':. 1‘2 _, {fifl‘i‘ um J is. ‘2‘:va_.‘!fi Y .‘H I L. ' #3 .‘i at THE INFLUENCE OF MICROLNVIRONMLNTAL MODIFICATIONS ON THE GROJTH AND DEVELOPMENT OF WARM SEASON VEGETABLE CROPS v. DY ROBERT LOUIS CUTHBERT AN ABSTRACT Submitted to the College of Agriculture, Michiéan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 66 19, /"—’MM ,fi} Approved W f W VX/r \\ ROBERT LOUIS CUTHBERT ABSTRACT The effect of midday Sprinkling, at very low irrigation rates (.Oh to .06"/hr.) on the growth and development of sev- eral warm season veéetable crops were evaluated during the summer of 1965. Results with different varieties of crops and mulching treatments aided in determining factors that mod- ified the effects of misting. Misting between the hours of 10:00 a.m. and 3:00 p.m. during periods of high atmospheric stress resulted in reduced early yields, but significantly increased total yields of tom- atoes, muskmelons, and cucumbers by 15, 19, and 50 percent respectively, Yield variations were associated with differ- ences in the number of fruit produced, indicating misting was most beneficial in preventing flower abscission and the with- drawal of water from develOping fruit. Varieties differed in their response to misting as did plants grown on soil with different treatments. .Misting was more effective in increasing yields of crops grown on culti- vated soil than on plastic mulch. The use of plastic mulch with or without the soil fum- igant Vorlex, increased the fruit set and yields of all three crops which can be attributed to the higher soil temperature and improved soil conditions that promoted more rapid root development and water absorption under the plastic. Experiments were conducted in the greenhouse in October and November to evaluate the influence of various factors on cotyledon expansion of several cucurbits and on the growth ROBERT LOUIS CUTHBERT ABSTRACT - 2 and development of two varieties of summer squash. Significant chances in cotyledon size from variations in soil moisture levels, different salts, and various microenv- ironmental modifications were observed. Increasing the min- imum available soil moisture level resulted in increased cot- yledon size. However, compared to the low moisture level, in plots where heat was added, misting increased the cotyledon size to the same extent as increasina the moisture level from 20 to 80 percent. Addins potassium to plants also increased their cotyledon expansion. Fresh weight, dry weibht, and relative leaf area of both varieties of summer squash were increased as the minimum level of soil moisture increased although the percent dry weight de- creased. Misting increased the fresh weibht of plants, and at the lower moisture levels increased plant growth to the same extent as increasing the soil moisture level by 20 per- cent. The two varieties of squash responded differently to various environmental treatments and different salts. THE INELUENCE OF MICROENVIRONMENTAL MODIFICATIONS ON THE GROWTH AND DEVELOPMENT OF WARM SEASON VEGETABLE CROPS BY ROBERT LOUIS CUTHBLRT A THESIS Submitted to the Colleée of Agriculture, Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1966 ACKNOWLEDGEMENTS The author wishes to express sincere appreciation to .Dr. R.L. Carolus for his valuable assistance and guidance in conducting these investigations. I wish also to thank Mr. Amos Lockwood and Mr. Bernard Bible for their assistance in caring for the field plots. Io my wife Bonnie, my sincere thanks for her support and encouragement, as well as for assistance in preparation of the manuscript. TABLE OF CONTENTS Introduction Literature Review Irrigation of Tomatoes Irrigation of Cucurbits Polyethylene Mulching Field Experimentation Materials and Methods for tomatoes, muskmelons, and cucurbits Statistical Assumption and Methods Climatic conditions Results Tomatoes Musknelons Cucumbers Discussion Irrigation Mulching Greenhouse Experimentation Haterials and Methods Results Cotyledon size Growth and Development of Summer Squash Discussion Summary and Conclusions Literature Cited \DCOQN ll 11 12 16 18 18 25 30 34 37 59 59 41 41 47 55 56 59 Table Table Table Table Table Table Table Table Table Table Table Table Table Table II III VI VII VIII XI XII XIII XIV LIST OF TABLES Temperature and rainfall during the 1965 season relative to the average. Meterolbgical conditions during the growing season of 1965 (Average of 10 day intervals). Yield of tomatoes as related to variety, irrigation, and mulching in a contin- ously misted experiment. Yield of tomatoes as related to variety, irrigation, and mulching in a sequamat- ically misted experiment. Mean square values from a statistical analysis of tomato data. Quality of tomatoes as related to variety, irrigation and mulching. Yield and quality of muskmelons as related to variety, irrigation,and mulching in a continuously misted experiment. Yield and quality of muskmelons as related to variety irrigation, and mulching in a sequamatically misted experiment. Mean square values from a statistical analysis of muskmelon data. Yield and quality of slicing cucumbers (Cv. Ashley) as related to irrigation and mulching. Mean square values from a statistical analysis of cucumber data. The relative influence of treatment on the average maximum and minimum ambient temp- eratures and vapor pressure gradient dif- ferences. The quantity of water applied to maintain available soil moisture levels under var- ious micro-environmental conditions. Internal squash leaf petiole temperature under different microenvironmental cond- itions. Page 17 17 19 2O 21 22 26 28 31 32 42 42 42 Table Table Table Table Table Table XV XVI XVII XVIII XIX XX Relative cotyledon size of muskmelons and cucumber as influenced by soil moisture levels, different salts, and environmental conditions. Cotyledon expansion as influenced by various treatments and their inter- aetiano Mean square values from a statistical analysis of pumpkin and squash coty- ledon data. Growth and development of summer squash as influenced by variety, soil moisture level, soil salt level, and environment- al conditions. Growth of squash plants as influenced by various treatments and their inter- action. Mean square values from a statistical analysis of two varieties of summer squash. 45 48 49 50 HNTRODUCTION Crops are frequently injured by excessive transpiration during periods of high temperatures and low humidity. High solar radiation received directly by the plant as well as that reflected and reradiated from the soil surface, also contribute to the high water loss by increasing plant temperature above that of the surrounding air. Even when soil moisture is ade- quate diurnal wilting of plants, caused by excessive transpir- ation during hot dry weather, may cause a serious reduction in plant growth and crop yields, if the condition persists. If an economic technique can be found to remove atmosph- eric stress during hot weather, it is possible that the avail- able soil moisture may not need to be maintained at a high level. If evaporating water can be used to create a more fa- vorable micro-climate for plants through lowering temperatures and increasing humidity, the rate and magnitude of water loss from the plant will be minimized and the necessity of maintain- ing a high moisture level in the soil would be reduced. In this study, tests were conducted to determine the ef- fect of midday sprinkling, at very low irrigation rates, on growth and development of several warm season vegetable crops. Different soil moisture levels, soil salt levels, and mulch- ing treatments were also utilized to help determine under what conditions misting showed the maximum benefits. 2. REVIEW OF LITERATURE Kramer (23) reported that plant growth and crop yields are controlled directly by plant water stress and only indir- ectly by soil water stress. He based this on observations that during periods of high temperature and low relative humid- ity even plants growing in soil near field capacity may be subjected to severe water stress. It is probable that a water deficit in the plant has some affect on every process. Stomatal opening appears to be in- fluenced by many water sensitive plant processes. With an abundant water supply stomatal opening is thought to be in- fluenced by light activating photosynthesis (50); however, when the plant is subjected to a severe internal water deficit the regulator of stomatal aperture appears to be an osmotic system(26). According to Magness et a1 (29) apple leaf stom- ata begin to close prematurely long before soil water falls to the permanent wilting percentage. Premature closing is undesirable because although it reduces the amount of trans- piration in some species, it also eliminates carbon dioxide absorption for photosynthesis (35). Several workers (1, El, A6); have shown that photosyn- thetic rates decrease rapidly or approach zero as wilting begins. Furthermore, recovery to the original rate after ir- rigation takes several days (1). Similar results have been obtained for the recovery of transpiration to the original rate after irrigation (20). Vaadia et a1 (#7) indicated that the inhibiting effect of internal water deficits upon photosyn- 3. thesis are intimately related to the water balance of the tis- sues through the effects that such deficits may have on dif- fusion rates into and out of the leaves and through the pos- sible effects of changes in photoplasm hydration under these conditions. The accelerated conversion of starch to sugars during water deficits has been observed by many workers (11,53,60). It has been shown that increased amylolytic activity is invol- ved in the disappearance of starch. Generally the rapid re- duction is not compensated for by corresponding increases in sugars (60), suggesting that respiration rates might have increased because of the water deficits. Schneider, et a1 (A1) and Upchurch (R6) found this to be the case, and Schneider and Childers (Ml) observed that flaccid leaves respired 62 percent more rapidly than those of turgid plants. One