8031*. AND ATMOSPH£R$ kfiFUJENCfiS 0R1 PLANT WATER EALRN'CE WITH SPECIAL REFERERCE m BWJMEART 0F fiLEfiY (APiUM GRAVEOLfiNS) Thesis for the Degree of Ph. D. MICHEGAN STATE UNWERSWY GERARD: H. QUEBELS 1967' THESIS LIBRARY Michigan State University This is to certify that the thesis entitled SOIL AND ATMOSPHERIC INFLUENCES ON PLANT WATER BALANCE WITH SPECIAL REFERENCE To BLACKHEART OF CELERY (APIUM GRAVEOLENS) presented by Gerard H. Gubbels has been accepted towards fulfillment of the requirements for Ph .D o degree in Horticulture ’4 ,2”. am“? Major professor Ihne September 194 1961, 0-169 ABSTRACT SOIL AND ATMOSPHERIC INFLUENCES ON PLANT WATER BALANCE WITH SPECIAL REFERENCE TO BLACKHEART OF CELERY’(APIUM GRAVEOLENS) by Gerard H. Gubbels Characteristics of the celery plant and the develop- ment of blackheart were studied under various conditions of plant water balance affected by atmOSpheric conditions, soil moisture levels, osmotic concentrations and ion balances. The application of low rates of irrigation (mist) to reduce plant water stress on hot days resulted in higher total fresh and dry weights, lower percentage of dry matter, higher sucker weight and no difference in marketable weight of celery grown in mineral soil and in nutrient solutions. No differences were present in muck soil. Mist applications during low temperature conditions reduced growth rate. TranSpiration rate was reduced up to 27% but no marked changes in ion uptake accompanied this decrease. Misted plants showed the same degree of blackheart severity as con— trol plants despite the increased vigor of the misted plants. Low minimum soil moisture level (20-30% of the avail- able soil moisture) in mineral soil resulted in lower fresh and dry weights, a higher percentage of dry matter, and no Gerard H. Gubbels consistent difference in the efficiency of water use as com- pared to high minimum soil moisture level (70-80% ASM). The application of 750 pounds of Ca plus 652 pounds of Na per acre and double those rates to mineral soil to increase osmotic concentration of the soil solution resulted in higher fresh weight but similar dry weights compared to the control using the same volume of water. In nutrient solutions, 4.8 atm. and 0.3 atm. osmotic concentration of the same ion balance generally resulted in lower fresh and dry weights but higher percentages of dry matter compared to a 1.2 atm. solution. Water—use efficiency was lowest at the 0.3 atm. concentration but not significantly different at 1.2 and 4.8 atm. Blackheart symptoms were the most severe at the 1.2 atm. concentration. In soil and nutrient solutions, fresh weight gen- erally increased with decreasing Ca/K ratio but an associ- ated decrease in the percentage of dry matter left only a small increase in dry weight. The large increase in fresh weight with decreasing Ca/K ratio was offset by a large increase in the sucker weight which resulted in no differ- ence in marketable weight. Very low Ca/K ratio in soil and nutrient solutions resulted in a higher water—use efficiency while moderate Ca/K ratios resulted in no differences. High Ca/K ratio in nutrient solutions caused lower efficiency. Gerard H. Gubbels Blackheart symptoms increased with decreasing Ca/K ratios in nutrient solutions. Blackheart symptoms increased in severity with increasing fresh weight of plant tops, sucker weight and K content of heart tissue, but decreased with increasing per- centage of dry matter, Ca, B and Ca/K ratio in heart tissue. SOIL AND ATMOSPHERIC INFLUENCES ON PLANT WATER BALANCE WITH SPECIAL REFERENCE TO BLACKHEART OF CELERY (APIUM GRAVEOLENS) BY ..f r. c' Gerard Hi? Gubbels A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1967 3-7~EY ACKNOWLEDGMENTS The author wishes to eXpress his sincere apprecia- tion to Dr. A. L. Kenworthy for his guidance and assistance throughout this research project and in the preparation of the manuscript. Appreciation is also eXpressed to Dr. R. L. Carolus for his help and advice in conducting the eXperi— ments and to Dr. J. B. Harrington, Dr. C. M. Harrison, Dr. R. E. Lucas, and Dr. C. W. Nicklow for their helpful suggestions. The author wishes to eXpress appreciation to his wife, Margaret, for her assistance and encouragement. ii TABLE OF CONTENTS Page INTRODUCTION . . . . . . . . . . . . . . . . . . . . . 1 LITERATURE REVIEW . . . . . . . . . . . . . . . . . . 3 I. Plant Water Balance . . . . . . . . . . . . . 3 II C MiSt Irrigation C O O O O O O O O O O O O O O 5 III. Soil Moisture . . . . . . . . . . . . . . . . 7 IV. Osmotic Concentration . . . . . . . . . . . . 8 V 0 Ion Balance 0 O O O O O O O O O O O O O O O 0 10 VI. Blackheart . . . . . . . . . . . . . . . . . . ll OUTDOOR EXPERIMENTS O O O O O O O O I O O O O O O O O 18 I. Effects of Soil and Environmental Treatments on Celery Grown Under Controlled Soil Moisture Conditions (1965) . . . . . . . . . 18 II. Effects of Soil and Environmental Treatments on Celery Grown Under Controlled Soil Moisture Conditions (1966) . . . . . . . . . 26 III. Effects of Soil and Environmental Treatments on Celery Grown Under Field.Conditions (1965) . . . . . . . . . . . . . . . . . . . 45 IV. Effects of Soil and Environmental Treatments on Celery Grown Under Field Conditions (1966) . . . . . . . . . . . . . . . . . . . 49 GREENHOUSE EXPERIMENTS ~. . . . . . ... ..... . . .-. 53 I. Effects of Ca/K Ratio and Environmental Conditions on Celery Grown in Nutrient Solutions . . . . . . . . . . . . . . . . . 53 II. Effects of Ca/K Ratio, Solution Concentration and Environmental Conditions on Celery Grown in Nutrient Solutions . . . . . . . . . . . . . 