WMH {’fiANAGEMEM 1N mm PROBUGHDN f , Thesis for. the Degree of Ph. 5); MEG-{EGAN STATE Umvmsm— ’ ANA F. (mm A 1973 h- t. .‘ a. . n .54 O r“ ql ‘ .9 nv A)» A J ital“, G r“! i, .w‘iibl' III. ABSTRACT WATER MANAGEMENT IN POTATO PRODUCTION By Ana F. Garay The present acreage of irrigated potatoes is the largest among irrigated crops in Michigan. In terms of total amount of irrigation water used, potatoes rank second only to golf courses. The use of irrigation water on one of Michigan's best cash crops is not only going to be main- tained but will probably be accentuated in the present decade. Irrigation is being used primarily to supplement in- adequate rainfall during the growing season. However, the wide usage of supplementary irrigation is not matched in knowledge, acceptance and use of modern irrigation manage- ment techniques required for more efficient use of the water applied. This study was initiated to develop better irrigation management techniques in potato production. The experimen- tal objectives and results were: 1. To determine the effect of time of initiation of irri- gation on the quality and yield of tubers. In 1971, irrigations were started at 50, 60 and 70 days after Ana F. Garay planting. In 1972, the initial irrigations were applied at 30, 50 and 70 days, respectively. In 1971, the plots irrigated at 50 days showed a significant yield increase compared to the plots receiving the ini- tial irrigation at 70 days. Ample rainfall during the 1972 growing season eliminated any differential soil moisture effects and masked any yield differences due to the time of initiating irrigation. To measure the effect of two levels of irrigation cool- ing. Intermittent, low volume sprinkler irrigation was applied in 1971 whenever the temperature was higher than 75 and BOOF. In 1972, temperature levels were changed to 80 and 85°F. Data from this experiment did not in— dicate any appreciable benefit from these cooling treatments. To compare two quantities of water applied per irriga- tion. In 1972, a l/2-inch irrigation was compared with a 1-inch irrigation. No significant yield or other vi- sual differences were observed. During wet periods of the growing season the l/Q-inch irrigation resulted in water saving which could reduce nutrient leaching. To evaluate the effect of periodic applications of small amounts of nitrogen fertilizer through the irrigation system. The 1972 data showed measurable yield increases with the periodic nitrogen application. In Kennebec potatoes the treatments resulted in an average increase Ana F. Garay of 69 cwt/acre. For Russet Burbank potatoes the equi- valent value was 71 cwt/acre. To devise an accurate and simple scheme for scheduling crop irrigations. Irrigation frequency and quantity, precipitation gains, evaporative losses, soil type, and crop stages were considered and programmed into this scheme. Weather pan evaporation data were used to estimate soil water losses. A water balance chart was devised from this data for computing and graphically demonstrating the soil water status on a daily or weekly basis. WATER MANAGEMENT IN POTATO PRODUCTION By Ana Ff‘Garay1i9. A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Crop and Soil Sciences 1973 d gm ‘1 a. ledge: Therar wark u ent A Cr m. ACKNOWLEDGMENTS Sincere appreciation is expressed to Dr. R. Kunze, Dr. R. Chase and Prof. E. H. Kidder for their assistance and guidance during this study. Dr. Kunze's active super- vision in the preparation of this manuscript is acknow— ledged. Recognition is also extended to Dr. Ch. Cress, Dr. E. Erickson and Dr. L. Robertson for serving on the guidance committee and assisting in the writing of this thesis. A very special thanks is given to Mr. and Mrs. Theron Comden on whose farm the experimental part of this work was done. The two busy, yet very pleasant summers Spent in their home will be remembered by the author with deep affection and gratitude. Financial assistance by the Agency for International Development (USA) and the Instituto Nacional de Tecnologia Agropecuaria (Argentina) is gratefully acknowledged. ii n m!!! 1' ' {LUSLA‘Kt A v1v—'- A7 IJLIOL v o -‘ “w. “I &~.H‘ \l' MN- 1:.“ " TABLE OF CONTENTS .ACKNOWLEDGMENTS . . . . . . . . . . . . . . . SLIST OF TABIES . . . . . . . . . . . . . . . ZLIST OF FIGURES . . . . . . . . . . . . . . . IENTRODUCTION . . . . . . . . . . . . . . . . IIITERATURE REVIEW . . . . . . . . . . . A. C. Water requirements of potatoes and responses to irrigation . . . . . . l. 2. 3. Crop development and water needs Tuber malformation as related to soil moisture . . Available water level and potato responses . . . . . . . . . . . . Temperature requirements of potatoes and responses to irrigation cooling 1. Critical values of ambient temperature . . . . . . . . . 2. Critical values of soil temperature 3 Irrigation cooling studies Factors in scheduling potato irrigations ELAIDERIALS AND METHODS . . . . . . . . . A. B. Experimental site and crop management Field layout of the experimental plots 1. 2. 1971 experiments . . . . . . . . 1972 experiments . . . . . . . . Irrigation system . . . . . . . . . l. 2. 1971 . . . . . . . . . . . . . . 1972 . . . . . . . . . . . . . . iii Page ii Vi :- -q U1 4: .t 10 ll 14 17 17 2O 2O 20 23 23 27 ”'1 (T) -'\:Y 7 m In}; d‘dal :17)- KT) P3’] '1" n-. 41V; CCW‘? H5? 5 D. Meteorological measurements E. Additional field instrumentation and measurements F. Irrigation scheduling procedure . G. Harvesting procedure RESULTS . . . . . A. Weather conditions during the period of irrigation . B. Timing of initial irrigation treatments C. Day irrigation versus night irrigation treatments D. Frequency of irrigation treatments E. Irrigation cooling treatments . F. Partitioning of nitrogen fertilization treatments G. Crop factor for pan evaporation values H. Procedure for scheduling potato' irrigations . I. Comparison of measured pan evaporation with evaporation estimates DICUSSION . . . . A. Timing of initial irrigation B. Day versus night irrigation C. Frequency of irrigations D. Irrigation cooling E. Scheduling of irrigations CONCLUSION . . . . . . . LIST OF REFERENCES iv Page 28 29 3O 3O 33 33 40 M2 44 an 46 49 55 58 58 59 59 60 63 68 7O Table l. 3L0. LIST OF TABLES Soil moisture retention at different depths and tension values on a McBride sandy loam soil . . . . . . . . . . . Planting and harvesting dates, plant spacing and fertilization . . . . . Summary of weather conditions in June, July and August of 1971 and 1972 . . Crop development in 1971 and 1972, Russet Burbank variety . . . . . . . Effect of the timing of initial irrigation on yield, grade and specific gravity of Russet Burbank and Kennebec potatoes, 1971 and 1972 o o o ‘ o o o o o o o o 0 Effect of day versus night irrigation on yield, grade and specific gravity of Russet Burbank and Kennebec potatoes, 1971 o o o o o o o o o o o o o o o 0 Effect of frequency of irrigation on yield, grade and specific gravity of Russet Burbank and Kennebec potatoes, 1972 o o o o o o o o o o o o o o o 0 Effect of irrigation cooling treatments on yield, grade and specific gravity of Russet Burbank and Kennebec potatoes, 1971 and 1972 . . . . . ... . . . . Effect of partitioning the nitrogen fertilizer on yield, grade and specific gravity of Russet Burbank and Kennebec potatoes, 1972 . . . . . . . . . . . Comparison of pan evaporation values and other evaporation estimates for selected days in 1972 O O C O C . C O O O O O Page 18 19 34 110 41 43 45 47 L18 56 Figure 1. 2o 3. 