Iv1531_1 RETURNING MATERIALS: Place in book drop to LIBRARIES remove this checkout from J-l-[Sl-IL. your record. FINES wiII be charged if book is returned after the date stamped beIow. THE EFFECT OF DRIP IRRIGATION ON MICHIGAN VINEYARDS, AND THE GROWTH AND PHYSIOLOGICAL RESPONSES TO WATER DEFICITS ON CONCORD AND SEYVAL GRAPEVINES. BY HECTOR MAURICIO ESCAMILLA-SANTANA A THESIS Submitted to Michigan State University in partiaI fquiIIment of the requirements for the degree of MASTER OF SCIENCE Department of HorticuIture 1985 To my parents for their principIes and exampIe through my Iife. To my wife AngeIica for aII her support and understanding. ii ACKNOWLEDGEMENTS I wouId Iike to express my sincere gratitude to: My major professor Dr.(L StanIey HoweII and Drs. James A. FTore and Vincent BraIts for their directions, kindIy criticisms, and heIpfuI suggestions anng the study and during the writing of this thesis. Dn. George Hogaboani and his USDA assistants for their cooperation and the greenhouse space faciIities that made possibIe to carry experiments. Dr. Delbert Mokma and Dr. RonaId Perry for their time, interest, equipment, and advice that made it possibIe to obtain the desorption curves of the soiIs used. The data coIIected and preparation of both fieId studies and greenhouse experiments would not have been possibIe without the heIp of nu/coIIeagues James Lempke,Loran PeerboIt,Timothy MansfieId,Keith StriegIer and David Miller. The Nationai Grape Cooperative and especiaIIy to William Greveiding for their interest, cooperation and financiaI support of this research project. DougIas Neisch euui Robert VanVIeck for their care and contribution of the vineyards in this project. TABLE OF CONTENTS Page LIST OF TABLES . . . . . . . . . . . . . . . . . vi . LIST OF FIGURES . . . . . . . . . . . . . . . . viii INTRODUCTION . . . . . . . . . . . . . . . . . . 1 LITERATURE REVIEW . . . . . . . . . . . . . . . . 2 SECTION I THE EFFECT OF DRIP IRRIGATION ON GROWTH AND YIELD COMPONENTS ON CONCORD AND SEYVAL GRAPEVINES IN MICHIGAN. Introduction . . . . . . . . . . . . . . . . . . 14 Materials and Methods . . . . . . . . . . . . . . . 15 Results and Discussion . . . . . . . . . . . . . . 23 General comments and suggestions for further field studies . . 34 SECTION II SENSITIVITY OF GROWTH AND STOMATAL CONDUCTANCE OF CONCORD AND SEYVAL GRAPEVINES TO DROUGHT. Introduction . . . . . . . . . . . . . . . . . . 37 Experiment I. DROUGHT SENSITIVITY OF DIFFERENT GROWTH COMPONENTS OF CONCORD AND SEYVAL GRAPEVINES. Materials and Methods . . . . . . . . . . . . 38 Results and Discussion . . . . . . . . . . . . 46 Conclusions . . . . . . . . . . . . . . . 76 Experiment II. THE EFFECT OF A CYCLIC SHORT TERM DROUGHT ON CONCORD GRAPEVINES. Materials and Methods . -, . . . . . . . . . . 38 Results and Discussion . . . . . . . . . . . . 70 iv Conclusions SECTION III EFFECT OF DROUGHT STRESS AT DIFFERENT STAGES OF BERRY DEVELOPMENT ON CONCORD AND SEYVAL GRAPEVINES. Introduction . Experiment 1. EFFECT OF DROUGHT STRESS DURING PREBLOOM, FULL BLOOM AND FRUIT SET ON CONCORD AND SEYVAL GRAPEVINES. Materials and Methods . Results and Discussion Conclusions Experiment II. EFFECT OF DROUGHT STRESS AT STAGES I, II, III AND ONE WEEK BEFORE HARVEST ON SEYVAL GRAPEVINES. Materials and Methods . Results and Discussion Conclusions REFERENCES APPENDIX A. UNIFORMITY OF THE DRIP IRRIGATION SYSTEM B. METHODOLOGY PROBLEMS AND ALTERNATIVES 77 79 80 86 93 80 90 93 96 LIST OF TABLES Table 10. SECTION I . Soil characteristics of Lawton and Fennville, Michigan . Pruning severities in 1983 and 1984 on Seyval grapevines at Fennville, Mi. . . . . . . . . . . . . . Soil moisture, yield and quality components of Concord grapevines at Lawton, Michigan. . . . . . . . . Effect of irrigation treatment on yield and quality components of irrigated (I) and non-irrigated (NI) Seyval grapes at Fennville, Mi. 1983. SECTION II . Environmental conditions presented at the time of stomatal conductance measurements. Air temperature (T 0C), relative humidity (RH%) and photosynthetic photon flux density (PPFD umol/m2 5) April 11- 17. . . . . . Environmental conditions presented at the time of stomatal conductance measurements. Air temperature (T 0C), relative humidity (RH%) and photosynthetic photon flux density (PPFD umol/m2 s) May 5-10.. . . . . . . . Time when statistical differences began for plant indicators on Concord and Seyval grapevines under conditions of drought. . Soil moisture tension at which statistical differences started to appear on potted drought stressed Concord and Seyval grapevines. . . . Cumulative growth for lateral shoots on drought stressed Concord and Seyval grapevines. . . . . Percent reduction in the growth components of Concord and Seyval grapevines compared to the control at the end of the drought treatment. . vi Page . 15 . 18 . 32 . 33 .44 . 45 66 . 67 . 67 . 69 11. 12. 13. 14. 15. 16. SECTION III Time when statistical differences began for plant indicators under cyclic drought conditions on Concord grapevines. April 12-170 0 o o o o o o o o o o o o o o o o 0 Time when statistical differences began for plant indicators under cyclic drought conditions on Concord grapevines. May 5-10. . . . . . . . . Effect of drought stress at different stages of berry development (pre-bloom, full bloom and fruit set) on Concord and Seyval grapevines. . . . . . . Effect of a short term drought stress (4 days exposure) on Seyval grapevines at different stages of berry development. APPENDIX A Field data for uniformity evaluation of the drip irrigation system at Lawton and Fennville, Michigan. . . . . . Statistical uniformity due to emitter flow rate, hydraulics, and emitter performance . vii 71 73 88 92 iv iv LIST OF FIGURES Figure 11. 12. 13. . Training system at Lawton (A - Geneva double curtain) and at Fennville (B - High head), Mi.. . . . . Schematic layout of the Concord drip irrigation research plot at Lawton, Mi. . . . Schematic layout of the Seyval irrigation research plot at Fennville, Mi. . . . . . . . . . . . . . . . Monthly evaporation minus monthly precipitation and mean temperatures of the period 1974- 1982, and during 1983 at Lawton, Mi. . . . . . . . . . . . . Monthly evaporation minus monthly precipitation and mean temperatures of the period 1974-1982, and during 1983 at Fennville, Mi. . . . . . . . . . . . . . Variation in soil moisture percentage within blocks during the 1983 season at Lawton, Mi. . . . . . . . Variation in soil moisture percentage within blocks during the 1983 season at Fennville, Mi. . . Soil moisture tension changes at Fennville, Mi. (1983). SECTION II . Seyval leaf showing procedure for determination of leaf area. 10. Watering practices on Concord grapevines, (I) irrigation and (S) no irrigation period. . . . . . Sensitivity of growth components and stomatal conductance to drought on Concord grapevines. . . . . . . . Sensitivity of growth components and stomatal conductance to drought on Seyval grapevines. . . (A) Change in soil moisture tension on irrigated and non- irrigated Concord grapevines. (B) Rate of shoot elongation affected by soil moisture tension (SMT) changes on Concord grapevines. . . . . . . . viii Page 16 19 20 24 26 28 28 31 4O . 43 . 47 . 49 14. (A) Leaf area rate of growth affected by changes in SMT on Concord grapevines (B) Stomatal conductance affected by changes in SMT on Concord grapevines. 15.(A) Cumulative shoot diameter and (B) shoot diameter 16. fluctuations affected by changes in soil moisture tension (SMT) on Concord grapevines . . . . . . . . (A) Changes in soil moisture tension (SMT) on irrigated and non-irrigated Seyval grapevines. (B) Rate of shoot elongation affected by SMT changes on Seyval grapevines. 17.(A) Leaf area rate of growth and (B) Stomatal conductance 18. 19. 20. 21. 22. affected by changes in soil moisture tension (SMT) on Seyval grapevines. . . . . . . . . . . (A) Cumulative shoot diameter and (B) shoot diameter fluctuation affected by changes in SMT on Seyval grapevines. Influence of drought on trunk diameter of Concord grapevines. SECTION III Berry growth and the time of drought on Seyval grapevines . APPENDIX A Drip irrigation uniformity chart. APPENDIX 8 Soil moisture distribution in relationship with the position of the tensiometer. . . . . . 54 . 56 . 60 . 62 . 64 . 75 . 84 ii ABSTRACT THE EFFECT OF DRIP IRRIGATION ON MICHIGAN VINEYARDS, AND GROWTH AND PHYSIOLOGICAL RESPONSES TO WATER DEFICITS 0N CONCORD AND SEYVAL GRAPEVINES BY Hector Mauricio Escamilla The effect of irrigation on yield and quality was tested on Concord and Seyval grapes. Greenhouse studies were conducted on phenological and physiological responses todrought. Irrigation had no effect on yield and quality of Seyval after the first year. Shoot elongation and stomatal conductance were more sensitive to drought than shoot diameter and leaf area. Growth continued on lateral shoots afterlnain shoots stepped growing. Preconditioning to drought yielded vines better able to withstand a second drought. Clusters at pre-bloom, full bloom, and fruit set were sensitive to drought. Drought during pre-bloom induced fewer seeds/berry and reduced berry weight. Drought may contribute to delayed ripening of grapes. An acute drought during stage I caused cluster dessication , but did not affect yield and quality at stage II, veraison, and l-week before harvest. INTRODUCTION Michigan ranks the fifth among grape producing states with approximately 6360 ha. Although in a temperate climate, Michigan may have periods of drought during the summer coupled with high temperatures. Most Michigan vineyards are located within 40 Km of Lake Michigan. The vineyard soils are predominantly sandy, well drained, and with low water holding capacity, increasing the importance of supplemental irrigation.The usecfiidifferent irrigation systems has gradually increased and there are currently about 235 ha, where 55 % are by drip irrigation. Drip irrigation is one of the most efficient systems because of its low energy requirements for operation, its efficiency of water distribution, and its low volumes of application. However, very little research has been conducted in the viticulture of the Northeastern United States to help determine the effects of supplemental irrigation, apprOpriate amounts and rates of water application to meet grapevine's needs. This research project was divided in 2 areas: (a) Field and (b) greenhouse studies with the following particular objectives: 1. Quantify the effect of supplemental irrigation on Concord and Seyval grapes at those critical periods where additional water would be beneficial to to vine size, yield, and quality of grapes. 