68 GENERAL DISCUSSION . . . . . . . . . . . . . . . . . . 88 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . 95 LITERATURE CITED . . . . . . . . . . . . . . . . . . . 98 iii L IST OF TABLES Table Page 1. Top growth, water use, and wilting of celery plants in relation to environment, ion balance and soil moisture level . . . . . . . . 22 2. TOp growth, water use, and wilting of celery plants in relation to nutrition, environment and soil moisture level . . . . . . . . . . . . 30 3. Mineral content of celery heart tissues related to nutrition, environment and soil mOisture level I O O C O C C C O O O O O O O O 36 4. Mid-day soil, air and leaf temperatures in mist and control plots. Mean of seven days during which mist was applied (August 27 to September 2, 1966) . . . . . . . . . . . . . . 4O 5. The effect of environment and nutrition on the growth of celery plants (1965) . . . . . . 48 6. The effect of environment and nutrition on the growth of celery plants (1966) . . . . . . 51 7. Growth of celery plants related to environment and nutrient solution Ca/K ratio . . . . . . . 58 8. Mineral content of celery heart tissue in relation to environment and nutrient solu— tion Ca/K ratio . . . . . . . . . . . . . . . . 61 9. Blackheart ratings, transpiration and Ca/K ratio in celery heart tissue related to environment and nutrient solution Ca/K ratio . . . . . . . . . . . . . . . . . . . . . 63 10. The relationship of blackheart ratings and nutrient solution Ca/K ratio to celery plant characteristics (simple linear correlation coefficients) . . . . . . . . . . . . . . . . . 64 iv Table 11. 12. 13. 14. 15. Growth of celery plants related to environment, nutrient solution Ca/K ratio and concentration . . . . . . . . . . Mineral content of celery heart tissue related to environment, nutrient solution Ca/K ratio and concentration . . . . . . . Blackheart ratings, tranSpiration and Ca/K ratio in celery heart tissue related to environment, nutrient solution Ca/K ratio and concentration . . . . . . . . . . . . . Relationship of blackheart rating and nutrient solution Ca/K ratio to celery plant characteristics (simple linear correlation coefficients) . . . . . . . . . Mean daily 8:30 a.m. and 2:00 p.m. leaf, heart, air and solution temperatures (C) between August 25 and September 5, 1966 . . Page 72 75 78 80 81 Figure l. 2. 10. LIST OF FIGURES Celery plant showing severe blackheart symptoms . . . . . . . . . . . . . . . . . . The effect of the interaction of environ- ment and soil moisture level on the degree of wilting of celery plants (0 - no wilt, 10 - severe wilt). . . . . . . . . . . . . . The effect of the interaction of environ— ment and N level on top fresh weight of celery plants . . . . . . . . . . . . . . . The effect of the interaction of N and available soil moisture (ASM) on the dry weight of celery top growth . . . . . . . . The effect of the interaction of soil moisture level and environment on the dry weight of celery top growth . . . . . . . . The effect of the interaction of Ca/K ratio and soil moisture level on marketable weight of celery . . . . . . . . . . . . . . The effect of the interaction of Ca/K ratio and soil moisture level on the volume of water transpired per gram of dry matter produced by celery . . . . . . . . . . . . . The effects of the interaction of Ca/K ratio and N on the P content of celery heart tissue . . . . . . . . . . . . . . . . . . . The effects of the interaction of N level and soil moisture on the Ca/K ratio in celery heart tissue . . . . . . . . . . . . The effects of the interaction of Ca/K ratio and environment on the B content of celery heart tissue . . . . . . . . . . . . . . . . vi Page 13 23 31 31 33 33 34 37 37 37 Figure 11. 12. 13. 14. 15. l6. 17. 18. 19. Page The effect of mist on leaf and can0py temperatures on a typical hot day (August 28, 1966). Maximum air temper— ature was 29.4 C; relative humidity, 41%: pan evaporation, 4.57 mm.; wind travel, 56 Km.; sky, mostly sunny. Mist duration was approximately 60 sec. per application . . 41 The effects of the interaction of Ca/K ratio and environment on the t0p fresh weight of celery grown in nutrient solutions in the greenhouse . . . . . . . . . . . . . . . . . . 59 The effect of the interaction of Ca/K ratio and environment on the fresh weight of celery roots grown in nutrient solutions in the greenhouse . . . . . . . . . . . . . . . . . . 59 The effect of the interaction of Ca/K ratio and nutrient solution concentration on marketable weight of celery . . . . . . . . . 73 The effect of the interaction of Ca/K ratio and nutrient solution concentration on the percentage of dry matter in celery roots . . . 73 The effect of the interaction of Ca/K ratio and nutrient solution concentration on the K content of celery heart tissue . . . . . . . 76 The effect of the interaction of Ca/K ratio and nutrient solution concentration on the volume of water tranSpired per gram of dry matter produced . . . . . . . . . . . . . . . 76 The effect of mist on transpiration rate on a typical hot day (August 26, 1966) with some cumulus cloud. Mist was in Operation from 9:00 a.m. until 4:00 p.m. . . . . . . . . . . 83 The relationship between transpiration, blackheart rating and growth rate from August 17 to September 18, 1966. (1) Mean daily tranSpiration; (2) Mean black— heart rating; (3) Mean growth rates . . . . . 