of the first effects of water deficit is a decrease in or cessation of elongation of stems and elongation of leaves and fruits, because these processes are dependent on turgid cells. Loomis (28) and Loomis and Thut (RS) concluded that the supply of water to the growing point is the most important factor affecting the rate of growth of corn. Their work in- dicated that water supply is limited and growth reduced by (1) bright light, (2) deficient soil moisture, and (3) low humid- ity, important in the order named. Nightingale and Mitchell (33) found that tomatoes grown in moist soil at a constant temperature were much smaller and more fibrous if kept at a h. relative humidity of 35 percent than when grown at a relative humidity of 70 percent. This demonstrates the importance of atmOspheric conditions on the internal water balance of plants, even when moisture is adequate. A decrease in leaf size from lack of turgidity is esp- ecially serious because it decreases the photosynthetic sur- face. According to Watson (56), yield of crops is more closely related to leaf area than to variations in photosynthetic efficiency per unit of leaf area. Hence, the first require- ment for high productivity is a large leaf area. Wadleigh and Gauch (Sh) found that enlargement of cotton leaves ceased by the time the soil moisture stress reached 15 atmospheres and Slayter (hZ) also reported a decrease in stem elongation and a slowing of the rate of increase in dry matter with increas- ing soil moisture stress. The effects of water deficit and dehydration are equally important (31, 36). In general, water deficits hasten matur- ation of cells and tissues, increase the thickness of cell walls, and decreases succulance. This not only decreases the size of plants and their yields, but may also affect quality. Gates (15) found that even moderate wilting affects plant growth and claimed that it is erroneous to suppose that plant growth is only affected near the permanent wilting point. He found, relative to tomato plant weight, that moderate wilt- ing caused a reduction in leaf weight increase relative to stem weight increase. He further showed that, after recovery from wilting, growth rates of moderately to slightly wilted plants Se soon increased above the growth rate of the controls, although total growth was reduced. Perhaps this was because growth was checked more than photosynthesis by incipient wilting. William and Shapter (38) found that the effects of moderate wilting on the distribution of dry matter in barley and rye varied with the stage of growth at which the plants were allowed to wilt. The plant parts growing most actively at the time a water de- ficit occurs are most affected. They also found that in ad- dition to a reduction in growth, the rate of photosynthesis per unit of leaf area was reduced, uptake of phosphorus was reduced and nitrOgen content of leaves was decreased, whereas that of stems increased. Plant-water relations consist of a group of inter-related and interdependent processes. Thus, the internal water balance or degree of turgidity of a plant depends on the relative rate of water absorption to water loss, and is affected by a com- plex of atmospheric, soil, and plant factors that modify the rates of absorption and transpiration (22). The transpiration rate of a well watered plant is con- trolled by leaf area, internal leaf structure, thickness of cutin, and extent of stomatal opening, and by such environ- mental factors as solar radiation, humidity, temperature, and wind. The rate of water absorption depends on the rate of water loss, the extent and efficiency of root systems, soil aeration and temperature, as well as by the soil moist- ure tension (M7. 23). 6. The rate of absorption even in moist soils during periods of atmospheric stress tends to lag behind the rate of trans- piration, primarily because of resistance to the movements of water into roots (21). On hot sunny days the rate of trans- piration exceeds absorption causing severe midday water de- ficits, even in plants growing in moist soil. Such deficits usually are eliminated by absorption during the night, but as soil moisture is depleted, absorption becomes more difficult and midday deficits are more persistant, until permanent wilt- ing finally occurs. Thus, plant water deficits can be caused by excessive loss of water, by reduced water absorption, or a combination of both. Deficits caused by excessive transpiration are usually shorter and less severe than those caused by inadequate absor- ption, but periods of hot, dry, windy weather can cause severe damage, even to plants in moist soil. Conversely, during fog- gy, showery, humid weather, even plants in dry soil may be subjected to relatively small water deficits. Thus, the effects of soil moisture supply may be greatly modified by at- mospheric conditions (27). Stoker et al (A3) found that midday sprinkling in hot weather benefited crops by keeping their leaves turgid and stomates open, and in preventing a midday decrease in photo- synthesis. The cooling effects of sprinkling might also re- duce respiration, thereby increasing net photosynthesis. Bloodworth et al (2) concluded that showers inadequate to increase soil moisture materially reduced internal water 7. (deficits. Irrigation by sprinkling during periods of high evapo-transpiration were of considerable benefit if wetting the leaves increased photosynthesis and decreased respiration. Dew and atmospheric moisture may also increase growth because it produces direct rehydration of tissues (uh). Tomatoes (Lycopersicon esculentum) Vittum et a1 (S2) reported that tomatoes are extremely sensitive to small changes in their local or microenvironment, and are greatly affected by many different factors. During the five year period 1952-1956, irrigating whenever available water in the upper 2h inches of soil dropped below 50 percent of field capacity, reduced early yields of marketable tomatoes, but significantly increased late and total yields. He also found that more green or immature fruit remained in the field after the last harvest on irrigated plots. ”Cordner (9) found that in Oklahoma, where temperatures are frequently above optimum for tomatoes, irrigation resulted in increased yields. He indicated that irrigation tends to reduce the percentage of blossoms set and that frequent light irrigations.are expecially detrimental to fruit set. Campbell (3) obtained increased tomato yields by irrigation in Miss- issippi. Schleuser et a1, (MO) working in Michigan, found that irrigation was beneficial when rainfall during the grow- ing season was 9 inches or less. They found the application of h inches was more beneficial than the application of either 11 or 16 inches as the increased rates resulted in low- er fruit set. Heavy irrigation in Alabama increased yields 8. in dry years, but had little effect in wet years (55). Lambeth (25) in Missouri obtained progressively larger yields as the soil moisture was maintained above 25, 50, and 75 percent of field capacity.” Soil moisture on the unirrigated plots, which received a total of 3.96 inches of rain, was reduced to near wilting point to a depth of 36 inches. A total of 12.5 inches of irrigation water was required to maintain the soil moisture above 75 percent of field capacity. Vittum (51) found that in years of low rainfall in New York, irrigation markedly in- creased total yield but delayed maturity and reduced the per- centage of number one fruit. Molenaac and Vincint (37) found that irrigation increased the severity of cracking. Janes and Drinkwater (19) reported cracking was associated with high soil moisture conditions, however, later they reported that climatic conditions which affect the environment of the plant seem to be the most im- portant factors which caused cracking. .Cucurbits (Cucumis mgl2,ggg Cucumis sativis) Whitaker and Davis (57) reported that cucurbit plants require considerable moisture when making their most vigorous growth and up to the time the fruits mature, if maximum yields are to be realized. Experimental data on irrigation of cucurbit crops is lim- ited. McClatshie (30), working in Arizona, applied 2.6 feet of water in twelve irrigations to 9 crop of cantaloupes, and 3.2 feet in thirteen irrigations to a crop of watermelons. 9. He suggested similar quantities for other cucurbits. Headley and Fulkerson (17) in western Nevada, did not record the amount of water applied, but expressed the opinion that excessive water, during the ripening period, resulted in a reduction of sugars. Fleming (l3) concluded from data collected over a three year period with cantaloupes in British Columbia, that irrig- ation water, applied weekly at the rate of one-half inch per irrigation, gave the greatest total yield with the largest number of quality melons. He found no difference in soluble solids content associated with rates of water application. His data indicated that regular, small weekly irrigations, gave slightly larger yields than the same total amount of water applied in larger quantities with longer intervals between irrigation. Doneen and MacGillivray (10) have recommended rates of water application for most of the cultivated cucurbits. With the soils and climate found in the arid regions of the western United States, these investigators showed that the frequency of irrigation and the amount of water necessary to produce successful crops, depend on the depth and thoroughness of root development, on the amount of available water the soil can hold, and on the rate of water loss from the soil. Polyethylene Mulching Rowe-Dutton (39) stated that the purpose of any cultural operation is to increase yields, earliness, or quality of the crops by modifying environmental conditions. Many workers have claimed these benefits from polyethylene mulching. 