2. To measure the sensitivity of different vine growth components and stomatal conductance to drought and to cyclic acute, short term drought on Concord and Seyval grapevines. 3. To determine the effect of drought stress at different stages of berry development. LITERATURE REVIEW WATER RELATIONS Water is important for several physiological and morphological functions in vine growth and deVelopment. According to Kramer (40) water is important in plants as follows: 1) Constituent- it forms 80-90 % of the fresh weight of herbaceous plants; 2) Solvent- it is a solvent and a carrier for gases, minerals and other solutes for the whole plant; 3) Reactant- it is involved in reactions such as photosynthesis; hydrolytic processes such as the amylase-mediated hydrolisis of starch to sugar in germinating seeds; and 4) Maintenance of turgidity- it plays an essential role in the maintenance of turgor in order to maintain cell enlargement and growth. Turgor influences the opening of stomata and movement of leaves, flower and petals. Hence, lack of turgidity reduces plantds growth and development. Water loss in plants is dependent on transpiration, which is influenced by environmental conditions. Continuous water uptake is necessary to replace transpirational losses. Plant water uptake is mainly done by its roots, but a small amount is absorbed through leaves and even through twigs (42L The movement of water depends on the existence of gradients of decreasing water potential (61). The components of water potential (TM) are: T’w =\fisi-Ym +Vfl) wherel’s is the osmotic potential,‘rm is the matric potential, and‘Fp is the turgor potential.Vfi1is usually low and negative.In fully turgid tissues‘Ys is numerically greater than‘fp, so that‘fiw is negative. ARID ZONES AND HUMID AREAS Areas receiving less than 200 mm of precipitation per year are arid, those receiving 200-500 nun are semiarid, from 500-750 are subhumid, and above 750 humid. This classification (21) is often misleading since distribution of the precipitation during the year can vary. It may occur that a humid location receives most of the rain in a very poor annual distribution, resulting in a season with two or three months of drought. Therefore, an area with a high precipitation level but poor distribution is sometimes considered a semiarid zone. Michigan has the lowest summer rainfall of any state East of the Missisippi river. This lack of rainfall may generate a drought problem (47). Hence, irrigation may represent a desirable agricultural practice. TECHNIQUES FOR RESEARCHING WATER RELATIONS. Kramer (40) indicated that a satisfactory method of monitoring plant water status should have most of the following characteristics: 1. There should be a good correlation between rates of physiological processes and the degree of water stress measured by the method. 2. A given degree of water stress measured by the selected method should have similar, physiological significance in a wide range of plant materials. 3. The units employed to express water status should be applicable to plant material, soil, and solutions. 4. The method should be as simple, rapid, and as inexpensive as possible. 5. The method should require a very small amount of plant material for a measurement. Relative water content (RWC), is the expression of tissue water content as a percentage of the fully turgid water content: RWC= Field wt. - Oven dry wt X 100 turgid wt - Oven dry wt The use of RWC allows one to follow changes in water content with a minimum of apparatus. Leaves are obtained from plants under study and weighed, then floated on water for 4 hrs to allow them to obtain maximum turgidity and reweighed. Dry wt is obtained afterwards (211 Unfortunately, a given RWC does not represent the same level of water potential in leaves of different species or ages, or from different environments (40). Leaf xylem water potential, can be obtained by using a pressure chamber*(62). The chamber does notrneasure xylem potential directly. The method measures the pressure necessary to raise the potential of the xylem sap at atmostpheric pressure (7). The method consists of sealing the petiol of a leave in the chamber top so that the cut end of the petiol projects to the outside while the leaf blade is subjected to pressure on the inside. As pressure is applied to the blade, the water potential of the cell sap rises until it equals that of the sap in the xylem vessels at atmospheric pressure. At this point xylem sap emerges at the cut surface and the pressure required to cause this is recorded. WATER RELATIONS IN GRAPEVINES Water status influences the physiological and the biochemical processes and conditions which determine the vegetative growth and yield components of grapevines (43,69,34). Under good cultural practices, nutrition, temperature and soil moisture, the seasonal growth cycle of bearing grapevines is described by Winkler, et al (79) as follows: A very rapid and succulent growth of the shoots in spring and early summer, a rapid slowing of shoot growth as the berries rapidly enlarge, and a gradual slowing of the shoots growth toward the ripening period with many shoots stopping growth by the time the grapes are ripe. During the growing season the soil moisture in the root zone fluctuates between field capacity and permanent wilting point.(PWP). When the soil moisture drops below the PWP there is no readily available moisture surrounding all of the roots and the grapevines begin to wilt in late afternoon or stop their growth (29,34). However, Furr and Magness (24) reported in their studies with apples that stomatal activity and fruit growth were affected, even when soil moisture in parts of the root zone was considerably above the PWP. SYMPTOMS OF DROUGHT STRESS IN VIIIS Under conditions of drought stress the rate of growth in grape shoots dimishes or stops (73) while the growing tips gradually change from soft yellowish-green to the harder or grayish-green of the mature leaves (79). Young leaves and tendrils wilt (79,28). Young tendrils may also abscise (28). The shoot tips dry out, leaves curl, and the older leaves become dry, die and eventually drop (77,28) Mid-cane leaves, well exposed to the sun, develop unpatterned areas of necrosis (79). Leaves of drought stressed grapevines tend to hang vertically (73,68). Leaf angles greater than 60 between the junction of the petiole and lamina were associated with low transpiration rates and high stomatal resistance in "Perlette" grapevines (68L EWought stress during enlarging of berries will cause a reduction in berry size (73). Shriveling of the berries may occur at all the stages of development . under conditions of drought stress (28). PLANT RESPONSE TO DROUGHT STRESS Drought stress and root development Hofacker (31) observed an increased ratio of root to shoot weight in stressed "Aris" and "Muller-Thurgau" grapevines. With a relatively dry treatment "Shiraz" grapevines had a greater root production than with a wet treatment (22L.These reports suggest that roots are less sensitive to drought stress than aerial parts. Richards and Cockroft (1974) (cited by 60) concluded that soil water potential lower than -50 Kilo-pascals (0J5 bars) had little effect on root elongation rates, but that few roots grew in soils drier than -1500 kilo-pascals (15 bars) Drought stress and shoot growth in grapevines Irrigated grapevines have a higher growth response (pruning weigth) than stressed vines (69,54,14). Grapevines adjust to drought stress by reduced shoot growth as a result of limitations imposed by water supply (34,79,16). Stomatal closure on stressed grapevines has been observed at a leaf water potential of -13 bars, and shoot growth rate is inhibited at lower tensions (68). Becker and Zimmerman (6) also found that restricted water supply reduced the vegetative growth, the transpiration coefficient, and consequently the amount of water necessary for the production of 1 Kg dry matter in the shoots. Drought stress and trunk diameter fluctuations Trunk diameter fluctuations have been shown to be a good reference for scheduling irrigation on fruit trees. The principle of this method is based on the fact that radial changes are influenced both by growth and by the degree of hydration of the tissues. Trunk growth rate and total seasonal growth in almonds was affected primarily by soil water. Of secondary importance were crop density conditions (72). Scheduling irrigation by trunk growth requires uniformity in age, vigor and crop load of the trees and uniformity in the soil. Smart (68) noted that trunks of stressed grapevines commence to shrink at WLof -7 bars or sooner in the earlyrnorning, subsequently'declining, while irrigated vines had maximun rates of shrinkage about midday. Similar observations were made by Verner, et al (74) on apples, prunes and cherries. Drought stress and leaf area. An increase in leaf area directly increased the amount of the grape cr0p (78). Water deficiency in apples, peaches and prunes caused a reduction