MSU ’ LIBRARIES m .‘ ‘15” JUL? & WW ? 2 3 (z ‘ 35:» ii" 3 I994 RETURNING MATERIAL§z Place in book drop to remove this checkout from your record. FINE§ will be charged if book is returned after the date stamped below. ,,_. —_- ‘- - - --. -‘1 --—.--——-- o--- _-.. --—.— v”. -...—-—.--—- m.._._ UTILIZATION OF SOIL-APPLIED NITROGEN BY HIGHBUSH BLUEBERRIES (Vaccinium gozymbosum L.) BY Jorge Benjamin Retamales A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1988 ABSTRACT UTILIZATION OF SOIL-APPLIED NITROGEN BY HIGHBUSH BLUEBERRIES (Vaccinium corymbosum L.) BY Jorge Benjamin Retamales The efficiency of soil-applied N fertilizer use in highbush blueberry was studied in 2 separate sets of experiments. To determine the effect of N fertilization on N status in leaves and soil, leaf mineral composition, cold hardiness, and fruit yield and weight, the following treatments were applied at bud break (BB) and petal fall (PF) to 8- and 15-year-old 'Bluecrop' blueberry bushes in 1986 and 1987: single urea, 76 kg N/ha at BB; split urea, 38 kg N/ha at BB and PF; controlled-release fertilizer (Osmocote 3-month duration), at 38 or 76 kg/ha, BB; Osmocote 8-month duration at 38 or 76 kg/ha, BB; and control (no N). Leaf, topsoil (1-15 cm depth) and subsoil (25-40 cm) samples were collected at 4-11 week intervals. Soil N03" and N114+ levels were higher following treatment with urea than with Osmocote. Higher levels of N03“ and NH4+ were found in single urea than in split urea plots, except during the second season when split urea resulted in higher levels late in the season. Soil nitrogen levels varied greatly between seasons. Leaf N was higher in urea- than in Osmocote- treated plots, and split urea resulted in higher leaf N than single urea. Treatment differences generally increased during the second season. Leaf N was little affected by rate or formulation of Osmocote. Nitrogen treatments decreased leaf Ca, Mg, B and Al, but had no consistent effect on cold hardiness of fruit buds and terminals. Yield and fruit weight in 1987 were not affected by nitrogen treatments. The fate of fertilizer urea applied to 22-year-old 'Bluecrop' bushes was studied by applying 14.74% 15N- enriched urea at bud break at a rate of 40 kg N planted/ha. Fertilizer N was observed in leaves 2 weeks after application and reached a maximum (16.5% of total leaf N) 3 weeks after application. By the end of the growing season plants had recovered 32% of the applied N. Leaves accounted for 32% and stems 32% of fertilizer derived N in plants. Less than 15% of fertilizer N remained in the soil at the end of the season, most of it in organic forms. To the memory of my father and to my mother for the many lessons that are not found in books. To Beatriz, my wife, for her courage, love and unlimited understanding. To my children for illuminating every day with their smiles. iv ACKNOWLEDGEMENT I wish to express my deepest gratitude to my major professor, Dr. Eric J. Hanson, for his direction, encouragement and constructive criticism during the course of my doctorate program. I also extend my appreciation to Drs. James Tiedje, Boyd Ellis, Stan Howell and James Hancock for their cooperation as members of my guidance committee. My special thanks to the Michigan Blueberry Growers Association for funding part of this research, to Ken Hodgeman for allowing us to use his planting in these studies and to John Nelson for his valuable suggestions and wisdom. My gratitude to my fellow graduate students for sharing this important part of my life. A special thanks to John Cline, for giving its true meaning to the word friendship. To my wife Beatriz and my children, my sincere and profound appreciation for their understanding, love and tolerance in the good and not so good days during the preparation of this ("our") thesis. Guidance Committee: The journal paper format was chosen for this thesis in accordance with departmental and university regulations. The thesis is divided into three sections which are intended for publication in The Journal of the American Society for Horticultural Science. vi TABLE OF LIST OF TABLES . . . . . . LIST OF FIGURES . . . . . LIST OF APPENDICES . . . . INTRODUCTION . . . . . . . CONTENTS Section I soil N I. Effect Studies on blueberry: levels. Abstract . . . . . . Introduction . . . . Materials and Methods Results . . . . . . . Discussion . . . . . Literature Cited . . applications on to inorganic highbush soil N Section II soil N II. Studies on blueberries: Abstract . . . . . . Introduction . . . . Materials and Methods Results . . . . . . . Discussion . . . . . Literature Cited . . applications Plant effects. to vii Page ix xi xiii 12 13 14 15 19 26 31 35 36 36 38 42 48 53 Section Fate of 15N-labeled urea highbush blueberries. Abstract . . . . . . . Introduction . . . . . Materials and Methods . Results . . . . . . . . Discussion . . . . . . Literature Cited . . . SUMMARY AND CONCLUSIONS . . APPENDICES . . . . . . . . . BIBLIOGRAPHY . . . . . . . . viii III applied to mature 56 57 57 58 62 65 7O 75 78 92 LIST OF TABLES Table Section I Studies on soil N applications to highbush blueberry: I. Effect on inorganic soil N levels. 1. Effect of nitrogen treatments on soil ammonium levels in a younger 'Bluecrop' planting. 1986 . . . . . . . . . . . . . . 2. Effect of nitrogen treatments on soil nitrate levels in a younger 'Bluecrop' planting. 1986 . . . . . . . . . . . . . 3. Effect of nitrogen treatments on soil ammonium levels in a younger 'Bluecrop' planting. 1987 . . . . . . . . . . . . . 4. Effect of nitrogen treatments on soil nitrate levels in a younger 'Bluecrop' planting. 1987 . . . . . . . . . . . . . . 5. Effect of urea and ammonium sulfate on soil ammonium levels in a younger 'Bluecrop' planting. 1987 . . . . . . . . . . . . . . 6. Effect of urea and ammonium sulfate on soil nitrate levels in a younger 'Bluecrop' planting. 1987 . . . . . . . . . . . . . . Section II Studies on soil N applications to highbush blueberries: .II. Plant effects. 1. Effect of nitrogen rate/source on leaf mineral composition in 'Bluecrop'. 1987 . . ix Page 20 22 23 24 27 28 47 Section III Fate of 15N-labeled urea applied to mature highbush blueberries. 1. Absolute and relative dry weight and percent N in different tissues of mature 'Bluecrop' highbush blueberry . . . . . . . . . . . . . Percent atom excess and distribution of fertilizer derived N in different highbush blueberry tissues . . . . . . . . . . . . . Tgtal N, percent atom excess and recovery of N-enriched fertilizer in different soil layers . . . . . . . . . . . . . . . . . . . 63 66 67 LIST OF FIGURES Figure Section I Studies on soil N applications to highbush blueberry: I. Effect on inorganic soil N levels. Section II Studies on soil N applications to highbush blueberries: II. Plant effects. 1. Effect of soil nitrogen applications on seasonal foliar N levels in younger 'Bluecrop' bushes (arrow indicates second application of split urea). NS, *, ** - nonsignificant or significant at the 5% and 1% levels, respectively . . . . . . . . . . Effect of soil application of urea before bud break (single) or before bud break and at petal fall (split) on seasonal foliar N levels in younger 'Bluecrop' bushes (arrow indicates second application of split urea). NS, *, ** - nonsignificant or significant at the 5% and 1% levels, respectively . . . . . Effect of soil applications of urea or Osmocote on seasonal foliar N levels in younger 'Bluecrop' bushes (arrow indicates second application of split urea). NS, *, ** - nonsignificant or significant at the 5% and 1% levels, respectively . . . . . . . . xi Page 43 44 45 Section III Fate of 15N-labeled urea applied to mature highbush blueberries. 1. Seasonal changes in total nitrogen in leaf 39d percent of leaf nitrogen derived from N-labeled fertilizer (applied on 4/21) to mature 'Bluecrop' plants . . . . . . . . . . xii 64 LIST OF APPENDICES Appendix Daily precipitation (cm) at the experimental plots during the 1986 growing season (April-October) . . . . . . . . . . Daily precipitation (cm) at the experimental plots during the 1987 growing season (April-October) . . . . . . . . . . Effect of nitrogen treatments on soil ammonium levels in an older 'Bluecrop' planting. 1986 . . . . . . . . . . . . . . Effect of nitrogen treatments on soil nitrate levels in an older 'Bluecrop' planting. 1986 . . . . . . . . . . . . . . Effect of nitrogen treatments on initial (4/21) and final (9/10) levels of inorganic nitrogen during second season of applications in an older 'Bluecrop' planting. 1987 . . . . . . . . . . . . . . Effect of rate and source of nitrogen on leaf N levels in older 'Bluecrop' blueberry plants. 1986 . . . . . . . . . . . . . . . Effect of rate and source of nitrogen on leaf N levels in older 'Bluecrop' blueberry plants. 1987 . . . . . . . . . . . . . . . Effect of nitrogen source on leaf nitrogen levels in younger 'Bluecrop' blueberry plants. 1987 . . . . . . . . . . . . . . . Effect of nitrogen source and rate on hardiness of 'Bluecrop' blueberry stems and fruit buds. Values are percentage alive averaged over several test temperatures. Winter, 1986-87 . . . . . . . . . . . . . xiii Page 78 79 80 81 82 83 84 85 86 10. 11. 12. 13. 14. Effect of nitrogen on hardiness of 'Bluecrop' blueberry stems and fruit buds. Values are percentage alive averaged over several test temperatures. Winter, 1987- 88 . . . . . . . . . . . . . . . . . . . . Effect of nitrogen source and rate on hardiness of 'Bluecrop' blueberry stems and fruit buds in the field. 2/10/88 . . . . . Effect of nitrogen treatments on yield and fruit weight in younger 'Bluecrop' blueberry plants. 1987 . . . . . . . . . . Effect of nitrogen treatments on yield and fruit weight in older 'Bluecrop' blueberry plants. 1987 . . . . . . . . . . . . . . . Effect of urea and ammonium sulfate on yield and fruit weight in younger 'Bluecrop' blueberry plants. 1987 . . . . xiv 87 88 89 9O 91 INTRODUCTION The highbush blueberry (Vaccinium corvmbosum L.) belongs to the family Ericaceae, which is unusual in its cultural requirements (3). Highbush blueberry plants are exacting in soil and climatic requirements (16, 35), and grow better on acid peat or sandy soils (3). Enough winter low temperature should be present to develop deep hardiness (7). Areas to be planted should be open to the prevailing air currents so cold air can drain out (7). In most plantings, N is the only element required each year (16), and consistently gives the greatest plant response (20). Standard N Fertilization Practices Nitrogen needs can be estimated by appearance and vigor of plants (7, 20), if a plant is deficient. Therefore, the N levels in fully expanded current season's leaves taken between 7/15 and 8/15 (17) are believed to give a more accurate indication of N status in the plant. Leaf N between 1.65 to 2.1% is adequate for highbush blueberries in Michigan (15); whereas for the Pacific Northwest, the optimum range is 1.8 to 2.0% N (20). Nitrogen sources most used by growers are (NH4)2804 and urea (7, 15, 20). Recommended rates for mature plantings l . 