84 vii INTRODUCTION Plant water balance is important in many plant processes. Growth, photosynthesis and respiration are among the major plant processes that are adversely affected by a deficit of water in the plant. Plant water balance may be affected by a combination of plant, atmospheric and soil conditions. The atmOSphere may be modified by light rates of irrigation and thus prevent or reduce the development of water stress in the plant. Manipulation of the soil mois- ture level, the ion balance and the salt concentration in the soil may further alter the water balance. Blackheart of celery, a physiological disorder char- acterized by the deterioration of heart tissue, has been closely associated with the water relations of the plant. Blackheart symptoms generally appear during or after peri- ods of high temperature, at which time transpiration and moisture stress would be at a maximum. Low soil moisture level and high salt content have also been linked with the disorder. These two factors play a significant role in the water balance of plants. A low Ca content in the celery heart tissue is characteristic of plants exhibiting black- heart symptoms. In the case of celery, Ca may affect the water balance in the plant or the converse may be true-—the water balance may affect the Ca uptake and/or metabolism. The purpose of this study was to determine the effects of soil and atmospheric treatments on the water balance of celery and the incidence of blackheart. LITERATURE REVIEW I. Plant Water Balance The activity of many of the processes within the plant may be affected by the water status of the tissues. A cessation or checking of cell division or cell enlargement or both may result from a substantial decrease in the hydra- tion of the protOplasm in the cells of a meristematic tissue (34, 42). Reduction in the water content of leaf cells may result in a reduced rate of photosynthesis. Slavik (41) stated that even slight reductions of the water potential directly reduced photosynthesis. In work by Denmead and Shaw with corn (8), measurements of dry matter production suggested that once the soil moisture content was less than the turgor loss point, the plants virtually ceased to assim- ilate. Moss (36) reported that probably the first effect of moisture stress was to cause the stomates to close.) Pisek and.Winkler (37) found that stomates usually began to close when water content had fallen only 2 to 12% below saturation in the leaves. A water deficit may increase respiration rate to the extent that damage and even death of the tissue may follow (42). In summarizing the effects of water stress on plant growth, Kramer (27) listed further effects such as: in— creased root-shoot ratio; increased thickness, cutinization and lignification of cell walls; reduced leaf area; in- creased leaf thickness; increased conversion of starch to sugar, altered nitrogen metabolism, increased rate of RNA destruction; altered mineral metabolism; and rapid senes- cence of leaves. Plant water balance may be affected by a combination of plant, athSpheric and soil conditions (26). Kramer (27) reported that water stress develOped in plants when the rate of water loss by transpiration exceeded the rate of absorp— tion by the roots. Transpiration was affected by leaf area and structure, extent of stomatal opening and the steepness of vapor pressure gradient from leaf to air (27). Rate of absorption by the roots was controlled by the rate of water loss, extent and efficiency of the root system, soil aera- tion, soil temperature, concentration of the soil solution and the soil moisture tension (27). Water absorption tended to lag behind water loss because there was resistance to movement in the plant, most of which occurred in the roots where water had to cross the relatively compact layers of cells in the epidermis, cortex and endodermis (27). Kramer (27) emphasized that the water status of the soil gave no indication of the water status of the plant because even with the soil water near field capacity, the plant could still be under considerable moisture stress due to atmo- Spheric conditions. The lowest stage in plant water stress has been termed incipient wilting (34). In this stage the loss of turgor is partial and does not result in visible drOOping or rolling (34). This is in contrast to temporary or tran- sient wilting in which there are visible signs of wilting with subsequent recovery of turgor (34). In permanent wilt- ing, the plant wilts and does not recover unless moisture is added to the soil (34). Gates (14) found that with tomato plants even moderate wilting reduced total growth and claimed that it was erroneous to suppose that plant growth was only affected near the permanent wilting point. Wil- liams and Shapter (53) working with barley and rye confirmed this, and furthermore found that the plant parts growing most actively at the time of a water deficit were most affected. II. Mist Irrigation* The application of low rates of water to plant foliage was reported by Stocker et al. (44) to have bene- fited crOps by keeping their leaves turgid and stomates Open, and in preventing a midday decrease in photosynthesis. *An application of low irrigation rates through Sprinklers delivering small sized water drOps. other studies (4, 7, 47) have indicated that during periods of high temperature evaporative cooling from very low irri- gation rates of .04 to .06 inch per hour reduced plant and air temperature and increased relative humidity in the plant canOpy. This resulted in a reduced rate of transpiration and reduced moisture stress in the plant with subsequent increase in yield and quality in some crops. Gates (15) stated that leaf temperatures