. Plant Anal. 20:935-947. Lauer, D.A. 1986. Russet Burbank yield response to sprinkler-applied nitrogen fertilizer. Am. Potato J. 63:61- 69. Lesczynski, D.B., and C.B. Tanner. 1976. Seasonal variation of root distribution of irrigated, field-grown Russet Burbank potato. Am. Potato J. 53:69-78. Lorenz, O.A., B.L. Weir, and J.C. Bishop. 1974. Effect of sources of nitrogen on yield and nitrogen absorption of potatoes. Am. Potato J. 51:56-65. MacMurdo, W., R.H. Prange, and R. Veinot. 1988. Nitrogen fertilization and petiole tissue testing in production of whole seed tubers of the potato cultivars Sebago and Atlantic. Can. J. Plant Sci. 68:901-905. Muller, S., and K. Beer. 1986. The relationsips between soil inorganic nitrogen levels and nitrogen fertilizer requirements. Agriculture, Ecosystems and Environment. 17:199-211. Ojala, J.C., J.C. Stark, and G.E. Kleinkopf. 1990. Influence of irrigation and nitrogen management of potato yield and - quality. Am. Potato J. 67:29-43. Roberts, 8., and H.H. Cheng. 1985. Advances in nitrogen ,management for Russet Burbank potatoes. Proc. Wash. Potato Conf. and Trade Fair. pp 41-47. Saffigna, P.G., D.R. Keeney, and C.B. Tanner. 1977. Nitrogen, chloride, and water balance with irrigated Russet Burbank potatoes in a sandy soil. Agron. J. 69:251-257. 126 Vitosh, M.L. 1971. Fertilizer studies with irrigated potatoes. Research report No. 142, Mich. State. Univ. A.E.S. 11 pp. Vitosh, M.L. 1984. Irrigation scheduling for potatoes in Michigan. Am. Potato J. 61:205-213. Vitosh, M.L. 1985. Nitrogen management strategies for potato producers. Mich. State. Univ. Ext. Bull. W009. 4 pp. Vitosh, M.L. 1990. Potato fertilizer recommendations. Mich. State Univ. Ext. Bull. E220. 8pp. Westermann, D.T., and G.E. Kleinkopf 1985. Nitrogen requirements of potatoes. Agron. J. 77:616-621. Westermann, D.T., G.E. Kleinkopf, and L.K. Porter. 1988. Nitrogen fertilizer efficiencies on potatoes. Am. Potato‘J. 65:377-386. - HICHIGAN smTE UNIV. LIBRRRIES WIWWWWWIINNINWIIHIHIMIHI”(NW 312930088501 1 1