2 vary from 73 kg N/ha in Michigan (15) to 150 kg N/ha in the Pacific Northwest (7). Higher organic matter in many Michigan soils might supply the difference from mineralization of organic N (7). Commonly, growers fertilize once at bud break, although two to three applications are recommended, especially in sandy soils (3, 7, 15, 34). Multiple applications are thought to extend the period when the nutrient is available to the plant (3, 7). Ammonium Versus Nitrate Fertilization Reports comparing the use of NO3'-N to NH4+-N for blueberries conflict. Plant growth in most studies has been doubled when NH4+-N has been supplied (2, 18, 31, 36, 37, 38), but in other studies N03'-N was superior (6, 25). Early studies by Doehlert and Shive (6), reported that NO3'- N was superior to NH4+-N, but the N03” solution was not buffered and became more acid with time indicating greater cation than anion uptake; best growth was produced with solutions containing 40% of the total N as (NH4)2504. Cain (2) presented evidence indicating the superiority of NH4+-N and attributed this finding to an association between NH4+-N and Fe nutrition. However, Oertli (25) obtained good yields at pH 6 in water culture with both NH4+-N and N03'-N when chelated Fe was added, but at pH 4, NO3'-N was more beneficial than NH4+-N. Townsend (38) suggested that pH levels and forms of N fertilizer act independently in lowbush blueberry (y. auqustifolium A.), but their effects _ 4 Robertson (32) used relative nitrification rates (the proportion of the total mineral N that is converted to N03-- N by the end of an incubation period) to correlate data from several studies, and found that even though pH may be an important regulator of nitrification in a particular soil, it is not a good predictor of nitrification across a wide range of soils. Little nitrification occurs in acid soils with addition of an acid-forming fertilizer such as (NH4)ZSO4 (28). Lime or urea applications commonly increased nitrification rates, at least temporarily (27, 28). Often low nitrification rates appear to be due to low populations of nitrifiers (30). If this is the case, practices which favor nitrification such as application of lime or urea, will increase nitrification after a lag period (27, 39). c) Biological denitrification. This process involves the use of NO3' as a terminal electron acceptor in respiration, and leads to the formation particularly of N2 and N20 which are subject to gaseous losses (13). Numerous obligatory aerobic bacteria are capable of carrying out NO3‘ respiration in the absence of 02 (12, 13). High organic matter (12) and continuous fertilization in blueberry soils could lead to significant N losses by denitrification (8). Losses might be higher when urea fertilizer is used since urea tends to induce higher N03'-N formation (27). Efficiency of N Application No studies on this subject have been reported in bush fruit crops. Research with 15N-labelled fertilizer have shown 56% recovery in citrus (10) and 60% recovery in apples (19). Since blueberries possess a shallow root system (7, 34) and are often grown in coarse textured soils (7, 16, 35), efficiency of application would be expected to be lower in this species. Means of Improving Efficiency Efficiency of application can be improved by minimizing losses and maintaining a high level of nitrogen available for plant uptake at periods of highest demand. Ammonia volatilization can be reduced by prompt irrigation after fertilizer application (1) or by incorporation of urea where irrigation is not available (24). Nitrate leaching and denitrification losses could be minimized by reducing soil N03' levels (12). Nitrification inhibitors have proven effective in some studies on annual crops (22, 33) and these chemicals could prove particularly useful in blueberries given the preference of the species for NH4+-N (2, 31). Multiple fertilizer applications have been recommended for blueberry (3, 7, 15), but the practice has found little acceptance by growers in Michigan. A single application of controlled-release fertilizer could provide the benefits of multiple applications by maintaining adequate fertilizer levels in the soil during the season (22). 6 Research reported in this thesis deals with the efficiency of N fertilizer use by highbush blueberries, and methods to improve fertilizer N recovery by this species. Literature Cited Bouwmeester, R.J.B., P.L.G. Vlek and J.M. Stumpe. 1985. Effect of environmental factors on ammonia volatilization from an urea-fertilized soil. Soil Sci. Soc. Amer. J. 49:376-381. Cain, J.C. 1952. A comparison of ammonium and nitrate nitrogen for blueberries. Proc. Am. Soc. Hort. Sci. 59:161-166. Cain, J.C. and P. Eck. 1966. Blueberry and cranberry. p. 101-129. In: N.F. Childers (ed.) Fruit Nutrition, 2nd Ed. Hort Pub., New Brunswick, N.J. Court, M.N., R.C. Stephen and J.S. Waid. 1964. Toxicity as a cause of the inefficiency of urea as a fertilizer: I. Review. J. Soil Sci. 15:42-48. Dancer, W.S., L.A. Peterson and G. Chesters. 1973. Ammonification and nitrification of N as influenced by soil pH and previous N treatments. Soil Sci. Soc. Am. Proc. 37:67-69. Doehlert, C.A. and J.W. Shive. 1936. Nutrition of blueberry (Vaccinium corymbosum L.) in sand cultures. Soil Sci. 41:341-350. 10. 11. 12. 13. 14. 7 Doughty, C.C., E.B. Adams and L.W. Martin. 1981. Highbush blueberry production. Pac. Northwest Ext. Bull. 215. Eaton, L.J. and D.G. Patriquin. 1984. Nitrogen cycling in lowbush blueberry soils. Proc. of V North Amer. Blueberry Research Workers Conf., Gainesville, Florida, 1-3 February. Ernst, J.W. and H.F. Massey. 1960. The effects of several factors on volatilization of ammonia formed from urea in the soil. Soil Sci. Soc. Amer. Proc. 24:87-90. Feigenbaum, S., H. Bielorai, Y. Erner and S. Dasberg. 1987. The fate of 15N labeled nitrogen applied to mature citrus trees. Plant Soil 97:179-187. Ferguson, R.B., D.E. Kissel, J.K. Koekiller and W. Basel. 1984. Ammonia volatilization from surface- applied urea: Effect of hydrogen ion buffering capacity. Soil Sci. Soc. Am. J. 48:578-582. Firestone, M.K. 1982. Biological denitrification, p. 289-326. In: F.J. Stevenson (ed.) Nitrogen in agricultural soils. Agronomy vol. 22, Amer. Soc. of Agronomy, Inc. Madison, Wis. Focht, D.D. and W.D. Verstraete. 1977. Biochemical ecology of nitrification and denitrification. Adv. Microbial Ecol. 1:135-214. Hammet, L.K. and W.E. Ballinger. 1972. A nutrient solution-sand culture system for studying the influence 15. 16. 17. 18. 19. 20. 21. 8 of N form on highbush blueberries. HortSci. 7:498- 500. Hancock, J. and E. Hanson. 1986. Highbush blueberry nutrition. Mich. State Univ. Coop. Ext. Serv. Bull. E- 2011. Hanson, E. and J. Hull. 1986. Plant tissue analysis for determining fertilizer needs of Michigan fruit crops. Mich. State Univ. Coop. Ext. Serv. Bull. E-449. Hanson, E.J. and J.F. Hancock. 1988. Hints on growing blueberries. Mich. State Univ. Coop. Ext. Serv. Bull. E-2066. Herath, H.M.E. and G.W. Eaton. 1968. Some effects of water table, pH and nitrogen fertilization upon growth and nutrient-element content of highbush blueberry plants. Proc. Amer. Soc. Hort. Sci. 92:274-283. Hill-Cottingham, D.G. and C.P. Lloyd-Jones. 1975. Nitrogen-15 in apple nutrition investigations. J. Sci. Food Agric. 26:165-173. Hoover, E., C. Rosen, D. Wildung, J. Luby, L. Hertz, J. Heaps and W. Stienstra. 1984. Blueberry production in Minnesota. Agric. Ext. Serv. Univ. Minnesota Bull. AG- FO-2241. Keeney, D.R. 1980. Prediction of soil nitrogen availability in forest ecosystems: a literature review. Forest Sci. 26:159-171. 22. 23. 24. 25. 26. 27. 28. 29. 9 Maynard, D.N. and O.A. Lorenz. 1979. Controlled- release fertilizers for horticultural crops. Hort. Rev. 1:79-140. Mills, H.A., A.V. Barker and D.N. Maynard. 1974. Ammonia volatilization from soils. Agron. J. 66:355- 358. Nelson, D.W. 1982. Gaseous losses of nitrogen other than through denitrification. p. 327-363. In: F.J. Stevenson (ed.) Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agron., Inc. Madison, Wis. Oertli, J.J. 1963. Effect of form of nitrogen and pH on growth of blueberry plants. Agron. J. 55:305-306. Olson, R.A. 1983. The impacts of acid deposition on N and S cycling. Env. Exp. Bot. 23:211-223. otchere-Boateng, J. and T.M. Ballard. 1978. Urea fertilizer effects on dissolved nutrient concentrations in some forest soils. Soil Sci. Soc. Amer. J. 42:503- 508. Overrein, L.N. 1967. Immobilization and mineralization of tracer nitrogen in forest raw humus: I. Effect of temperature on the interchange of nitrogen after addition of urea-, ammonium-, and nitrate-N15. Plant Soil 27:1-19. Overrein, L.N. and P.G. Moe. 1967. Factors affecting urea hydrolysis and ammonia volatilization in soil. Soil Sci. Soc. Amer. Proc. 31:57-61. 30. 31. 32. 33. 34. 35. 36. 37. 38. 10 Pang, P.C., C.M. Cho and R.A. Hedlin. 1975. Effects of pH and nitrifier population on nitrification of band-applied N and homogeneously mixed urea nitrogen in soils. Can. J. Soil Sci. 55:15-21. Peterson, L.A., E.J. Stang and M.N. Dana. 1988. Blueberry response to NH4-N and N03-N. J. Amer. Soc. Hort. Sci. 113:9-12. Robertson, C.P. 1982. Nitrification in forested ecosystems. Phil. Trans. R. Soc. Lond. 296:445-457. Schmidt, E.L. 1982. Nitrification in soil. p. 253- 288. In: F.J. Stevenson (ed.) Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Scott, D.H., A.D. Dreyer and G.M. Darrow. 1978. Commercial blueberry growing. U.S.D.A. Farmer's Bull. 2254. Shoemaker, J.S. 1978. Small fruit culture. Fifth Ed. The AVI Publishing Co., Westport, Conn. Townsend, L.R. 1966. Effect of nitrate and ammonium nitrogen on the growth of the lowbush blueberry. Can. J. Plant Sci. 46:209-210. Townsend, L.R. 1967. Effect of ammonium nitrogen and nitrate nitrogen, separately and in combination, on the growth of the highbush blueberry. Can. J. Plant Sci. 47:555-562. Townsend, L.R. 1969. Influence of form of nitrogen and pH on growth and nutrient levels in the leaves and 39. 40. 41. 11 roots of the lowbush blueberry. Can. J. Plant Sci. 49:333-338. Vitousek, P.M., J.R. Gosz, C.C. Grier, J.M. Melillo, W.A. Reiners and R.L. Todd. 1979. Nitrate losses from disturbed ecosystems. Science 204:469-474. Volk, G.M. 1959. Volatile loss of ammonia following surface application of urea to turf or bare soils. Agron. J. 51:746-749. Watkins, S.H., R.F. Strand, D.S. DeBell and J. Esch, Jr. 1972. Factors influencing ammonia losses from urea applied to Northwestern forest soils. Soil Sci. SOC. Amer. Proc. 36:354-357. Section I STUDIES ON SOIL N APPLICATIONS TO HIGHBUSH BLUEBERRY: I. EFFECT ON INORGANIC SOIL N LEVELS 12 13 Abstract Inorganic soil nitrogen levels (N03' and NH4+) were monitored for 2 years on fertilized soils planted to 8- and 16-year old highbush blueberries. Urea was applied at 76 kg N/ha in either a single application at bud break or in two applications (split) at bud break and petal fall. Osmocote, a controlled-release N fertilizer, of two different residual effects (3 mo. and 8 mo.) was applied at 38 kg N/ha or 76 kg N/ha at bud break. In a separate experiment, soil N03- and NH4+ were monitored in sites planted to young bushes receiving (NH4)ZSO4 or urea at 76 kg N/ha. Nitrogen fertilization increased inorganic N shortly after application and the lowest levels were found in Osmocote treated plots. Urea increased soil NH4+ and N03' levels significantly, especially in early and mid-season samplings, compared to Osmocote. The effect of urea application on N03' and NH4+ soil levels varied with moisture conditions in the given season. Levels of inorganic N early in the season were generally greater in plots receiving a single application of urea. Limited carry-over to the next season occurred when split applications of urea were used. Nitrate levels were higher in plots treated with urea, as compared to ammonium sulfate, and some nitrate leaching occurred in the urea-treated plots. 14 Introduction In contrast to most other plant nutrients, no mechanism for long-term storage of plant-available fertilizer N exists in soils (14). The goal of an efficient N fertilizer program is to maintain adequate levels of N available to the plant and to minimize fertilizer losses. Cain and Eck (4) in their review of blueberry nutrition stated that split fertilizer applications have proven valuable in extending the period during which applied nutrients are available to plants, although little could be found documenting the benefits of split applications in blueberries (8). Controlled-release fertilizer may provide another means of increasing the efficiency of fertilizer use (13). The effectiveness of these materials in blueberry production needs to be determined. Most research on N use in blueberries has focused on plant responses to different rates and N sources. Little attention has been given to the affects of fertilizer on inorganic soil N fractions. Besides the economic implications of fertilizer losses, concerns for ground water quality create incentives to increase fertilizer use efficiency. The exacting soil and climatic conditions required for successful blueberry growing has concentrated production in relatively small areas in Michigan (9) and other producing states (11), which might increase the potential for N03' contamination of ground water. 