in shoot growth and leaf size (9). Irrigated "Cabernet Sauvignon" grapevines had an increased leaf area (14). An adequate water supply combined with shade increased the exent of leaf surface in "Riesling" and "Muller-Thurgau" grapevines (6). This is important considering that a reduction in the leaf area of vines also caused a reduction in the amount of assimilates produced and the quality of grapes (79). LEAF WATER POTENTIAL, STOMATAL APERTURE AND PHOTOSYNTHESIS AFFECTED BY DROUGHT STRESS The pressure technique described by Scholander, et al (62) has been extensively used in water relation studies. Water in the xylem of a transpiring plant was subjected to negative pressure and the pressure became more negative as drought stress increased (26). The use of leaf water potential as a guide to study stress in plants (7,35,8,49,22) and for irrigation timing has been reported (43,69,48,50,26). Another method for measuring drought stress in plants is via stomatal aperture. Guard cells are very sensitive to water deficits and the premature closure of stomata is often the first indicator of developing drought stress (41). However, stomata do not always respond isolely to water stress, so the correlation between stomatal aperture and water balance is not always pefect (5). Stomatal aperture has been also used at an irrigation criterion (3,66,67). Leaf conductance (cm/s) and resistance (s/cm) have been used to describe stomatal function. Stomatal conductance is the proportional parameter relating the flow of water vapor through the stomatal pore to the driving force (33). Conductance is affected tu/ incident quantunl flux density (radiation), leaf temperature, ambient humidity, carbon dioxide concentration and bulk leaf water potential (12). The term diffusive leaf conductence should be used more frequently, because transpiration, leaf water status and net photosynthesis are often directly related to conductance, whereas they are inversely related to resistance (27) . They also suggest that conductance should be expressed as a flow density per unit difference in relative partial pressure of water vapor between leaf and air with units 2 millimol/hizs because the vapor pressure gradient is more appropiate as driving force than the absolute humidity gradient. However, some authors still refer to stomatal resistance expressed in s/cm or conductance with units cm/s. Warrit, et al (75) showed in ‘Malus that an increased leaf to air vapor pressure deficit reduced stomatal conductance and a linear relationship was established between stomatal conductance and leaf to air vapor pressure deficit. Stomatal resistance of stressed "Shiraz" grapevines increased to 20 sec/cm as leaf water potential fell to -13 bars under field conditions (68). Liu, et al (45) observed similar results on potted "Concord" grapevines. Their data showed that when leaf water potential reached - 16 bars, stomatal closure was essentially complete (15-25 sec/cm) and photosynthesis was minimal (1-5 mg carbon dioxide/dmz h). However, in field studies Liu (44) concluded that stomatal closure due to drought stress was never observed for mature, non senescent leaves, even when water potential was as low as -16 bars. Kriedemann and Smart (43) observed that photosynthesis declined at leaf water potential below -5 bars and fell to O at about ~12 bars to -15 bars in potted "Sultana" grapevines. A prolonged leaf water potential at less than -16 yielded a large increase in abscisic acid and an incomplete recovery of photosynthesis despite opening of the stomata after rewatering (45) . All these reports, and that of Freeman, et al (22) agreed that since stomatal conductance, carbon dioxide assimilation, and rate of photosynthesis were directly related, low stomatal conductance, carbon dioxide assimilation and rate of photosynthesis were being reduced. 10 Floral initiation and drought stress Irrigation reduces floral initiation under those conditions where increased shoot length and leaf area result in a decline in light penetration to the renewal area (51,14). Primary bud development can be depressed by excessive water flow in the bud tissues (14). However, fruitfulness (expressed as the number and weight of bunch primordia per bud) was progressively depressed with increased of water stress (13).Therefore, irrigation during the period of bud formation has an important role influencing potential crop yield in arid zones. Drought stress and berry development In arid areas, soil moisture rather than temperature Allexander (1) or light intensity affect fruit set in grapevines (2). Alexander (1) added that water stress during or post-bloom would cause the bunch to shrivel. ' If enough of the soil in the root zone reaches permanent wilting point when the berries are enlarging rapidly they will not reach full size (73,34,6). Even if water was applied after the period of rapid berry growth, the undersized fruits did not attain normal size (34). Drought stress prior to veraison reduced berry size was the yield component most sensitive to drought stress (68). Stress during veraison caused a decrease in color of grapes probably due to reduced carbohydrate availability (28). Maturity drought stress and fruit maturation Ripening processes are delayed by drought stress conditions (28). The delay is greater if stress is applied during the lag phase and is 11 directly proportional to crop load remaining after stress (68). However, under conditions where irrigation caused strong vegetative growth and the fruit was shaded, maturity was delayed (30). Maturity was also delayed in situations where soils were deep and have a high water holding capacity (77). Finally, drought stress reduced total amount of sugar per berry (16,34,6). METHODS OF IRRIGATION Comparing drip, flood, and sprinkler irrigation on the response of St. Emilion (Ugni blanc) grapevines, Peacock et al (55) concluded that the principal benefit with drip irrigation was increased efficiency of water use. At the same time, yields and quality were mantained the same for the 3 methods. The only problem found with drip irrigation was that salts and sodium concentrated at the surface 100 cm from the row. Location of vineyards is the most decisive factor in determining the possibilities and limits for a profitable drip-irrigation investment (71). Drip irrigation in vineyards has generally been a promising investment under conditions of moderate to steep slops which have limited top soil and low water holding capacity. Under these conditions irrigation has improved yields and quality of harvested grapes. One of the problems of drip irrigaticu1is the cost of the system. Reed, et al (59) ranked the cost of the 10 irrigation systems most commonly used as follows: 12 IRRIGATION SYSTEM COST/ACRE/YEAR* Drip 225.95 Permanent set sprinkler 219.60 Hose drag 204.20 Furrow 185.75 Hand move sprinkler 164.60 Wheel line sprinkler 140.60 Center pivot sprinkler 133.50 Center pivot corner system 125.90 Flood - Well water 121.00 Flood - district water 117.35 * Cost/acre/year: Includes expenses of water applied, investment, depreciation, interest, taxes and energy costs. ' 13 THE EFFECT OF DRIP IRRIGATION ON GROWTH AND YIELD COMPONENTS ON CONCORD AND SEYVAL GRAPEVINES IN MICHIGAN. INTRODUCTION Michigan has approximately'6360 ha.of producing vineyards. The use of supplemental irrigation has gradually increased, and is currently about 235 ha. (107 ha of sprinkler and 128 of drip irrigation, (Thomas, personal comnnunication 1984). Very little information is available to help growers determine appropriate amounts and rates of water application to meet grapevine needs. Although annual precipitation would be sufficient if apprOpriately distributed over time, high temperatures and evaporation frequently combined with the probability of low rainfall of June and July to induce periodic drought stress due to the limited amount of water in the soil. Depending on the time and duration of that stress, vine damage and economic loss may occur. When one adds these problems to the common condition of very sandy, well-drained soils with low water holding capacities characteristic of Michigan vineyards, irrigation becomes a potentially valuable potential practice for the state's viticulture. The objective of this study is to quantify the effect of supplemental irrigation on Concord and Seyval grapes in those critical periods where additional water would be beneficial to vine size, yield and . quality of grapes. l4 15 MATERIALS AND METHODS Studies were conducted on two important grape cultivars at two locations (comercial vineyards) in Michigan. Seventeen-yearrold Concord grapevines (Vitis labruscana Bailey) at Lawton, MI (latitude 42 13' N; longitude 85 51' W; and 241 m of elevation) trained to a Geneva double curtain (GDC) system (Figure 1.A) were selected for the first plot. Rows were orientated East to West, separated 3.05 m, and the vine separation within vines isiL54 m. Eight-year-old grapevines of the hybrid direct producer (HDP) Seyval (Seyve-Villard 5-276) trained to a High head system (Figure 1.B ) at Fennville (latitude 42 36' N; longitude 85 09' and 216 m of elevation) were selected as the second plot. At this location the rows are orientated North-South, the distance between rows was 3.05 m,and vine separation was 2.54 m. Soil characteristics are described in Table 1. Table 1. Soil characteristics of Lawton and Fennville, Michigan. LOCATION TEXTURE pH F.C. P.W.P. A.W. (94) DO (76) LAWTON Sandy-loam 4.7 9 3.2 5.8 FENNVILLE Sandy-loam 5.8 15.5 5.2 10.3 F.C.= Field capacity P.W.P.= Permanent Wilting percentage A.W.= Available water ANALYSIS OF DATA _ Lawton: The experimental design was a Split-plot, where main plots 16 (B) , 1'__ Q.mn40.7m Emitter””’d' 1 ET Tensiometer Figure I. Training system at Lawton (A - Geneva double curtain, after Shaulis, et al (65)) and at Fennville (B - High head), Michigan. 