10. LIST OF FIGURES Layout of field experiments in 1971 . . . . . Layout of field experiments in 1972 . . . . . Irrigation system for the 1971 experiments . . . . . . . . . . . . . . . . . Instrument layout for the weather station on the Montcalm County Experimental Farm Mean daily temperature and relative humidity and daily total wind movement, 1971 . . . . . Mean daily temperature and relative humidity and daily total wind movement, 1972 . . . . . Rainfall and pan evaporation data, 1971 . . . Rainfall and pan evaporation data, 1972 . . . Water balance chart for scheduling potato irrigations (Treatment 1), 1971 . . . . . . . Water balance chart for scheduling potato irrigations (Treatment 1), 1972 . . . . . . . vi Page 36 37 38 39 52 INTRODUCTI ON During the period 1961-70, Michigan produced an average 220 hundredweight of potatoes per acre and a total of 7.5 million hundredweight from 36,000 acres (16). Agri— cultural predictions indicate that for 1980 those figures will be 300, 24 and 80,000 (15) for yield, production and acreage, respectively. None of the other important crops in the state are expected to exhibit changes of such mag— nitude. The increase in yield is expected to come from the use of better quality and management of soil and from better management of the potato crop. Irrigation will have a major impact on this yield increaSe according to the same prediction study. Furthermore, it is estimated that most of the total projected increase of irrigation water use in Michigan will go to potato production. In fact, this trend is already evident. A recent survey of land irrigation (38) showed that in 1970 one—half of the 40,000 ac res of potatoes were being irrigated. This figure re- presented 22% of the total agricultural irrigated acreage and ranks potatoes in the first place among all the irri- ga”ted crops. In terms of acre-inches of water applied pcThatoes were second only to turf, mainly golf courses. Presently an average of 6 inches of irrigation water per year is being used for potatoes. If one-half of the pro- jected increase in potatoes in 1980 is irrigated, as is the present acreage, then the potato crop is likely to be- come the major water user in the state. The need for careful use of our water resources, coupled with the fact that irrigation is a major cost in potato production, make it necessary to ascertain higher efficiency of water use. A rising increase in potato production is greatly dependent not only on an increase in irrigation acreage but also how efficiently this practice is carried out on each farm. Because Michigan receives approximately 30 inches of precipitation per year, irrigation is used only on a supplemental basis. Although the practice of supplemental irrigation is widely accepted and used in potato produc- tion, there is no indication that the science of applying the proper quantity of water at the right time is practiced 01‘ even known among growers. A fixed amount of water at regular intervals is still the main basis for planning irrigation. There are several reasons for advocating a more technical approach to irrigation management. First, the pO‘tato plant is sensitive to both a deficiency and an ex- cess of soil water. The enhancement of soil moisture con- trol may be best accomplished through a precise regulation of the time and amount of irrigation. Second, the variable nature of rainfall and atmospheric water demand precludes the use of predetermined and fixed irrigation needs. And third, if the use of irrigation water is going to be ex- tended to uses other than supplying water to a crop, a more flexible approach to irrigation scheduling is needed. For all these reasons a need for better irrigation management is evident. Specifically such management must <2onsider not only local climatic conditions but also the :special characteristics and properties of each soil. The gaotato variety and quality of the produce desired should aalso enter into the role of water management. All of these c:onsiderations must be integrated into a general water rnanagement plan for each farm. This was a two year study dealing with various as- Ioects of soil water management in potato production. The expecific objectives were: 1. To determine the effect of the time of initia- tuion of irrigation on the quality and yield of tubers. 2. To devise an accurate and simple scheme for de- 't€3rmining the frequency and volume of crop irrigations. SOil-crop-climate data are considered in this scheme. 3. To measure the effect of two levels of irriga- t i on cooling. 4. To measure the effect of two volumes of i I‘rigation. 5. To evaluate the effect of periodic nitrogen a“I3plications through the irrigation system. LITERATURE REVIEW A. Water requirements of pptatoes and responses to irrigation 1. Crop development and water needs In considering the water requirement for potato growth three phases of the development of the plant should 'be taken into account according to Steineck (cited by ESingh (30)), each one of which influences yield. The first Iohase corresponds to stolon formation which in normal years starts about 3 weeks after emergence and determines the po- ‘tentiality for the setting of tubers. This is followed by 'the tuber setting stage approximately 4—5 weeks after emer- ggence. The number of tubers as a component of yield de- Iaends on this phase. The next phase of tuber growth which :Lasts until maturity is the most important in determining tflne weight of a single tuber. The author concluded that a Iwegular supply of water from the beginning of stolon for— mation to maturity is necessary to ensure high yields. By restricting the water supply at different stages ‘31? development of the potato, several authors had intended ‘ttb determine when the plant is most susceptible to water Stress. De Lis et al. (5), working with the White Rose 4 variety, found that withholding irrigations at any of the potato growth stages (with the exception of the one from planting to emergence) caused a decrease in tuber yield, but when the water stress occurred from stolonization to the beginning of tuberization, the yield decrease was greater. They concluded that the White Rose variety passes through the most critical water requirement period during this stage. In India, Hukkeri et a1. (8) investigated the same problem, imposing an artificial moisture stress at (equal periods of 20 days after planting. Their results sshowed that water stress during the period 0-20 days after EDlanting did not affect the yield as much as the other sstress periods. The stress during the stolon formation and ealongation stage, coinciding with 20-40 days after planting {Deriod, resulted in the greatest yield reduction. 