may rise well above the Optimum range of physiological activity (25 to 30 C for many temperate region plants) when transpiration is no longer able to keep up with the rising heat load as the solar radiation approaches its midday peak. This can result in a temporary reduction or cessation of photosyn- thetic activity (15). McMillan and Burgy (32) by the use of lysimeters found that the total evapotranspiration of a stand of grass was identical whether the surface of the stand was wetted or dry, indicating that the tranSpiration rate was reduced pro- portionally to the evaporation of the Sprinkled water. The effect of transpiration rate on the ion uptake of intact plants has been reviewed by Slatyer (40). From the exten- sive work on this subject, he concluded that transpiration increased uptake under some conditions, eSpecially when the requirements of the plant were high and ion concentration was also high both within the stele and external to it. Michael and Marschner (35) found that mustard plants grown at relative humidities so regulated that transpiration was reduced to 1/7 to l/10 of that in dry air absorbed consider— ably less Cs, slightly less Ca and P, but K absorption was not affected. Work done by Freeland (13) indicated that with plants grown in nutrient solutions an increase in transpiration resulted in an increase in mineral absorption but different mineral ions were not absorbed at the same rate and the rate of absorption of each ion varied with the kind of plant used. In his eXperiments, high transpiration caused bean and corn plants to take up relatively less Ca and more K. III. Soil Moisture Water was not found to be equally available to the plant over the entire range from field capacity to permanent wilting (8, 26). Actual transpiration was found to decrease with decreasing soil moisture (8, 26). Denmead and Shaw (8) found that soil moisture content at which the decline in relative transpiration rate occurred, varied from a volumet- ric soil moisture content of 23%.when the potential rate was 1.4 mm/day to 34% when potential transpiration rate exceeded 6 mm/day. Carolus et a1. (7) found that as the available soil moisture level (ASM) increased from low to high, under high temperature conditions, tomato fruit number increased 47% and fruit size 49%; however, under low temperature con- ditions fruit size did not vary significantly and fruit num— ber was reduced 23%. Janes (23) working with celery found that rate of growth was retarded when soil moisture was depleted to 40% of field capacity compared to plants in which the moisture levels were maintained above 60 and 80%. The plants at the low soil moisture were smaller and of lower quality. In studies with potatoes, Wheaton et a1. (52) reported that depletion to the 10 or 40% level before irrigating resulted in lower yields of marketable potatoes when compared to higher minimum soil moisture levels. Furthermore, more bushels of potatoes per inch of applied water were obtained with those treatments producing the highest yields. IV. Osmotic Concentration High osmotic pressure of the root medium has been reported to contribute to water stress in plants (3, ll, 21, 26, 39). Kramer (26) stated that it made little difference whether water absorption was decreased by high osmotic pres- sure of the soil solution or by high soil moisture tension. Slatyer (39) claimed that a real water stress was induced by osmotic substances but the effect was not identical with that of soil water tension. He found the imposition of osmotic substrates caused an initial, rapid outflow of water and loss of turgor. There was a gradual recovery in turgor as solute uptake and increase in internal osmotic potential caused an inflow of water. Other workers in this field (11, 21) have noted the progressive stunting of plants and the attendant smaller darker green leaves which in most cases resembled drought symptoms. They supported the view that a water deficit induced by high osmotic pressure of the root medium was the factor restricting growth. Plants on saline soils may not show symptoms of wilting despite the fact that their growth may be limited by moisture availability (3). The relatively high osmotic pressures of the soil solution in saline soils maintained a moderate moisture stress throughout the irrigation cycle (3). TranSpiration rate generally decreased with increased osmotic pressure in the nutrient medium (10, 11, 28). Eaton (10) grew corn and tomato plants with their roots divided between two or more solutions of unequal concentrations. The plants developed more roots and absorbed more water in the dilute than in the concentrated solutions. He found that osmotic pressures rather than Specific ion effects were pri- marily involved. Eaton (11) further reported an increase in the efficiency of water use by several crops at moderate salinity but a decrease at higher levels of salinity. In water culture eXperiments Kidson (25) found increased osmotic concentrations resulted in a reduction in the Ca level in the leaves of tomato plants. Geraldson (l7, 18) noted that excessive total salts can cause Ca to be low in celery heart tissue, but a predominance of Na may be the important factor in reducing Ca uptake. 