15 The objective of the present research was to study the seasonal changes in soil NH4+ and N03” following applications of urea (split or single applications), controlled-release fertilizers, and (NH4)ZSO4 in order to better understand the dynamics of soil N transformation in highbush blueberry soils. Materials and Methods The effect of N fertilizer applications on inorganic soil N was studied over two consecutive years in three experiments at a commercial site near Grand Junction, Michigan. The topsoil (0-15 cm in depth), belongs to the Kingsville-Pipestone complex and is a mixture classified in the mesic entic haplaquods - mesic Mollic Psammaquents (2) with sandy loam texture (77.9% sand, 12.4% silt and 9.7% clay), pH 4.3, organic matter (0M) 7-9% and cation exchange capacity (CEC) 22-25 meg/100 g. The subsoil (25-40 cm depth) is a loamy sand texture (83.9% sand, 9.4% silt, 6.7% clay), 0M 5-7%, pH 4.5 and CEC 17-18 meg/100 g. In each experiment, plots consisted of two bushes of similar size with one or more buffer plants between adjacent plots. Fertilizer was applied to a 60 cm x 60 cm surface at the base of each plant. Soil samples were taken at times specified below by drilling five cores (2.2 cm diameter) from within the treated area of each plot. The top 1 cm was discarded to avoid fertilizer contamination, and the remaining soil was divided into two separate sections 16 comprising the topsoil where most roots were located (1-15 cm depth) and subsoil (25-40 cm depth) which was generally devoid of roots. Five cores were collected from each plot and soil from each section was thoroughly mixed in a bucket. Representative samples were placed in plastic bags, which were sealed and stored at 4°C and extracted with l M KCl within 48 hours (10). The extract was stored at 1°C until analyzed with a flow injection analyzer (Lachat Instr., Mequon, Wisc.) for exchangeable NH4+ using the salicylate method (Lachat Method No. 12-107-106-2-A); and for N02“ + N03” using a copperized cadmium column for N03” reduction to N02- as proposed by Keeney and Nelson (10) (Lachat Method No. 12-107-04-1-B). Results are reported as N03- since only trace amounts of N02' are to be expected given the low pH and moderate fertilization in the research plots (18). To calculate levels of inorganic N per hectare, a constant soil density of 1.3 g/ml (2) was assumed and soil moisture was determined in all samples by measuring weight loss from 10 g of moist soil dried at 60°C for 48 h. The organic matter content of soil samples was determined by comparing the weight of 10 g of air dried soil before and after ashing at 500°C for 6 hrs. Organic matter was used as a covariate, when statistically significant, to reduce variability among plots. 17 Experiment I The effects of various fertilizer treatments on inorganic soil N levels was studied on 'Bluecrop' bushes planted in 1978 (younger plants). Treatments were replicated 10 times in a randomized, complete block design. Five of the replications were located where supplemental irrigation (overhead sprinklers) could be provided. The following treatments were initiated in 1986 and repeated in 1987: 1) single urea, one application of 76 kg N/ha (2 N) at bud break (4/9/86 and 4/21/87); 2) split urea, two applications of 38 kg N/ha (1 N) at bud break and petal fall (5/27/86 or 6/16/87); 3) Osmocote 3-month duration (19:6:12) (Sierra Chemical Co., Milpitas, Cal.) at 1 N applied at bud break: 4) Osmocote 3-month duration at 2 N applied at bud break; 5) Osmocote 8-month duration (17:6:10), 1 N at bud break: 6) Osmocote 8-month duration, 2 N at bud break; and 7) control (no N). Osmocote materials contain NH4NO3, (NH4)2HPO4, Ca(HPO4)2 and K2804 coated with multiple plastic polymers. In the first year (1986), five soil samples were taken separately from irrigated and non-irrigated areas just before fertilization (4/9) and from each plot at 4-11 week intervals until the end of the season. Fewer soil samples were collected in 1987 to avoid excessively disrupting the root zone. The specific blocks to be sampled on each date were selected at random; seven replications were used on 18 5/5/87, six replications in mid-season (5/26 and 6/26) and five on the last sampling date (9/10). Ex eriment II The fertilizer treatments detailed in Experiment I were repeated in adjacent plants established in 1970 (older) to determine if older bushes might utilize more N or influence soil N levels differently. Six, two-bush replications were used, arranged in a randomized complete block design. The experimental area received about 10 and 15 cm of overhead irrigation in 1986 and 1987, respectively. Soil samples in 1986 were taken on the same dates as in Experiment I. In 1987, samples were collected only twice, before application (4/21) and at the end of the season (9/10). Phosphorus and potassium were applied as superphosphate and KCl, respectively, to urea and control plots in Experiments I and II to supply these elements at rates similar to the ones provided by 3 mo. (19-6-12) or 8 mo. (17-6-10 plus minors) Osmocote fertilizers. Experiment III A study was initiated in 1987 to compare the effects of urea and (NH4)ZSO4 on levels of inorganic soil N. Younger 'Bluecrop' plants adjacent to the previous experiments were used. Two-bush plots received either no fertilizer or 76 kg N/ha as urea or ammonium sulfate on 4/21. Treatments were replicated seven times in a randomized complete block . 19 design. Topsoil and subsoil samples were taken as previously described at 3-11 week intervals beginning 2 weeks after application. Statistical Analysis Analysis of variance were done on data transformed to log (inorganic N levels + 1). The following orthogonal contrasts were established to determine treatment effects in Experiments I and II: 1) control (no N) was compared to all nitrogen treatments (nitrogen effect); 2) split urea application was contrasted with single urea (split/single): 3) urea, either single or split, compared to Osmocote treatments at 76 kg N/ha (urea/Osmocote): 4) Osmocote 3-month residual treatments were compared to 8-month residual at either rate (Osmocote:residual): and 5) Osmocote treatments at 38 kg N/ha contrasted with Osmocote treatments where 76 kg N/ha was applied (Osmocote:rate). In Experiment III, control (no N) was compared to fertilized plots (nitrogen effect) and urea was compared to NH SO in a second contrast urea ammonium sulfate). 4 2 4 Results Experiment I 1986. Topsoil NH4+ levels were higher in N fertilized plots than controls on 5/3 and 5/23 but not later in the season (Table 1). Urea treatments resulted in significantly 20 . 3+ cog—65:60:00 +515 mod” on Bfiommcmhu But so new»? on $336,888 .mEEH in .8 66 65 66 6.836236 no bemoflnsfieoz . t. .. .62 s . Adam mév 35.350 unmumcoo m magnum P8 366 gag comm 5 Wand—sandman 8339: so commm N 62 62 62 62 6. 62 62 62 62 62 3E "8.8860 mz m2 mz m2 m2 .4 mz m2 mz m2 gag "30008.60 s m2 m2 m2 m2 m2 mz mz rs %% muoooem0\dmnD. m2 m2 mz m2 m2 m2 m2 mz .3. m2 magmbfimm “8.5 62 62 62 62 62 62 62 62 .3. .3. 68666 cmmoufiz m2 m2 m2 mz .3. m2 m2 m2 .3 a. xucmcflg m2 m2 m2 m2 m2 m2 m2 mz mz m2 TE .90 3 8:63.658 6268826666 ma 6.~ Tm 64 m.m fin Tm 4.6 6.6 TE. 6s .8 6 8.80260 64 EN 6:6. 9m ma Em 6.6 Tm 6.6 6.6 mm .9: 6 380560 64 6.~ 6.~ Tm Em Em 4.... 6.6 6.3 6.6 6s .02 6 38260 64 TN m.~ 6; 64 ~16. 6.6 66 «.6 ms mm .9: m 8.8960 ~.m Tm Nam 64 m6 Tm 6.m 6.6 To 6.6m 6s ”:36 68: «:6. Wm EN EN Tm 9m Hm H4. 22 Tom 65 64656 8.5 o.~ Tm Wm 64 6A 6.~ o.m m.m 6:6. Em o Hoficoo c6332 2&6 23. 616 mm\m Q6 616 NS 36 86 Q6 6&3 ugg onm 99 flame 67H soc fimmo 3mm z 8&2 9: 6.5225 6me 6:353 .Qouomgm. b.0950» o 5 mace/ma eBEQEE flow so mucmeflmwfi. :69qu Mo Dummmm .H M6368 21 higher early season NH4+ levels in topsoil than Osmocote. Topsoil N114+ levels in split-urea plots were significantly lower than single urea plots on 5/23 (4 days before the second application). Subsoil NH4+ levels remained fairly constant during the season, and were not strongly influenced by treatments (Table l). Nitrate levels at both depths were extremely variable shortly after application (5/3) (Table 2). Topsoil N03- levels were significantly higher in fertilized plots than controls on 5/23, 6/18 and 7/22 and subsoil N03” was higher on 5/23 and 6/18. Urea- and Osmocote-treated plots had comparable N03' levels at either depth. lggl. Soil NH4+ levels in plots planted to young bushes were similar in 1987 (Table 3) and 1986 (Table 1). Nitrogen applications significantly increased topsoil NH4+ levels on all but the last sampling date (Table 3). When single and split urea applications were compared, single applications resulted in significantly greater topsoil NH4+ levels early in the season (5/5), whereas split urea produced higher NH4+ levels late in the season (6/26, 9/10). Higher NH4+ levels were also observed in subsoil samples from split urea plots on 6/26 (Table 3). Urea treatments resulted in significantly higher topsoil NH4+ levels than Osmocote on all dates except 9/10. Highest NO3' levels in fertilized plots were reached on 6/26/87 (Table 4), nearly 2 months after application and were much lower and occurred later than those obtained in 22 . 44+ 4636,3500 Imoz + Imozv mod“ cu 608.40.496.99 3% co mam»? x $494.48:qu $4964 *4 no wm m5 um #:8344403 .40 4444834454202 I .3. .4 dz .4 4% 6.4V >443ch 9:39:00 6 94.4.5636 can. 366 ”646.44% 58 5 344954369: 9454649: :0 commm .6. ES: 65 68696.42 m2 m2 « mz m2 m2 m2 mz « m2 mumu "muooosmo 62 62 62 62 62 4 62 62 62 62 46.464994 ”8.89460 m2 m2 mz mz mz m2 m2 m2 m2 m2 BoooEmO\mm.4D m2 m2 m2 m2 mz mz mz m2 m2 m2 mHmfiwbfl 44mm "8.49 m2 m2 .3. .3. m2 mz a. 6:4 .3. mz powmmm 586342 mz mz ,3. m2 m2 mz m2 .1. .3. m2 xucgflg 62 62 62 62 62 62 62 62 62 62 4.2 .696 6 6 8:64.880 68:8462646 6.6 6.4 6.6 4.6 6.664 6.6 6.6 4.66 6.64 6.664 66 .9: 6 380.50 6.4 4.4 6.6 6.6 6.66 4.6 6.6 4.64 6.6 6.664 66 .9: 6 8.8960 6.6 6.6 6.6 6.6 6.46 6.6 4.6 4.64 6.44 6.66 66 .9: 6 8.89:8 4.4 6.6 6.6 6.6 6.66 6.4 6.6 4.44 4.64 4.664 66 .9: 6 389:8 . 6.4 6.6 6.6 6.6 6.66 6.6 6.44 4.46 6.44 6.464 66 6.4466 8:: 6.6 6.6 6.64 6.6 6.64 6.4 6.6 6.64 6.64 6.664 66 6469.46 8.5 4.4 4.4 6.4 4.4 6.664 6.4 6.6 6.6 6.6 6.66 6 483:8 869342 64x6 -\6 64\6 666 66 64\6 6~\6 64\6 666 66 6&6: “6:95.894. 64-64 4:66 568 644 686 fimmo 36m 2 .wmma .3653 388546. .8656» 6 :4 64684 86.94: 448 so $5698.44 5624.4: no “68666 .N GHQNB 23 .44+ :04vmuu:mo:oo +4mzv 004 on omfiuoum:muu 6460 :0 m4m>4m:¢ x .>4m>4uommmmu .m4m>m4 44 no 46 0:» um #:60444:m4m 40 #:60444:o4m:oz I 44 .4 .62 w .44:\6 6.46 >U4m:mo u:mum:oo a 0:45:660 0:0 mumo 6:44mfimm £060 :4 64:030456608 0994640: :0 ommmm 6 62 62 62 62 62 62 62 62 mum: "6:000:60 mz mz mz 4 mz m2 4 mz 46504604 ”04000560 62 62 62 62 62 44 44 44 muoooemo\6muo mz 4 62 mz 4 44 62 4 04m:46\u44mm "604D 62 62 62 62 62 4 44 44 #00440 :0004442 m2 4 mz mz mz 44 44 44 xucmfiuwmua 62 62 62 62 62 62 62 62 4.: .6:6 66 mocm4um>oo >00:mo444:m4m 6.4 0.4 4.6 6.4 4.4 6.6 6.6 6.6 66 .0: 6 wHOUOEmo 4.4 6.4 6.6 6.4 6.4 6.6 6.6 6.4 66 .o: 6 6:000:60 6.0 6.4 6.4 6.4 o.4 6.6 4.6 6.6 66 .0: m mHOOOEmO m.o 6.4 4.6 6.6 6.4 4.6 6.6 4.6 66 .0: m muoooamo 6.4 4.6 6.6 6.6 6.4 6.46 6.6 4.64 66 444:6 66:6 6.6 6.4 6.6 6.6 6.6 6.6 6.64 6.66 66 646:46 66:6 6.4 4.4 0.6 6.4 6.0 m.N 6.6 6.6 o 4044:00 :mvoup4z 64\6 66\6 66\6 6\6 64\6 66\6 66x6 6\6 6:\6: acmeummue 64-66 2:06 66666 6414 2:06 spawn mum: 2 Am:\z mxv 68:4:0EE< .6664 .mc4ucm4m .mouoms4m. umo::o> m :4 m4m>m4 :54:o::6 4406 :o mucmeummuu :wmouu4: mo uommmm .6 04:68 24 .44+ :04umuucmocoo Imoz + 6026 m04 on Umfiuoum:mnu 6460 :0 m4m>46:< x .