2. Tuber malformations as related to soil moisture Several potato varieties have the tendency to pro- duce misshapen tubers (knobs) under adverse growth condi- ‘tdions. A common observation was that their production is é§1?eater when drought periods occur during the growing sea- Stand and that irrigation has the effect of reducing or sup- IDIFessing its occurrence (22, 31). Hence misshapen tubers €§Enuerally were associated with water stress. However, ob- £3Eirvations (22,26) have been made in which water supplied t337 irrigation did not reduce the numbers of knobs and even jL11£rreased their incidence. The abnormality apparently is more complicated than the simple water stress-misshapen tubers relationship. Nichols and Ruf (17) conducted an experiment under controlled conditions in which they compared the reaction of Russet Burbank and Kennebec varieties to several levels of osmotic stress in the root medium. The stress was ap— plied for continuous periods and for 2-day periods followed by sudden stress relief, both beginning at tuber set. The plants, stressed for short periods and then relieved, had more malformed tubers than the plants grown under continuous stress. Under the short period stress regime the incidence of malformed tubers increased with the level of stress. Ilnder the continuous stress regime, however, no trend was observed. The control plants (no stress other than those :imposed by the nutrient solution - about 0.7 atmospheres) Inad more misshapen tubers than the plants subjected to l eand 5 atmospheres stress. Although Russet Burbank showed 'the greater reaction both varieties did react to the short 19eriod stress. In conclusion, water stress level did not zincrease significantly the occurrence of misshapen tubers Ilut an irregular moisture regime did. 0n the other hand Boadlaender et a1. (2) carried Chat a glasshouse experiment under controlled temperature and drought conditions, in order to identify the environ- ?Hmental factor causing second growth in tubers. Their 7 results showed that the high temperature level (82°F) in- duced second growth irrespective of the moisture level. Furthermore, the drought treatment alone did not induce second growth. Also Yamaguchi et a1. (41) found that at high soil temperature (8O-85OF) the tubers developed near the surface and were misshapen. These studies seem to indicate that temperature is the primary factor in inducing malformation in tubers and an irregular water regime a contributing or predisposing factor. 3. Available water level and potato response The three-year greenhouse experiment that EStruchtmeyer (36) carried out with the Kathadin variety in bdaine is a good illustration of the influence of the soil rnoisture level on yield of potatoes. Maintaining minimum Ilevels of 15, 30, 50 and 75% of available water, he was sible to Show that the tuber yield decreased as the soil rnoisture level decreased. The same trend was obtained in eeach year of the investigation. However the reports on field trials do not always £3how such consistent results. Wheaton et a1. (39) grew E>0tatoes in.Michigan under 10, 40, 40-70, and 70% soil moisture levels during 1955, 1957 and 1958. The yields at tdne two higher moisture levels were the best, but none of tflnem were consistently superior to the other soil moisture levels throughout the three years. In another study conducted in East Lansing by Chase et a1. (4) during 1965, 1966 and 1967 the 30, 45, 65 and 85% levels were compared against the non-irrigated control. The irrigated treatments increased yields from 17 to 35% for the Sebago variety and from 18-30% for the Russet Bur- bank, but no significant yield differences among the irri- gated levels were observed. Specific gravity tended to de- crease and percentage of knobby tubers increased with le- vels below 45% in Russet Burbank. The possible explanation for the similarity of response in the different levels in this study is, according to the authors, the small differ- ence (1 atmosphere) in soil water tension between the high- est and the lowest irrigation level. Jensen and Middleton (11) suggested that no more than 30% of the soil water capacity be used by potatoes before the next irrigation. Notwithstanding occasional in- consistencies of results, a review of the literature on soil-moisture relationships for potatoes (16, 28, 29) shows that there is general agreement on the following points: a. Potatoes are very sensitive to levels of soil water that prevent adequate aeration. b. Potatoes respond negatively to low soil water levels which should never, as a practical rule, be allowed to drop below 50% of the soil avail- able water. B. Temperature requirements of potatoes and responses to irrigation cooling 1. Critical values of ambient temperature Ora Smith (31) concluded that in many potato produ- cing areas yield and quality of potatoes are kept below their maximum by the prevalence of high temperatures at some time during the growing season. Bodlaender (1) pointed out that the potato species originated in areas where the average temperatures are between 590-65OF; hence these temperatures may also be the most favorable tempera- tures for potato development. Controlled experiments in greenhouses and growth chamber in Pasadena and Wageningen reviewed by Bodlander (l) have shown that: a. emergence was always accelerated by high temper- atures. Two weeks difference was found between 550 and 72 0F; b. stem elongation reached its optimum at 650, was 'very low at 48°F and stopped growing at 43oF; c. the number of leaves formed was positively cor- related with temperature; d. tuber formation started earlier and the number of tubers formed were greater at low temperatures. High Jaight temperatures decreased tuber yield more than high day ‘temperatures. Higher yields were obtained with potatoes egrown at 860-630F day-night temperatures than at the 730- '? 30F regime; 10 e. maximum tuber weights were obtained at interme- diate temperatures. Under summer conditions the optimum temperature was from 64 to 68oF. Potato varieties respond differently in relation to temperature. Bodlaender (l) subjected seven potato varie- ties to temperature regimes of 610, 720 and 810R. Two of them had their maximum yield at 720F and the remaining five at 610F. However, the average decrease in yield from 610 to 720F was only 3.5% as compared to 37% from 720 to 84oF. Iritani (10) analyzed air temperature and potato yield data in Southern Idaho for an 11-year period. He found a negative correlation between yield and the accumu- lative June and August temperature below 48oF, which roughly corresponds to the early development of the plant and the tuber enlargement periods. A highly negative cor- relation was found between yield and temperatures above 85oF in July. This last period coincides with tuber ini- tiation and early growth of the tuber. 2. Critical values of soil temperature Soil temperature has an important effect on potato plant development, especially on tuber initiation and {growth. White Rose and Russet Burbank potatoes were grown 'by Yamaguchi et a1. (41) at four soil temperatures: 50-550, (So-65°, 70-750 and 80-85OF. A 50F difference was main- ‘tained between day and night conditions. Both shoot emer- gence and foliar growth were optimal at 700-75OF. Tuber 11 initiation, tuber yield, specific gravity and starch con- tent were highest at the two intermediate temperatures. In a later study Eliot Epstein (6) used the Katha- din variety to measure the effect of temperature on three growth stages: planting-emergence, emergence-30 days after, and 30 days after emergence-maturity. During the third stage the yield increased up to 72oF and then sharply de- creased at 84oF. Specific gravity started to decline at 72°F and the number of tubers was greatest at the lowest temperature. As was also reported by Yamaguchi, the shape of the tuber was affected at 84oF. From all this information it appears that both air and soil temperatures above 700-75OF are detrimental to po- tato yield and quality. 