10. Carolus and Downes (S) and Woodbury (59) found that mulch- ing with black polyethylene resulted in greater total yields and a greater percentage of the yield harvested early. Max- imum response to mulching was obtained from muskmelons and squash while tomatoes, peppers, and eggplant yields were in- creased to a lesser extent. Heslip (18) reported that black plastic mulch increased the yields of cucumbers 28 percent, tomatoes 31 percent, squash 58 percent, and muskmelons 81 per- cent above those on cultivated soil. Similar results were ob- tained by Riekels (37) on tomatoes and muskmelons. Collins (8) reported only a 10 percent increase in muskmelon yields and a 2n percent increase in tomato yields from mulching. In general, the cucurbits tended to respond more to mulching than tomatoes. Clarkson (7) states that yield increases are not the re- sult of the plastic material alone, but are due to the influ- ence of the plastic on the Soil, microclimate, and diseases. Carolus (h) and Heslip (18) reported that increased yields from mulching are the result of conserving soil moisture, in- creasing soil temperature, protecting the surface roots, and increasing aeration of the soil surface. These factors resulted in increased nutrient availability and stimulated nitrification (1h). Weed control and reduced cultivation are other benefits of mulching that aid in preserving soil moisture and fertility (l2). Ries (38) reported that herbicides and shallow cultivation used for weed control in pickling cucumbers resulted in yields equal to those obtained with black plastic mulching. He stated that black plastic had no additional advantages except to keep the soil undisturbed. 11. FIELD EXPERIHENTATION Materials and Kethods Irrigation experiments were conducted with tomatoes, muskmelons and slicing cucumbers in 1965 on a sandy loam soil on the horticultural farm at East Lansing. Before transplant- ing 600-800 pounds of 5-10-10 fertilizer was broadcast and disced into the area. A starter solution of four pounds of 10-52-17 per 50 gallons of water was used at the rate of one- half pint per plant or hill at the time of transplanting. A low rate of irrigation application (termed mist irrig- ation in this report) was compared to regular irrigation pra- ctices on crop yield and quality. Two types of irrigation, continuous and sequamatic, used to apply the mist were com- pared with regular irrigation in separate fields. The contin- uous system utilized rotary sprinklers fitted with 1/16 inch nozzle tips. Sprinklers in the sequamatic system had 5/32 inch nozzle tips regulated by valves with each of the three sprink- lers on a line operating five minutes out of twenty in a sequ- encing cycle. Both systems were spaced and adjusted to apply .03 to .06 inches of water per hour between the hours of 9:00 to 10:00 a.m. and 3:00 to h:00 p.m. and were operated when the air temperature was above 75°F with relatively clear skies and a relative humidity of less than 70 percent. An attempt was made to apply about as much water as might be lost by evapo- transpiration during periods when water loss exceeded .Oh to .06 of an inch per hour. 12. The available soil moisture in the regular irrigation plots was maintained by adding one inch of water per week when rainfall the preceding week failed to equal one inch, and in misted plots by adding one inch of water when rainfall during a three-week period failed to equal one inch. The clear and black polyethylene plastics used in these experiments, 3% feet wide and 1% mils thick, were laid approx- imately three weeks before planting with a tractor mounted 'attachment. The soil fumigant, Vorlex, was injected 8 inches beneath the soil surface immediately prior to laying the phastic at a rate of 15 gallons per acre. After one week holes were cut in the plastic at 5 foot intervals, with a h inch post hole digger to allow for water infiltration and for the gases of the fumigant to escape. A herbicide, Alanap, was applied to the soil between the strips of plastic to control weeds during the early part of the season. Statistical Assumptions and Methods Irrigation experiments requiring large plot areas par- ticularly when the environmental aspect is being considered, do not lend themselves to a large number of small replicated plots or conventional treatment. Consequently, the problem of making comparisons of effects of such treatments arises, particularly for statistical evaluation. Under such circum- stances it is lOgical to superimpose controlled variables on small plots in the fields treated differently and then to compare the consistency of the response in the two or more plots to arrive at a generalized response to the main plot 15. treatments. The assumption thus is that the treatments imposed on the sub-plots essentially overwhelmed the inherent difference or variation within the fields not related to the main field treatment. An example of consistancy of effect is indicated 'in the raw data below for the total fruit number for tomatoes on the continuously misted plots. Re . 1 MIST m REGULAR Soil B B+V Soil B B+V Pa 568 756 814 4 ms 752 729 1156 546 605 696 G 466 1056 864 592 519 628 Re . 2 ‘ ' . g . 425 815 752 ' 360 456 656 NH 826 1008 861 771 1064 845 G 657 848 859 416 624 578 The analysis of these data shown below indicate a high level of statistical significance; and should suffice to indicate the validity of the assumption that sub—plots may be used to assay irrigation effects. DF SS MS F TOtal 55 1,598,351 . Mist x Convent. _l _§10,4§§ 510 455 120.04*** Error 54 87,916 2,586 Tomatoes (Lycopersicon exculentum) The plants were started in the greenhouse and transplan— ted to a coldframe in 5 inch peat pots prior to field setting. A plot design was used in which mist versus regular ir- rigation practices were the main plots and mulching treat- ments and varieties were the sub-plots- Four plants of each variety spaced 2% feet apart within 1h. the row were set in 20 foot rows, spaced 6% feet apart. The treatments were replicated h times with two plots harvested and totaled together for each replicate used in the analysis of the data. The plants were transplanted into the field May 31, and the fruit harvested from August 9 to September 20, with early yield for Fireball calculated to Aguust 30, and for Morton Hybrid and Glamour to September 7. Fruit were harvested when well colored, from the eight plant plots, at approximately weekly intervals, and sorted into marketable and unmarketable on the basis of canning grades. At the end of the season, all immature fruit over one inch in diameter were counted and weighed. Muskmelons qucumis meloz Three week old muskmelon plants in 3 inch peat pots were set in the field June 5. A plot design was used, consisting of mist versus regular irrigation as main plots and mulching treatments and varieties as sub-plots. Both the mist and regular irrigation treatments contained sub-plot compar- isons consisting of cultivated soil, black plastic with vor- lex and clear plastic with vorlex, each planted with two var- ieties, Delicious and Howell Spartan. In the field with se- quamatic irrigation black plastic mulch was used for the con- trol instead of cultivated soil, and the variety Supermarket Hybrid was used instead of the Howell Spartan varieties. A plot consisted of 6 hills, of 2 plants each, spaced 5 feet apart in rows spaced 6% feet apart with each treatment 15. replicated twice. Vine ripened fruit were harvested from August 18 till September 20 with early yield calculated to August 31. The melons were sorted into marketable and unmarketable grades on the basis of size, quality, and defects. At the end of the season all immature fruit were counted and weighed. Cucumbers (Cucumis sativus) Ten day old Ashley slicing cucumber plants in 3 inch peat pots were set in the field June 1h, 1965. A plot design was used consisting of mist versus regular irrigation as main plots and mulching treatments as sub—plots. Both the mist and regular irrigation treatments obtained sub-plot comparisons consisting of cultivated soil, black plastic with vorlex and clear plastic with vorlex. The field using sequa- matic irrigation was similar except that black plastic was substituted for the cultivated soil treatment. A plot consisted of 6 hills, of 3 plants each, spaced 5 feet apart in rows, Spaced 6% feet apart, with each treatment replicated twice. The fruits were harvested from July 29 till September 8 as they reached marketable size on the vine with early yield calculated to August 9. The fruit were sorted into marketable and unmarketable on the basis of U.S. grade standards, with those that met U.S. #1 grade standards classed as marketable. At the end of the season all immature fruit were counted and weighed. 16. Climatic Conditions Temperature and rainfall during the 1965 season relative to the average are indicated in Table I. Atmospheric stress conditions during 10 day periods in 1965 are shown by the data in Table II, which indicate that periods of high evapo- transpiration are associated with high temperature, a large vapor pressure gradient, and increased pan evaporation. Table I 17. Temperature and rainfall during the 1965 season relative to the average.