17 (irrigated and non-irrigated) were arranged inairandomized complete block design, and the sub-plots were vine size (0.79 Kg, 0.91-1.3 Kg, and 1.47 Kg), using a total of 24 vines per sub-plot, 44 per plot and and a total of 176 experimental vines. However, since the irrigation system did not operated during 1983, data was analyzed as a radomized block and further evaluated using regression analysis of the soil moisture coefficient and the different plant yield and quality variables. Fennville: This plot was a randomized complete block design with 10 blocks, two treatments (irrigated and non- irrigated) and 5 vines with a total of 100 experimental vines. PRUNING Lawton: The average vine size at pruning for Concord grapevines was 1.15 Kg of cane prunings and vines were balanced pruned (64) to a 30+10 pruning severity (i.e., 30 buds retained for the first 0.45 Kg of cane prunings and 10 buds for each additional 0.45 kg). The fruiting nodes were retained on 5 node canes. In 1984 the grapevines were pruned in the same way. Fennville: Seyval grapevines in Michigan must be pruned very severely because this cultivar produces very large clusters and thus tends to overcrop, flower cluster thinning is often a recommended practice. The base bud is counted in this cultivar when pruning because this bud, unlike the situation in Concord, generally is fruitful. Table 2 describes the pruning severities for 1983 and 1984. In 1983 cane weight was not obtained because vines had been pruned 18 prior to plot establishement; only bud number data was collected. For 1984 vines were grouped into 3 categories and bud number was set based on vine size and vineyard experience with the cultivar (Table 2). TableZL Pruning severities in 1983 and 1984 on Seyval grapevines at Fennville, Mi. YEAR Cane wt. Bud No./vine* Percent of vines in (Kg) this category 1983 ----- 17 13 ..... 18-22 51 ..... 23 36 1984 0.34 16 59 0.34-0.45_ 20 31 0.45 24 10 * Base bud also counted SOIL MOISTURE Soil moisture changes were followed during the growing season at both locations. Samples of 90 cc of soil were taken (0-20 and 20-40 cm depth) in each experimental block of the study, wrapped in polyethylene bags weighed, later oven-dried for 24 hr at 105 °C, and then weighed again. Soil moisture was determined by substraction. Tensiometers were placed at 30, 60 and 90 cm depth within the rows at appr0priate locations within the plot based on its topography (Figs 2 and 3). These tensiometers were used also to follow soil moisture tension changes at those levels hithe soil(Figs.2 and 3) 19 .mgmumsowmcmy we cowgwmoo mgu use HQFa mgp we xzomcmoaou mg“ mcwzocm .wz .c0p3m4 um papa :ocmmmmc :owuam_ecw awcc acoucou mgu Go uzoxmp uwpmsmsum_.~ «gamed 332:. >7. j a. . g . a u v .. L .o_1..uuma_c.._i::z 30 y .uooac u. x \ >_ on. v 1.39.: \ on. u “can v \ L — \ \ m an . ,_ +1. *1 9 ..3.1. emimct-.. m . 5 x x m u “ u 9:3 ii: I x _: a . 1m . u “ a . 5..” > :Nio: cochbmcccp a a w a _ . m \ \ p a .P O a a _ a N m x \ . 33050.33 : 30 w wLSL w v>.m> t_C:u_:m O 8. “ V.—Ofl\k ‘“ mm .6 a“. a M a. w ”e 9: nU . c _ x w m 2;; mm— X V..§_\ " n . u a. L . .2. 3 Es: .U \ . \ u \ . \ . 1 r I . \ . .im 2.... U h A 11”— _ s L 20 .mco.oeo_mco. do guaou new co_umuo. 0:“ tam .o_a on“ Lo xzamcooacu ecu m:_zo;m ._z .o.__>ccmu um .o_a socmomoc comumm_cc_ _c>>om on. to uao>m_ u_umEo:um.m 0c:m_m .3305 X1— x uo_a teamm_cc_icoz "H x. :_> ~07... Dugout: m ._> 3; Ill .08 I _> .03 30 > :12. coecobmco: o .OOu 0003 c087? O > +_ J. mcouoao_mcoh O >_ ”I oao o>.m> v_o:o.3m 0 j .566 x 00h. zoo: a 322:1 .533 n- ..«\M oar. nu Ullllll - 21 IRRIGATION LAYOUT Vines were either a non-irrigated control or irrigated during the growing season to mantain an adequate soil moisture tension. Tensiometers (Model "RA"-Irrometer, Co.)1were used to produce automatic irrigation control. Lawton: In 1983, three tensiometers (model "RAN) were put at 60 cm and connected in series (wire No.14 solid direct burial UF-UL listed) which controlled the 24 volt solenoid valve (3/44, 240-06-03) Figure 2. The tensiometer controls were set at-JLZO bars which would prevent the soil from getting below the soil moisture tension at field capacity for these kind of soils (-0.33 bar, 58). The system was set such that each of the 3 tensiometers needed to be -0.20 bars or more negative to initiate the operation of the system. This was unaceptable because the irrigation system at Lawton did not turn on during 1983. .In both locations the electrical connections were in series and the depth of tensiometers set at 60 cm. In Fennville the irrigation system applied only 17.2 m3/ha. In 1984 the electrical layout and the depth of tensiometers was changed in 1984 to provide a better response to inadequate soil moisture in the root zone of the vines. Therefore, in 1984 tensiometers (model "RA") were set at 30 cm and the electrical layout connected in parallel so any given tensiometer could turn on the system when SMT was at -0.20 bars. Two emitters C1785 l/hr) were placed 60 cm from the trunk on each side of the vine (Fig 1 B). The time of irrigation was recorded by a the timer (Fig. 2) so that the amount of water applied could be calculated. 22 COLLECTION OF DATA VINE DATA Each year both vegetative and reproductive yield were estimated as weight of cane prunings and fruit weight and quality indices respectivelly. The weight of cane prunings was taken in the Spring prior to bud burst and the allocation of bud number per vine made at the same time. At harvest, each vine was individually harvested and the fruit weight and the number of clusters per vine recorded. This allowed a calculation of cluster weight. Concord clusters were individually sampled for 50 berries (5 apical berries from 10 clusters selected ramdomly; (53)).This sample was weighed to determine average berry weight and thus allow for a calculation of average berry set per cluster. These same 50 berries were then mascerated and the soluble solids measured using an Abbe refractometer (Model-3L, Bausch and Lomb, Inc.). This berry sampling procedure varied for Seyval grapes. The 50 berry sample was collected from the 5 vines within each block and in addition to weight and soluble solids, the pH and the titratable acidity were measured. SOIL DATA At two week intervals gravimetric soil moisture determinations and soil tensiometer readings were made, and the amount of water applied via irrigation was calculated. 23 RESULTS AND DISCUSSION WEATHER The weather patterns of Michigan (Lawton, Fig. 4 and Fennville, Fig. 5) are characterized during the summer by high temperatures and evaporation, and low precipitation. This situation increases vine transpiration and evaporation from the soil water. SOIL MOISTURE Gravimetric sampling: The sandy-loam soils at both locations have a very low water holding capacityu The percentage of soil moisture in late June, early and mid-July were very low at both locations (Figures 6 and 7). There were areas where soilinoisture varied among Blocks and this corresponded to changes in slope of the plot. In Lawton, Block I has the highest soil moisture level during the growing season while the Block IV has the lowest soil moisture level. At Fennville, Blocks VII, VIII, IX and X seemed to have a higher moisture content while the blocks I, II, III, IV, V and VI were lower. Tensiometer readings: Tensiometers were a useful tool which helped to follow soil moisture tension (SMT) changes at 30, and 90 cm of depth. SMT was greater at 30 cm of depth while very minor changes occurred at the 90 cm depth. The Fennville data (Figure 8) show those soil moisture changes at 30 and 90 cm of depth in an irrigated (I) and non-irrigated (NI) plot. SMT at 30 cm in the NI plot were more negative(up to-4L54 bars). At 90 cm in the non-irrigated plot SMT went up to 4137 bars while in the 24 Figure 4. Monthly evaporation minus monthly precipitation and mean temperatures of the period 1974-1982, and during 1983 at Lawton, Michigan (Source: Agricultural Weather Service, Entomology Dept., Michigan State University, East Lansing, Mi.) EVAPORATION — PRECIPITATION (MM) MEAN TEMPERATURE C 25 a 1974—1982 [J 198.3 :VNMNMN ‘VMNNN MONTHS 25 15- lO-i 51 H MEAN TEMP. 1974-1982 o—o MEAN TEMP. 198.3 MONTHS 26 Figure 5. Monthly evaporation minus monthly precipitation and mean temperature of the period 1974-1982, and during 1983 at Fennville, Michigan (Source: Agricultural Weather Service, Entomology Dept., Michigan State University, East Lansing, Mi.) EVAPORATION - PRECIPITATION (MM) MEAN TEMPERATURE C I I I as A N O ? O 27 N 1° L 1974—1982 B 1983 I\\\\\\\\\ A: : \\\\\\\\\\\\\V \\\\\\\\n ' SI C 1+ L L [II F ENNVILLE 25- A M I J J MONTHS I I S 20- 15-1 10- H MEAN TEMP. 1974—1982' H MEAN TEMP. 1983 FENNVILLE MONTHS T T S 28 Figure 6. Variation in soil moisture percentage within blocks during the 1983 season at Lawton, Mi. (For topography information of each block see figure 2). Figure 7. Variation in soil moisture percentage within blocks during the 1983 season at Fennville, Mi. (For topography information of each block see figure 3). Soil moisture percentage for grouped blocks represent the averaged value. SOIL MOISTURE 96 SOIL MOISTURE % 29 20 X IBLOCK 0 II 15- 0 III IO-i 5.. LAWTON O . . f a r 0 J J A 0 MONTHS 20 15— =51 10-4 BLOCKS 1‘! and II QIII and IV 5‘ n 0V and VI AVII and VIII FENNVILLE XIX and X 0 A . . . f . O J J A 0 MONTHS 3O irrigated plots SMT never were more negative than-4132 bars at 30ouu 5A Aac>ucA o. 005:0 05A can. scan. sou-03905.0 ouawn.0l ..ou uo Is. 0A» on cooaounuo 959.0.0I v.00. . 00. 0.0. ~0.p. 00. 00 00 0a.. 0b.. 00<00>< 00. ..m. -.0. 0w. 0v .00 .n.. .0.. n.0v A 00. 0.0. 00.0. .n. mm .0 .0.. 00.. 0.00 c>. v0. 0.0. 00.0. mm. 0v 00 mn.. 00.. 0.00 A 00. 0.0. n0»0~ 00. mm Pm 0v.. 00.. p.>m a... 00. 0.0. 00.0. On. 00. 