10 V. Ion Balance The water economy of several Species was found by Schmied (38) to be modified by supplying them with B, Cu, Mn or Zn. In summarizing the general effect of fertilizers on water use, Viets (48) stated: "Whether fertilizers increase consumptive use not at all or only slightly, all evidence indicates that water—use efficiency, or dry matter produced per unit of water used, can be greatly increased if fertilizers increased yield." Wostmann (54) found that plants in complete nutrient solutions with high K transpired more than in high Ca solu- tion, while single salt solutions of Ca(NO resulted in 3)2 higher transpiration rates than such from KNO3 solutions. Furthermore, if the ratio of K to Ca was varied in culture solutions, then the transpiration, calculated in mg/square decimeter of leaf surface increased with increasing K supply. Biebl (5) concluded that in single salt solutions and highly unbalanced K applications to the soil, tranSpiration rates were lowered due to the K. However, in several salt or mixed applications, high K applications increased tranSpira— tion values. In eXplaining these results Biebl (5) summa- rized the antagonistic effects of K and Ca. He stated that K promoted swelling of the protOplasm which resulted in reduction of water loss while Ca promoted contraction which resulted in increased water loss; K affected the morphologi— cal-anatomical conditions of the periderm, facilitating 11 water loss while Ca had the Opposite effect, resulting in cuticular transpiration being lower due tO Ca than to K; the Opening Of the stomata was promoted by K and retarded by Ca. VI. Blackheart Blackheart Of celery was first reported in 1897 by Kinney (46). It has since been reported in almost every area where celery is grown with most severe occurrences in California, Texas and Florida. In some years all or a large portion Of a crOp has been lost. Investigators generally have agreed that blackheart is a physiological disorder (1, 2, 12, 18, 29, 45, 46, 49). The first symptom is the development of brown lesions on the tips Of tender leaflets in the heart or crown of the plant (2, 18). Then the whole leaf turns brown and finally the leaf and petiole turn black (2, 18). In severe cases the entire center Of the plant decays and a secondary infection by Erwinia carotovora may cause a slimy black rot to occur (45). Figure 1 shows a celery plant with severe blackheart symptoms. Foster and Weber (12) found that plants grown to maturity and then allowed tO remain in the field were most subject tO blackheart. Blackheart was most severe in Flor— ida in the late crOp during April and May because the celery was near maturity at the time when conditions conducive to blackheart development generally occur. 12 Figure l. Celery plant showing severe blackheart symptoms. l3 14 Most investigators have agreed that the disorder is closely tied tO unbalanced water relations and heavy fertil- izer applications, especially of N (l, 2, 6, 12, 19, 20, 45, 46, 49, 50, 51). Other conditions reported as associated with blackheart have been: over maturity (12), vigorous growth (46), excess K (20), deficient K (29), low Ca (2, 17, 18, 45), high soluble salts (l, 6, 17, 18, 46, 49), and hot, dry weather (46). Landry (29) Observed that the addition Of K to some soils decreased blackheart, but in nutrient cul- tures, a high Ca/K ratio was relatively more effective. Beckenback and Spencer (1) Observed that blackheart was associated with high NO 'nitrogen and excess soluble salts 3 in the soil. Westgate (49) concluded that blackheart in- creased with the use Of excess fertilizer and the accumula- tion of soluble salts. In eXperiments by Foster and.Weber (12), blackheart was produced repeatedly in the field by flooding. About 48 hours after the water reached the sur— face from sub-irrigation the disorder appeared in the grow- ing hearts. United States Department Of Agriculture workers (46) after an extensive survey concluded that blackheart was caused by drought or by excessive soil moisture due to heavy rains or excessive irrigation. Excessive irrigation appar- ently caused asphyxiation of the roots and ultimate death Of the root hairs, thus creating a condition of drought. In Florida, blackheart was more prevalent on light sandy soils 15 than on muck soils indicating a better water balance on muck. They concluded that heavy fertilizer applications, vigorous, succulent, rapidly growing plants were most severely affected. Cannell et al. (6) in studying the effects Of irriga- tion and fertilizer found that yields increased with decreas- ing soil moisture tension while blackheart increased with increasing moisture tension and increasing fertilizer rates. Leaf concentration Of Ca, Mg and Mn increased with the drier moisture treatments while P, B and Mo decreased. P content in the petioles increased in the lower soil moisture tension treatments. In studying the effect Of soluble salts on the prevalence and severity Of blackheart, Geraldson (17, 18) grew celery in nutrient solutions ranging in concentration from 1500 to 12,000 ppm soluble salts with the ratio between salts constant. All Of the plants develOped blackheart, but symptoms develOped sooner and were more severe in the lower than in the higher concentrations. The Ca content Of young leaves was markedly less in blackhearted plants than in healthy plants (0.1 to 0h¢% as compared to 0.5 tO 1.0%). Analyses Of older leaves indicated variations of 2.5 to 4.0% Ca, but these differences were not significant. Ca solutions applied directly to the heart Of celery plants completely controlled blackheart. Regardless Of the amount Of Ca in the nutrient culture all plants develOped black- heart unless a foliar Ca spray was applied. Although Ca l6 sprays tO the hearts Of the plants once or twice a week dur- ing conditions when blackheart is likely tO occur are recom- mended as a