* Rainfall Temperature NORTH ‘1965’ Average 1965* Average May I.3h* 3.73 463.6*% 57.1 June 2.8h 3.3h 66.h 67.h Jury .79 2.58 69.8 71.7 August 3.73 3.05 63.0 70.2 September b.78 3.60 63.h 62.0 Total 1?.ufi $0.30 * - Recorded at Horticulture Farm ** — 0F Table II Keterological conditions during the growing season of 1965. (Averages of 19 day periods) Temperature Vapor Rax. Kin. Mind Pan Pressure Daily Daily' Velocity' Evap. Deficit* DATE 0F 0F lfiles/Day In./Day mm. Hg. 671 - 6/10’_’ 77.2 56.1 76.0 .19 10.86 6/1—1 —6/20 76.2 19.1 79.6 .29 15.09 6/21 -6/30 83.1 58.1 80.3 .29 16.03 7/1 - 7/10 81.1 55.8 70.8 .25 15.16 7/11 -7/20 82.5 56.h 70.9 .31 18.22 7/21 -7/30 83.7 57.0 71.3 .33 17.96 7/31 -8/9 80.3 60.0 81.2 .20 12.h5 8/10 -8/19 83.8 62.0 67.9 .28 16.96 8/20 -8/29 7h.1 51.6 59.2 .19 12.79 8/30 —9/8 72.h 51.2 75.8 .13 6.87 9/9 — 9/18 77.7 511.6 711.8 .12 10.38 * — Calculated from relative humidity data taken between h:30 and 5:00- p .m. 18. Results Tomatoes The effects of soil treatments and variety on the yield and quality of tomatoes with continuous and sequamatic mist irrigation are shown in Tables III and IV, with the signi- . ficance of the data indicated in Table V. Irrigation: The "continuous mist" application had no effect on early marketable yield, but increased total marketable yield by 3.0 tons per acre (Table III). Misting increased early yield of the Fireball variety by 19 percent, however, the early yield of Morton Hybrid and Glamour were reduced 16 and 23 percent respectively. These differences might be at- tributed to the early maturing and determinate type growth in Fireball which may tolerate a lower temperature for optimum growth or to an atmospheric stress condition that influenced blossom drop during June in the non-misted plots. By misting, Fireball and Morton Hybrid were increased in total yield by 38 and 21 percent respectively, but the yield of Glamour was reduced. The yield increases were related more to an increase in number rather than an increase in size as the average increase in number for misting was 31 percent, and the increase in size was only 6 percent (Tables III and IV). This would indicate that the misting treatment was more beneficial in preventing flower and fruit abscission due to the withdrawal of water from these tissues during atmospheric stress periods. As atmospheric stress conditions were mod- erate in 1965, presumably they are more critical in influe- Table TTT 1.1.4. 19. Yield of tomatoes as related to variety, irrigation, and.mulching in a continuously misted.experiment. Regular Irrigation Mist Irrigation Gen. FBa MHb Gc Avg. FB NH G Avg. Avg. EARLY KKT. YIELD in Tons/Ad Cultivated Soil 6.8 1218 9.8 9.7 9.0 9.3 8.0 ’8.8 9.2 Black Plastic 8.8 12.8 9.6 10.1 11.2 10.8 5.5 9.2 9.6 B. P. & Vorlex 10.2 15.7 9.0 11.6 10.2 13.8 8.3 10.8 11.2 Average 8.5 13.5 9.57710.5 710.1 11.3 7.3 9.6 TOTAL'MKT. YIELD in Tons/A Cultivated Soil 10.8 18.2 17.3 15.8’ 713.9 21.h 718.0 17.7 16.5 Black Plastic 13.7 21.6 21.1 18.8 22.9 30.8 15.2 22.9 20.8 s. P. a Vorlex 18.0 29.0 22.9 3.3 22.5 30.7 26.8 26.5 28.9 Average 1h.2 22.9 20.h 19.2 19.7 27.6 ‘19.9 22.2 ‘_ Tmmtno.ma.anl Per 8 Plants Cultivated Soil 296 300 238‘ 278 386 3065' 288 313 296“ Black Plastic h20 380 28h 361 60h hl6 291 h37 399 B. P. a Vorlex 531 396 305 811 583 568 355 502 857 Average 516 359 276 350 52h h30 295 L17 TOTAL NUMBER 8281 per 8 Plants cultivated Soil 808 658 *808 889 *895' 779 561 612 550 Black Plastic 508 838 571 636 775 868 952 865 751 B. P. & Vorlex 688 769 603 672 773 998 861 877 775 Average 517 75h 526 699 681 802 791 785 a - Fireball Cv. b - Morton Hybrid Cv. c - Glamour Cv. d - Early marketable yield of Fireball to August 30, and Morton Hybrid and Glamour to September 7. 2C1. Table IV Yield of tomatoes as related to variety, irrigation, and mulching in a sequamatically misted experiment. Regular Irrigation Fist Irrigation Gen. FEa KHb 00 Avg. FB PH G Avg. Avg. EARLY EXT. YIELD in Tons/Ad cultivated Soil 3.6» 12.0 5.81 7.1 6.8 10.67 9.0 78.8 78:0 Black Plastic 10.1 18.6 13.3 18.0 9.9 13.5 10.1 11.2 12.6 B.P. 3: Vorlex 9.14 12.7 700 907 906 13.6 60,4 909 908 Average 7.77718Jh 8.7 10.3 8.8 12.6 8.5» 10.0 TOTAL MKT. YELD in Tons/A cultivated Soil 5.8 16.0 12.2 11.3 78:8 17.1 19.0 15.0 13.2 Black Plastic 15.3 26.6 28.7 22.2 18.6 20.3 20.8 18.0 20.8 B.P. a Vorlex 20.0 27.8 22.7 23.8 20.7 28.8 19.8 22.8 23.1 Average 13.7 23.3 19.9 19.0 11.7 21.9 19.7 18:8 fi_ TOTAL TIC. MIST. FRUIT per 8 plants Cultivated Soil 170 288 193 208 231 279 250 253 229 Black Plastic 370 825 319 371 369 299 272 313 382 B.P. a Vorlex 571 882 3~ 878 558 888 3 3 395 825 Average 370 335 293 350 385’ 358 278 32 TOTAL IITT‘IBER FRUIT per 8 plants Cultivated Soil 282 860 339 387 32. 616 886 863 805 Black Plastic 878 687 850 537 582 626 858 581 539 B.P. & Vorlex 752 1001 728 829 737 1956 750 888 837 Average E89 716 508 571 536 763 550 616 a - Cv. Fireball; to September 7. b — Cv. Morton Hybrid; 0 - Cv. Glamour d’- Early yield.of Fireball to August 30, and Morton Hybrid and Glamour lean Square Va ues from a 21. Statistical analysis of tomato data. Early Total Total Total Mkt. Kkt. N0. Hkt. Number DF Yield Yield Fruit Fruit A. COVWrIT?" FISTIIG TIA-3T 0.1. Total 35 Replication 1 8.2 17.6 2838 12732 Variety 2 51 .1996 207 .139? 101296-85 15 3 379:9:- Soil Treatment 2 10.8 210.7“8 79852%* 1828955Y Irrigation 1 1.5 129.25% 80939** 3108°55v Var. x Soil Treat. h 7.8 8.6 5976 70L? Var. x Irrig. 2 18.2% 17.0 5588 15292 Soil Treat. x Irrig. 2 3.0 9.8 2896 9213 Error 21 6.8 18.6 2379 713338 B. SETUAE“TIC PISTING FACT Cpl Tote 35 Replication 1 8.7 13.8 820 1300 Variety 2 103 . 8H- 221 .199:- 30808-2 1987 5 9:4. Soil Treatment 2 68.9rw 315.9** W81 0%: 538178** Irrigation 1 1.0 1038 18315-393 Var. x Soil Treat. h 7.3 20.5 17710** 11559* V2.r. x Irrig. 2 6.6 8.3 1638 7 Soil Trea . x Irrig. 2 15.7** 27.1% 8-65% 10633+ Error 21 8.6 10.8 3379 8730 Y - Significant at .05 level 5% - Significant at .01 level Table VI 22. Quality of tomatoes as related to variety, irrigation, and mulching. Avg. weight .4 a of Total Number of hkt. Fruit Blossom Blotchy Pounds End Rot Fruit A.Cm@VWGB ViiISTY Fireball .21 .18 5.05 Iorton Hybrid .39 .32 1.05 Glamour .83 3.03 2.80 SOIL TREATHEYT 1tivated Soil .38 1.21 2.50 Black Plastic .38 .73 2.65 B.P. & Vorlex .38 1.12 3.75 IRRIGATION Nist .35 .85 3.70 Regular .33 1.53 2.15 STQUAKATIC VXRILTY Fireoafl .23 .8 6.8 Norton Hybrid .37 2.5 3.6 Glamour 0,—1.3 .9 bob, SOIL TREATMENT Cultivated 3011 .35 .3 3.2 Black Plastic .37 .9 5.5 Bop 94'. Vorlex 032 2.1 So? IRRI GATT ON Regular .33 1.8 3.8 23 ncing fruit set than fruit sizing, as an available soil moist- ure level, maintained at approximately 50 percent of field capacity, is more adequate in maintaining fruit enlargement than in preventing abscission. In a nearby area, "sequamatic misting" had no significant effect on either early or total marketable yields, number of marketable fruit, or average fruit weight (Tables IV and VI). However, the total number of fruit in this experiment was significantly larger, indicating that misting was of benefit late in the season on a soil that was heavier than the one on which the continuously misted crop was grown. The lower yields that occured with the sequamatic misting could be attributed to either a difference of soil characteristics between the experimental and control plots, the delay in getting the mist system in Operation and/or the inability of the system to fun- ction at water pressures below 8Spsi. thereby giving incom- plete coverace during times when plant water stress was high- est. 7 Although sequamatic misting was not beneficial to the yield of plants grown on plastic, on cultivated soil it incr- eased both early and total yields, particularly in the Fire- ball and Glamour varieties because of an improved fruit set (Table IV). The lower yield increases from misting of toma- toes grown on black plastic as compared to those from cultiv- ated soil could be attributed to a difference in water stress conditions between the two soil treatments. On this soil which was a little heavier than the one on which the continu- 21.. ously misted crop was grown, the plants growing on plastic were able to maintain their water balance without misting due to higher soil timperatures, greater root development, and the resultant increased rate of water absorption. However, plants growing on cultivated soil because of reduced root develop- ment and soil temperatures were unable to maintain their water balance during periods of high atmospheric stress and the mist- ing was highly beneficial. Misting had no effect on fumigated plots. In both fields misting reduced the percentage of fruits with blossom end rot and increased the percentage of blotchy fruit (Table VI). Soil Treatments: When compared to cultivated soil, early and total yields were significantly increased with black plastic mulch in the field with sequamatic misting (Table IV), while in the field with continuous misting only total yields were increased (Table III). Vorlex applied under the plastic re- sulted in a significant increase in total yields above that produced on plastic without fumigation. The yield increases with Vorlex could be attributed to the fumigant eliminating soil borne diseases and insects that effect root deve10pment. On the sequamatically misted field the Fireball variety res- ponded most to plastic treatments with a significant increase in the number of marketable fruit above that of either Morton Hybrid or Glamour (TableIV). As the size of the tomatoes was approximately the same for all soil treatments, yield in- creases were the result of a greater number rather than a lar- ger fruit. 25. No significant differences were recorded for the percent- age of blossom end rot and blotchy fruit, however, there was a tendency for increased amounts of both disorders when plots were covered with plastic and when vorlex was used with plastic. The incidence of blossom end rot was highest in Morton Hybrid, followed by Glamour and Fireball. Fireball had the highest incidence of blotchy fruit followed by Glamour and Morton Hybrid. Muskmelons The effects of soil treatment and variety on the yield and quality of muskmelons with continuous and sequamatic mist as compared with normal irrigation are shown in Tables VII and VIII with the significance of the data indicated in Table IX. Irrigation: "Continuous mist" irrigation decreased early marketable yield by 73, but increased total marketable yield by 78 bushels per acre (Table VII). The two varieties resp- onded differently to misting with the early yields of the Howell decreased 77 percent and Delicious only 8 percent. The reduced early yields of the Howell could be attributed to the mist delaying the already late maturing tendencies of the var- iety by increasing early plant growth. The higher total yflalds with mist were associated with significant increases in fruit number as there were no significant differences in fruit weight with any of the treatments. On fumigated plots Continuous misting increased total marketable yields 55 percent with black plastic and 75 percent with clear plastic above that from con- ventional irrigation. Table VII 26» Yield and quality of muskmelons as related to variety, irrigation, and mulchinfi in a continuously misted experiment. Regular Irrigation Hist Irrigation General Del.a H.S.b Avg. Del. H.S. Avg. Avg. EARLY PKT. YIELD in EU. . /AC Cultivated Soil 133 93’ KO 1E6 AhO 93 117 3. Plastic ?: Vorlex 293 2LL1 270 3b 13 13L 227 C. Plastic 8: Vorlex 333 138 -61 23 66 177 219 Average 271 175 22h 261 L1 151 TOTAL NKT. IBLD in Bu./ A Cultivated Soil 231 233’ 2L3 297 “L23 360 30 B. Plastic 2 VCrlex 32L 531 L27 L33 578 505 L66 C. ginstic E Vorlex 392 62h 503 L’6 6L8 SL7 527 Average 315 B_E70 393 392 SL9 4L71 1 TAL ND. IKT. FRUIT per 6 Hills Cultivated Soil 2 28 2L 26' 7L6 35 30 B. Plastic & Vorlex 32 SO hl 16D 50 L5 C. ilas tic x Vorlex 36 57 h6 L6 61 53 A9 Average 30 LS_ 37 38 36' L6 TOT AL. 