3. Irrigation cooling studies In response to the problem of high temperatures with its corresponding high evaporative demand the effect of temperature reduction with sprinkling ("irrigation cool- ing", "mist irrigation" or "air conditioning") is being studied in potato crops with varying success. In Muscatine, Iowa (9), the regular irrigation of iL" at 3-4 days intervals was compared with "mist" applica- ‘tions of 0.05" per hour from 11 A.M. to 4 P.M. when daytime fair temperatures rose above 8OOF in 1966 and 1967. In 1968 “the applications were changed to 0.10" per hour when tem- jperature rose above 85°F. Additional water was applied, as l2 needed, to supplement soil moisture. The results of this three-year study showed that the response varied consider- ably between seasons. In 1966 and 1968 a significant res- ponse was obtained for all the varieties treated (Norland, Norgold, Viking and Kennebec) in contrast with very little or negative response in 1967. The degree of response dif- fered according to the variety. The Kennebec variety was the most responsive with an average yield increase of 38%. The early maturing variety, Norland, gave the least res- ponse with a 9% average increase. The "mist" treatment also resulted in significant increases in the percent of total solids. In 1966 a substantial reduction in the amount of second growth was noted for Norgold and Kennebec. According to these data the practice of "mist" irrigation could be advantageous for some varieties, especially Kennebec. Chase et al. (4) tested the effect of irrigation- cooling in Michigan on Sebago and Russet Burbank potatoes grown under four soil moisture levels plus a control. Irri- gation cooling was applied when the air temperature rose «above 85oF, at a rate of 0.08 inches per hour for a period c>f 2-3 hours. When the yields of all the irrigation-cooling “treatments were averaged for the three year experiment and Clompared with yields from plots with no irrigation-cooling 'the values showed a 7% increase for Sebago and 3.5% in- <2rease for Russet Burbank. The yearly responses varied l3 reflecting differences in temperature conditions. The high- est response was obtained in 1966 which was characterized as unseasonably warm and dry with a yield increase of 12% in Sebago and 8% in Russet Burbank. The latter variety showed a trend toward increasing specific gravity. The res- ponses obtained in this study were not large enough to make this practice profitable under Michigan conditions. Sanders et a1. (25, 26, 27, 28) have published a series of papers reporting the experimental results for a 3—year study (1967, 1968, 1969) in Minnesota in which they assessed the influence of irrigation methods on potato mi- croenvironment and leaf water relations, growth and develop- ment, nutrient content of leaves and tuber quality factors. The methods compared were: no irrigation, mist irrigation, furrow irrigation and mist plus furrow irrigation. The mist irrigation consisted of low volume sprinkler applica- tion from 11:00-15:00 CDT at a rate of 0.11, 0.12 and 0.08 inches per hour in 1967, 1968 and 1969 respectively. The mist was applied for 8 seconds every 8 minutes when the temperature reached 72oF. The 3-year average yield value :for the mist treatment was 4% lower than the furrow treat- Inent and the mist plus furrow yield was 11% lower than the :furrow value. The only year the mist treatment was superior ‘to the furrow irrigation was during the "stressing" year of 31967 and then the difference was not significant. The EIuthors also reported that misted plots yielded tubers 14 which contained less dry matter and had more hoLkmmBart and secondary growth. The modal ambient temperature depression by misting in the canopy was 50F at 56 cm height, 3.2OF at 33 cm and 2.5OF at 10 cm when radiant energy flux was high (greater than 500 ly/day). At lower energy fluxes the de- pression temperatures were also lower. C. Factors in scheduling potato irrigation In a subhumid area, like Michigan, the two basic considerations in planning potato irrigations are the rate at which the crop depletes the soil moisture reservoir by evapotranspiration (ET) and the amount of this depletion that is replenished by precipitation. Irrigation must sup- ply the deficit. A good farm irrigation program requires an accurate, rapid and simple procedure for calculating the daily water deficit. If the procedure is to be accurate, daily evapotranspiration data are needed. While precipita- tion is a discontinuous process, its measurement presents no problem. Evapotranspiration, on the other hand, is con- tinuous, highly variable, and its actual measurement in- ‘Volves considerable work, time and usually sophisticated :Lnstrumentation. For this reason in practical irrigation Inanagement the measurement of pan evaporation is a conve- Ilient way of estimating the daily evapotranspiration. Based on rate of evapotranspiration studies in IDavis, California and on an evaluation of the literature croncerning pan evaporation data Pruitt, (19, 20, 21) 15 considers that the pan evaporation method, when well stan- dardized, constituted a very useful tool in estimating evapotranspiration. Stanhill (32, 33) in Israel tested eight different methods of estimating ET from climatic data and concluded that the methods based on open surface evaporation calcula- ted by Penman's method or measured with standardized pan evaporation gave the most accurate results. He also pointed out that when time and cost are considered the pan evapora- tion method is the most satisfactory. Young (42) did a similar comparison in potato and tomato crops (Michigan) and reached similar conclusions in regard to the Penman and pan evaporation methods; however, he indicated that more work in determining the local correction factor for the pan evaporation method was needed. For potatoes this factor changes with the stage of development of the crop as a consequence of the relatively low evapotranspiration during the early and late growth stages. Once a certain degree of development is reached though, several authors (19, 33, 34) have found a nearly <:onstant linear relationship. During his study Young (42) found that for the last Ebert of June when the crop was not yet fully developed the Ineasured ET was 0.07 inches per day compared to 0.23 inches IDer day for pan evaporation. For periods of a fully dev- Eeloped crop the values were 0.16 and 0.23 inches per day 16 for ET and pan evaporation respectively. He used Bouyoucos block readings to calculate ET. Swan (37) in Wisconsin found an average measured evapotranspiration rate (lysime- tric measurements) of 0.21 inches per day for periods when the surface cover was greater than 50%. The peak value was 0.24 inches per day. In Carrington, North Dakota, Stegman and Olson (34) determined water use by potatoes with the soil moisture sampling method and summarized their 5—year data in relation to days after emergence. From emergence to 30 days after, the daily ET value rose from 0.08 to 0.20 inch per day. The average ET value for the 30-80 day period was 0.22 inch per day with a peak of 0.24 inch at 50-60 days. The soil moisture extraction pattern was also studied in this work showing that potato plants extracted 57% of the water from 0-12, 33% from 12-24, 8% from 24—36 and 2% from 36—48 inch depth. MATERIALS AND METHODS A. Experimental site and crop management The data were collected at the Montcalm Experimen- tal Farm in Montcalm County, Michigan, during the growing seasons of 1971 and 1972. The climatological summary (14) for the nearest weather station (Greenville) indicates a mean annual tem- perature of 47.6OF and a mean annual precipitation of 31.4 inches for the 1940—69 period. June, July and August have average monthly mean temperatures of 67.8, 72.2 and 70.6OF and an average mean precipitation of 3.1, 2.5 and 3.4 inches, respectively. Temperature extremes greater than 90°F occur 14 times during an average summer. During the crop season, May-October, the estimated class "A" pan eva- poration equals 28 inches which is 10.5 inches greater than the average precipitation for the same period. The soil is classified as a McBride sandy loam, 0 'to 2% slope, and described (29) as a well drained soil with £1 weak fragipan development at 14-25 inches and a C horizon eat more than 48 inches depth. Core samples were taken from 'the 0-24 inch layer to determine the moisture characteristic éxnd bulk density values necessary for the calculation of 17 l8 .momeflaaos 0 mo omwsm>m Gm ma msam> manpmflos pct szQOp gasp zomm* mm.m am.a mfi.m mm.c ms.s ma.m oa.HH om.