general cultural practice by Lucas and.Wittwer (30), it has been reported by Bergman (2) that many growers have applied Sprays without marked success. Geraldson (18), Landry (29) and Bergman (2) Obtained data showing that blackheart symptoms generally increased in severity with decreasing Ca/K ratio in nutrient solutions, but rate Of growth and yield were higher at low Ca/K ratios. Takatori et al. (45) noted that an increase in N content Of nutrient solutions without an increase in Ca resulted in increased blackheart. Higher Ca levels in the nutrient solutions containing high N reduced the percentage and severity. Increasing the N concentration of the nutri- ent solution reduced the Ca absorption Of the plants and increased the K absorption. In an eXperiment with tomatoes, Geraldson (20) found that excess soluble Mg, K, Na or NH salts or a deficiency 4 of soluble Ca salts caused a decreased Ca uptake and an increased prevalence and severity Of blossom-end rot Of tomatoes. On an equivalent basis, NH affected the Ca up- 4 take most severely, while Na had the least effect. Other investigations (16, 31, 33) have pointed out that Na had an adverse effect on the uptake of Ca. Geraldson (20) has prOposed that all Of the factors most frequently associated with the occurrence and severity 17 of blackheart can be placed into two categories—-excessive soluble NH K, Mg, or Na or a deficiency Of soluble Ca 4! causing a decrease in Ca uptake; and, excessive total salts, even when Ca ratio is considered adequate, causing a de— crease in Ca uptake. OUTDOOR EXPERIMENTS The water balance Of celery was studied using treat- ments thought to be conducive to moisture stress and those not conducive combined in factorial arrangements to deter- mine the relative effects Of each. In the following eXper- iments low soil moisture, high K and Na, and high osmotic concentrations were employed in an attempt to increase mois- ture stress while misting, high soil moisture, high Ca and low osmotic concentrations were employed to decrease stress. I. Effects 9: Soil and Environmental Treatments 22.Celerijrowth Under Controlled Soil Moisture Conditions (1965) Procedure Utah 52-70 celery seed was sown in muck and grown to transplanting size. On July 2, 1965 the plants were trans- planted on the Michigan State University Horticulture Farm into drums 2 feet in diameter and 2 feet high containing Plainfield sand to which 2 inches of Houghton muck had been mixed into the surface. At the bottom Of each drum was a 3-inch layer Of coarse sand tO facilitate drainage. The drums were sunk into the ground to near the level Of the surrounding soil. Prior to planting, 10-52-17 fertilizer at 18 19 200 pounds per acre and KNO at 300 pounds per acre were 3 applied. Five plants were grown in each drum. On August 2, the following treatments were added in a Split—split plot design with two replications: Main plots 1 Mist 2 Control Sub-plots 1 Control 2 1500 lbs. Ca/A as CaCl2 3 2190 lbs. K/A as KCl 4 1305 lbs. Na/A as NaCl 5 750 lbs. Ca plus 652 lbs. Na/A as Cl salts 6 1500 lbs. Ca plus 1305 lbs. Na/A as Cl salts Sub—sub-plots . 1 Low soil moisture (20—30% ASM) 2 High soil moisture (70—80% ASM) Mist was applied from small mist nozzles between the hours Of 10:00 a.m. and 4:00 p.m. on days when the tempera- ture rose above 24 C except on days Of changeable weather, when mist was applied during only part Of this 6-hour period. A Mist-A-Matic Model B control system (B. C. Geiger, North Wales, Pennsylvania) was used to control the mist. It con— tained a counterbalanced metal screen which tipped down and turned Off a solenoid valve when water accumulated. When the water evaporated, it tipped back up turning the solenoid valve on. The counterbalance was adjusted so that the foliage was moist with no appreciable amount Of water being added to the soil. The mist system was Operated on 24 days for 124 hours. 20 The sub-plot salt treatments were added in three applications-eAugust 2, August 9 and September 1, totaling the amounts indicated above. Treatments 2, 3, 4 and 5 were the same osmotic concentration, and treatment 6 double that” concentration. Moisture levels in the sub-sub-plots were permitted to go down to 20-30% Of the available soil moisture (ASM) and 70-80% ASM in the low and high treatments respectively and then brought back up tO field capacity. Delmhorst gypsum blocks (Delmhorst Instrument CO., Boonton, N. J.) were placed at a depth Of 6 inches, the readings from which indicated when the plots had drOpped to the prescribed mois- ture level. The salt treatments prevented the moisture blocks from functioning satisfactorily, thus sub—sub-plots were watered according to the requirements of the control plots for each soil moisture level. Metal covers were placed over the plots when rain threatened, enabling soil moisture levels tO be controlled. The volume Of water applied was recorded. Ratings Of relative wilting were made on days during which wilting occurred on any plot. The mean was calculated by dividing the sum Of the wilt rating by the overall number Of days ratings were made. Leaf samples were taken on October 2, 1965 for dry matter determinations. Leaves Of medium age were cut just below the first node and dried in an oven held at 65 C. 21 The volume of water transpired per gram Of tOp dry matter was calculated by dividing the volume Of water applied tO the soil by the relative dry weight Of the top of the plant. The analyses Of variance were performed on the resulting data as indicated by Snedecor (43) and mean com- parisons made by the method described by Duncan (9). Results The results are presented in Table 1. As reflected by measurements on tOp growth Of plants, the misted plants were not significantly different from the control plants in fresh and dry weight, percentage dry matter, and water transpired per gram Of dry matter produced. However, the interaction Of environment X soil moisture was significant (Fig. 2). The wilt rating was the same in both low and high soil moisture in the misted plots while there were higher wilt ratings in low than high soil moisture in the control plots. 