00 0n.. 00.. ..00 A 00. 0.0. No.0. 0N. 00 00 00.. 00.. v.00 a.. 00. 0.0. 00.0. 00. 0v 00 mm.. 00.. 5.00 A _ 00. «.0. 00.0. 0.. 00 50 .n.. 00.. 0.0.. 0. 0...M 00. 0.0. 00.0. 00. w. vv .0.. .... 00< mm. 0.0. v0.0. 0v. 0' 0' .0.. n... ~.0v A v0. 0.v. 00.0. 00. .0 av 90.0 00.. 0.00 ¢>. «0. ~.0. ...0. mm. n. 0' «0.. 00.. 0.00 A «0. 5.0. «0.0. .0. 00 cc 00.. 00.. 0.00 a... 0m. o.0. o0.0. 0n. an v. ae.o 0... ..0m 0 . 00. 0.0. .~.0. 0.. 0' vv m... .... 0.00 o.. 00. 0.0. n..0. 0v. . vv vv N... .... p.v0 A . . om. o.m. om.0. pw. .. a. Ga.o m... m.oe a. v .-a o .0. p.n. 00.». 0o. 00 mm 00.0 00.0 uo< .0. 0.0. .0.n. 0.. .' mm 00.0 0v.0 ~.0v A >0. 0.0. m0... .0. 00 cm 00.0 00.0 0.00 c>~ .h. v.0. 00.0. 00 00 an 05.0 00.0 0.00 A 00. 0.0. 00.0. 00. we on .0.. 00.0 0.00 c... 00. 0.0. 0..v. ON. 00 cm m... 00.0 ..00 A 00. 0.0. ~0... 00 pm nu m>.0 00.0 v.00 a.. 00. 0.0. 00.9. mm. mm wn 00.0 09.0 0.00 A 00. 0.0. 00.0. 0.. p... cm 00.0 00.0 0.0.. a. 0.0“ .ao.uuo0 00. 000. 000. v00. 000. :000. a:o.m> o=.>\na «waxzz «mats: ex u::sm.c= on .0000 n.20 can.» ¢0b0=.0 0:0 920.5: us<0 4.00 x0000 00.0 0:.> ..v00.1n00.. =u¢.:o.: .co.:¢a A. oo:.>oaau0 unaccoc .o o.:c::auco h...¢:c can a...» .os:.a.cl n.00 .r o.Acb 1.... . Ala-nun \ IIII--\ In! Ah ~2~<§ \~\ I 1 I a . ct C .u.> -I..I\..v.......~..c...c \v~.LL....,: .L :3... . LIKE, . v2.2: I. -..:a.- ..Z-.-...>..:... .2 (112;: .n.)).6..1 «~20 I33: 2:... Au. thud-on... -5-.. 53 ad..5::..:.34 ).d . . ‘33 t...‘ F.- .'.\A .... ....v.:~r..... . t... .1... o a. so. u ... u \ 33 .mmucocot.mLau..m..3m o: 0..: wi<>oz< umz mz A..o mz a... m: m..~ mz mo.. ma .a m: mam .N .2 m2 a..o m. a... m. m..~. m: G... a. N. m: «mm .N . . .IIIIIIIIIII .eoc.\cm oa.>\mx «UAmaau 02.. .awm.. oa.>\ao auz_<.ue <. :a xLRm n.m_. \mm_eeum \memhmasu .IPtMAMBIIUzau man. .zuz.eaou .a moaacm .asaom ._z. aooaa.ce_ ice: tea ... 00.n0.gs. no m.:m:onsou A...u=a use 0.0.» cc .cwsuowgu :O.Ao0.gc. 0o .00000 .c 000'. : \ = ~ <1 ‘ ‘ ' c3 3‘ . Si 2; U I s j 2 1: .~ 3 lb* SEWMLHNNGMED T H SEYVAL NON—IRRIGATED “ O r 1 r I r r r r f r T I fir h T fiI T = O 5 10 15 20 25 62 Figure 17.A. Leaf area rate of growth affected by changes in soil moisture tension (SMT) on Seyval grapevines. Figure 17.8. Stomatal conductance affected by Changes in soil moisture tension (SMT) on Seyval grapevines. 63 25 I q o—e. SEYVAL NON-IRRIGATED I— , H SEYVAL IRRIGATED g 20~ m 1 o ‘1 8T 151 >— BEE 1 Ex: I g 10— $0 : o: I < . LL 5- < .. Lu . .In] ‘1 .1 O Y 7 o 25 0.6 H SEYVAL IRRIGATED A 9—0 SEYVAL NON—IRRIGATED T 0.5- 0 th‘ 0.4— 2 o v LIJ 0.5— o z E- r O 0.2- / 3 «a e = . o O.l-I o . 0.0 r I l I O 5 IO 15 2O 25 64 Figure 18.A. Cumulative shoot diameter affected by changes in soil moisture tension (SMT) on Seyval grapevines. Figure 18.8. Shoot diameter fluctuation affected by changes in soil moisture tension (SMT) on Seyval grapevines. The values represent the difference of the shoot diameter at 07:00 hrs and 15:00 hrs. SHOOT DIAMETER (CM) SHOOT DIAMETER FLUCTUATION (CM) 65 o—o SBVAL NON-IRRIGATED H SEYVAL IRRIGATED l r 5 10 15 2O 25 DAYS .0 u 0.2‘i L .0 I ‘L .0 O 1 l .3 II. I N A I | Cu 1 9—0 SEYVAL NON—IRRIGATED H SEYVAL IRRIGATED O 20 25 DAYS .A<>Cz< aaa-~v o:_a> ; 5:8 ac »D__.;a;:;; . .nn:u> _ A a:vadaagd .2 go o:_z> 3 zonaazau:_u Leuvsaqe do:;n “12$ Ladoaa.s 555:3 " :n :aaohm 55 cans saga ace; "u:<; :cuuam:o~o acoza go 34:: "an: N ao:n»o=a:oo —au:aouc " x 66 (‘4 7| L0 v-N <3 C a“? C O 0‘ vt‘ 5“ ”NO 3“. 2 ~37 3‘) z 4<>>2n 2:22:22 nae; Axvum— I AxCH>cv z: 9 c 4<>>ur ._~_..ugz.~nv A;a:_fix:A:V 9 > ;<>>2: :zcuzcc A.n;; .xtxkvv . :n G N ;<>>Zfi ._~.A.“V~_A.n. c:«; c ;<>»zn m» A_~..vu.zavp. 2m: :2 4<>>22 n 22:22:: W x N I #— m » < a 5 a > o m v =39snaum ~a>aom 3:: cgco:ou :o aheaaaav:q a=a~3 Lou :nmo: moacvgouuqa ~au‘aa‘uaan :v:: 95.? .> 3;: Co mvmapoca ca Lmuuo m:_o> u msu Co xu_pwamaocm a a 12 a m No.m a52_28aeaca uzeS ARV a=_e> a 6:5 ----- m: L6 ASP—peaeeca Whoozm S<¢mh<5 a e a a _m a a a m ~m_m m a o 8 mm“ a a a a u Any a=_a> a 6:5 m.~ o o v. C6 »D__2eaeeta wmm Sm. e-.o emo.o nac.o ewo.o emo.o aao.o mo.o om.o _m -.o eA~.o emo.o ewo.o eNo.o er.o a-.o eo.o e~.o _m_m Ae.o avm.o am~.c aoa.o akm.o am~.o ame.o o~.o Nm.c _m_ mm.o aem.o am~.o amm.o ace.o am~.o aA¢.o a~.o Nm.o u Aav a=_a> a 655 5.3 mg. no. m. o go. o a La »S___eaaeea muzonogm ugoucou co m=o_u_vcou . . azmzogu Ecmuuugosm Lone: mgououpc:_ ace—n so» comma mmucmgou8_u poo—umpuuum ems: we,» A~ u4m Co mpm>.a:m cm Lmuym mzpm> m 8:» Co zup_woenoga x 73 Hz H mspw> m ms» IIIIIIIIII mz mo mew—pamnogm um<4 ---------- m2 ARV as... L .26 La >D___aaeeea whoozm S m mg» IIIIIIIIII mz m we xu__wnwnogm mmm M 855.0 ao~.o amfi.o ea-.o aeo.o aAH.o aem.o aam~.o am.o Hm.o Hm emo.o emo.o Demo.o aeo.o amo.o neo.o emo.o a-.o mm.o mm.o Hmfim aeo.o awo.o ewo.o ufio.o amo.o evo.o emo.o emo.o 53.8 m~.o _m~ 83.0 £2. 2:5 3:8 Sod 2:5 6:5 find 38 $5 8 253 as... L .25 Ho. Ho. 50. o ac. Ho. #8. mo. m .L6 »33_Paaeoca uuzmqogm ugoucou co mccwuwucou uzmzogu EgmuuuLozm Lace: mcoueo_uc_ “cm—a Low gamma mmucmgmww_u pmumumwumam can: mswh .mq mpncp 74 stressed vines. On May 9th no differences appeared in 95 for all treatments indicating that recovery from drought had taken place. On May 10 at 10:30 hrs all values of gsswere the same showing that full reCovery had ocurred. The trunk diameter growth Changes measured by linear transducers indicated that contraction of the trunk diameter occurred under conditions of drought stress (Fig. 18L. Even though no statistical differences appeared between the irrigated and stressed vines on the 6th and on the 7th data indicated that this plant indicator is also quite sensitive to drought. On May 6th gS for the stressed vines was lower than the control and the same day the trunk of the drought stressed vines shrank considerably. Upon rewatering on May 7th trunks responded faster than 9S and expansion of the stressed trunks was observed. This suggested that under conditions of drought trunks were a good indicator of stress. If devices such as linear transducers are designed for field operation and at lower price, irrigation scheduling based on this may become a feasible practice. 75 x—ilRRKMfiED G—e NON -|RR1GATED CUMULATIVE TRUNK DIAMETER (mm) < Figure T 1 19. T T FT I T T T I I T l T T 2. 3 4 5 6 7 8 9.10 11 12 13 14 15 DAYS Influence of drought on trunk diameter of Concord grapevines. 76 CONCLUSIONS - EXPERIMENT I The RSE appeared to be of equal or greater sensitivity than gS in both Concord and Seyval grapevines. However, the percent of Change of these plant indicators associated with the time under drought stress was higher in both cultivars for RSE under conditions of relatively fast developing drought (Figs. 11 and 12). The critical soil moisture where differences started was -O.38 bars and -0.44 bars for Concord and Seyval grapevines respectively. Even though main shoots of drought stressed Concord and Seyval grapevines stopped their growth, some growth continued in the lateral shoots. Shoot diameter fluctuations appeared as a physiological sensitive parameter to drought stressed Seyval, but not in Concord grapevines. In practice with the methodology used its use as an indicator of drought in the field seems difficult because it is time consuming and expensive. Shoot diameter shrinkage preceeded the time when the cumulative shoot diameter started decreasing. A.marked trend occurred for both cultivars as to greater shrinkage during the afternoon up to the point where no night recovery was observed. Stomatal conductance appeared as sensitive as shoot diameter fluctuations for Seyval grapes, and appeared less sensitive to drought than RSE in both cultivars. The leaf area rate of growth was less sensitive to drought than the other plant indicators measured. 77 CONCLUSIONS - EXPERIMENT II Under conditions of an acute drought stress no difference Hithe sensitivity of RSE and g5 took place in potted greenhouse grOwn Concord grapevines. Higher gS of preconditioned vines than those with first drought experience indicates an acquired gain in tolerance to a second period of drought. 78 EFFECT OF DROUGHT STRESS AT DIFFERENT STAGES OF DEVELOPMENT ON CONCORD AND SEYVAL GRAPEVINES INTRODUCTION Cell number, volume and density are described as the components of fruit weight (5). These components combined with environmental conditions and management techniques, determine fruit size and weight of the fruits at harvest. The accumulative berry growth (berry diameter, length, volume, or weight) results in a general sigmoidal growth curve (57,75) that consists of: (I) a period of rapid growth, (II) a period of slow growth (Lag phase), and (III) a final increase in growth. The high temperatures and evaporation, combined with the low precipitation that characterize Michigan's summer, increases vine's water deficit, and both yield and quality can be affected. Grapes during ' the early stages of fruit develOpment are very susceptible to water deficits (28). Water stress during or inmediately after bloom may cause the bunch to shrivel (1). If the stress occurs during the rapidly enlarging phase, berries will remain undersized even if water is applied afterwards (34).‘The total amount of sugar is also reduced with drought (16). The objective of Experiment I was to determine the effect of drought stress at pre-bloom, full bloom and fruit set stages on Concord and Seyval grapevines. The objective of Experiment II was to determine the effect of drought stress during Stage I, II (lag phase), Stage III (veraison) and 1 week before harvest on yield and quality components of Seyval grapevines. 