'Ul :333. FRUIT per 6 Hills cultivatt Soil 287 39 33 BED ’66 53 LB B. Plastic 1 Vorlex SS 2 6 6O 82 71 67 C. Plastic “ Vorlex S2 72_¥ 62 71 81 76 69 Average fig» 61 53 57 75‘ 67 AVG. WEIGHT NET. FRUIT in pounds Cultivated Soil 2.h 2.0 2.2 2.5 2.0 2.3 2.3 B. Plastic & Vorlex 2.2 2.L 2.3 2.5 2.1 2.3 2.3 0. Elastic & VCrlex 2.L 2.L 2.L 2.2 2.3 2.3 2.h Average 7.2.? 2.3 2.3 2.2:. 2.1 2.? a - CV. Delicious; c - Early yield through August 31 b— CV. Howell Spartan Yield and. quality of musiciaelons and mulching in a sequamatically misted experiment. Table V TTT _.‘...L 273 as related to vs riety, irrigation, Res mul r erigation Fist Irrigation General Del . a S‘Lib Avg . Del . 3P1 Av: . Avg. EAILY I-IKT. YIELD in BIL/5L6 Black . .stiC '53 179 317 260 79 1'70 2‘: B.P. 1 Vorlex 355 112 23L 21L 30 122 178 C. P. 51: Vorlex 5:"; 175 3332 BT‘E 113‘ 138 2170 :‘.ver 2. ae H39 135 2 93 2 3 4 32 172.3 T611172. III in Bu./A H8011 i‘19-51‘2310 501 559 530 357 L37 3’) 104 3.? . & Vorlex LL5 579 512 357 366 362 L37 Col“. ’3: VOI‘L’BX 6011 761 683 LG 581 he; SJ9 Ave ra. 3e 5.7.7.7673? . .577 SW 37 h hél Til-3 TCTAL 230. 1311‘ . REIT per 6 Hills Black Plastic LO Ll L1 30 39 35 33 B.P. 8t Vorlex bl 1L5 1L3 36 37 37 140 C.P. a: Vorlex 5‘4 55 55 Ll 5b 58 52 Ave r133 HS M27 L6 3 6 113 10 TOTEL “HATER FRUIT per 6 _ Black Plastic B737 1;?) 52 Mi 1; if; 119 B.P. a Vorlex 59 53 S9 62 53 to 60 C.P. x; Vorlex 72 67 7o 68 75 72 71 Ave r 2. 3e 6 2 375 __:o O 53 ‘79 37 AVG. E'J'ZIGEH‘ NET. FifiJIT in pounds Black Plastic 7. 9 3.1 3.0 2.7 2.6 2.7 2.9 B.P. a Vorlex 2.5 2.8 2.7 2.2 2.2 2.2 2.5 C.P. a Vorlex 2. 5 3.2 2.9 2.3 2.L 2.L 2.7 Aver-age 2,5 3.0— 2.9 2._1L_ 2.11 2.11 2&3. Table IX Kean square values from a statistical analysis of muskmelon data. Early Total Total Total 11kt . I‘ik‘t . No . Mkt . Numbe r DF Yield Yield Fruit Fruit A . CONT 331,7 CU S FICTQx Total 23 Replication 1 323 1617 h0 h3 Variety 1 SSth-tez— 1111161 5x4.- 168 3% 19083!- SOil Treatment 2 11120** lth88** 865** 1699** Irrigation l llhhl** 35805** h95** llh8%* Var. x 3011 Treat. 2 2083 th11* S9 13 Var. x Irrig. 1 8288** 36 82 17 Soil Treat. x Irrig. 2 358 3363 8 72 Error 13' 1533 1 3u33 28 55 B. S QUAEATIC FACTOR Total 23 Replication l 2&81%* 16150** 37 226%* Variety 1 l19286** 62h2h** lhO** 13 Soil Treatment 4 3975** 5252h** h2l%* luul** Irri gation 1 52267¥<++ 11.8 acts-H'- 2 5 3M 10 Var. x Soil Treat. z 3&8 5909 10 10 Var. x Irrig. l 3883** 1291 D3 ha Soil Treat. X Irrig. _E’ th6 1599 __2 .Jfli Error 1 705 3393 3 b9 * - bignil1cant at .Ub level ** - bignilicant at .01 level 29. "Sequamatic misting" decreased early and total market- able yields, and the number of marketable fruit (Table VIII). The lower yields with sequamatic misting might be attributed to either the poorer inherent soil structure in the misted plots reducing or hampering root growth, or operational and pressure difficulties with this system which resulted in in- complete coverage during times when plant water stress was highest. sequamatic misting was much more detrimental to the early yield than to total yield of the Supermarket Hybrid variety, but was more detrimental to the total yield than to the early yield of Delicious. This difference in varietal response to early misting could be attributed to a delay in maturity associated with an increase in early vegetative grow- th in the late maturing Supermarket Hybrid. Soil Treatments: In the continuously misted field, the use of plastic with vorlex increased early yields by approximately 100 percent over those obtained from cultivated soil (Table VII). In total yield the use of the fumigant with black plastic re- sulted in an increase of 165 and with clear plastic an in- crease of 226 bushels per acre over those obtained from plants on cultivated soil. The increased yields from clear over black plastic is probably due to a higher soil temperature. The fumigant was apparently of little value in the sequamatically misted field as indicated in the data from Table VIII, however the use of clear plastic with the fumigant resulted in higher total yields than black plastic and was particularly favorable to the yield of Supermarket Hybrid. The lower yields that 30. occured with the use of vorlex under black plastic (Table VIII) could be due to a lack of adequate aeration before the plants were set, resulting in temporary injury. I Yield variation was associated with the number of fruit, rather than with their size. Variety: The Delicious variety consistently had the highest early marketable yields, but was significantly lower than either Howell or Supermarket Hybrid in total yield. The lower total yields of Delicious were due, at least in part, to powd- ery mildew and fusarium wilt infecting the plants during the mid to late season period. However, there was no observable differences in the amount of disease between the misted and non-misted plants. Cucumbers The effect of soil treatments on the yield and quality of slicing cucumbers from continuous and sequamatic misting are shown by the data in Table X A and B, with the significance of the data indicated in Table XI. Irrigation: Continuous misting had no effect on early yield, but increased total marketable yield by 50 percent (Table X A), while sequamatic misting reduced early yield by 28 percent, but increased total yield by 16 percent (Table X B). In the sequamatically misted plots, misting plants growing on black plastic with vorlex reduced early yield, but increased total yields above those obtained from plants growing on clear plastic with vorlex. The decreased early yield from the black plastic plus vorlex treatment could be attributed to inadequate Table X Yield and quality of slicing cucumbers (CV. Ashley) as irrigation and mulching. related to Regular Irrigation Fist Irrigation A. 0011133083 8011 5 Va 0 vb Avg. Soil 8 v c v Avg. Early Hkt. Yiold (au./175 23 209 221 151 ‘D6’ 206 188 ‘ID7 Total th. Yield (Bu./A) 207 h77 508 397 387 77h 627 596 Total No. ikt. Fruit (No.) 52 129 188 110 101 202 16h 156 Total Number Fruit (No.) 85 193 225 168 183 307 208 233 Avg. Fruit weight (lbs.) .86 .79 .75 .80 .71 .81 .82 .78 B. SEQUAMATIC 32d, B v c v Avg. RP B v c v Avg Early Kkt. Yield (Bu./A) 11 191 191 165‘ 7h 119 161 118 Total th. Yield (Bu./A) 533 801 79h 709 66h 969 8 h 826 Total No. ukt. Fruit (1o.) 97 163 1&9 136 129 193 175 166 Total Number Fruit (Ho.) 12h 233 212 190 16h 276 293 2hh Avg. Fruit woight (163.) .87 .8 .36 .85 .81 .81 .80 .81 a - Black Plastic Vorlex; b - Clear Plastic Vorlex c - Early yield through August 9 d - Black Plastic Table XI Kean square values from a statistical analysis of the cucumber dati. _.—-" th. Yield I‘umber of Fruit DF Early Total ER . Total A.CCTIEGB F‘CTCR Total 11 Replication 1 h08 80252 1200 71c; 5011 Treatment 2 37170“ 1113706“ 9521-:x- 11.3222 Irrigation l 65 99190% 63L0e 1267 9* Soil Treat. x Irrig. 2 2772 6650 557 3351 Error 7 1891‘ "25181 IE 92 “$558 B. mUAnA'l'lu rlCTOR Total 11 Replication l 533*% L73395“ 327 37' Soil Treatment 2 75817:» 902 09% 1.501%1595‘11 * Irrigation 1 6hLO** h0833** 2561** 9020-" Soil Treat. x Irrig. 2 lust- ? L23 7 354 Error -3 ILO 737? 436 632 * - Significant at .0? level %w - Significant at .01 level 33. aeration of the soil before setting the plants as the fumigant would volatalize at a more rapid rate under the clear plasfic due to higher soil temperatues. However, after the fumigant toxicity was reduced under the black plastic, the combined ef- fect of the misting and the plastic on plant growth and fruit set increased total yields above those obtained on the clear plastic. Soil Treatment: In the continuously misted field, when compared to cultivated soil, the use of black plastic and the fumigant increased early yields from MOO to 800 percent in the misted and regular irrigation treatments respectively (Table X A). The use of plastic increased total yields in this experiment from 50 to over 100 percent. In the sequamatically misted field, when compared to black plastic, the use of black plastic and the fumigant increased early yields 60 to 72 percent and total yields us to 50 percent in the misted and regular ir- rigation treatments respectively (Table X B). Clear plastic with vorlex slightly decreased total yields in both fields. This could be attributed to the detrimental effect of a higher soil temperature during the day on cucumber plant and root growth with the clear plastic when compared to black plastic. Yield variation was associated with the number of fruit as there was no difference in their size. 31;- Discussion Irrigation: According to Kramer (23), any variation or modi- fication of the plants microenvironment that would reduce plant water stress should result in increased growth and yield. This is the principle involved in mist irrigation. Stocker et al (h3) and Bloodworth et a1 (2) have observed that midday sprinkling of crops in hot weather or showers too light to affect soil moisture may be quite beneficial in de- creasing plant water deficits, by keeping leaves turgid and stomates open, and thus preventing a midday decrease in photo- synthesis. The cooling effects of sprinkling could also re- duce respiration, thereby increasing net photosynthesis. These observations are in agreement with the average results obtained under continuous misting on a light sandy loam soil, while on the sequamatically misted plots, on a heavier sandy loam soil in 1965 a year of only moderate atmospheric stress, misting was beneficial to tomatoes grown on cultivated soil, but was of little benefit to tomatoes grown on plastic, and reduced yields of muskmelons and increased yields of cucumbers. Misting experiments with various crops and varieties in 1965 indicated that in a year of below normal temperatures, continuous misting compared to conventional irrigation resulted in total yields that were increased 15 percent in tomatoes, 19 percent in muskmelons, and 50 percent in cucumbers. sequamatic type misting increased the total yields of cucumbers by 17 per- cent, but decreased the yields of tomatoes and muskmelons by 2 and 27 percent respectively, when compared to their controls. 