©a ms.a :m-ma mm.m am.: om.m ma.m mm.m mm.ma mm.ma mm.om ac.a ma-m m:.: ma.w mm.m mm.oa ms.HH ms.:a mm.ma He.mm mm.a m-o .Epm .Epm .Epw .sem ma .snm m .scm m .spm a mm.o oa.o no.0 coaeasepmm spamsoo Amazosav ssaom scams Haom mcofimcmp poprHcCH pm manpmaoe HHom mo pswflmz pcmoamm .Hfiom emoa zucmm mpfinmoz n Go mmSHm> COHmCmp pct mnemmc pamsmmmfie pm soapsmpma manpmfloe Haom .H manna the s 137: ,7 A J J 19 available moisture capacity. These data are presented in Table 1. Using 0.1 atmosphere as the upper limit of avail- able water, a value of 3.4 inches of water was stored in the soil for the 0-24 inch depth. Two varieties of potatoes (Solanum tuberosum) were utilized in this study: the Kennebec (K) variety is a high yielding, rounded tuber of good quality; and the Russet Burbank (RB) variety is a long tuber with russetted and netted skin and high processing quality. The planting and harvesting date, plant Spacing and fertilization informa- tion are given in Table 2. Table 2. Planting and harvesting dates, plant spacing and fertilization Plant . Year Planting Harvesting Spacing Fertilization (date) (date) (inches) (lbs/A)* 1971 4/30 9/22 RB-l4 a 175(33—O-O)+2OO 0-0-60) b 800 14-14-14)+1 Mg K-l2 c 70 N 1972 5/10 9/15 RB-l4 a 200(0-0-60) 10 b 800 l4-l4-l4)+l6 Mg (N. eXp.) K-12 c 120 N ‘4 ‘*a) plowdown; b) plant; 0) sidedress The row width was 34 inches. The potatoes received Iregularly scheduled sprays along with other experimental I>otato plots for control of weeds, insects, and diseases. 20 B. Field layout of the experimental plots 1. 1971 experiments In 1971 three aspects of water management in pota— toes were studied: (1) the effect of timing of the initial irrigation (TI); (2) day versus night irrigation (DN), and (3) the effect of irrigation cooling (IC). The first two were combined in one experimental area which consisted of (4(TI) x 2(DN) x 2 varieties) 16 treatment combinations, in a split-split plot design with 4 replications. The irrigation cooling experiment consisted of a check and two levels of irrigation cooling. When the tem- perature rose above 75oF, the plots corresponding to level 1 were sprinkler irrigated 5 minutes every 30 minutes, and when the temperature rose above 85oF the plots in level 2 received the same treatment. The treatments, with 3 re- plications each, were arranged in a completely randomized design. Figure 1 shows the arrangement of the experimental plots in the field. Each plot contained ten rows and Ineasured 28 by 25 feet. The two center rows of Kennebec and 2 rows of Russet Burbank were harvested for yield data. {The other rows were considered as borders. 2. 1972 experiments The experimental treatments in 1972 were frequency Of irrigation (2 Fl levels); timing of initial irrigation (4-TI levels); irrigation cooling (2 IC levels) and *‘b ‘11 c.) 21 periodic applications of nitrogen fertilizer with irriga- tion water (2 N levels). The two frequency of irrigation treatments were a l/2-inch water application whenever the available soil moisture balance indicated that a deficit of 1/2 inch had occurred and a 1-inch water application whenever that defi- cit developed in the soil. Instead of starting the (TI) treatments at 50, 60, and 70 days after planting as in 1971, the 1972 irrigation treatments were started at 30, 50 and 70 days after planting. These changes were considered and adopted after the 1971 data were analyzed. The (TI) treatments and check (no irrigation) were randomized within the irrigation frequency treatment plots. In 1972, the criteria for IC at level 1 was changed from 75 to 800F and from none Specified to 65% or less re- lative humidity. For level 2 the only change was 80 to 85°F. The irrigation cooling was supplied at the rate of 1 gallon of water per 1/2 minute every 15 minutes. Because of changes in the method of application large amounts of water would have been applied under the 1971 criteria: hence the temperature levels were raised and a relative humidity value included for level 1 in 1972. All plots, including the check plot received a regular irrigation of 1 inch of water when needed. OZ.JOOU ZO.F(0.N_N_. .FZh—Qd_nuh—a)hu .‘C-I-ua‘ Lunc- 22 4an CH mucmfifiummxm tawny .Ho 8.50.39 .H mnsmflm 2282... o... u v 95.30 .2... oz .. goo—.0 . on n n N 2 O.NU— 3 3 .. om : I N _ .23. . 3:03 .o..._ .. .o. 95cc... .2... «>2. on .o «to: .3... u _ e232... .8 - m 8:32.. £22 - 4 mhzw2h_ xUOJm _: xuonm :50: All m 0 Wu.— " .3382 .263 .o. No. .36 n N _ N N c n No. .325 e _ N N m _ v m . __ xooam ‘ _ xuOJm " " .zszmaxm m m 023000 ZO_.—._ goose .= gooam No. .2 No. .25 .2 N2 .2 N2 .3 .35 No. .0. .86 .2 N2 25 pool, 15 ft diameter and 4 ft height filled every other day from the farm irrigation system, b. Centrifugal pump with 2 horsepower electric motor, c. Aluminum irrigation pipes 4" diameter for main lines, d. Garden hoses 25 and 50 feet long for the lateral lines, e. Perforated rubber hoses used for irrigating (TI) and (DN) experimental plots, f. Risers with rotating sprinkler heads for the irrigation cooling treatments. Figure 3 shows the layout of the irrigation system and the use of the perforated hose for sprinkling a plot area. The perforated hose was taped on a 4" aluminun pipe which was held above the plants with stakes. These units could be moved from one plot to another. The (IC) plots received normal irrigation from the farm irrigation system as adequate irrigation could not be provided with the (IC) equipment. Because of continual leakage from the 4" aluminum pipe the main lines were replaced with 2" plastic pipe in mid-summer of 1971. The new system performed flawlessly and water loss problems were resolved. ‘ffi .mucmEHHomxm ahma on» How Emumwm :oNummHnHH .m mnsmflm \\\\\3\\ \NXN\\\\\SB§QQQ\C\ .3. -e m .332, 3:3» .0533 I 3 .230 2 :2. ‘I IO «.05....3 5.! :02. €23:- d :2. .a I . 3 322, 3:3 O .23... 38.2.... e. .x .4, .x v. ... U... x. .1. .z. .. . st..:’:“’e.../ ‘ I - _1 IIIIIIII 3:: so... .2230. 233k. .6 a... am 3”: r--- I I ..--- - +---- ----- Ii 1- L 27 2. 1972 To improve uniformity of water distribution, to minimize handling of equipment and to exercise better con- trol of metering water, several changes were introduced into the system in 1972. A main line with a sufficient number of valves was placed along each tier. Each plot was equipped with an elevated, rotary sprinkler connected to the main line with a garden hose. The amount of irrigation applied to each plot was controlled with a metering device set for a specified volume of water. When this volume was delivered, the valve closed automatically. For the irrigation cooling treatments a 15-minute clock timer was connected to the pump and was programmed to operate 1/2 minute every 15 minutes. Normal irrigations could be supplied when needed with the (IC) equipment and the farm irrigation system was not necessary. The injection of liquid nitrogen fertilizer into the suction side of the irrigation pump simplified the pro- cedure of applying the periodic nitrogen fertilization treatments. The fertilizer solution, diluted to 20 gallons in an open container, was drawn into the pump and mixed with the irrigation water. Gate valves in both suction lines were required to get the proper mix between the reser- voir water and the fertilizer solution. 