0f the ion balance treatments the K, Na, and low Ca-Na treatments yielded the highest tOp fresh weights, followed by the Ca and high Ca-Na treatments and lastly the control (Table l). The percentages Of dry matter followed in approximately the reverse order with the control highest and the K, Na and low and high Ca-Na treatments lowest. 22 Table 1. TOp growth, water use, and wilting Of celery plants in relation tO environment, ion balance and soil moisture level Volume Visual Weight per of water wilt plant (gm.) tran- ratings Percent- Spired age Of per gram 0-nO wilt Total Total dry dry wt. lO—severe fresh dry matter (ml.) wilt Environment 1 Mist 461 a1 56 a 12.3 a 312 a 0.13 a 2 Control 411 a 52 a 12.7 a 362 a 1.19 a Ion Balance 1 Control 344 d 51 be 15.0 a 348 ab 1.12 a 2 Ca-1500 414 bed 52 be 12.7 b 342 ab 0.70 b 3 K-2190 520 a 61 a 11.8 be 292 c 0.69 b 4 Na-1305 501 ab 57 ab 11.4 c 315 be 0.57 b 5 Ca-750, Na-652 438 abc 51 be 11.8 bc 355 ab 0.55 b 6 Ca—1500, Na-1305 401 cd 48 c 12.1 be 371 a 0.31 b Soil Moisture Level 1 20-30% ASM 408 b 50 b 12.4 a 349 a 0.76 a 2 70-80%.ASM 464 a 58 a 12.5 a 325 a 0.56 b Interaction Environ. X Soil moist. ** 1Values followed by uncommon letters are significantly dif— ferent at the 5% level. **Significant at the 1% level. WILT RATING Figure 2. 23 1.4 . CONTROL 102 b 1.0 P 0.8 t 0.6 r 0.4 t 0.2 b MIST i :— 4. 0.0 J .1 Low High SOIL MOISTURE LEVEL The effect of the interaction Of environ- ment and soil moisture level on the degree Of wilting Of celery plants (0-nO wilt, 10-severe wilt). 24 This resulted in the tOp dry weights being more nearly equal but with the K and Na treated plants highest. The K and Na treatments resulted in the most efficient use Of water, using 292 and 315 ml. water per gram Of dry matter produced respectively. The high Ca-Na treatment was least efficient as it resulted in 371 ml. per gram. The control plants had a significantly higher degree Of wilting than did the salt- treated plants. The high Ca-Na treatment showed the lowest degree Of wilting, although it was not significantly lower than that Of the other salt treatments. The high soil moisture level resulted in higher fresh and dry tOp weights, 464 g. and 58 g. respectively, than those Of the low soil moisture level, 408 and 50 g. reSpectively (Table 1). Table l and Fig. 2 indicate that there was a lower degree Of wilting in the high than the low moisture plots. No blackheart symptoms appeared during the course Of the exPeriment. Discussion Misting was effective in reducing the degree Of water stress in the plants (Table l and Fig. 2). Misted plants tended to be higher than the control plants in fresh and dry weights and lower in percentage dry matter. These differ- ences may be attributed tO the reduced degree Of plant water stress which is in agreement with the findings Of other workers (4, 7, 14, 47, 53). 25 The K and Na treatments were most efficient in water use and, also, produced the highest fresh and dry weights (Table 1). This was in agreement with Viets (48) who con- cluded that if a fertilizer treatment increased yield there was generally an accompanying increase in the water-use efficiency. This was also in agreement with Biebl (5) who concluded that plants receiving very high K applications had lowered transpiration rates. The high Ca treatment, on the other hand, did not change the transPiration rate compared to the control, but it did produce a more succulent plant with a lower percentage of dry matter. Eaton (11) reported an increase in water-use efficiency at moderate salinity and a decrease at high levels Of salinity. The high Ca-Na treat— ment showed this trend but the value was not significantly different from that Of the control. The lower degree Of wilting in the salt treatments compared to the control was in agreement with the findings Of Bernstein and Hayward (3). Other workers (10, 11, 28) found that transpiration rate decreased with increasing osmotic pressure and thus a moder- ate moisture stress may have been maintained throughout the irrigation cycle (3) and may have limited the growth Of those plants whose water-use efficiency was not boosted with high K or Na. Thus equal weights Of dry matter were produced under high soil moisture tension (control) as under high osmotic tensions (treats. 