35. Recent studies by VanDenBrink et al (h9) have indicated that during periods of atmospheric stress, evaporative cooling from very low irrigation rates (.Oh to .06"/hr.) will reduce plant foliage and air temperature in the microclimate of a plant canopy varying with the relative humidity by from 10 to 20°F. Calculations based on the diffusion of water as vapor from a free water surface, indicate that transpirational loss from plant stomates, during foliage and air cooling and with higher resultant relative humidity might possibly be reduced by from 60 to more than 90 percent. A recent study by Van Bavel et al (h8) indicated that 70 to 75 percent of daily transpir— ational losses occur between 10:00 a.m. and h:00 p.m. This method of relieving plant water stress would promote the util- ization of available soil moisture to lower soil depths, aid in promoting flower formation and fruit set, and regulate plant and fruit size and quality (6). In these experiments the increased yields derived from misting were due to an increase in the number of fruit in- dicating that it was most beneficial in preventing flower abscission. Marketable fruit numbers were increased by 19, 2n, and Al percent respectively for tomatoes, muskmelons, and cucumbers grown under the continuous mist system. Fruit size was not significantly affected by misting, however under more severe stress conditions Carolus et al (6) found that size was also a factor. There was a difference in the response of varieties to misting in these experiments. Among the tomato varieties, 36. only Fireball responded to misting with an increase in early marketable yield. For the season, Fireball and Morton Hybrid responded most to misting with total yield increases of 38and 21 percent respectively, while Glamour was not materially af- fected. The Delicious variety of muskmelons responded most to early misting but early yields were lower than those from conventional irrigation. These responses may be due in part to the differences in time at which the varieties matured, in their optimum temperature requirement, or in their ability to maintain a satisfactory internal water balance during periods of high atmospheric stress. Misting was most effective in increasing the total yields of crops grown on cultivated soil, followed by those grown on black plastic, and with black plastic and the fumigant, and least responsive with clear plastic and the fumigant. This response may be related to the benefits derived from plastic mulch, which promote root growth and water absorption. The fumigant would further increase root growth by eliminating soil borne diseases and insects that affect root development. Clear plastic would not result in as great a water stress as black plastic because clear plastic allows greater penetration of solar radiation reducing the amount of reflected heat and increasing soil temperatures. Therefore, with lower plant temperatures reducing transpiration and higher soil temperat- ures decreasing water viscosity and increasing the rate of absorption, plant water stress would be reduced. 37. Two physiological abnormalities of tomatoes, blossom end rot and blotchy ripening, are associated with plant water stress or lack of it. Blossom end rot, a physiological dis- order due to an excessive withdrawal of water from fruit was reduced by mist to approximately one-half of that in the con- trol plots. Blotchy ripening, a physiological disturbance opposite in character to that of blossom end rot was nearly doubled by mist. By careful misting blossom end rot can be reduced without resulting in an increase in blotchy fruit. Soil Treatments: Mulching tomatoes in 1965 with black poly- ethylene increased total yields by to percent over that pro- duced on cultivated plots. Vorlex, a soil fumigant used with the black plastic increased the total yields of tomatoes, muskmelons, and cucumbers 63, SS, and 110 percent respectively, over that of cultivated plots. As compared to black plastic, clear plastic with the soil fumigant increased total yields of muskmelons and cucumbers by 27 and 36 percent respectively. In this study as well as in earlier work reported by Heslip (18), Carolus and Downes (5), and Riekels (37), cucurbits were found to respond most to mulching. The resultant increase in yields with vorlex, a soil fum- igant were probably due to an elimination of soil organisms and diseases such as fusarium wilt that reduce crop growth and yields. However, further study with this material is needed to determine the time interval required for proper aeration of the soil under the plastic prior to planting to prevent retardation of early plant growth. 38. There was a difference in the response of varieties to plastic mulching in this experiment. Among the tomato varie- ties Fireball responded most to mulching with significant in- creases in both early and total marketable yields. Morton Hybrid responded the least. These results are in agreement with those of Heslip (18), who also found the most response to mulching with Fireball. The muskmelon varieties responded approximately the same to the mulching treatments. 39. GREENHOUSE EXPLRIMENTATION Materials and Methods Experiments were conducted in the fall of 1965 in the Plant Science greenhouses at Michigan State University in East Lansing, to determine the influence of water balance on plant growth. Forty-eight barrels (2 feet in diameter by 2% feet deep) filled with a sandy loam soil were used. The ef- fect of various treatments on squash (Cv. Zuccini and Seneca Prolific), cucumbers (Cv. Ashley), muskmelons (Cv. Delicious), and pumpkin (Cv. Youngs Beauty), were evaluated. The relation between cotyledon expansion and plant water stress and the of. foot of different microenvironments on the growth and develop- ment of two varieties of summer squash at various salt and soil moisture levels were measured. A plot design was used with infrared heat lamps, with and without mist, mist irrigation alone, and a control as main plots and variety, soil moisture level, and soil salts as sub- plots. The heat lamps were placed 18 inches above the bar- rels with three lamps for every four sub-plots. Misting noz- zles, regulated by a solenoid valve in the water line which was activated by a counterbalanced section of screen which sim- ulated evaporation from a leaf maintained a minimum water film on the plant foliage. The lamps were automatically operated with a time clock from 9:30 a.m. to 3:30 p.m. and the "misters" from 10:00 to 3:00 p.m. Salts of calcium chloride, at the rate of 185 pounds of actual calcium per acre and potassium chloride at the rateof ‘1'." to. 270 pounds actual potassium per acre were involved in sub-plot comparisons. In addition all treatments received an applica- tion of a 10-52-17 analysis starter solution at the rate of 200 pounds per acre after seedling cotyledons had been meas- ured. The available soil moisture level maintained at 20, to, 60, and 80 percent of field capacity was evaluated daily from Delmhorst moisture blocks placed in the barrels at depths of h and 8 inches. Prior to planting the moisture levels were allowed to drop to within 5 percent of their respective min- imum levels and maintained there by tying black plastic over the barrel tops to prevent further evaporation. The seed was planted September 29, at a uniform depth of one-half inch and measurements of the cotyledons were made the following week when the first true leaves of the plants ap- peared. Four squash plants, 2 of each.of two varieties, were then grown for an additional two month period, after which, measurements of fresh weight, dry weight, number of male flow- ers, number of female flowers, number of fruit set, and of rel- ative leaf area were made. Hygrothermographs were used throughout the experiment to monitor the temperature and relative humidity in the plots. Internal leaf petiole temperatures were determined with ther- misters inserted in the apex of the hollow petioles during three sunny days in late November and early December. ul. Results The effects of the various microenvironmental treatments on relative temperature and vapor pressure deficit differences are indicated in Table XII. Relative to the control, misting decreased ambient air temperatures by 20F, mist with heat in- creased it 10F, and heat alone raised it 20F, Potential trans- piration based on air temperature and expressed as a vapor pre- ssure deficit was reduced by h.75 mm Hg. for the misted treat- ments, 3.75 mm Hg. for the mist used with heat lamps, but was increased by 0.66 mm Hg. with the increased ambient temperature associated with infrared heat lamps. Water loss is indicated by the quantity of water required to maintain the moisture levels (Table XIII). At the 20 percent moisture level there was no difference in water loss between treatments, however, at the higher moisture levels the heated plots required the most water and the misted plots the least. Relative to the control, the internal temperatures of mature squash petioles averaged 70F higher under the heat lamps and hoF lower with misting (Table XIV). These values would be much higher during the longer days of summer when in- coming solar radiation is greater and if they had been used in calculating vapor pressure gradients, the vapor pressure de- ficit values would have shown considerably more variation from the controls. Cotyledon Size: Relative to the growth at the 20 percent av- ailable soil moisture level, on the average of all crops, in- creasing the soil moisture to to, 60, and 80 percent of field 42. Table XII The re 'Ltive influence of treatment on the average maximum and minimum ambient temperature and.v:por pressure dechit differences. (‘ver*"e of a two wee: period) Temperature Vapor Ir res sesur PLOP I-Iaximum 1.1111 mun Deficit (mm . Pg. )3:— Control 0 0 0.00 Heat Lam, 3 +2 0 $0.66 Heat «r Iiiist +1 0 3. 