79 80 MATERIALS AND METHODS This study was done in two experiments due to space limitation as follows: EXPERIMENT I. EFFECT OF DROUGHT STRESS DURING PREBLOOM, FULL BLOOM AND FRUIT SET ON CONCORD AND SEYVAL GRAPEVINES. EXPERIMENT II.EFFECT OF DROUGHT STRESS AT DIFFERENT STAGES OF BERRY DEVELOPMENT 0N SEYVAL GRAPEVINES. GRAPEVINES In Experiment I, potted one-year-old Concord and Seyval grapevines were grown outdoors during 1982 in 19 liter pots with prOper nutrition and water supply. In 1983 both cultivars were pruned back to 2 buds per vine to obtain a total of 4 cluSters in each. Vines were grown from early February until late June. Two vines of each cultivar were grown a week earlier to be use as reference to assign drought treatments. Grapevines were positioned in a greenhouse with an average mean temperature of 25 °C,a mean maximum of 28 °C, and a mean minimum of 21°C, with a range of i 4 °C during the study. In Experiment II, one-year-old Seyval grapevines were managed as in Experiment I. Fertilization was made early in the study (Stage I) and in the middle (end of lag phase) of the study with 1 liter of soluble fertilizer (Peters 20-20-20) to yield 400 mg/l of nitrogen. SOIL A soil mixture 2 sandzl perlite:1 peat (v:v:v) was used in Experiment I. In Experiment 11, the soil mixture was composed of 2 sand:1 perlite:1 loamy soil (v:v:v). These light soil mixtures were 81 used to produce have a fast developing drought. Fertilization consisted of 21-liter applications of water soluble (20-20-20) fertilizer (300 ppm of N) early in the study (burst) and during stage II of berry develOpment. In Experiment I,the container media water holding capacity(70) was 19.9 %, and the PNP 4.2 %. In Experiment II was 18.13 %, and the PWP 3.1 % . In both experiments the bottoni(2.5 cm) of each pot was filled with a layer of gravel «L4 -CL8 cm) to facilitate drainage and aereation. Soil moisture changes were followed with the lysimeter technique weighing the whole pots and with the use of tensiometers (Appendix). Tensiometers were place in the middle of the pot and soil moisture tension (SMT) changes followed during the study. EXPERIMENTAL DESIGN AND DROUGHT STRESS TREATMENTS In Experiment I, there were 4 treatments including a control which was irrigated every other day to mantain 80 - 100 % available moisture in the soil. Drought stress treatments were applied at pre-bloom, 50 % bloom and at fruit set bylwithholding irrigation for 4-6 days before vines reached the phenological stage where treatments were desired. The experimental design of Experiment I was a Completely Randomized Design with 7 single-vine observations per treatment. In Experiment II, five treatments arranged in a Randomized Complete Block Design with 4 single-vine replicates per treatment and were tested as follows: (A) Control vines were irrigated every other day to mantain 80- 82 100 % available moisture during the study (Fig.20). (B) Stage I - (Cell division and cell elongation phase) Drought was applied 10 days after fruit set. (C) End of Stage II - (Lag phase) When a reduction in the rate of growth of the berry becomes evident. (D)Stage III - (Veraison) When softening and change in color take place. (E) One week before harvest. Treatments were applied based upon a berry growth curve (Fig. 20). During the study'a berry growth curve was obtained by measuring the diameter of 3 berries per cluster (basal, middle and apical) every other day (07:30 hrsL in one cluster per vine with a digital micrometer (Mitutoyo, Co.). VARIABLES MEASURED Yield components: i) In Experiment I, percent of fruit set was obtained by counting the total number of flower primordia in each cluster and by counting the number of berries at harvest. In Experiment II, percent of fruit set was calculated based upon the numbem'of berries before and after the drought period for each treatment. ii) Berry weight was obtained by weighing the clusters and dividing their weight by the number of berries in each cluster. iii)Berry volume in both experiments was obtained by displacement of water by the cluster and dividing the volume displaced by the number of berries in the cluster. 83 Quality components: i) For Concord grapes in Experiment I, juice soluble solids expressed as Brix was determined with a Abbe refractometer(Bausch & Lomb, Inc). ii) For Seyval grapes in experiments I and II, juice soluble solids expressed as Brix, pH, and titratable acidity (TA) expressed as grams of tartaric acid/100 cc of juice were measured on a pH meter and via titration with 041 N NaOH respectivelly. 84 Figure 20. Berry growth and the .time of drought on Seyval grapevines. A: Control; B: Stress at stage I; C: Stress at stage II; D: Stress at veraison; E: Stress one week before harvest. 85 (WW) HEEWVIO A8838 DAYS AFTER BLOOM 86 RESULTS AND DISCUSSION - EXPERIMENT I Creating stress treatments at the precise phenological stage was problematic. In justa fewobservationsin each treatment, drought occurred at the exact desired time. The small numbers preclude statistical analysis, therefore observations are give for drought treatments of drought during bloom and fruit set in Seyval and pre-bloom and fruit set on Concord grapes. SEYVAL Drought during pre-bloom stage of 41 % of the water holding capacity'of the pot (NHCP) developed during 16 days did not produce a significant reduction in the percentage of fruit set. Weight and volume per berry were reduced when drought occurred at pre-bloom. This effect could be due to the greater number of fully developed seeds per berry. Fruit size and shape are often related to seed number. Hormones produced by the seed may be responsible for these effects (20). A relationship between increased berry size and the seed number has been shown to occur in grapes (57,79). Seed number per berry was directly related to accumulation of 14C-photosynthates, fresh weight, and dry weight (15). The lower number of seeds could be caused by an induced lower viability of pollen developed during prebloom stage. Similar observations were made by Modlibowska (52) where the number of seeds/fruit decreased proportional to a decrease of soil moisture during the prebloom stage. Even though no differences were observed for soluble solids 87 and pH, a higher percentage of soluble solids and an higher pH was found in the control than was found in the pre-bloom drought stress treatment. The lower acidity for the control suggests the possibility of a maturity delay for the prebloom stressed vines (Table 13). As mentioned, problems occurred in this experiment in inducing drought at the proper stage. This was also the case for the bloom and fruit set treatments. Only one of the six observations of the stress at full bloom experienced drought when 40 % of the flowers in the cluster were open. Soil moisture in that pot was 52 % of WHCP and was developed during an 18 days period (Table 13). Upon rewatering, berries at this stage continued to desiccate and eventually the whole cluster dried. One of the six vines stressed at fruit set experienced a 49 % of WHCP and a similar desiccation. CONCORD Three of the sixlcontrol and full bloom treatment vines produced inflorescences. There were 5 vines in the prebloom stage and 4 vines in the fruit set stage. Drought treatments in the latter group resulted in cluster desiccation in all but 1 vine, when the soil moisture in the pots decreased to 40% and 44 % of NHCP. Vines stressed during full bloom were exposed to 46% of NHCP and 3 vines retained their clusters after that exposure. Considering the amount of treatment variation concerning vine numbers the number of vines with clusters before and after the drought stress, and that statistical comparisons were limited to the control and drought stress at full bloom, a few comments can be made: Fruit set was 88 “casummgu mzu a? co_uo>cmmno mco »_co we u m caucus - .V .._N o._ om.~ em.“ m~.m m.ofi-o.o a 8mm a_=ra - - am.HN a.“ am.~ mo.~ ¢~.a a.mH-~.m soo.n __=L - - m.o~ m.o No.H fim.~ mm.fi H.m -m.~ a soo_a-aca - - ae.- m.H mm.H sm.~ NH.N «.mfi-m.mfi .ocueoo aeouzou u u i u n . noo.o ¢.o~um.o umm u_:gm u i u l u u noo.o o.-:~.m Eoopm ppam -~.o eo~.m a¢.e~ am.~ amo.~ o-.~ mm~.o~ ~.m -~.m soo_n-mc¢ awed £3” 8.8 mo.~ emu; Sm; 3mg 5.24.3 33:8 .o<>>um a co to a assumpoe _pom .<.» :a xvcm xccma\mummm waspo> xccmm a: agcmm uom u_:cm we omen: .mmaogm pm>amm new ucoucou mo Aumm u_:gy new soopn __=m .Eoo_n-mcav unusao_m>mu Acton mo mommam acmcmww_u co mmmcum usmaocc mo gummeu .mH m_nwh 89 not affected when the soil moisture dropped below 38 % of NHCP during full bloom. Soil moisture levels of 26 % and 32 % of NHCP caused dramatic reduction in fruit set of vines stressed at the pre-bloom and fruit set stages respectivellyn The stress was too great. Even though statistical comparisons did not show differences among the 4 treatments, percentage of fruit set in pre-bloom and fruit set was considerably reduced and only one of the 3 vines set fruit. The average number of seeds per berry, and weight per berry for the control appeared slightly higher than the berries from vines stressed at full bloom. This supported the results derived from Seyval.' However, no statistical differences appeared and nothing conclusive can be stated. Soluble solids were statistically different between control vines and stressed vines during full boom (Table 13). This, and the soluble .solids of the vines stressed at pre-bloom and at fruit set (1- observation) supported the Seyval , where drought during pre-bloom, full bloom and fruit set delayed maturation of the crop. 90 RESULTS AND DISCUSSION - EXPERIEMENT II Berry diameter (36,80) was measured by taking 3 berries per cluster (1 basal, center, and apical position). Monitoring berry growth by berry volume changes by displacement of water (28) was not desirable. Submerging the cluster into water caused berries to fall from the cluster. EFFECTS OF DROUGHT STRESS FOR A SHORT PERIOD OF TIME In Stage I, drought stress, as measured by tensiometer -O.7O + 5 bars and developed in a period of 3 - 4 days, caused berries to desiccate and whole clusters to abscise. At this time berries had a diameter of 3.6 mm (2 weeks after bloom) and this indicated that