>4m>4uommmmu .m4m>04 44 no 46 any um u:604u4:m4m no 6:604u4cm4m:oz t 44 .4 .62 h .44:\6 6.46 >u4m:mo u:mpm:oo 6 m:4asmmm 0:6 6660 6:446:66 £066 :4 mucmemusmmmfi 6454640: :0 ommmm 6 62 62 62 62 62 62 62 62 6666 "66666666 62 62 62 62 62 62 62 62 46664666 "66066660 4 62 62 62 62 4 44 62 66oooa66\6666 62 62 62 62 62 62 62 62 646:46\64466 "6666 m2 mz m2 4 m2 44 44 4 #00440 :mwonp4z mz mz m2 4 m2 44 44 m2 xu:mfipmmhe 62 62 62 62 62 62 62 62 2.: .660 66 66:6466>oo >00:604u4:m4m 6.6 6.4 6.4 6.4 6.6 4.46 6.44 6.64 66 .o: 6 66ooo:6o 6.6 4.4 4.4 6.6 4.6 6.64 6.64 6.64 66 .o: 6 66060666 6.6 6.6 6.6 6.4 6.4 6.64 6.64 6.64 66 .o: 6 66060666 4.6 4.6 6.6 4.64 6.6 6.64 6.64 6.44 66 . .o: 6 66060666 6.6 6.4 6.6 6.6 6.4 6.66 6.46 6.6 66 64466 6666 6.4 6.6 6.4 6.6 4.6 6.66 6.66 6.44 66 646646 66:6 6.6 6.6 6.6 6.4 6.4 6.6 6.6 6.64 6 4066660 :mmouu4z 64\6 66\6 66x6 6x6 64x6 66\6 66\6 6x6 6:\64 6:6:666:e 64:66 2:66 66666 64:4 2:66 66666 6666 2 26:\2 646 66666642 .6664 .66466646 .mouoms4m. 406::o> 6 :4 m4m>m4 066444: 4406 :0 66:6546044 :660444: 40 uomuum .4 64:69 25 1986 (Table 2). Nitrogen treatments increased topsoil N03" levels at all dates except for 9/10 (Table 4), while subsoil N03- levels were increased by fertilization only on 5/5. Plots fertilized with urea had higher NO3' levels than Osmocote on 5/26 and 6/26 (topsoil) and on 9/10 (subsoil) (Table 4). Experiment II 1986. Fertilizer applied to older plants (Appendices 3 and 4) had less pronounced effects on inorganic soil N levels than when younger plants were treated (Experiment I). Most significant differences in NH4+ levels were found in the topsoil, where the single application of urea showed higher NH4+ levels than the split application on 5/3, 5/23 and 9/18 (Appendix 3). Topsoil NH4+ levels were higher in urea plots than Osmocote plots only on 5/3. Although several treatments significantly affected soil N03" levels in 1986, effects were small and/or inconsistent from date to date (Appendix 4). 1987. Levels of NH4+ and N03' on 4/21/87 (Appendix 5) were similar to those obtained seven months before on 9/18/86 (Appendices 3-4). Fertilized plots had similar topsoil N03” levels, but significantly higher NH4+ concentrations before fertilization occurred on 4/21/87 (Appendix 5). Plots receiving split urea application had higher NH4+ in the topsoil before fertilizer application (4/21) and higher subsoil N03- at the end of the 1987 season 26 (9/10). Nitrate levels on 9/10 were higher in Osmocote treated plants as compared to urea (Appendix 5). Experiment III 1987. As expected, fertilized plots had higher NH4+ levels than control plots (Table 5). Levels at either soil depth were not affected differently by N sources (urea or ammonium sulfate). Topsoil N03” levels were increased by N applications, but both N sources affected NO3' levels similarly (Table 6). In the subsoil, significantly higher N03“ levels were found in urea-treated plots on 5/5 and 9/10 as compared to (NH4)ZSO4. Organic matter, when used as a covariant, was not related to the levels of NH4+ or N03" in the soil, except for NH4+ levels in the 25-40 cm depth (subsoil) of plots with older plants in 1986 (Appendix 3) or in plots with younger plants in Experiment III where the 1-15 cm depth (topsoil) was sampled (Table 5). Discussion Most of the literature on blueberry nutrition indicates that they preferentially absorb NH4+ over nitrate (3, 17). As a result, nitrification might be undesirable in blueberry soils because the likelihood of leaching losses is increased. Nitrification may be inhibited by low soil pH (6). Robertson (18) has suggested that low pH may affect 27 .44+ :0466Hu:60:oo +4mzv 004 on omauowm:6uu 6666 :0 646%46:< x .h4m>46066664 .64m>m4 44 Ho wm 6:» #6 #:60444:m46 no #:60444:m46:oz a 44 .4 .62 h .44:\6 6.46 >p4mcmn 6:666:00 6 6:45:666 6:6 6660 6:446:66 £066 :4 66:66645666: 6454640: :0 6666m 6 62 62 62 62 62 62 62 62 6666466 .:4\6666 62 62 62 4 62 44 44 44 606666 66606642 mz wz m2 4 m2 44 44 44 XHGmEummHB 62 62 62 62 62 4 62 62 4.6 .660 66 6066466>0o >60:60444:O4m 6.4 6.6 4.4 4.6 6.6 4.6 0.66 4.66 66 6666466 .64 6.6 6.0 6.6 6.4 6.4 6.6 6.44 4.46 66 6666 6.4 6.6 4.4 6.4 6.4 6.6 4.4 6.4 6 4066600 :6604642 64\6 66\6 66\6 6\6 64x6 66\6 66\6 6\6 66\64 666666666 64:66 2606 66666 64:4 4606 66666 266\2 666 N :54:o::< .hmmH 466::o> 6 :4 64m>m4 254:0656 4406 :0 6664456 :54:05E6 mumm z .m:4u:64m .mouows4m. 6:6 664: 40 vommwm .6 64:69 28 .44+ :046666:60:00 Imoz + mozv 004 06 6666066:666 6666 :0 646246:4 x .246>46O66666 .646>64 44 60 4m 6:6 66 6:60464:@46 60 6:60464:m46:02 : 44 .4 .62 2 .646\6 6.46 2646:66 6:666:00 6 6:48:666 6:6 6666 6:446866 6066 :4 66:666666666 66666406 :0 66666 6 4 62 62 4 62 62 62 62 6666466 .E<\666D 4 62 62 62 4 44 4 62 606666 :6606642 4 62 62 62 4 44 4 62 x6:6E66668 62 62 62 62 62 62 62 62 4.2 .660 wv 60:6466>00 260:60464:m4m m.v m.m 6.m 6.6 m.m m.o~ m.m4 6.w 66 666M43m .Ed 6.6 0.6 6.6 6.66 m.m 6.66 6.m~ 6.64 66 . 666D m.m 6.6 6.m 6.6 m.4 6.6 6.6 6.04 o 4066:00 :6006642 66\6 66\6 66\m m\m 66\6 66\6 66\m 6\m 66\66 666666666 64:66 2666 66666 64.6 6606 66666 6666 2 .66\2 666 66666642 .6666 .66466666 .60606646. 666::02 6 646>64 666664: 4406 :0 6666466 5:4:0666 6:6 666: 60 60666m .6 64668 29 nitrification indirectly by depressing mineralization. Soil pH in the present study was 4.3-4.5 and N03- levels were significantly increased by urea application in 1987 (Tables 4 and 6). Schmidt (19), observed nitrification does occur at pH 4-6 and postulated that soil microsites having a relatively high pH may account for increased nitrification in acid soils. Low nitrification rates in acid soils could be due to lower populations of nitrifiers. Applications of urea have been shown to increase nitrification after an initial lag period (15, 20). Higher nitrification rates have been seen on previously fertilized than on non- fertilized lowbush blueberry soils (7), which supports this explanation. Topsoil NH4+ levels were higher in mid-season in urea- treated plots than in plots receiving Osmocote (Tables 1 and 3, Appendix 3). Since nutrient release from Osmocote granules is reportedly not affected by soil pH or microbiological activity (13), we anticipated higher levels of NH4+ in mid- and late-season soil samples with the 3- and 8-month formulations, respectively. Because the Osmocote products used contain coated NH4NO3, it is possible that a portion of the N03” was lost by leaching or denitrification. Although N03- levels in subsoil would indicate that leaching was more prominent in plots receiving urea than Osmocote (Table 4, Appendix 4), we sampled only at intervals during the season. It is likely that some leaching beyond 40 cm might have occurred between sampling dates, probably during 30 high rainfall (Appendices 1 and 2) and when levels of nitrate in the soil were high (5, 12), such as late May 1986 or August 1987. It is unclear why NH4+ or NO3' levels were not increased 3 weeks after the second application of split urea in 1986. Increased NH4+ levels is expected if hydrolyzation exceeds immobilization. Levels would decrease if part of the NH4+ is nitrified, bound to soil colloids or absorbed by the crop. Significant increases in leaf N levels on 6/18 (Section 2, Figure 2) suggests rapid absorption of hydrolyzed urea by the plant. Our data provides evidence that a limited amount of topsoil NH4+ may carry over from season to season when split urea applications are used (Appendix 5). However, the quantities were relatively low and are not likely to be an important source of N the following year. It has been reported that the addition of urea may increase nitrification rates in soils (15, 16), whereas, addition of an acid-forming fertilizer, such as (NH4)ZSO4, decreases nitrification rates (16). Our findings agree with these reports (Table 6). In this study, soil organic matter was not closely correlated with N03” or NH4+ levels, and could not be used as a covariate to reduce variability among replications. These results differ somewhat from research on blueberries in West Germany (1) where in non-fertilized plots it was 31 found that organic matter content was correlated with N03- but not NH4+ levels in the soil. These studies demonstrated that 1) the levels of inorganic N were significantly lower after application of a controlled-release fertilizer than in urea-treated plots; 2) the frequency of urea application (single vs split) had differential effects on soil NH4+ and N03. that varied from year to year and seemed to depend greatly on environmental factors. Initial soil inorganic N levels were higher when single applications were used, but tended to decrease below levels of split-urea once the second half of urea was applied; 3) limited NH4+ carry over from year to year was obtained with split urea applications; 4) some N03” was found in the subsoil when fertilizers were applied and leaching in plots receiving urea appeared to be greater shortly after application than in Osmocote treated plots; and 5) preliminary results indicate that NO3' levels were higher when urea, rather than (NH4)ZSO4, was used as the N source. Higher N03” levels below the root system suggest that leaching losses may be greater when urea is used. Literature Cited 1. Blassing, D. 1986. Kriterien zur standortwahl von Kulturheidelbeeren. Diss. Univ. Hannover, W. Germany. 2. Bowmann, W.L., F.R. Austin, R.E. Evon, B.O. Knapp, J.D. Larson, R.W. Neilson, T.M. Smith, W.E. Hogan and H.J. Kredo. 1986. Soil survey of VanBuren County, 10. 32 Michigan. Soil Cons. Serv., U.S.D.A. Govmt. Printing Office, Washington, D.C. Cain, J.C. 1952. A comparison of ammonium and nitrate N for blueberries. Proc. Amer. Soc. Hort. Sci. 59:161-166. Cain, J.C. and P. Eck. 1966. Blueberry and cranberry. p. 101-129. In: N.F. Childers (ed.) Fruit Nutrition, 2nd Ed. Hort. Pub., New Brunswick, N.J. Coppock, R. and R.D. Meyer. 1980. Nitrate losses from irrigated cropland. Div. of Agric. Sci. Univ. of California. Leaflet 21136. Dancer, W.S., L.A. Peterson and A. Chesters. 1973. Ammonification and nitrification of N as influenced by pH and previous N treatments. Soil Sci. Soc. Am. Proc. 37:67-69. Eaton, L.J. and D.G. Patriquin. 1984. Nitrogen cycling in lowbush blueberry soils. Proc. of North Amer. Blueberry Research Workers Conference, Gainesville, Florida, 1-3 February. Hancock, J. and E. Hanson. 1986. Highbush blueberry nutrition. Michigan State Univ., Ext. Bull. E-2011. Hanson, E.J. and J.F. Hancock. 1988. Hints on growing blueberries. Michigan State Univ., Ext. Bull. E-2066. Keeney, D.R. and D.W. Nelson. 1981. Nitrogen- inorganic forms. p. 643-698. In: A.L. Page et al. (eds.) Methods of soil analysis, No. 9, Part 2. 2nd ed. Am. Soc. of Agron., Madison, Wis. ll. 12. 13. 14. 15. l6. 17. 33 Kender, W.J. 1966. Environmental relationships, p. 75-93. In: P. Eck and N.F. Childers (eds.) Blueberry culture. Rutgers Univ. Press, New Brunswick, N.J. Legg, J.C. and J.J. Meisinger. 1982. Soil nitrogen budgets. p. 503-566. In: F.J. Stevenson (ed.) Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Maynard, D.N. and C.A. Lorenz. 1979. Controlled- release fertilizers for horticultural crops. Hort. Rev. 1:79-140. Olson, R.A. and L.T. Kurtz. 1982. Crop nitrogen requirements, utilization, and fertilization, p. 567- 604. In: F.J. Stevenson (ed.). Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Otchere-Boateng, J. and T.M. Ballard. 1978. Urea fertilizer effects on dissolved nutrient concentrations in some forest soils. Soil Sci. Soc. Amer. J. 42:503- 508. Overrein, L.N. 1967. Immobilization and mineralization of tracer nitrogen in forest raw humus: I. Effect of temperature on the interchange of nitrogen after addition of urea-, ammonium-, and nitrate-N15. Plant Soil 27:1-19. Peterson, L.A., E.J. Stang and M.N. Dana. 1988. Blueberry response to NH4-N and NO3-N. J. Amer. Soc. Hort. Sci. 113:9-12. l8. 19. 20. Robertson, ecosystems. 