'is t —2 -l 41.35 * - Theed on temperature and re la ative bur idity at 2:0. p.31 Table XIII The quantity of water (liters) applied to maintain available soil moisture levels under various microenvironmental conditions. vaicro envirorment al Conditi on s Control Heat heat 4» I-‘List SOIL l-CCIS U. E Lamps 1113 0 20,5 Of F.C. 7oz} 7.6 7.5 7.6 LL07. of F.C. 27.6 16.2 5.6 5.6 60; of F.C. 5.7 no.5 9.5 9.5 803 of F.C. 37.8 tS.h 13.2 13. 2 -::- - F‘s-:perhnent was started with barrels at their reflective minimzm levels with water added from October 9 to December 7. Table XIV Internal squash leaf petiole temperatures under different micro- envi ronment :11- conditions. (0 F) ( Avg . of three days? Nicroenvironmental Conditions Control he at Heat +- list T EYE.” OF DAY Lamp 8 Mi st 11:00 a.m. 70 77 7h 66 12 :00 noon 73 83 73 69 2:00 p.m. 66 71 70 6h Table XV Relative cotyledon size of muskmelon and cucumber as influenced by soil moisture levels, different salts, and environmental condit- ions (Expressed in cm2). Crop MOISTURE LEVEL MuSkmelon Cucumber Average 20% of 11:3. 11.3% 3.9 14.1 h0% of F.C. h.8 h.2 h.5 60% of F.C. 5.1 h.9 5.0 80% of F.C- 6.3 6.1 6.2 * - Average from 72 plants ENVIROI-II~"£ZI=?TAL C 0}? DIT IOV'S Infrared Heat 3.7% 2.9 3.3 Control h.7 h.6 h.7 Mist+ Heat 5.11 5.0 5.2 M1313 6.7 605 606 * - Average from 72 plants LSD - Moisture &.Environment .05 .5 . .01 .6 SOIL TREATMENT sigh Calcium [1.6% h.3 11.5 Control 5.0 h.9 5.0 High POta-SSium 5.8 Sch 5.6 Average 5.1 h.9 * - Average from 96 plants LSD - .05 .01 lllllr'lllln 1‘} Table XVI Cotyledon expansion of squash and pumpkin as influenced by various treatments and their interactions. (Length x Width in cm.) A. N ISTURE X ENVIROHMENT Heat Heat Control Mist Mist Avg. 2oz 11.Ld 12.6 13.0 16.1 13.3 hos 12.1 15.2 15.7 17.1 15.h 60% 15.1 13.5 1h.6 17.3 15.1 80% 16.5 16.h 20.0 23.8 19.2 0. 0210p x swmorna‘sz-TT 3? 13.18 13.1 16.2 16.7 1h.3 7. 13.7 13.5 111.5 17.11 111.8 YB 15.? 16.7 18.7 21.6 18.2 E. SALT x ENVIRCEITNT Ca. 15.18 12.3 thh. 15.3 1h.E K 1h.2 17.6 18.6 22.8 13.h Ctl. 13.1 13.h 11.1 17.1 1b.; Avg. 1h.2 1h.h 15:9 18:6' 5. D. URUP X MOISTURE 11.99 13.0 15.0 13.6 1h.8 17.7 lh.2 13.9 17.3 17.h 17.h 22.7 CROP X SALT Ca K Control 13.1f 16.0 13.7 13.0 18.3 13.1 17.0 20.7 16.7 T-7O'ISTUFLI‘J X SALT 20% MO% 60% 80% 12.2e 1h.0 13.6 17.9 15.6 17.9 17.1 22.6 12.0 1h.3 1b.? 17.0 a - Seneca Prolific Squash; b - Zuccini Squash; c - Youngs Beauty Pumpkin d - Average of 5h plants; 6 - Average from 72 plants; f - Average flrom 96 plants Table XVII Mean square values from a statistical analysis of cucurbit coty- ledon data. Pumpkin Cucumber & FACTOR DF & Squash DF Muskmelon Total 1113 9S CI‘Op 2 21728-3‘c-X- 1 308** Soil Moisture 3 221513.31- 3 2011,5322;- Soil Salt 2 23690-3191- 2 1071-38:— Environment 3 111818-13? 3 11565331- Eoist. 2: Salt 6 560%} 6 1711* Moist. x Environ. 9 1357—x-29 9 68 Salt 1: Environ. 6 3598*)? 6 126 Crop x Moist. 6 72761-3? 3 29 Crop x Environ. 6 1137* 3 6 Crop x Salt )4 1017-33-3? 2 59 Error 95 T7175 137- 738' * - Significant at .05 level ’34- - Significant at .01 level L160 capacity increased the relative cotyledon size (estimated as .width x length in cm.) by 15, 16, and A6 percent respectively (Tables XV and XVI). Relative to growth with infrared heat and 20 percent available soil moisture, misting plants at the low moisture level increased cotyledon expansion of squash and pumpkin to the same extent as increasing the moisture level to 80 percent (Table XVI A). However, when heat was replaced by misting at the 80 percent moisture level, the synergistic ef- fect resulted in an increase of 209 percent in cotyledon ex- pansion. Cucumber cotyledons showed the greatest expansion as the level of available soil moisture was increased from 20 to 80 percent followed by pumpkin, muskmelon, and squash res- pectively. Compared to the control, treating the plants with pot- assium significantly increased their cotyledon expansion at all moisture levels, while calcium had little effect (Table XVI F). The expansion of the cotyledons of the Zuccini squash was more pronounced with high potassium than that of the other varieties (Table XVI D). With mist the potassium treatments produced the largest cotyledons, while with added heat calcium treatments produced the largest cotyledons (Table XVI E). This might be related to the influence of calcium in preventing water loss, resulting in a relatively greater growth under stress condit- ions (37). Compared to the control, heating the plants reduced coty- ledon size 9 percent, while heat plus mist and mist alone resulted in an increase in cotyledon size of 10 and 32 percent 1&7- respectively. In muskmelons, cotyledon size increased M3 per- cent as a result of misting (Table XV) and in cucumbers, squash, and pumpkin increases from misting were Al, 29, and 27 percent respectively (Tables XV and XVI). Growth and Development of Summer Squash: After the measure- ments were completed on cotyledon expansion the cucumber, musk- melon, and pumpkin seedlings were removed from the barrels and the squash varieties allowed to continue development. The effects of the various treatments on their growth and develop- ment, and their statistical evaluation are presented in Tables XVIII, XIX, and XX. With every increase in the minimum level of available soil moisture above the minimum, a significant increase in fol- iage fresh weight was obtained (Table XVIII). In comparison with the leaf size on plants with a 20 percent available soil moisture level, the relative leaf size (estimated as width x length in cm.) of the sixth leaf on the plants was significantly increased with soil moisture minimum levels of 60 and 80 per- cent of field capacity. Dry weight increased with increasing moisture except between the no and 60 percent levels and the percent dry matter decreased as the fresh weight increased. Thus at the higher moisture levels the plants grew more rap- idly and had larger leaves, but a lower percentage of solids due to their utilization in growth. There was a tendency for the number of male and female flowers to increase with in- creasing soil moisture. Compared to the control, potassium significantly increased Aéi. .59 c_ suu_z x romeo; - a so ~.: N.. _o. .m _.m mm mo. - on; N._ o.: («a .m_m x:.: infilv (Limmm maamwuqmulmmqn o. ~.m .N mN: :.4 m_ no: s:_u_mu ;m_= m. o.m .N :o: 5.: m. :0: .otscou hzmzheumHnmqu mm 5.: mm. _o. mm o.m No. mo..co._>cm a. um_oz - own o. ~.m mow mom qqmm QN :om Mada _._ m.: Nu .o: m.: .N was new: smashes. m. m.» ON «m: m.: m. _:: .orucou m. m.~ mm an: m.m _~ man one: + um_z ‘mquqqmquAqquamamqmmu |||d4 I} i 03 win Nu d2 .qdiwo; flood o._ m.m .N om: _.: _« ~_m .u.u to New 0. ~.m o~ :wm :.m m. 0mm .0.“ do gee o. _.m m. so» :.m :. mmw .u.a so yea .imuanmmnnuqdn mm :.m mm .o. m.~ as me. - an; a. xm.¢ m. mum s.: N“ a.» _=_mqmu o. o.~ «mam :,m m. emu u_»._ota ouocom __ N nu >puqmqu u.:au o_q50m o-ox ooL< mew; u;m_03 swung .m>< :3 «>323. to a gaming .mco_u.pcou _ ucoEcoL. cm was __0m ._o>o_ ogsum_oe __0m .>uo.go> >3 nausea—we. no gmoson Leeann mo ucoeao_v>ov was zuzoaw ___>x o_noh I 9.0.1. I DI‘I' . a D I I t '01. 0" o . I 0 “‘ln. 9 C v v 1 1|: ' . . 4 V . Ill' ‘1 'I’ 1 I. u 0 '1 .. .- 01..' ‘01- 0 ‘.ln?. .ll t D I - O 1‘b.cl... ..D. a v Q..- '0 . 0.. . I It..". I .. .a .v. !!|‘1.!. I . . ~ ..-.. . .. .. .-. h9. Table XDC Growth of squash plants as influenced by various treatments and their interactions. I. 22:32 wiles? A. MOISTURE x 12v1300t332 2. h0181JHE x SALT Heat+ Fist Control Heat Mist Avg. Ca K Control 20; 325c 209 172 325* 252 2512 277 216 003 319 308 220 096 336 267 002 299 605 369 531 726 h33 517 512 53h 502 805 500 712 331 750 709 593 938 560 c. VARIITY'X vvv:acrrg;_ D. ViRITTY x SiLT sea 1539 291 M05“' 252 295 300f 303 270 Z b 532 539 570 753 612 511 78? 515 Avg. H07 508 hofi E. VRRIETY X HCISTURE 205 30% 603 80% SP 1618 213’ 351 39 Z 355 h5h 678 958 II. “RY'WEIGHT F. MOISTURE X EYVIROXEEKT G. XOISTURE X SALT Heat+ Mist Control Nest Mist Avg. Ce K Control 202 20.66 11.3 10.5’ 13.3*‘1h 13.2d 13.3 1516 DO? 21.0 16.3 1h.5 20.3 18 13.7 25.3 15.0 60% 16.3 21.1 26.8 19.1 21 20.2 22.2 20.1 805 2h.8 2t.0 33.1 25.3 2h 21.5 32.5 23.5 Avg. 187 2h 19 a - CV. Seneca Prolific; b— CV. Zuccini , c - Avg. from 2h plants; d— Avg. from 32 plants; 6 - Avg. from h3 plants; f - Avg. from 6h plants Table XX I-‘Iean square values from a statistical analysis of summer squash data. Fresh Leaf FACTOR DF *.-Ieight Weight Area Total 95 Variety 1 2112888112921- 2537-x-ze 773821o<+ Soil Moisture 3 92767 3-x-x- 639:8:- 197132-212:- Soil Salt 2 218 915-214,? 281-29.:- 1011118269.? Environment 3 7h702* 1.1 111.68%:- Moist. x Salt 6 66739* 89.".- 10106 Moist. x Environ. 9 102001.“ 121.31% 19572 Salt x Environ. 6 58886 29 3618 Var. x Moist. 1211979“- 12 7031 Var. at Salt 2 1.597291% 61 13395 Var. x Environ. 3 115089w: 52 . 