28 D. Meteorological measurements A weather station was installed in the southwest corner of the experimental plot. The meteorological para- meters measured and the instrumentation used are listed below: Temperature and relative humidity - Daily re- cords of the air temperature and relative hu- midity were obtained with a hygrothermograph, housed in a standard USWB shelter at 1.20 m height. Daily maximum and minimum temperatures were also recorded. Wipg_- The 24-hour wind values were obtained with a circular-dial, 3-cup anemometer at 2 meters above the surface. Precipitation - A non-recording, eight-inch diameter standard weather bureau precipitation gauge was used for this purpose. Evaporation - Evaporation measurements were made with: a. A USWB-Class A evaporation pan (10 inches deep and 47 1/2 inches diameter) was accom- panied by a five-digit odometer type, 3-cup anemometer to measure 24-hour wind values at 60 cm above the surface. b. A Lambretch drum recording evaporation gauge was housed in a standard instrument Shelter. F—I 29 5. Net radiation - This parameter was measured with a ventilated and temperature compensated net ex- change radiometer (Beckman and Whitley). This instrument was mounted 40 inches above the crop canopy in a plot adjacent to the weather station. Its output was recorded by a potentiometric recorder. The daily observations of max-min temperature, wind, evaporation and precipitation were made at 8:00 A.M. CST. Instrument arrangement in the weather station is Shown in Figure 4. E. Additional field instrumentation and measurements Soil moisture tension: In eight selected irrigated plots soil moisture tension was monitored with sets of ten- siometers placed at depths of 4, 10, 16 and 22 inches, giving a total of 32 tensiometers. In four of the non- irrigated plots Bouyoucos blocks were installed at the same four depths giving a total of 16 blocks. Soil temperature: Three recording soil thermome- ters with dual probes were randomly installed at 4- and 12-inch depths. They were placed in plots corresponding to the (IC) experiment in 1971, and in a check plot and in plots of the (TI) experiment in 1972. Soil moisture measurements: In 1972 soil moisture measurements were made at the 0-6, 6-12, 12-18 and 18-24 inch depth. These gravimetric soil moisture measurements 30 were converted to volumetric values by multiplying the gra- vimetric measurements by the bulk density of the soil. The soil moisture stress associated with a particular moisture content was given by the tensiometric readings obtained at these same depths. The soil moisture values obtained be- tween periods of rainfall were used to estimate the loss of soil water in that period and to relate soil water loss to the pan evaporation loss. F. Irrigation scheduling procedure Irrigations were scheduled by keeping a daily bal- ance sheet of the water lost or gained by the soil. The daily pan evaporation values corrected by a crop canopy factor determined the estimated soil water losses and preci- pitation and irrigations the soil water gains. If precipi- tation exceeded the storage capacity of the soil, the excess was disregarded in calculating the balance of soil avail- able water. When the balance indicated a deficit of l or 1/2 inch, depending on the treatment, that amount of water was applied to the respective plots. With certain modifica- tions, the procedure followed the guidelines described by Jensen and Middleton for scheduling irrigation from pan eva- poration data (11). G. Harvesting procedure Two rows of each variety were machine harvested from the center of each experimental plot. The Russet Burbank tubers were graded into four groups: (1) smaller than 31 .Ehmm Hmpcmeflhmmxm zpcsoo Eamochz any Go Goapmpm sesame: esp pom pzohma pquSprCH ’4 : mhswam 32 1 7/8 inch; (2) between 1 7/8 and 10 ounces; (3) greater than 10 ounces, and (4) off-type tubers. For the Kennebec variety the off-type classification was not considered be- cause of the absence of misshaped tubers. Also, because of a more round tuber shape, the maximum size was graded by linear measurement (3 1/4 inch maximum) rather than using the weight determination. RESULTS A. Weather conditions during the period of irrigation The 1971 and 1972 growing seasons presented two well-defined and different weather patterns. Data to sup- port this statement are shown in Table 3 and Figures 5, 6, 7 and 8. Though the mean daily temperatures for July and August were the same in 1971 and 1972, the mean maximum temperatures were higher and the mean minimum temperatures lower in 1971 when compared with the 1972 values. The most significant difference in regard to temperature is that ob- served during the last part of June which coincided, in both years, with the critical tuber setting stage of the crop. The mean daily temperature for this period was 12.4% higher in 1971 than in 1972 and temperatures above 95°F were recorded for the last three days of June in 1971. On the other hand during the same period in 1972, a daily maximum temperature as low as 53°F was recorded, and no daily maximum temperatures were higher than 850E. These temperature differences were reflected in the average pan evaporation values of 0.30 inch/day for 1971 and 0.18 inch/day for the same period in 1972 (Table 3). 33 34 .mpowsma haamp .2.m mu.2.¢ w one on psommmnsoo* mmwmsm>< MO sa.o e.ma om o.ma masses TI. mic g cm mNé one 98 Tam Tms Shawna woo NN.o s.c mm mm.m m.om o.mc m.sm s.ms sass Aom-mav mH.o m.N caa mm.a m.mc s.ac N.Nm m.as mesa mmwmsm>< .HO mN.o m.ma mm EN.: mampoa TL NN.o To mm SN 0.8 mom m.mm Tom Semi wo wN.o c.m Nm NN.H w.Nc H.mb o.mm m.am ease Aom-mav om.o ©.m ms mm. o.ow H.3s m.mm m.mm ones .mc coca Sosa awe fiev . . A AAHanv %mpoav A mass Asoeav mampop moHWWWsc Agata gas xmz specs stow soap um>os one: GOHprHQHomHm m>apwama mates manpwnmmEmB nouoas>m com mafise use: scum: .msma Una Hema mo pmzws¢ can hash amaze CH mGOHpHcCOo sonata: mo zsmEESm .m manta 35 The highest daily pan evaporation value recorded, 0.50 inch, occurred on June 28, 1971. In 1971 the total pan evaporation for June, July and August was 14.6 inches greater than the total precipi- tation, while in 1972 this difference was only 0.7 inch. This seasonal variation resulted because of an 8.7-inch in- crease in rainfall and a 5.2-inch decrease in pan evapora- tion in 1972. Two items of interest are noted in the precipita- tion pattern of 1972 (Figure 8): the amount and timing of the rainfall during the stolonization and tuber setting phases, most critical with respect to yield, were suffi- ciently adequate to preclude any lack of soil water. Not only was the rainfall well timed to maintain an adequate water supply but many rainfalls were near or exceeded one inch of water. In summary, the 1971 season was hot and dry with a low relative humidity, and the 1972 season was cool and wet with a high relative humidity. The stolonization and tuber setting phases of the potato crop were affected by these two contrasting weather conditions. Table 4 illustrates this effect. The plants grew and developed faster in 1972. The plant vigor exhi- bited during the stolonization and tuber setting phases was due to the cool temperature and the ideal moisture condi— tions that prevailed during these growth stages. 36 .~ .’ . .-o- :2— ‘ - s. ’—¢"-‘- 3 ’. ------ I. ’ ~'~. -- \ !’ J0—0-'-.—.- ~ O-o-I-.-.-.-. "':— '.’ f~~ ‘0‘. --- 0-. -~ ..-0- ‘~ .~O~ ’v 's “. -0-.—.-.‘ 0‘ ~32..- ~”“ -.- ~‘~ .‘0-o—".—.-.-.. ’ 0- -.~ .4" ' ‘m.’ ------ ‘.-'~ -Oo' -°‘. -0 \‘ \ o ""’ I.’.’ and.-- —‘ .\ -fl..- 0"; ---‘ 0... £ ’ .~'~ ‘s I. ' - I -:::::: 9’. - ---- ” .‘O—. a" ‘7'... ' ‘o-o-.-.- 0' .-" C o . -----‘ -o-o—o"‘.‘ ‘3 -O-. ‘ -o-o-o-.-.-.-b - “ .‘o .9:- ." -- \ . ’ . o-o-O-°’°-.‘.- qfl-r—o-.-.-. \ ‘. I - ------' ‘O-.-.-. “- ----- 0". ‘~ .~.~. ’ 0’ “' ‘0‘ ’.’ " ofl”.‘. .---- .‘.-.-.-.-Jo- ‘§I fi-0-0"-'-. -‘. .-.-.- . “‘ .-O .’ ‘-. -- I -’ ..’ ~~ '5 "‘ ’0', ' ' l SBI‘T'IVA BAIIV'IBH I5 20 25 30 AUGUST -- total wind,mi/doy X 290 IO I5 20 25 30 5 l0 IS 20 25 30 5 JULY -- relative humidity,°/ox IOO J U N E — temperature ,‘F X I00 Mean daily temperature and relative humidity and daily total wind movement, Figure 5. 1971. 37 -gp-u. dlfl:::. -‘ flan—-C"--- ‘ ‘- -o-o-° ”Int-Pf“ . ‘c «’0‘ ’0’. r. I" I ~ 0". O ‘0 a" .v"' ’0 C ofl". ‘ .L—oa-H‘” . ‘. -0 —. fl.-. 7- o‘.’ ’.‘.’ Q ~ 0.. O .0 ””2- ’ O —.‘ O —"’. o ‘. ‘°~ 0-.-. e‘.’.- --- .I ‘.~.‘.’ C---- .- -~ .-.-.- ‘5 ..- ° " ‘°‘ .0..-. -.-.-.-. o "-. ’.’.’ ’ o v‘ v I...- ‘.~o ----a ..°. " .’I‘ " . ” -O-.-.- . d ' o '0' ‘\. O - ~ ~ fl" ..’ ~ .’ ~‘ ’ ‘ O - ------- ‘0‘. ’v I ’ -.’.-.-o-o I I. C’ 0 -C" ’ J.-_- -&. --"°-0- “" .~.-. --—— -.- ." -‘=- -..-O - ------- -.-O-. ..~ .2:- o-“'-’- .ao-u—°‘"— ‘ -"’—- " 1.- -- -- ~~~ "‘ - o- o.-:=‘.. - "4721.1... ‘- °< 0‘. I I 51 ‘ 1 l l I J 1 05 an F- £01 E) 1: to (N SBfl'IVA BALLV'IBH C) I5 20 25 30 AU 6 US T -- total wind, mi/day X 290 I0 5 I5 20 25 30 IO I5 20 25 30 5 J U LY -- relative humidity,% X I00 J U N E — temperature,’FX I00 Mean daily temperature and relative humidity and daily total 1972. wind movement, Figure 6. 38 .Hnma .muMp coflumuomm>m can can Hammcflmm .n musmflm hwaond >43... mzaa on 8 8 n. o_ n o» No n. o_ r. on N 8 m. J a d _ ._ l- . — — d _ :0 l_. a... as: ('0!) WTVJNIVU (“II NOIlVUOdV/G NVd 3 f? .Nmma .mpmc cowumuomm>m can one Hammcflmm .m shaman Pw303< >42. mzas On mm ON 0. O. o On mm ON 9 O. n on mm ON 0. O OD¢WN 3.. a we. a ('0!) ‘I'IVJNIVH (u!) NOIiVHOdVAB NVd 40 Table 4. Crop development in 1971 and 1972, Russet Burbank variety. Days after planting 1971 1972 Plant emergence 30 20 50% surface cover 45-50 35-40 100% surface cover 65-70 55-60 Stolon initiation 40-45 25-30 Initiation of tuber set* 50-55 35-40 Completion of tuber set+ 65-70 45-50 *Practically all plants examined exhibited either swollen stolon tips or up to 1/2-inch diameter tubers. +Practically all plants examined exhibited tubers l l/2-inch diameter or less. B. Timing of initial irrigation treatments The amounts of water applied to Treatment 1, 2 and 3 in 1971 were 10, 8 and 6 inches respectively. In 1972 the same treatments were irrigated with 3.75, 2.75 and 1.0 inch of water. During the warm and dry year of 1971 initiating irrigation at 50 days instead of at 70 days after planting produced a 42 cwt/acre yield increase in Russet Burbank and 43 cwt/acre increase in Kennebec (Table 5). Initial irri- gation at 60 days gave intermediate yields. Knobbiness was reduced from 21.5% to 13.4% by the earlier irrigation in ”Iv pr f OquxI-d "\atlttu 41 .zpmfinw> some canvas mates maEpsoap 039 mammsoo 09* .mwma CH meoapmoaammm seams =m\H can ea one mo mommam><+ .Hbma CH mpCmEpwmAp coapmwflnaa unwaz can man 039 mo mewmhm>¢t .m.qmao.o aco.a amo.H sco.a who.a Hmo.a moo.a mso.a mso.a mpa>osw .ooom - - - - - o.mH 3.:H :.NH m.oH msopep Apnoea a mu .m.c N.m m.mm m.ms m.om c.0s m.mo m.mm s.wm m.mm assess H.oz .m.p e ww .m.s N.sN com Swm mNa smm cam SNm smm cam +Ae\psov cares .mssomoo.o moo.a Hmo.H moo.H smo.a moo.H Hso.H mso.a mso.w apa>asw camaocam - - - - - m.os m.HN m.:a :.mH nuance apnoea a mu .a.s c.: m.ms :.ss N.as m.ms o.m: m.mm H.mm s.Hm atone» H.oz .m.: m “w N.ma mod mmN com mNm and NmN Nom :mm *A<\p3ov caoaw +mowwhwmwww momno .pmmah.psmae.pmwne mwmso .mthe.pmth .pwwae pamcqum . ompchmm xcsnhsm pmmmsm .mnma can Head amoon-spam omnmccmm can xswphsm pmmmsm mo hpa>wnw oauaooam use spasm .camaa so soapmwaaaa Hmapasa mo masses one to possum .m manta 42 Russet Burbank, and specific gravity showed a tendency to decrease with the later irrigations in both varieties. The percentage of U.S. No.1 tubers was not changed signifi- cantly by these treatments. The Similarity of values for percentage of U.S. No.1 tubers and the significant changes in yield values are a consequence of the increase in over- size tubers in the earlier irrigated treatments. Hence, the earlier irrigations increased yields, produced larger tubers, gave higher specific gravities and tubers were less deformed. Adequate amounts and distribution of rainfall during the earlier part of the irrigation period of 1972 eliminated any differential moisture stress between the treatments and masked any yield differences due to the time of initiating irrigation. It is interesting to observe though, that even under these circumstances, specific gravity tended to be greater with the earlier irrigations, and this increase was statistically significant. C. Day irrigation versus night irrigation treatment These treatments did not produce any significant difference in the crop yield characteristics under consider- ation. Table 6 shows these results. Night irrigation had a negative effect on the percentage of U.S. No.1 tubers in Russet Burbank variety but this effect was not statistically significant. No differential disease incidence was observed in the experimental plots subjected to these treatments. 43 .zpoHHm> can namepmonp wasm canHS mates COHpmwfiHHH no Comfiamdsoc* .m.s mo.o moo.H Nco.H moo.H sco.H mmo.H Nco.H Abo.H mco.H epHemaw .omnm x .m.c pH.m m.N o.aH N.HH H.aH m.m s.mH m.mH H.cH assess ouHmso>o e m .m.d ma.m m.ms m.ss N.ae m.ms s.ms o.ss m.:s c.ms mamas» H.oz .m.: e m .m.s m.mN seH HmN aNm eom mmH owN mmN amm Ha\psov cHoHs .m.s mo.o mmO.H oso.H aso.H mso.H moo.H Nso.H mso.H mso.H apHamaw .omam m. .m.: mH.m m.m m.mH 0.0m m.Hm 4.: s.mH e.mH S.SN assess oNHmsm>o a m - To: N.mN m.mH mi: 14.3 0.3 m4: {NH 2on3 Enos. e m .m.c ma.o m.m: s.om 0.0m c.ma m.:z m.mm N.om m.am mamasp H .oz .m.: e m .m.s m.mN omH omN com Nam mmH mmN com SNm Ha\p3ov chHw m mocoaoeNHo m N H H mo House romeo .pmmHB..pmm E .mmmms x0030 Immopmwspmmmw .pmoAB sesacsaem eoHesmHuaH pstz eopr H sH a oHMfiommm use ocmaw .vaHH :0 soapmeHHH unwac mamao> awe mo pommmm .HsmH ammopwpom omnmsqmm can Mawnnsm pmmmzm mo muH>me .c oHnme 44 These results were considered sufficiently conclusive to exclude this objective in the 1972 experiments. D. Frequency of irrigation treatments Irrigations of 1/2 inch of water resulted in some benefit as compared to irrigations of 1 inch of water per application in 1972. Table 7 shows that a higher yield re- sulted for Russet Burbank when it was irrigated at 1/2 inch as compared to 1 inch per application. Several of the irri- gations were followed by heavy precipitation and the 1/2- inch treatment received less than 3.0, 2.5 and 0.5 inches of irrigation for Treatments 1, 2 and 3. These data suggest that the plots receiving 1 inch were depressed more by ex- cessive water. The Kennebec variety did not suffer a simi- lar yield decrease with the heavier application but the per- centage of U.S. No.1 tubers and the specific gravity were less. All the differences Observed were not statistically significant. E. Irrigation cooling treatments Treatment 1 of the irrigation cooling experiment had 34 days of irrigation cooling resulting in a total of about 2.3 inches of water applied in 1971. Treatment 2 had 14 days with 1.0 inch of total water applied. In 1972 the com- parable figures were 30 days with 2.6 inches of water for Treatment 1 and 10 days with 0.7 inch of water for Treatment 2. 