34 G.P. 1982. Nitrification in forested Phil. Trans. R. Soc. Lond. 296:445-457. Schmidt, E.L. 1982. Nitrification in soil. p. 253- 288. In: agricultural F.J. Stevenson (ed.). Nitrogen in soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Vitousek, P.M., J.R. Gosz, C.C. Grier, J.M. Melillo, W.A. Reiners and R.L. Todd. 1979. Nitrate losses from disturbed ecosystems. Science 204:469-474. Section II STUDIES ON SOIL N APPLICATIONS TO HIGHBUSH BLUEBERRIES: II. PLANT EFFECTS. 35 36 Abstract The effect of nitrogen applied at 38 kg/ha (1 N) or 76 kg/ha (2 N) was studied in three separate experiments for its effect on plant performance in 'Bluecrop' blueberries. In the first experiment, urea (2 N), split urea (2 x 1 N), Osmocote (controlled-release fertilizer) 3 or 8 mo. duration at 1 or 2 N, were applied for 2 years to 8-year-old plants. Treatments were duplicated in older bushes in a second experiment. Urea 2 N and (NH4)ZSO4(2 N) were applied for one season to 9-year-old plants in a third study. Nitrogen applications increased leaf N of 8-year-old plants on most sampling dates. Split urea treatments often resulted in higher leaf levels than single urea or Osmocote applications. In older plants the effect of treatments on leaf N was similar but less pronounced. Urea and (NH4)ZSO4 resulted in comparable leaf N levels. Leaves sampled from younger and older plants at the end of the second year were lower in Ca, Mg, B and Al in nitrogen treated plants. Nitrogen treatments had no consistent effect on cold hardiness of stems and apical fruit buds of younger plants. Fruit yield and size were not affected by N treatments in any of the experiments. Introduction The effect of nitrogen applications on yield, plant growth and leaf mineral composition of highbush blueberry 37 plants has received considerable attention. Most reports agree that multiple N applications may provide benefits over a single application (5, 9, 10), but the practice has found little acceptance among growers in Michigan. The use of controlled-release fertilizer has shown promise in fruit crops in general (17) and in blueberry in particular (6, 18). The effectiveness of these products has not been demonstrated in highbush blueberries in the field. Controlled-release fertilizers may allow growers to make single applications and obtain the benefits of multiple fertilization. In Michigan, the N sources most used by growers are urea and ammonium sulfate. Research comparing these two sources on highbush blueberry in the Canadian province of Nova Scotia under different environmental conditions (3) indicates that both sources are equally effective. As shown by Cain and Eck (5), recommendations vary greatly among different highbush blueberry growing regions and is likely that results previously reported are not applicable to highbush blueberries growing under Michigan conditions. The objective of this research was to compare the effects of different N sources and/or timing in highbush blueberries to determine: 1) if the efficiency of fertilizer use can be improved, and 2) the effect on plant performance. 38 Materials and Methods General Three experiments were established to study the effect of rate and sources of N on leaf mineral concentrations, stem and bud cold hardiness and yield of 'Bluecrop' in a commercial planting at Grand Junction, Michigan. A detailed description of soil characteristics is given in Section 1. In Experiment I, the effect of rate/source of the following N treatments, were studied in 1986 and 1987 on bushes planted in 1978 (younger plants) using 10 replications: 1) single urea, one application of 76 kg N/ha (2 N) at bud break (4/9/86 and 4/21/87); 2) splut urea, two applications of 38 kg N/ha (1 N) at bud break and petal fall (5/27/86 or 6/16/87); 3) Osmocote 3-month duration (19:6:12) (Sierra Chemical Co., Milpitas, Cal.) at 1 N applied at bud break; 4) Osmocote 3-month duration at 2 N applied at bud break; 5) Osmocote 8-month duration (17:6:10), 1 N at bud break; 6) Osmocote 8-month duration, 2 N at bud break; and 7) control (no N). Treatments were duplicated in adjacent irrigated plants established in 1970 (older) in Experiment II using 6 replications. In 1987, the effects of urea and ammonium sulfate, on younger plants were studied (Experiment III). Two bush plots were used, in a randomized complete block design with seven replications. Superphosphate and KCl were supplied to urea and control treatments to provide P and K at rates equivalent to the ones applied in Osmocote treatments. 39 Leaf Sampling and Analysis To determine the effect of applied fertilizer on leaf N levels in all three experiments, 20 recently emerged (first sampling) or 12 fully expanded leaves from the mid-section of current season growth (later samplings) were collected per plant at four to seven week intervals during the 1986 and 1987 growing seasons. Leaves were dried at 60°C for one week, ground in a Wiley mill to pass a 30 mesh screen, and digested in H2804 using K2804 and Se as catalyzers in a block digestor. Total N concentration was determined in a Quikchem flow injection analyzer (Latchat Instr., Mequon, Wis.) using Kjeldahl procedure (Latchat method 13-107-06-2-B). Leaves collected from six replications at the termination of Experiments I and II (8/10/87) were used to determine the effect of N treatments on leaf mineral concentrations. For this, previously dried leaf samples were randomly chosen from four replications in Experiment I (two in irrigated and two in non-irrigated) and two in Experiment III. Samples were ashed at 550°C for six hours, and ash was dissolved in a 3 N nitric acid solution containing 1000 ppm LiCl. Samples were filtered (Whatman No. l), and two subsamples were used to determine leaf mineral concentration (P, K, Ca, Mg, Zn, Fe, Cu, Mn, B and Al) using a Plasma Spectrometer. 40 Cold Hardiness The effect of N treatments on cold hardiness of current season stems and terminal flower buds of young plants was studied by sampling two-bud terminals of intermediate vigor (7-10 cm) from the periphery of irrigated and non-irrigated plants in Experiment I in the winters of 1986-87 (10/14, 12/11 and 3/5) and 1987-88 (10/13 and 2/10). A random drawing was done to determine plots to be sampled and enough material was collected on each date to run a control (+1°C) and five to six test temperatures per N treatment. Three stem pieces per treatment were attached to an adhesive tape covered with dampened gauze, rolled up in aluminum foil, placed in a thermos flask with a 26-gauge copper-constantan thermocouple inserted into the stem and connected to a potentiometer to record stem temperature (4). Fifteen to eighteen flasks were prepared on each sampling date to provide three replications for each of five to six cold treatments. Once prepared, flasks were placed in a freezer, cooled at 2-4°C/h and removed at 3-4°C intervals according to a pre-established temperature stress range. Flasks removed from the freezer were placed at 1°C for 24 h (4). Gauze and aluminum foil were removed and stems were placed in a humid chamber (approx. 100% R.H) for 7 days at room temperature. Apical and sub-apical flower buds and stems were visually evaluated for percent survival as determined by the absence 41 of brown coloration. Buds showing >6 brown flowers were considered dead. Flower bud survival in the field was studied by sampling 100 terminals (7-10 cm) from each N treatment on 2/10/88 as described above. Samples were separated in 4 groups (replications) of 25 terminals, placed in beakers containing distilled water and left at 20°C for 10 days. Percent bud survival was determined as described above. Analysis of variance and orthogonal comparisons were done on arc sin transformed data. Yield and Fruit Size The effects of N treatments on yield and fruit size was determined in 1987. Plants were harvested on 7/6 and 7/16 with hand vibrators (Experiment II) or by hand (Experiments I and III) and total fruit wt was recorded. Average fruit size was measured by counting the number of fruit fitting 3 container. Plants were not harvested in 1986 into a 200 cm because yields were severely reduced by a severe frost prior to full bloom. Statistical Analysis The following orthogonal contrasts were established to determine treatment effects in Experiments I and II: 1) control (no N) was compared to all nitrogen treatments (nitrogen effect); 2) split urea application was contrasted with single urea (split/single); 3) urea, either single or split, compared to Osmocote treatments at 76 kg N/ha 42 (urea/Osmocote); 4) Osmocote 3-month residual treatments were compared to 8-month residual at either rate (Osmocote:residual): and 5) Osmocote treatments at 38 kg N/ha contrasted with Osmocote treatments where 76 kg N/ha was applied (Osmocote:rate). In Experiment III, control (no N) was compared to N fertilized plots (nitrogen effect) and urea was compared to (NH4)ZSO4 in a second contrast (urea/ammonium sulfate). Results Leaf N Experiment I Nitrogen concentrations decreased as the season progressed and tended to stabilize at the end of the season (Figures 1, 2 and 3). In 1986, the application of N to younger plants produced significantly higher N concentrations on 6/18, 8/28, and 9/26, while in 1987, nitrogen fertilization significantly increased N levels at all sampling dates (Figure 1). Split urea applications resulted in greater leaf nitrogen than single applications on several dates (Figure 2). In 1986, split applications significantly increased leaf N shortly after the second half was applied. In 1987, the effect was significant only at the last sampling date. Plants receiving urea (split or single) always contained higher leaf N levels compared to those receiving Osmocote (Figure 3). In 1986, these differences became significant following the application of the second half in LEAF NITROGEN (7. Dry Matter) LEAF NITROGEN (‘7. Dry Matter) Figure l. 43 3- 0-0 CONTROL 0—. NITROGEN NS\\ 1986 2- 1.. O L MAY I JUN I JUL I AUG I SEP 3.1 0-0 CONTROL 0—. NWROGEN 2... 1J 0 4 MAY I JUN I JUL I AUG I SEP DATE Effect of soil nitrogen applications on seasonal foliar N levels in younger 'Bluecrop' bushes (arrow indicates second application of split urea). NS, *, ** - nonsignificant or significant at the 5% and 1% levels, respectively. 44 ,3 3‘ 0-0 SINGLE UREA 3 \ o—o SPLIT UREA 5 NS \ J \ E ‘\ o a \ 1-86 o 24 &\-°/ 2 '1 “c3 00: 1-I Ns Ns I: 2 LL. J < L5 0 J. MAY I JUN I JUL I AUG I SEP B 0—0 SPUT UREA ‘5 2 d a 1987 o 23 5: z 4 LLJ 8 a: 14 t: z E _1 O L MAY I JUN I JUL I AUG I SEP Figure 2. DATE Effect of soil application of urea before bud break (single) or before bud break and at petal fall (split) on seasonal foliar N levels in younger 'Bluecrop' bushes (arrow indicates second application of split urea). NS, *, ** - nonsignificant or significant at the 5% and 1% levels, respectively. LEAF NITROGEN (% Dry Matter) LEAF NITROGEN (7. Dry Matter) Figure 45 3- o-o UREA \ H OSMOCOTE 24 J 1.. J L 0 I I I I MAY JUN JUL AUG SEP 37 0-0 UREA H OSMOCOTE 1987 2.4 J 1_ ** * 4 0 I I I I MAY JUN JUL AUG SEP DATE 3. Effect of soil applications of urea or Osmocote on seasonal foliar N levels in younger 'Bluecrop' bushes (arrow indicates second application of split urea). NS, *, ** - nonsignificant or significant at the 5% and 1% levels, respectively. 