18326 Error ‘37 m 7.0.3 "W52— * - Significant at .05 level ea:— - Significant at .01 level 51. the fresh and dry weight at the to and 80 percent moisture levels (Table XIX B & G). The fresh weight of the plants of both varieties increased relatively the same with each increase in soil moisture, although the fresh weight of Zuccini was con- sistantly higher (Table XIX E). Calcium had little effect on the foliage growth, dry we- ight, or relative leaf area when compared to the controls (Table XVIII). High potassium increased all three values, as well as the number of male and female flowers, although diff- erences in flower numbers were not significant. The fresh weight of Zuccini was greatly increased with high potassium while there was little effect on Seneca Prolific (Table XIX D). Relative to the infrared heat treatments, misting sign- ificantly increased the relative leaf area, but had little ef- fect on fresh or dry weight (Table XVIII). However, heat with misting decreased fresh weight, but had no effect on dry weight or relative leaf area. The varieties varied in their response to environmental conditions with Seneca Prolific having the largest fresh weight in the heated plots and Zuccini the larg- est fresh weight in the misted plot (Table XIX C). This var- ietal response difference could be due to the different clim- atic requirements of the two varieties, including their inher- ent ability to withstand atmospheric stress, or when grown to- gether, the shading effect of the Zuccini reducing growth of Seneca Prolific. In relation to moisture levels, the plants in the heated plots showed a marked significant increase in fresh and dry weight between the to and the 60 or 80 percent 52. available soil moisture levels (Table XIX B & G) which might be explained on the basis of plant water stress. In the heated plot, the to percent moisture level was too low for adequate absorption, and created a stress condition that reduced plant growth; while increasing the soil moisture to 60 or 80 percent provided for adequate absorption, which minimized stress, and thus increased growth. 53. Discussion Cotyledon Size: Knott (26) reported that cucurbits germin- ate equally well in soil moistures ranging from field capac- ity to the permanent wilting point. The observations made in this experiment, between moisture levels of 20 and 80 percent available soil moisture, are in agreement with Knott, however, there was also a direct correlation between available soil moi- sture level and cotyledon size; with each increase in the moi- sture level resulting in an increase in cotyledon expansion. This relationship is undoubtedly due to increased plant water stress at the lower moisture levels reducing seedling growth, because misting, which reduces plant water stress by environ- mental modification, increased cotyledon expansion of pumpkin and squash to the same extent at 20 percent moisture, as in- creasing the moisture level in the infrared heated plot from 20 to 80 percent. Environmental modification promoting conditions of plant water stress similarly decreased relative cotyledon size. Plants grown with heat resulting in the highest vapor pressure gradient or potential transpiration (Table XII) had the small- est cotyledon size. Misted plots which had the lowest vapor pressure gradient had the largest cotyledons. These vapor pressure gradient differences would have been much greater if the higher plant temperatures had been used (Table XIV) or if the experiment had been conducted in the longer days of summer when impinging solar radiation is greater. Conditions that promote plant water stress such as low soil moisture or high 5h. atmospheric stress have a direct effect on the growth of cu- curbit seedlings. When compared with the control, adding potassium in- creased cotyledon size by 22 percent, while adding calcium decreased their size by 3 percent. The effects of calcium in decreasing plant growth could be attributed to its effect on promoting a lack of balance in the soil solution and a mod- ification in the permeability to water and other nutrients (18). Growth and Development of Summer Squash: Growth and develop- ment of two varieties of summer squash, expressed as fresh weight, dry weight, and relative leaf area, as at the cotyledon stage, also showed definite response to soil moisture levels, different salt treatments, and various microenvironmental con- ditions (Table XVIII). With every increase in available soil moisture above the minimum a significant increase in fresh weight was obtained. when compared to the 20 percent level leaf size was also in- creased at the 60 and 80 percent minimum available soil moist- ure level and dry weight was increased with increasing moisture except between the no and 60 percent levels. Percent dry weight was decreased as fresh weight and soil moisture were increased indicating that at the higher moisture levels the plants become very succulent and probably have a higher shoot to root ratio. Misting was most effective in increasing growth at the 20 and to percent moisture levels and was equivalent to increasing the soil moisture by 20 percent in either the con- trol or heated plots. However, increasing the moisture level SS. in the misted plot to either 60 or 80 percent reduced the fresh weight below that obtained in the heated plots. This would indicate that misting at higher moisture levels reduces plant water stress to such an extent that a reduction in the rate of growth might occur. Overall, compared to the control, misting was the only environmental modification treatment that significantly in- creased growth of the squash plants, and could be attributed to decreased temperatures and reduced atmospheric stress in- creasing cell turgor, growth, and net photosynthesis. Both varieties of squash responded similarly to increa- sing moisture levels, although the response to the higher moisture level was most pronounced with Zuccini. The larger plant size developed by this variety could be attributed to a more rapid initial growth rate at a higher moisture level, which resulted in shading of the slower growing Seneca Prolific. Compared to the controls, potassium treated plants had a larger fresh weight and dry weight at the to and 80 percent moisture levels, while calcium had no significant effect at any moisture level. 56. SUMMARY AND CONCLUSIONS The effects of midday sprinkling, at very low irrigation rates (.Oh to .06"/Hr.) on the growth and development of sev- eral warm season vegetable crops were evaluated during the summer of 1965. Results with different varieties of crops and mulching treatments aided in determining factors that mod- ified the effects of misting. Misting between the hours of 10:00 a.m. and 3:00 p.m. during periods of high atmospheric stress, resulted in red- uced early yields, but significantly increased total yields of tomatoes by 15, muskmelons by 19, and cucumbers by 50 per- cent, over those obtained from plants on plots receiving one inch of water per week. Varieties differed in their response to misting and the practice was more effective in increasing yields of crops grown on cultivated soil than on plastic mulch. Misting was most beneficial in preventing flower abscission and the withdrawal of water from developing fruit during periods of high atmos- pheric stress as all yield variations were associated with differences in the number and not the weight of fruit produced. Experiments were conducted in the greenhouse in October and November to evaluate the influence of various factors on cotyledon expansion and on growth and development of several cucurbit species. Significant changes in cotyledon size were related to soil moisture, different salts, and various microenvironmental modifications. Increasing the minimum available soil moisture 57. level resulted in increased cotyledon size. However, compared to plants with low moisture and heat, misting increased the cotyledon size to the same extent as increasing the moisture level from 20 to 80 percent, and potassium increased their cotyledon expansion while added calcium had little effect. Fresh weight, dry weight, and relative leaf area of both varieties of summer squash were increased as the minimum level of soil moisture increased, although the percent dry weight decreased. Misting was the only environmental treatment that resulted in an increase in fresh weight. with low soil moist- ure, misting increased plant growth to the same extent as in- creasing the minimum soil moisture level by 20 percent. The two varieties responded differently to environmental treatments with Seneca Prolific making the largest growth with added heat and Zuccini with mist. Adding potassium increased the growth of plants while adding calcium had little effect. The results obtained in these studies seem to warrant the following conclusions: 1. Irrigation applied at rates of .Oh to .06 inches per hour during periods of high atmospheric stress may be used to regulate the growth differentiation balance of a crop, enhancing both yield and quality. 2. Misting was most beneficial in preventing flower abscission and the withdrawal of water from developing fruit as all yield increases were associated with an in- crease in the number of fruit produced. 3. Misting is more effective in increasing the yields of crops grown on cultivated soil than on plastic mulch. h. Crops and varieties differ either in their op- timum temperature requirements or in their inherent ab- ility to withstand atmospheric stress as indicated from the differential effects from misting. 58. S. Cucurbit cotyledon expansion is highl sensitive to plant water stress and is in luenced by fact rs that alter the water balance in the leaves. 6. Due to reduced transpiration and a lower plant temperature, misting squash plants can result in signi- ficant increases in total growth and greatly reduce the quantity of water needed in the soil media. 2. 6. 7o 9. 10.. 11. 12. 13. 1h. 59. LI TERATURE CI TED Ashton, F.M. 1956. Effects of a series of cycles of alter- nation 1ow and high soil water contents on the rate of apparent photosynthesis in sugar cane. Plant Physiol. 31: 266-27u ' Bloodworth, M.E., Page, J.P., and W.R. Cowley. 1956. Some applications of the thermoelectric method for measuring water flow ratesin plants. Agron. Jour. MB: 222-228 Campbell, J.A. 1953. 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