45 A .mpmflnm> can meEpmep mEmm aficpflz mates COHpNOHHQmm amazemp ComHHmdfioo* 1 mwewH00.0 a00.H mmo.H @00.H @00.H M00.H :00.H 000.H s00.H anaemsm .omam w m.c s0.0 0.eH m.HN 0.0H N.NH e.0 N.0H m.mH H.0H masses awamaos0 a m ..m.s mH.s m.ms m.es H.0m 0.ms :.wm m.es e.ms 0.3s masses H.oz .m.0 e m. .m.e s.mm mmm NH: HNe m0: 0am Ncm 0m: Hem Ha\psov cHoHH m.smH00.0 0S0.H m00.H mp0.H ms0.H Hs0.H @00.H Ns0.H 0R0.H aEHaaam .ooam ma .m.c s0.m :.NH s.0H 0.HH N.NH :.m H.m 0.0H m.HH asbpzp memao>0 e m. - N.:H 3.:H a.HH m.HH m.NH m.NH 0.NH H.HH masses apnoea a m. .8: HQ mHm 0.8 Two Two 4.8 9% H00 Two 283 H.oz .m.0 e m. .m.0 s.am mmm mmm me 0mm amm .Hm NHm eNm Haxssoc eHoHH a monogamch m N H m N H mo House xomno .pwmae..pmmma .vonB sommb .pwmaa .mwm B .pmmHE *Unmpqum QQHpNOHHmm¢ =m\H GoameHHQm< =H .man .mmoptpom omnmssmm 0st sarcasm pmmmsm mo mpH>me 0HMHommm 0am macaw «pHmHm no soHpthHHH m0 mosmscmsm hep mo vacuum .5 mHnt 46 The effect of irrigation cooling on yield, grade and specific gravity of potatoes in 1971 and 1972 is shown in Table 8. A yield increase, larger tubers and a greater specific gravity were obtained in 1971 by irrigation cool- ing. Russet Burbank and Kennebec responded similarly. A large variability in the check plots in 1971, thought to be a consequence of poor irrigation distribution from the farm irrigation system, suggests that these data be used with discretion. No significant responses between treatments were obtained in 1972. The ample rainfall and cool temperature did not permit a good test of the cooling effect during this growing season. Contrary to expectations, Treatment 2 (irrigation cooling at 850E) gave a higher yield than Treatment 1 (irrigation cooling at 800E). Again more water applied for cooling at 80°F may have been responsible for the lower yield. The results in this regard were consist- ent in both years. The tendency of specific gravity to in- crease with irrigation cooling was also consistent in both years. F. Partitioning of nitrogen fertilization treatments The yield, grade and specific gravity response to partitioning the nitrogen fertilizer is depicted in Table 9. Both varieties, Russet Burbank and Kennebec, gave Sig- nificant yield increases with later applications of nitrogen. 47 mw0.H 000.H s00.H as0.H ms0.H 0A0.H anaemsw .omam 0.0H N.NH s.mH N.HH H.HH s.NH masses mNHmso>0 e Hm - - - N.NH m.HH m.m assess apnoea e “m N.Ns m.se m.ms N.Nm m.0c 0.m0 masons H.oz .m.0 e Nmm mam Ham Ham mam 00m A<\psov oHoHH H00.H m00.H :00.H mao.H ms0.H 0S0.H soH>msw .ooam m.0 N.mH H.0H m.aH 0.mN 0.0N msopsp oNHmamso e .1 - - - H.0H chm 14.0 9803. apnoea e W. m.mm m.mm m.ms m.m0 :.00 m.mm whence H.oz .m.0 e mmN aNm mHm ch mam mHm Aaxbsov 0HmHN romeo Napacae, Hummoms guano Nanette, Hupmoas omnmgx xqspmsm pommsm .mea was Hbma ammovmpOQ omnmCme use Maspssm pmmmsm mo zpfi>muw OHMHoomm can spasm «pHmHh co mpnmEpmoHp mcHHooo cofipmwflHHH mo pommmm .m aHoae 48 .mpmHHm> some QHSpHS mcmme meEpmoHp mo mommammmap pump 09* .m.s N00. mm0.H m00.H @00.H as0.H NR0.H @00.H st>msm .obam - - - - N.SH 0.mH H.:N manner apnoea e .a.s m.a 0.0H w.mN m.mN H.HH a.:H s.m masses oaHmam>0 a .m.c s.m N.ss H.Hs :.Hs N.Nc m.H0 b.0m assess H.oz .m.0 e 0.0N Nam Na: 0m: mam RN: s.Hoa Haxpsoc 0Hon mocmsmmmau gonzo mupmeB, prmmHB Memmo m.pmonnr H.mNmHB Mo House omnchmx Mannasm pommsm IMwHwecmpm, .mbmH «mmopmpom omnmccmx 0am xcmpasm pmmmsm mo zpfi>mnw OHMHomdm paw oemsm «UHmHz :0 COprNHHHpHmw COMOHpac on» mGHCOHpHpra no vacuum .m mHQmB 49 However, the 1972 data alone, do not give a clear indication as to the optimum amount and frequency of later nitrogen applications. G. Crop factor for_pan evpporation values From gravimetric soil moisture data and estimated soil moisture data inferred from tensiometer readings, the evapotranspiration was calculated for selected time periods in absence of rains or irrigations in 1972. These values were used to calculate the evapotranspiration/pan evapora- tion (ET/PE) ratio. For June 26-30 the ratio was 0.63; for July 3-7, 0.74; for July 10—13, 0.89; and for July 22-24, 0.68. The average value was 0.73. The infrequency of rain- less periods, the short time span over which measurements were made, the inability to measure water loss resulting from deep percolation and the variability of the measured soil moisture contributed to the variability of the above ratios and prevented the precise monitoring of this ratio as crop development progressed. H. Procedure for scheduling potato irrigations To devise an accurate and simple procedure for de- termining the amount of water and frequency for potato irri- gations, soil, crop and atmOSpheric factors were taken into consideration according to the following scheme: 50 Soil Plant Atmosphere water holding capacity root depth wind ’//;::::;Itation profile depth growth stage temperature water require- rel. humidity ment Ability to hold Ability to Atmospheric Capacity and release absorb and demand for to res- water transpire evaporation tore soil water water I ‘/”””’,/" losses Evapotranspiration Soil water or gains Consumptive water use Pan evaporation losses, soil water gains and the soil water storage capacity were the basic parameters used in the calculation of the "soil available water balance". The steps for evaluating these parameters as used in this particular experiment were as follows: 1. Soil available water capacity calculation a. Soil type . . . . . . . . . . . McBride sandy loam b. Effective root depth . . . . . 24 inches c. Water retained by the 24" layer at 1/10 bar . . . . . . . 4.7 inches d. Water retained by the 24" layer at 15 bars . . . . . . . 1.3 inches e. Soil available water capacity (c-d) . . . . . . . . . . . . . 3.4 inches 2. Adoption of soil moisture level and volume of irrigation criteria 51 a. Amount of available water allowed to be depleted before irrigation . . . . 1.5 inches b. Amount of water applied per irrigation . . . . . . . . . . . . . . . 1.0 inches 3. Soil water gains assessment a. Precipitations record (P) b. Irrigations record (I) 4. Soil water losses estimation a. Pan evaporation (PE) measurements b. Evapotranspiration/Pan evaporation (ET/PE=CF) adapted to crOp growth stage c. Evapotranspiration (ET) calculation using the correction factor (CF) in ET = CF x PE 5. Computing daily net gains or losses of soil water with (P + I) - ET = Soil water gain or loss 6. Graphing the soil available water balance chart on a daily basis. The graphical representation of the daily soil available water balance on a chart has proved to be a useful tool in planning potato irrigations. Figures 9 and 10 show the available water balances kept for Treatment 1 of the (TI) experiment in 1971 and 1972. The two horizontal lines enclose an approximate 50% of the soil available water range. The actual soil moisture was maintained within these limits. In this particular case the percentage value is roughly equivalent to 1.5 inches. .HsaH .HH becaumowaH mcofiummHHHH cumuom msHHSUEQOm new phase mOCMHmn nous: .m mHsmHm 33 8.83.: .3 Sea .803” H0303 Fur. 03. .203. H9. .323. 3 £00 .203. 52 Pmaond >433 mZDHH Om mN ON n. O. 0 On 0N ON 0. O. D On 0N ON 0. O. = H H H H u H H H H H H H H H H H . - . H H . H H H u - H H . . H . H H H H . H H H H H H . m H H . H H . _ - u u _- - l H H H u H H H H H H H n H H u H H H H H H H H u H H . OZHPZ433 wzna. Om mN ON n. O. D On mN ON 0. O. 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