46 split urea treatment (May 27) and in the last sampling. In 1987, urea treatments increased leaf N at all sampling dates. Neither the duration or rate of Osmocote products consistently affected leaf N. Plants receiving short term Osmocote in 1986 had significantly higher leaf N on 7/22, whereas the long term Osmocote produced higher leaf N on 6/26 of 1987 (data not presented). The rate of Osmocote had no effect on leaf N in 1986, but the high rates of Osmocote increased leaf N significantly on 5/6/87 and 5/26/87. Leaf N Experiment II Trends in leaf N concentration in older plants were similar to Experiment I, but treatment effects, in general, were less pronounced (Appendix 6-7). Leaf N Experiment III The application of N (as urea or ammonium sulfate) to younger plants, significantly increased N levels on all sampling dates; however, both urea and (NH4)ZSO4 increased foliar N concentrations to similar levels (Appendix 8). Mineral Concentrations Combined samples of Experiments I and II revealed significant differences among treatments in the leaf concentration of Ca, Mg, B and Al (Table 1). Analysis of orthogonal contrasts indicated that these differences were associated with the application of a nitrogen fertilizer, except for the effect of high rates of Osmocote which 47 .hao>fluoommmu .mam>oa RH no Rm on» no unwofluwcoflm no unmoHMAcmfimcoz I RR .R .mz m .mcowumofiammn o no mammfi ucmmmumou mama N m2 RR mz mz mz mz mz mz mz mz much "muoooamo mz mz m2 m2 m2 mz mz mz mz mz Hmsowmou “muooosmo mz mz mz m2 m2 m2 mz mz mz mz muooogmo .m> nous mz mz mz RR mz m2 m2 m2 m2 mz mamcfim .m> uwamm "own: RR RR m2 m2 m2 mz RR R m2 m2 Homwum cmmouuwz "mcomflummfioo R RR m2 m2 mz mz RR R mz mz mpcmfiuwmua hmocmofluflcmflm woa v.oa w.mn m.m om ¢.mH SH.o om.o hm.o mo.o on .05 w OOOUOEmo mad m.om «.mm o.m mo w.>a om.o m¢.o mm.o mo.o mm .06 w muoooamo mad m.ma o.mm >.m on N.Hm om.o mv.o mm.o wo.o on .OE m muooosmo mHH a.om m.am o.m ch m.ma om.o H¢.o om.o mo.o mm .03 m muoooamo ooa v.0a m.mm o.m mm m.>a ma.o hm.o Rm.o mo.o on uflamm mono moa m.>H v.hm N.w mo o.va wH.o 0¢.o em.o mo.o on mamcflw nous mma m.HN «.mm >.m vb m.ma Hm.o m¢.o Rm.o wo.o o Houucoo cmmouuflz Hfi m a: DO mm :N ms mu m m mn\mx ucmfiuwmue Ema w much 2 NcOAOAmOQEoo HmucoEmam .Smma ..mouomoam. CH cofluflmomeoo Hmumcfla mama so wouoom\muou somONUA: mo uomuwm .H manna . 48 decreased B levels. Additionally, split application of urea reduced leaf Cu over single applications (Table 1). Cold Hardiness Results of controlled low temperature stress tests indicated that N treatments had inconsistent effects on the cold hardiness of apical and sub-apical fruit buds and current season stems of young plants for two years. High rates and long-duration Osmocote treatments tended to reduce flower bud hardiness, but not consistently (Appendices 9 and 10). Bud survival in 1988 in the field was not affected by fertilizer treatment (Appendix 11). Yield and Fruit Size Fruit yield in 1987 was not affected significantly by treatments in any experiment (see Appendices 12-14). Treatments had little effect on fruit weight, except for slightly higher fruit weight in single urea as compared to split-urea applications (Appendix 12). Discussion The effects of nitrogen treatments on leaf N concentrations were dependent on plant age. Younger plants showing greater response than older plants (Figures 1-3, Appendices 6 & 7). Comparing long term nutrition studies on lS-year-old (2) and 7-year-old blueberries (11), N applications increased leaf N levels 4 out of 5 years on young plants, compared to 2 out of 5 years on older plants. 49 Young plants may have less nitrogenous reserves and standing plant biomass than older plants, which could partly explain the difference. Support for this possibility is given by research with 15N-labeled fertilizer (Section III). Mature blueberry plants only derive about 15% of total plant N from applied fertilizer. In our study, urea resulted in significantly higher leaf N levels compared to Osmocote (Figure 3). Research in West Germany comparing controlled-release fertilizer to a mixture of ammonium sulfate and ammonium nitrate applied at similar N rates (18) has shown no differences in leaf N over 3 years. Fertilizer formulations and differences in soil and climate may account for the contrasting results. The lower leaf N levels resulting from Osmocote treatments (Table 3) are not clearly explained by soil data (Section II). Since Osmocote contains ammonium nitrate, leaching losses were expected to be higher but subsoil nitrate levels in these treatments do not provide support for this explanation, even though some of the nitrate could be present in the 15-25 cm layer which was discarded. Multiple applications of N have been recommended to improve uptake (9, 10). Split urea applications resulted in higher leaf N levels than single applications in our study (Figure 2). Cain and Eck (5) attributed the effect of split applications to reduced leaching and extended availability of N in the soil. This explanation is supported by our data on soil N levels (See Section I). The delayed increase in 50 leaf N in split urea in 1987 may be related to low soil moisture after the second application. Results of Experiment III indicated that urea and (NH4)ZSO4 were equally effective in supplying N to blueberries, although data were collected for only one year (Appendix 8). Trials over three years on highbush blueberries in Canada showed no difference in N levels when (NH4)ZSO4 and urea were compared (3). Even though urea needs to be hydrolyzed in order for NH4+ to be released, a reaction mediated by the enzyme urease which is inhibited at low pH, this effect could be overcome by the high organic matter content of the soil which would provide higher concentrations of the enzyme (16). High soil NH4+ levels were observed soon after urea applications in the present study (see Section I). Seasonal changes in leaf N concentrations reported in the present study are similar to those reported for other highbush blueberry cultivars (1, 13). In general, mid- season leaf N levels in our studies were within the standard range of 1.65 to 2.1% (12), except for below normal N levels in non-fertilized control and Osmocote treated plants in 1987 samplings. Leaf mineral concentrations in our experiments were within the normal range (5, 12) except for Cu which was lower than the standard value (15 ppm) (Table 1); In our study (Table 1), lower leaf Ca and Mg occurred with N applications. Controversy exists in the literature with 51 respect to how soil N applications affect leaf Ca and Mg (2, 7, 18). It has been suggested (12) that the lower fOIiar Ca and Mg concentrations may be due to an indirect effect of N on increased plant growth (14). Cummings (7) reported decreased foliar Cu levels after 6 years of N applications and he related this finding to changes in soil pH. Our data (Table 1), show that split urea had lower Cu levels than single applications. Even though pH changes were not measured, it is unlikely that the method of application of urea could markedly change soil acidity. No reference was found in the literature relating changes in leaf Al to N fertilization. The high soil acidity and organic matter typical of blueberry soils create conditions for high soluble Al levels in the soil (15), but the implications of this on leaf Al levels are not known. Boron levels were significantly increased by N treatments (Table 1). Orthogonal contrast analysis shows that plants receiving high rates of Osmocote had significantly higher B in their leaves. The 8-month duration formulation contains 0.02% B and if this is causing the difference, leaf B levels should have been different when comparing the two formulations. The supposition that a higher soil fertility level at the end of the season (especially with long term Osmocote) would induce plants to grow later in the season, lead us to study the effect of N fertilization on cold hardiness. In a 52 review of the literature on the effect of nutrition on cold hardiness (19), Pellet and Carter concluded that plants will cold-acclimate at a similar rate or to a similar degree if under optimum fertility levels. Because the fertility levels in our study, as judged by foliar mineral concentrations (Figures 1-3, Table 1, Appendices 6-8), were all in the normal range, we could not test the effects of inadequate or excessive N levels on cold hardiness of stems and fruit buds, although high rates or longer duration of Osmocote appeared to reduce bud hardiness but not consistently (Appendices 9 and 10). Townsend (20) in a long term study, found no strong association between growth and winter injury; although the time when growth occurred was not reported. Doehlert (8) has shown significant increases in yield following N applications. These results appear to be contradicted by Townsend (20), who stated that the difference would reside in greater winter injury in N fertilized plots. Research plots in our study suffered different degrees of winter damage during January 1987; this was evidenced in the cold hardiness evaluation on 3/5/87 (Appendix 9), and probably this factor had greater influence on yield in 1987 than nitrogen fertilization (Appendices 14, 15 and 16). In conclusion, our results show: 1) leaf N levels were significantly higher in urea-treated plots, as compared to Osmocote; 2) split urea applications resulted in higher leaf 53 N levels than single application; 3) differences among treatments were greater in the second season, with young plants being more responsive than older ones; 4) fertilizer treatments had no consistent effect on the cold hardiness of fruit buds and terminals; and 5) fruit yields and size were not affected by N treatments. Literature Cited Bailey, J.S., A.F. Spelman and B. Gersten. 1962. Seasonal changes in the nutrients in the leaves of Rubel blueberry bushes. Proc. Amer. Soc. Hort. Sci. 80:327-330. Bailey, J.S., B. Gersten, E. Vlach and G.W. Olanyk. 1966. Response of Rubel blueberry bushes to ammonium sulfate and sulfate of potash-magnesia. Proc. Amer. Soc. Hort. Sci. 89:237-242. Bishop, R.F., L.R. Townsend and D.L. Craig. 1971. Effect of source and rate of N and Mg on nutrient levels in highbush blueberry leaves and fruit. HortSci. 6:37-38. Bittenbender, H.C. and G.S. Howell. 1976. Cold hardiness of flower buds from selected highbush blueberry cultivars (Vaccinium australe Small). J. Amer. Soc. Hort. Sci. 101:135-139. Cain, J.C. and P. Eck. 1966. Blueberry and cranberry. p. 101-129. In: N.F. Childers (ed.) Fruit Nutrition, 2nd Ed. Hort. Pub., New Brunswick, NJ. 10. 11. 12. 13. 14. 54 Crocker, T.E. 1983. Use of sulfur coated urea, ammonium sulfate and urea phosphate on blueberries in Florida for N and pH control. Proc. Fla. State Hort. SOC. 96:226-227. Cummings, G.A. 1978. Plant and soil effects of fertilizer and lime applied to highbush blueberries. J. Amer. Soc. Hort. Sci. 103:302-305. Doehlert, C.A. 1940. Dates for applying blueberry fertilizer. Proc. Amer. Soc. Hort. Sci. 38:451-454. Doehlert, C.A. 1944. Fertilizing commercial blueberry fields in New Jersey. N.J. Agr. Exp. Sta. Circ. 483. Doehlert, C.A. 1953. Facts about fertilizing blueberries. N.J. Agr. Exp. Sta. Circ. 550. Eck, P. 1977. Nitrogen requirements of the highbush blueberry, Vaccinium corymbosum L. J. Amer. Soc. Hort. Sci. 102:816-818. Hancock, J. and E. Hanson. 1986. Highbush blueberry nutrition. Mich. State Univ. Coop. Ext. Serv. Bull. E- 2011. Hanson, E.J. and J.F. Hancock. 1988. Hints on growing blueberries. Mich. State Univ. Coop. Ext. Serv. Bull. E-2066. Herath, H.M.E. and G.W. Eaton. 1968. Some effects of water table, pH, and nitrogen fertilization upon growth and nutrient-element content of highbush blueberry plants. Proc. Amer. Soc. Hort. Sci. 92:274-283. 15. l6. 17. 18. 19. 20. 55 Korcak, R.F. 1987. Satisfying and altering edaphic requirements for acidophilic plants. J. Plant Nutr. 10:1071-1078. Ladd, J.N. and R.B. Jackson. 1982. Biochemistry of ammonification, p. 173-228. In: F.J. Stevenson (ed.). Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Maynard, D.N. and O.A. Lorenz. 1979. Controlled- release fertilizers for horticultural crops. Hort. Rev. 1:79-140. Naumann, W.D. and E. Kruger. 1985. Nitrogen supply of highbush blueberries. Acta. Hort. 165:229-236. Pellet, H.M. and J.V. Carter. 