berries were very sensitive to drought at Stage I. Complete desiccation of whole clusters and parts of clusters was reported during the three weeks following anthesis (1,28). Shriveling was observed during berry development. A SMT at the end of Stage II of -0.83 + 5 bars, at veraison of -0.82 + 8 bars, and 1 week prior to harvest -0.83 + 7.5 bars did not have a significant effect on Shriveling. Three to four days after the drought treatment occurred, some berries in Stage II and veraison abscised, but none abscised when drought stress C-(L83 + 7 bars) was applied 1 week prior to harvest. YIELD AND YIELD COMPONENTS Only treatment B, acute drought stress at Stage I, caused a statistically significant reduction in yield per vine, and berry volume and weight. Treatments (A, C, D, E) did not show any statistical 91 differences (Table 14). Percent fruit set differences were observed as mentioned earlier (Table 14). No statistical differences among treatments A, C, D, or E appeared. This suggests that acute drought for a short period of time (3-4 days) does not have a significant effect on fruit set. QUALITY COMPONENTS No statistical differences were observed among A, C, D and E treatments for Brix, pH and titratable acidity (Table14.) FACTOR AFFECTING BERRY SIZE At the end of the study, total leaf area among treatments was compared and no statistical differences were founcl(Table 14). However, 35% and 31% of the variablity in berry volume and weight respectively was associated with leaf area (at 1 % and 2% significance level respectively). This indicates that berry size of berries can be affected by leaf area and therefore, when a study of this nature is performed it is preferable to select vines with a similar leaf area. Leaf area may also affects fruit set in grapevines (17) 92 .mzou N to» upon cowmcmu mgsumwos F_om Ezewxmz nee .ucmsamwcu mmmcum pcmsocc oz“ swoon use mcommn Co conga: ms» mcwcmuwmcoo an umuwpau_mu How “was; “smegma " a w~m.o w~m.m mo.o~ mm.m¢ mHm.H mmm.H <~¢.m~ mo. + mm.o- hmw>m u o wmm.o wmm.m mm.m~ am.o¢ oHo.H mH¢.H mm¢.mm mo. + mm.on HH mw\gm cowmcmu a ovum a wow psmmmz mE:_o> mgaumwoe uwtmucm» :a chm “was; Accmm xtcmm n—mw> ea Fwom Fzmz~mu meson mo mommum “cmcmemmv um mmcw>mqmcm _m>>mm co chsmoaxm mxmc «V mmmcgm acmsogc Erma “Locm a yo powwow .efi wreak 93 CONCLUSIONS - EXPERIMENT I A pre-bloom drought treatment of 41% of WHCP did not induce a reduction in the percent of fruit set in greenhouse grown Seyval grapevines. The lower number of seeds per berry found in pre-bloom stressed Seyval grapes was related to the effect of the drought during this stage. Unstressed vines had more seeds and a higher berry volume and weight than stressed vines. Clusters of Seyval and Concord grapes were very sensitive to prolonged water stress during, pre-bloom, full bloom, and fruit set. The ocurrence of drought during early stages of development may contribute to delayed ripening of Seyval and Concord grapes. The lysimeter technique done by weighing of whole pots with a scale was a useful method for assessing soil moisture changes. For future studies, a greater number of vines resulting from larger populations of vines are suggested. This should yield a more homogenous group and reduce the sources of uncontrolled variation in environmental and soil moisture conditions influential in this experiment. CONCLUSIONS - EXPERIMENT II Berry diameter was a satisfactory means of evaluating berry growth and the double sigmoid curve of the fruit in Seyval grapes was produced. In the early stages of berry development (2 weeks after bloom) berries are very sensitiveeto a short term drought stress. A similar drought stress treatment applied at the end of Stage II, veraison and 1- 94 week prior to harvest did not have any effect on yield .he yield components, or quality components. Therefore, berries at the latter particular stages of development were more tolerant of an acute, short term drought stress. 95 REFERENCES 1. Alexander, 0. McE. 1965. The effect of hight temperature regimes or short periods of water stress on development of small fruiting Sultana vines. Austral. J. Agr. Res. 16:817-823. N o Alleweldt G. and w. Hofaecker. 1975. Einfluss von Umweltfaktoren auf Austrieb, Bluete, Fruchtbarkeit und Triebwaschstum bei der Rebe. Vitis 14:103-115 (1975). 3. Alvim, P. 1965. A new type of porometer for measuring stomatal opening and its use in irrigation studies. UNESCO Arid zone res. 25,325-329. 4) . Barnes J.FL and A.lL Putnanu 1983. Rye residues contribute weed suppression in no-tillage cropping systems. Jour. Chem. Ecol., VoT.9, No.8:1045-1057. 5. Barrs, H. D. 1968. 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Kaufmann, M. R. 1968. Evaluation of the pressure chamber method for measurement of water stress in citrus. Jour. Amer. Soc. Hort. Sci. 93:186-190. Kobayashi, A. M. Kuretani and H. Oto. 1963. Effects of soil moisture on the growth and nutrient absorption of grapes. Jap. Jour. Hort. Sci. 32:1-8. Kozlowski, T. T. 1965. Expansion and contraction of stems. Adv. Front. Plant. Sci. Vol. 10:63-74. Kozlowski, T. T. 1967. Diurnal variations in stem diameters of small trees. Bot. Gaz. 123 (1): 60-68. Kozlowski, T. T. 1968. Diurnal changes in diameters of fruits and tree stems of Montmorency cherry. Jour. Hort. Sci. (1968) 43:1- 150 Kramer, P. J. 1983. Water relations of plants. Academic Press, Inc. 487 pp. ‘ 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 99 Kramer, P.‘I, and Brix,lL 1965.lWeasurement of water deficit in plants. UNESCO Arid Zone Res. 25, 343-351. Kramer, P. J. and T. T. Kozlowski. 1979. Physiology of woody plants. Academic Press, Inc. 811 pp. Kriedemann, P. E. and R. E. Smart. 1971. Effects of irradiance, temperature and leaf water potential of photosynthesis of vine leaves. Photosynthetica. 5:6-15. Liu. w. 1974. Soil-Plant water relations in a New York vineyard. Cornell University, PhD Thesis. Liu. w.,FL Pool, N. Wenkert, and P. Kriedemann. 1978. Changes in photosynthesis, stomatal resistance, and abscisic acid of Vitis labruscana through drought and irrigation cycles..Am.‘L Enoi. Vitic. 29:239-246. Loveys B. R. and P. E. Kriedemann. 1974. Internal control of stomatal physiology and photosynthesis. I. stomatal regulation and associated changes in endogenous levels of abscisic and phaseic acids. Aust. J. Plant Physiol.,1974,1:407-15. Lucas R. and M. Vitosh.1978. High corn yields with irrigation. Ext. Bull. E-857, Farm Science Series. Machida Y. and T. Maotani. 1974. Studies on leaf water stress in fruit trees.lh Evaluation of the pressure chamber method for estimating leaf water potential of Satsuma mandarin trees. J. Japan Soc. Hort. Sci. Maotani T. and Y. Machida. 1976. Studies on leaf water stress in fruit trees. V. Seasonal changes in leaf water potential and leaf difussion resistance of Satsuma mandarin trees..L Japan Soc. Hort. Sci. 45:261-266. Maotani T. and Y. Machida. 1980. Leaf water potential as an indicator of irrigation timing for Satsuma mandarin trees in summer. J. Japan Soc. Hort. Sci. 49:41-48. May, P. 1965. Reducing inflorescence formation by shading individual Sultana buds.Aust.TL Biol.Sci.18:463-73. Modlibowska, I. 1961. Effect of soil moisture on frost resistance of apple blossom, including some observations on "ghost" and "parachute" blossoms. Jour. Hort. Sci. 36(3):186-195. Morgan, J. M. 1984. Osmoregulation and water stress in higer plants. Ann. Plant Physiol. 35:299-319. Neja R. A., w. E. Nildman, R. S. Ayers, and A. N. Kasimatis. 1976. Grapevine response to irrigation and trellis treatments in the 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 100 salinas valley. Am. J. Enol. Vitic., 28(1):16-26. Peacock, w. L., D. E. Rolston , F. K. Aljibury, and R. S. Rauschkolb. 1977. Evaluating drip, flood, and sprinkler irrigation of wine grapes. Am. J. Enol. Vitic., 28(4):193-195. Perry, R. L., S. D. Lyda and H. H. Bowen 1983. Root distribution of four vitis cultivars. Plant and Soil. 71,63-74. Pratt, C. 1971. Reproductive anatomy in cultivated grapes- A review. Am. J.Enol. Vitic. 22(2):92-109. Ravina, I. 1982. Soil water relations. In "CRC Handbook of irrigation technology". Vol.1 Ed. H. J. Finkel. CRC Press, Inc. Reed A. D., J. L. Meyer, F. K. Aljibury and A. W. Marsh. 1980. Irrigation costs. University of California, Leaflet 2875. Richards, 0. 1983. The grape root system. Horticultural Reviews 5: 127-168. Russell, R. S. 1977. Plant root systems. Their function and interaction with soil. McGraw Hill Book Co. 91-112 pp. Scholander, P. F. , H. T. Hammel, E. D. Bradstreet, and E. A. Hemmingsen, 1965. Sap pressure in vascular plants. Science 148:339-346. Shaulis, N.(L 1956.The sampling of small fruits for composition and nutritional studies. Proc. Am. Soc. Hort. Sci. 68:576-586. Shaulis, N. J. and G. D. Oberle. 1948. Some effects of pruning severity and training on Fredonia and Concord grapes. Proc. Amer. Soc. Hort. Sci. 51:263-270. Shaulis, N. J., E. S. Shepardson and T. 0. Jordan. 1966. The Geneva double curtain for Concord grapes. New York State Agr. Exp. Sta. Bulletin 811. Shimshi, D. 1964. The use of a field porometer for the study of water stressirlplants.1srael J.Agr.Res.14¢137-1. Shmueli, E. 1964. The use of physiological indicators for the timing of irrigation. Contrib. Natl. Univ. Inst. Agr. Rebouot, Israel, 1964. Smart, R. E. 1974. Aspects of water relations of the grapevine (Vitis viniferaL.Amer.Jour.Enol.Vitic”.25:84-91. Smart, R. E., C. R. Turkington and J. C. Evans. 1974. Grapevine response to furrow and trickle irrigation. Am. J. Enol. Vitic. 70. 71. 72. 73. 74. 75. 76. 77. 78. 79. .101 Spomer, L.IL 1975. Small soil containers as experimental tools: soil water relations. Commun. Soil Sci. and plant analysis 6(1):21-26. Stumm, Gh 1982. The drip-irrigation an alternative for the economic improvement of grape growing on steeo slopes. Die Hein- w i ssenchaft, 37. Jahrgang,(3):161-182. Uriu, K. 1964. Effect of Post- harvest moisture depletion on subsequent yield of apricots. Proc. Amer. Soc. Hort. Sci” 84:93-97. Vaadia, Y. and A.lL Kasimatis. 