1981. Effect of nutritional factors on cold hardiness of plants. Hort. Rev. 3:144-171. Townsend, L.R. 1973. Effect of N, P, K and Mg on the growth and productivity of the highbush blueberry. Can. J. Plant Sci. 53:161-168. Section III FATE OF 15N-LABELED UREA APPLIED TO MATURE HIGHBUSH BLUEBERRIES 56 57 Abstract To study the efficiency of fertilizer use by highbush blueberry, the soil surrounding four 22-year-old 'Bluecrop' plants growing in a sandy loam soil was treated before bud break (4/21) with 14.74% 15N-enriched urea at a rate equivalent to 40 kg N/ha. Leaf samples were collected at 1- 4 week intervals during the season. Plants were harvested at the end of the growing season (9/22), partitioned among different components, dried, weighed and analyzed by mass spectrometry. Fertilizer-derived N was observed in leaves 2 weeks after application, and accounted for the greatest percentage of total leaf N (16.5%) 3 weeks after application. Plants recovered 32% of applied N by the end of the growing season. Leaves accounted for 32% of this total. Shoot tissue accounted for 32% of fertilizer derived N in the plant, with the highest % accumulating in young shoots. Less than 15% of fertilizer N remained in the soil at the end of the season. Introduction Nitrogen is the nutrient element used most by highbush blueberry (Vaccinium corvmbosum L.) growers. Interest in reducing fertilization costs and potential for ground water pollution provide incentive to increase the efficiency of fertilizer use (12). 58 The fate of fertilizer N has been studied for several tree fruit species (6, 8, 10, 11, 22, 24), but to our knowledge, no studies have been conducted in bush-type species. Highbush blueberry soils in Michigan are low in pH and often high in organic matter (OM). These characteristics may affect the number and growth of microorganisms involved in soil N transformations (7, l4). Results obtained from research on tree fruit species are probably not applicable to the highbush blueberry. In woody species, efficiency of fertilizer application is difficult to assess, since part of the N taken up one year is stored in the plant for use in subsequent years (20, 21). The use of 15N-labeled fertilizer can be of value in studying the utilization and allocation of nitrogenous fertilizer within the plant. In this study, enriched 15N- urea was applied to mature blueberries to determine: a) when fertilizer N first appears in the leaves, b) the fate of fertilizer-derived N and establish the efficiency of fertilizer use and concurrently, c) the nitrogen content in different organs at the end of the season. Materials and Methods General The experiment plot was located in Grand Junction (Southwest Michigan). The soil belongs to the Kingsville- Pipestone complex (mesic Entic Haplaquods-mesic Mollic Psammaquents) (2). The topsoil (0-15 cm) has a loamy sand 59 texture (80.9% sand, 11.4% silt and 7.7% clay) with a cation exchange capacity (CEC) of 22-25 meg/100 g, 7-9 % OM and pH = 4.3. The subsoil has a loamy sand texture (83.9% sand, 9.4% silt, 6.7% clay), 5-7% OM, pH 4.5 and CEC 17-18 meg/100 9)- The soil surrounding four 22-year-old 'Bluecrop' plants of similar vigor were treated before bud break (4/21) with a 14.74% 15N-enriched urea solution (Isotec, Inc., Dayton, OH). A 120 x 120 cm area within the herbicide-cleared strip at the base of each plant received 14.95 g N in a 2 1 solution (40 kg N/planted ha); a control plot of one plant was sprayed with equal rate of non-labeled urea to establish 15N soil abundance. Soil moisture was near natural saturation at the time of application and plants received 11 mm of rain within 48 hours. Sampling Uptake of labeled urea was monitored by sampling 20-40 leaves from each bush at 1-4 week intervals starting one week after emergence (5/5). Oldest, recently emerged, leaves were taken on the first three sampling and later samples consisted of fully expanded leaves from the middle of the current season's growth. Fruits were harvested at commercial maturity on 7/10 and 7/28. On 9/22 a 30 cm wide x 60 cm deep trench was dug around the edge of the fertilizer treated area. Soil within the area was loosened with a pitch-fork and plants were lifted from the ground with a forklift using a chain attached to the base (crown) 60 of each plant. Soil adhering to crowns and roots was removed with a high pressure water hose. Small roots detached from the plants were also collected. Plants were stored at 4°C and later separated into the following components: leaves, current stems (l-year-old stems and branches), mid-age stems (2-, 3-year-old stems and branches), older stems (stems and branches > 3-year-old), small roots (< 1 cm in diameter) and crown (base of shoots and roots >l cm in diameter). Fruits were freeze-dried, and other tissues were dried with forced-air at 60°C for 3 weeks. Fruits, leaves and current stems were ground in a Wiley mill to pass 1 mm. Other samples were pre-ground in a hammer-mill pulverizer .(Am. Pulverizer Co., St. Louis, Mo.). A representative sample of all tissues was further pulverized to a fine powder by placing them in glass vials containing stainless steel rods of different sizes which were rotated at 100 rpm for 2 days. Residual soil N at the end of the experiment was measured by collecting soil at two different depths by removing eight cores at the base of each plant using a 2.5 cm diameter auger. Roots were removed from cores, washed and included in the previously described root portion of the plant. Topsoil (0-15 cm depth) represented the portion of soil where most roots were present, whereas, subsoil (25-40 cm) was generally devoid of roots. For calculation purposes, it was assumed that 25% of topsoil was occuppied 61 by roots and that density was constant throughout the profile (1.3 g/ml) (2). Total Nitrogen and 15N Analysis Percent atom excess in plant and soil samples was measured with a Tracer Mass (Europa Scientific, Cheshire, England) mass spectrometer. Between 5 and 10 mg of plant tissue were placed in tin cups for 15N analysis. Total N was determined with a flow injection analyzer model Quickchem (Lachat Instr., Mequon, Wis.) using Kjeldahl digestion followed by NH4+ analysis (Lachat method 13-107-06-2-B). Soil samples were separated in two groups for 15N determination. Total soil 15N enrichment and percent N determinations were done in the mass spectrometer on approximately 70 mg of dry soil, previously pulverized in a Retsch soil pulverizer (Brinkman Instr., Westbury, NY) to pass 0.5 mm mesh. Enrichment of the inorganic exchangeable portion was determined by placing about 70 ml of l M KCl soil extract (3) in a sealed plastic container to which MgO and Devardas alloy had been added to reduce ammonium and nitrate, respectively. The NH3 gas produced was captured in a filter paper saturated with 9 M H2804 suspended on a stainless steel wire, once dried the paper was placed in the combustion chamber of the mass spectrometer. Two containers with known inorganic N concentrations were included to monitor recovery (5). Enrichment in organic fraction was 62 determined by difference between total and inorganic enrichment. For calculations on atom percent excess and percent N derived from fertilizer, formulas 6 and 7 reported by Rennie and Rennie (16) were used. Results Dry Weight and N Content of Different Tissues The dry weight of plants averaged about 10 kg, with slightly over a third of this mass present in crown tissue and nearly 40% in stems (Table l). The highest concentration of N was found in leaves and lowest in stems greater than 2-year-old. Over half of N present in plants at the end of the season was in crown and roots (Table 1). An average of 3.41 g N was found in the fruit portion. Leaf 15N Content Through the Season Nitrogen derived from fertilizer was detected in newly emerged leaves 2 weeks after urea application, and represented the highest percentage of total leaf N 3 weeks after application, before full leaf expansion (Figure 1). The proportion of fertilizer-derived N in leaves declined in mid-season and remained nearly constant (about 11%) until the end of the season. Distribution of 15N—Enriched Fertilizer in Plants At the end of the season, plants contained nearly one third of N applied as fertilizer, with leaves accounting for 63 .mcoflumoflammu swan maocflm Moon mo .o.m + momma ucwmmumou sumo N .nmuuofi who no oompcmoumm mo Ummmmumxm mommflp CH 2 Hmuoa m oo.ooa 4m.am III oo.ooa om.omaoa unmam macs: mh.mH mm.¢HmH.mH «H.0HH¢.H mm.HH om.mwmflmh.mmaa uOOm Hm.mm mm.mHHN.hm No.oH¢h.o mm.wm Ho.mmeoo.mhmm CSOHU om.m ho.HHHN.b No.0Hmv.o mm.ma vo.mHmHoo.waH EmOm OHOIum m A Hm.h mm.onm.m No.0Hmv.o mh.ma gm.hmmflom.vmma EODm CHOIR» MIN Hm.m ma.oHNH.m mo.oflhb.o mw.OH Hm.bHNHmb.mhoa 80pm UHOIH> H 6H.v me.oHHv.m mo.onm.o no.m oo.mmHmm.Hnm Madam mm.wH mw.HHHw.MH vo.oflmw.a Hm.h ww.wmem.0¢h HMOA AHmuou no we Aucmfimxmv “we AHRUOU Go My AnamHm\mV z 2 >2 #3 >HQ #3 wuo msmmfla m>flumamm manaomns Hmuoe o>wumamm madaomn< N.>uumamsan amonnmfln .mouoos~m. ouzuma mo moommflu ucoummmflo :H z unmouom pom ucqflm3 who m>flumamu can musHom24 .H magma 64 g: 16- 22-yeor-old 'Bluecrop' V P c: R “4 3'3 g 12- . d I— o E} J .3 §> LI. 8 ‘ L5 3 ‘ _I E - - _‘_ _ _ _. _ 4‘ +2 2 z ’ z 4.1 ‘5 -1 2 _I . 5 O H N from fertilizer :- I Total N '— I I I T I APR MAY JUN JUL AUG SEP DATE Figure 1. Seasonal changes in total nitrogen in leaf and percent of leaf nitrogen derived from 15N-labeled fertilizer (applied on 4/21) to mature 'Bluecrop’ plants. 65 the highest proportion (Table 2). Intermediate amounts of 15N were allocated to the crown, roots and current season stems. The lowest fractions of applied N were observed in the fruits and stems that were greater than 2-year-old. The allocation to stem tissues was inversely related to their age (Table 2). Residual 15N-Urea in Soil An important portion of fertilizer derived N (14.1%) remained in the upper soil layer (0-15 cm depth) 5 months after application (Table 3). Most of this was associated with the organic fraction of the topsoil. Some urea-derived 15N was found below the root zone (Table 3). Discussion The efficiency of fertilizer use in highbush blueberry, represented as the fraction of the applied fertilizer that was either absorbed by the plant or remained in the soil within the root zone (potentially available for uptake), totalled nearly 50% (Tables 2 and 3). This percentage might be lower under commercial conditions, if fertilizer is applied less uniformly. Although the rate applied was nearly half the recommended rate for mature plantings in Michigan (73 kg/ha) (9), fertilizer was concentrated in the herbicide-cleared strip beneath each plant rather than broadcasted throughout the planting as commonly practiced commercially. 6 6 .mcofluooflamwu swan maqcflm usom mo mm + momma usmwmummu mama N .ucoam GA Ame.~mc >Mm>oomu Hmuou Na Emu: some um>flumc zmH N mcflcfl>flo an omcflmuno mmsam> s oo.ooa Nv.Nm III vcmam OHOQZ mm.HH hm.HHmw.m mo.oHom.o uoom 00.0H om.o.l+.wm.m oa.oH¢v.o EBOHU omK. No.0Hm¢.N 5H.0Hvb.o UHOIH> m A mm.m eo.owbm.m mN.ono.H oHqum mam ho.ma wh.ono.m mm.oHov.H UHOIN> H "Emum m¢.m vw.oH¢h.~ mm.loh.H uflsum aminn mo.mHv~.oa hm.oH¢o.H momq >m>wumaom Nowadomné mmmoxm ARV won: omnofluchZmH Eons w wommfle sou“ oo>fluoo z .mosmmfiu auumnmdan smoncmw: pamAJNUHo :A z 6m>flumc AJNAHAUAJU No coflusnfluumfln 6:6 mmmoxm Eoum usmouom .m manme 67 .mcoflumoflammu swan mamcflm noon Mo om + momma ucommummu muoo N III m¢m.ouoov.a woo.o Rmo.oHEoH.o Aflomnsm owImN sms.o oNo.oNvoH.o moo.o ooo.oHHoo.o oflcmmuocH mmm.mm mmN.¢Hoao.¢H III III oflcmmuo ooo.oo~ Nmm.¢H¢HH.vH voo.o mNo.onNN.o Haemooe mHIo Aflommoe :fl m>wuoamm magaomn< mmooxm ARV COHuomum gamma ANS awn: omsofiuchzmH scum N z Hmuoe HNom Bonn om>wuoo z CH MONAHAUAJU nmzofluchzmH N.muo>wH Aflom ucmumwuflo mo >Nm>oomu can mmmoxm Eoum ucmoumm .z Hmuoe .m magma 68 The proportion of the fertilizer recovered in the plant (32.4%) (Table 2) is low compared to studies using other 15N-labeled fertilizers on citrus (56% recovery) (6) land apples (60%) (10). Besides botanical differences, the partialized application through trickle irrigation in the first case, and the use of young plants grown in containers in the second, probably affected plant uptake of fertilizer. As shown previously in studies on tree species (1, 6, 8, lo, 13, 22, 23) a high proportion of 15N fertilizer was allocated to leaves and other young, metabolically active tissues (Table 2). In our study, this was especially evident in comparing stem tissue of different ages (Table 2). Roots and crown tissue accounted for a large share of the fertilizer taken up by the plant (Table 2) and the total N in the plant (Table 1). As in fruit trees (10, 19, 20, 21), these tissues may serve as important storage sites of nitrogenous reserves. By combining the percent N in fruits (Table l) with long-term yield data reported recently (17), we estimated that 5.6 kg N/ha might be removed from a mature planting in a typical crop. This estimate is much lower than previous studies in mature orange trees (40 kg/ha) (6), but slightly larger than research on young Calamondin citrus trees (11). This may be explained by the fact that fruit comprise a higher percentage of total plant biomass in a mature citrus tree (6) than in blueberries or young citrus plants. 69 Our data on biomass partitioning agrees closely with a previous study on non-cultivated highbush blueberries in Michigan (15), despite differences in the management received by both plant groups. Even though root distribution was not studied in detail, our observations indicate that most blueberry roots are restricted to the herbicide strip and that growers might improve fertilizer use efficiency by placing fertilizer within this zone. Since N rate was comparable to that required to achieve maximum yield (9), fertilizer-derived N left in the soil at the end of the season was expected to be low (4). Residual fertilizer N appeared to be immobilized by the high organic matter content of the soil (18). This explanation is supported by the high percentage of 15N present in the organic fraction within the root zone. At the end of this study, less than half of applied N could be accounted for in the plant and soil. The amount of the fertilizer-derived N remaining in the 15-25 cm portion of the soil was not measured. The rest of the applied fertilizer could have been lost by nitrate leaching, denitrification, NH3 volatilization or uptake by surrounding vegetation. Research on a nearby planting (Section 1) has shown relatively high levels of nitrate below the root zone following fertilization, indicating that leaching losses may be significant. This is likely considering the sandy texture of the soil and the presence of urea-derived 15N in the subsoil at the end of the season (Table 3). The 70 presence of an oscillating water table in these organic soils (2) could provide appropriate conditions for denitrification losses, despite the low soil pH (7). Volatilization losses of NH3 were probably not significant because of the low soil pH and moderate soil moisture when fertilizer was applied, with additional rain (11 mm) received within 48 h. Daily maximum temperatures ranged from 10-22°C in the first week after application, which should have also minimized NH3 volatilization losses (14). The area treated with fertilizer was devoid of vegetation throughout the growing season which presumably limited uptake of 15N by other species. Literature Cited 1. Atkinson, D., M.G. Johnson, D. Mattam and E.R. Mercer. 1978. The effect of orchard soil management on the uptake of nitrogen by established apple trees. J. Sci. Food Agric. 30:129-135. 2. Bowman, W.L., F.R. Austin, R.E. Evon, B.O. Knapp, J.D. Larson, R.W. Neilson, T.M. Smith, W.B. Hogan and H.J. Kredo. 1986. Soil survey of VanBuren County, Michigan. Soil Cons. Serv. U.S.D.A. Govmt. Printing Office. Wash., D.C. 3. Bremmer, J.M. and R.D. Hauck. 1982. Advances in methodology for research on nitrogen transformations in soils. 1p F.J. Stevenson (ed.) Nitrogen in 10. 71 agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Broadbent, F.E. and A.B. Carlton. 1978. Field trials with isotopically labeled nitrogen fertilizer, p. 1-41. 1p: D.R. Nielsen and J.G. MacDonald (eds.). Nitrogen in the environment. Academic Press, New York. Brooks, P.D., E.B. McInteer, T. Preston and M.K. Firestone. 1988. A diffusion method to prepare soil KCl extracts for automated 15N analysis. Soil Sci. Soc. Amer. J. (In press). Feigenbaum, S., H. Bielorai, Y. Erner and S. Dasberg. 1987. The fate of 15N labeled nitrogen applied to mature citrus trees. Plant Soil 97:179-187. Firestone, M.K. 1982. Biological denitrification, p. 289-326. Ip: F.J. Stevenson (ed.). Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Grasmanis, V.O. and D.J.D. Nicholas. 1971. Annual uptake and distribution of 15N-labelled ammonia and nitrate in young Jonathan/MM104 apple trees grown in solution cultures. Plant Soil 35:95-112. Hancock, J. and E. Hanson. 1986. Highbush blueberry \ \ nutrition. Michigan State Univ. Coop. Ext. Serv. Bull. E-2011. Hill-Cottingham, D.G. and C.P. Lloyd-Jones. 1975. Nitrogen-15 in apple nutrition investigations. J. Sci. Food Agric. 26:165-173. ll. 12. 13. 14. 15. 16. 72 Legaz, F., E. Primo-Millo, E. Primo-Yufera, C. Gil and J.L. Rubio. 1982. Nitrogen fertilization in citrus: I. Absorption and distribution of nitrogen in calamondin trees (Citrus mitis Bl.), during flowering, fruit set and initial fruit development periods. Plant Soil 66:339-351. Legg, J.O. and J.J. Meisinger. 1982. Soil nitrogen budgets, p. 503-566. 1p: F.J. Stevenson (ed.). Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of-Agronomy, Inc. Madison, Wis. Mead, D.J. and W.L. Pritchett. 1975. Fertilizer movement in a slash pine ecosystem: I. Uptake of N and P and N movement in the soil. Plant Soil 43:451-465. Nelson, D.W. 1982. Gaseous losses of nitrogen other than through denitrification, p. 327-363. 1p: F.J. Stevenson (ed.). Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Pritts, M.P. and J.F. Hancock. 1985. Lifetime biomass partitioning and yield component relationships in the highbush blueberry, Vaccinum corvmbosum L. (Ericaceae). Amer. J. Bot. 72:446-452. Rennie, R.J. and D.A. Rennie. 1983. Techniques for quantifying N2 fixation in association with nonlegumes under field and greenhouse conditions. Can. J. Microb. 29:1022-1035. 17. 18. 19. 20. 21. 22. 23. 24. 73 Siefker, J.H. and J.F. Hancock. 1986. Stability of yield in highbush blueberry cultivars. Fruit Var. J. 40:5-7. Stevenson, F.J. 1982. Organic forms of soil nitrogen, p. 67-122. 1p: F.J. Stevenson (ed.). Nitrogen in agricultural soils. Agronomy vol. 22. Amer. Soc. of Agronomy, Inc. Madison, Wis. Taylor, B.K. and B. Van den Ende. 1969. The nitrogen nutrition of the peach tree: IV. Storage and mobilization of nitrogen in mature trees. Aust. J. Agric. Res. 20:869-881. Titus, J.S. and S.M. Kang. 1982. Nitrogen metabolism, translocation, and recycling in apple trees. Hort. Rev. 4:204-246. Tromp, J. 1983. Nutrient reserves in roots of fruit trees, in particular carbohydrates and nitrogen. Plant Soil 71:401-413. Wallace, A., 2.1. Zidan, R.T. Mueller and C.P. North. 1954. Translocation of nitrogen in citrus trees. Proc. Amer. Soc. Hort. Sci. 64:87-104. Weinbaum, S.A., M.L. Merwin and T.T. Muraoka. 1978. Seasonal variation in nitrate uptake efficiency and distribution of absorbed nitrogen in non-bearing prune trees. J. Amer. Soc. Hort. Sci. 103:516-519. Weinbaum, S.A., I. Klein, F.E. Broadbent, W.C. Micke and T.T. Muraoka. 1984. Use of isotopic nitrogen to 74 demonstrate dependence of mature almond trees on annual uptake of soil nitrogen. J. Plant Nutr. 7:975-990. SUMMARY AND CONCLUSIONS The low recovery of 15N-labeled fertilizer as well as increased levels of inorganic N below the root zone in fertilized plots indicate that N losses were probably significant. The exact nature of the >50% losses is not known, although nitrate leaching, NH3 volatilization and denitrification could be involved. The importance of each factor would depend on environmental conditions, such as temperature and rainfall. Nitrification rate was expected to be low because of the low soil pH; but the rapid accumulation of N03- indicated that this was not true. If rainfall is heavy when soil N03' levels are high, N losses could be considerable. This might explain the advantage of split-urea application since the chances of nitrate leaching are reduced. Ammonia volatilization losses were not measured in our study and would be expected to vary greatly from season to season. Split-urea could again prove advantageous even though the second application usually occurs when ambient temperatures are higher. Blueberries are grown in areas of oscillating water tables and plantings could temporarily become waterlogged. Blueberry soils are also usually high in organic matter. 75 76 These two factors would provide conditions for potentially high denitrification losses depending on N03’ levels in the soil. We observed that most of the roots grew within the herbicide strip. Since most growers fertilize throughout the planting, losses due to poor placement may be high, especially in sandy soils with limited lateral fertilizer movement. In our study, use of Osmocote resulted in lower inorganic soil N and leaf N levels than urea. This indicates that Osmocote is less effective than urea under field conditions. Osmocote contains ammonium nitrate, and leaching losses may have been higher with these products. Since blueberries have been shown to prefer NH4+ over N03“, N03' present in blueberry soils would constitute a potential loss. Another important consideration is the cost of Osmocote, which is several times more expensive per unit of N than urea. Even though market prices for fertilizers oscillate, Osmocote would need to greatly improve plant performance before acceptance by growers could be expected. Osmocote could have a place in nursery fertilization where leaching losses and placement can be controlled. Since we studied a controlled-release fertilizer that released N03“ and NH4+, a source providing only NH4+ might prove more beneficial. Ureaform or sulfur-coated urea might be studied in future work. Sulfur-coated urea tends to 77 decrease soil pH, so that nitrification rates are expected to be lower than when urea is used. Split urea application increased leaf N levels and reduced losses. However, it is difficult to evaluate the economical benefits of this practice, since there are greater costs associated with an additional fertilizer application. Split urea applications could prove beneficial when applied to small plants or on very sandy soils. Split applications may have an added advantage in years of spring frost, since fruit load is reduced and N demands decrease. A single application at bud break could cause excessive plant growth which would theoretically be more prone to be winter killed. Since urea and ammonium sulfate are the N fertilizers most used by growers, comparative studies are needed to evaluate their effectiveness. Our preliminary study suggested greater leaching losses with urea. A long term study comparing ammonium sulfate to urea would be useful. A different approach to increasing the efficiency of fertilizer use would be the use of nitrification inhibitors. These products, might be especially suitable for blueberry production, given the preference of this species for NH4+. However, the high organic matter in blueberry soils would require higher rates of nitrification inhibitor and the sandy texture could displace fertilizer and inhibitor differently. APPENDICES 78 DAILY PRECIPITATION-GRAND JUNCTION-1986 1&0- ”LO- IGO- ELD- 5.03 4.0- :: III I III I I I. APR I MAY JUN JUL AUG SEP OCT DAILY PRECIPITATION (cm) A— DATE Appendix 1. Daily precipitation (cm) at the experimental plots during the 1986 grow1ng season (April - October). 79 DAILY PRECIPITATION-GRAND JUNCTION-1987 140- 12.0- 10.0; 8.0- 50- 4.0- DAILY PRECIPITATION (cm) 2.0- o.o-I Appendix 2. 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