1961. Vineyard irrigation trials. Am. J. Enol. Vitic. 12:88-98. Verner, L., w. Kochan, D. 0. Ketchie, A. Kamal, R. w. Braun, J. N. Berry, and M. E. Johnson. 1962. Trunk growth as a guide in ochard irrigation. Idaho Agr. Exp. Sta Res. Bul. 52:1-32. Warrit, B.,.L J. Landsberg and M. R. Thorpe. 1980. Responses of apple leaf stomata to enviromental factors. Plant, Cell and Enviroment 3:13-22. Hestwood, M. N. 1978. Temperate-zone pomology. Freeman and Co. 427pp. . Hildman, w. E., R. A. Neja, and A. N. Kasimatis. 1976. Improving grape yield and quality with depth-controlled irrigation. Am. J. Enol. Vitic. 27:168-175. Winkler, A.TL 1939.The relation of number of leaves to size and quality of table grapes. Proc. Am. Soc. Hort. Sci., 29:158-160. Winkler, A..L, J. A. Cook, N. M. Kliewer and L. A. Lider. 1974, General Viticulture. University of California Press. APPENDIX A UNIFORMITY OF THE DRIP IRRIGATION SYSTEM UNIFORMITY OF THE DRIP IRRIGATION SYSTEM The uniformity of water applied in any kind of irrigation systems is very important to obtain a'uniform water distribution. Knowing the emitter flow rate variation provides a basis for estimating variation of the total drip irrigation system. This results in better management of the irrigation system. In general the emitter flow rate is affected by hydraulic, manufacture and field conditions. The most important field conditions that affect the emitter flow rate are plugging, slope changes and temperature. Bralts and Kesner (10) described a method of submain line uniformity estimation for field determinations based upon the statistical uniformity coefficient. This was used for the evaluation of the drip irrigation systems at Lawton and Fennville. The method consists of chosing 18 emitters at random along the system, and by measuring the time that each of the emitters took to fill a 100 cc sum of graduated cylinder. The intersection point of Tmax and Tmin (T the three longest and/or shortest times measured) is plotted in Figure 21 and the uniformity of the emitter flow rate is obtained. This uniformity can be also calculated by the formula: Us=100(1-Vq)=100(1-Sq_) q where: Us Statistical uniformity of the emitter flow rate Vq = Sample coefficient of variation Sq = Standard deviation of the times to fill 100 cc q = Mean of the times needed to fill a 100 cc container. Obtaining the Us envolves various factors such as lateral line frictunu elevatflnidifferences, emitter plugging and emitter 11‘ manufacturer's variation (11). Using the same formula but using the standard deviation of 18 emitters and their mean value, it is obtained the hydraulic pressure uniformity Ush. To obtain the emitter performance uniformity; Use = (Us2 + Ushz) “2 where: Use = Statistical uniformity of the emitter performance. UNIFORMITY OF THE DRIP IRRIGATION SYSTEM The data taken in field is shown in Table 15, where the pressure and the time of the emitters to fill a 100 cc container of 18 emitters is organized for its evaluation. Sum ol the Three “Cohen Times (T max) 600 500 - 7 400 - G . 0 300 -. / 200 - loo - L 1 L l g 0 50 100 150 200 250 300 95% CONFIDENCE LEMITS .EL E;E 90 :3 80 :6 7O :10 60 :13 N-IB Sum of the Three Lowest Times (T mm) Figure 21.Drip irrigation uniformity chart (Source: Vincent Bralts). iv TABLE15. FIELD DATA FOR UNIFORMITY EVALUATION OF THE DRIP IRRIGATION AT LAWTON AND FENNVILLE, MICHIGAN. EMITTER LAWTON FENNVILLE PRESSURE TIME TO DRIP PRESSURE TIME TO DRIP (PSI) A 100 cc (PSI) A 100 cc 1 32.0 75.6 29.0 83.5 2 29.0 78.9 26.0 71.0 3 32.0 84.5 25.5 73.0 4 26.0 81.2 24.5 91.0 5 26.0 81.6 25.0 87.0 6 24.0 87.2 25.5 74.0 7 23.0 81.8 25.0 82.0 8 21.0 85.4 25.5 70.5 9 28.0 151.8 25.5 85.0 10 26.0 83.2 27.0 79.5 11 28.0 89.5 25.0 79.5 12 28.0 87.0 25.0 81.5 13 26.0 78.9 25.0 81.0 14 23.0 92.6 24.0 92.0 15 27.0 85.4 25.5 ' 92.5 16 23.0 73.9 24.0 76.0 17 28.0 71.0 26.0 89.5 18 24.0 92.0 26.0 73.0 TABLE16. STATISTICAL UNIFORMITY DUE TO EMITTER FLOW RATE, HYDRAULICS, AND EMITTER PERFORMANCE. STATISTICAL UNIFORMITY LAWTON FENNVILLE Us (%) US (%) Total (Flow rate) 80.1 + 7.3 91.0 + 1.0 Hydraulics 88.5 + 4.0 95.5 + 1.0 Emitter performance 16.3 . -7.5 APPENDIX B METHODOLOGY PROBLEMS AND ALTERNATIVES METHODOLOGY PROBLEMS AND ALTERNATIVES SELECTION OF SOIL Selection of the soil depends on the time required for the development of the drought stress and the duration of that stress. It is necessary to know the characteristics of the soil, its composition, texture, desorption curve, so planning of the study can be done. In light soils (2 sand: 1perlite: 1 loam) water loss will occur faster than in a soil with less sand and/or more clay. In Experiment I of section II the SMT occasionally could be at -02 bars in the morning and by the time of sunset down to -0.5 bars. Afterwards, changes occurred quickly, and the tensiometer was ineffective. Therefore, light soils are recommended only during those situations where a fast stress is required and its duration very short, otherwise severe damage could be induced in the plants. A heavier soil is suggested in the situations that do not require soil to dry fast. In such soils SMT changes are slower and one may have better control of the stressm One of the best methods of controlling soil moisture in potted experiments has been suggested by Lenz(personal communication). It is given as follows: i) Control - watering is done to replenish 100% of the evapotranspirational losses. ii) Stress treatments - watering can be done to replenish 75 %, 50 % or 25 % of evapotranspirational losses. SOIL MOISTURE MEASUREMENTS TENSIOMETERS The use of tensiometers in potted studies is problematic. Its use ii in experiments of water relations should be restricted. The experience of these studies indicated that they can be used only as a guide of the soil moisture status. Even the best calibrated tensiometers were functional only up to -0.85 bars. The values obtained must be related to the area around the ceramic tip of the tensiometer (Fig.22). Therefore, there are two considerations: i) the small area that the ceramic tip covers "x" (Fig.22) and, ii) while the surface of the pot dries faster due to evaporative looses, the lower part "B" may still be in contact with higher soil moisture. This phenomena causes a reduced validity of the tensiometer reading, suggesting an overall soil moisture of the pot, while roots closer to the surface will be expose to drought sooner than those located a lower levels. Another consideration could be pot size, use of smaller pots should allow readings to be more accurate. However, this causes other problems of restricted root growth. Figure 22qSoil moisture distribution in relationship with the position of the tensiometer. GRAVIMETRIC METHOD The gravimetric method has been reported to be among the best iii methods due to its accuracy; It represented a sampling problem for light soil mixtures for measuring soil moisture. Sampling with a soil moisture probe was possible only in the early stages of the study. When drought treatments were applied, the sandy soils easily fell out of the probe during sampling, thus complicating the soil nmfisture estimation. LYSIMETER Weighing of whole pots was the best method to measure soil moisture status in the pots. This was mainly because of the problems with tensimeter and that the soil fell out of the soil probe while sampling. Weight was obtained during the drought period up to the time of maximum stress. Knowing the water holding capacity of each pot (WHCP) and the fresh weight of the vine at the time of stress, weight of the pot, sticks and tensiometer the percentage of soil moisture in the pot was calculated as follows: % Soil moisture at FC = Wa - Wb FC - Field capacity of the soil -———-——- Wa - Weight of the soil at PC Wb Wb - Weight of the soil when dry (Eq. 1) field capacity of the soil was calculated by saturating with water 5 pots, covering the top of the pot to avoid evaporational losses, and allowing the gravitational water to drain. Weight was taken several times until no change occurred, at this point field capacity was achieved. The pots were oven dried, weighed again, weight of the pot substracted and weight of dry soil obtained. During the experiment pots were weighed before, during, and at the end of stress period. The weight of the whole pots 24 hrs after watering was made was taken as the weight at PC. This and with equation 1 allowed to determine the dry weight of the soil in all experimental units, as follows: solving for Wbl: Wbl + Wbl = Wa FC FC Then, the percentage of soil moisture was obtained by knowing the weight of the pot at the time of stress, the dry weight of the soil of each pot Wbl, substracting the weight of the plants, sticks, and tensiometers, as follows: % soil moisture = Ws - Wbl Wbl NUMBER OF PLANTS PER TREATMENT In these studies 6 vines per treatment was not enought. For further studies it is recommended to increase the number of vines per treatment to at least 10 "selected" vines. "Selection" of vines becomes to play an important role in the development of a study of this nature. There are several ways to form an experimental block such as: Initial fresh weight before transplanting of the vine, trunk diameter, shoot lenght, rate of shoot elongation, leaf area, number of inflorescences per shoot, lenght of the flower primordia and the number of flowers per panicle. All of these variables modify the source-sink relationships of the vine. Therefore, in order to increase the accuracy of studies of water relations and different stages of developments of the berries, those variables must be considered as basis of "selection" before the initiation of the experiments.