2, 5, 6). However, the lower 26 percentage of dry matter in treatments 2, 5, and 6 may have been caused by the different type Of moisture stress (39). The higher fresh and dry weights from high soil moisture compared tO those Of low soil moisture agreed with the Observations Of other workers (23, 52). This may be explained by the lower degree of plant water stress as indi- cated by the lower wilt ratings. The failure Of blackheart symptoms to appear despite the high K and Na, high osmotic concentration and low mini— mum sOil moisture and combinations Of these treatments may have been because Of a lack Of extremely high temperature in late August and September, when the plants were at a stage more susceptible. High temperature may be Of primary impor- tance for the development of blackheart symptoms and soil conditions may be secondary. A more vigorous rate of growth than eXperienced with these treatments may make the plants more susceptible tO blackheart. II. Effects 2; Soil and Environmental Treatments 23 Celery Grown Under Controlled Soil Moisture Conditions (1966) In the following exPeriment high N levels and com- plete nutrient solutions with different Ca/K ratios were used in addition to other treatments in order to avoid any nutrient deficiencies and to promote vigorous growth. A mineral soil was used as blackheart has been reported to be more prevalent on mineral soil than on muck (46). 27 Procedure Utah 52-70 celery seed was sown in vermiculite on March 15, 1966 and later grown on in a one-half muck-one- half sand mixture. On May 28, 1966 these plants were planted in drums as described in the previous experiment. The drums contained Hillsdale sandy loam. Four plants were planted in each drum. A four—foot high snow fence was set up to reduce the force of the prevailing winds. On June 4 and again on June 23, 10-52-17 fertilizer was applied at a rate Of 50 pounds per acre. On July 9, 1966 the following treatments were added in a Split-split-split-plot design with two replications: Main plots 1 360 lbs. N/A 2 720 lbs. N/A Sub-plots l Mist 2 Control Sub-sub-plots l 0 lbs. Ca plus 600 lbs. K/A 2 110 lbs. Ca plus 440 lbs. K/A 3 220 lbs. Ca plus 280 lbs. K/A Sub-sub-sub-plots 1 Low soil moisture (20-30% ASM) 2 High soil moisture (70—80% ASM). The N treatments Of the main plots were applied in three equal applications-—July 9, August 2, and August 12, totaling the amounts indicated above. The first and third applications were applied in conjunction with the sub-sub— plots as described below. The second application consisted of NH NO 4 3 solutions applied at one gallon per plot or drum. 28 The same misting equipment was used as in the previous eXperiment. Mist was applied between 10:00 a.m. and 4:00 p.m. on days when the temperature rose above 27 C, except on days Of changeable weather, when mist was applied during only part Of this 6-hour period. The mist system was Operated on 48 days for a total Of 246 hours. The sub-sub-plot treatments were applied in two applications, July 9 and August 12. The first application comprised 3 gallons Of Hoaglands NO. 1 solution (22) with the Ca, K, and N contents modified to give the desired.Ca/K ratios for the sub-sub-plot treatments and the desired N levels for the main plot treatments. The second application was made with only one gallon of solution containing three times the concentration in order to avoid leaching the plots at higher moisture levels. In order to facilitate the maintenance Of the desired soil moisture levels, Delmhorst moisture blocks were placed at a 6-inch depth in each Of the non-misted plots in the first replication and in each Of the misted plots in both replications. The volume Of water applied was recorded. Blackheart ratings were made at two to four-day intervals after the first symptoms were Observed. Ratings Of the degree Of wilting on days during which wilting occurred on any plot were made and the mean rating calcu— lated.by dividing the sum Of the ratings by the overall number Of days ratings were made. 29 On several days, air, soil, heart, and leaf temper- atures were recorded using thermisters connected to a Tele- thermometer. The leaf temperatures were recorded by small, flat thermisters taped tO the under sides Of the leaves. On September 14, 1966 total tOp weights were recorded. The plants were then stripped, marketable weights recorded and the length Of the outside marketable petioles measured. Medium-aged petioles complete with leaf blades were taken for dry matter determinations. The entire heart consisting of all leaves less than 8 inches in length and cut just above the stem plate was taken from each plant for chemical analysis. The four hearts per plot were combined into one sample. N content was determined by the Kjeldahl procedure, K by a flame photometer, and the other elements by a direct reading photoelectric Spectrometer (24). The analyses Of variance and mean comparisons were made by the methods previously indicated. Simple linear correlations Of blackheart ratings with all other recorded factors and treatments were also determined. Results The N treatments did not result in any significant differences in total, marketable and dry weight Of tOp nor in percentage of tOp dry matter, water use or wilting (Table 2). However, there was a significant interaction between N level and environment for total top fresh weight (Fig. 3) 3O Table 2. TOp growth, water use and wilting Of celery plants in relation tO nutrition, environment and soil moisture level Volume Visual Of water wilt tran- ratings Weight per plant Spired (grams) per gram Percent dry 0-no wilt Total Market- Total dry matter lO-severe fresh able dry matter (ml.) wilt Nitrogen Level 1 1 N—360 988 a 640 a 95 a 9.6 a 491 a 0.6 a 2 N—720 1002 a 216 a 91 a 9.1 a 464 a 0.9 a Environment 1 Mist 1044 a 665 a 96 a 9.2 a 428 a 0.3 a 2 Control 945 b 587 a 90 b 9.5 a 526 a 1.1 a Ca/K Ratio 1 Ca-OI K-600 1065 a 681 a 97 a 9.1 a 477 a 0.8 a 2 Ca-110, K-440 1007 a 628 ab 93 a 9.3 a 471 a 0.7 a 3 Ca-220, K-280 912 b 569 b 88 a 9.7 a 483 a 0.7 a Soil Moisture Level 1 20-30% ASM 877 b 546 b 87 b 9.9 a 463 a 1.1 a 2 70-80% ASM 1112 a 706 a 98 a 8.8 b 492 a 0.4 b Interactions N level X Envir. ** N level X Soil Moist. ** Envir. X Soil Moist. * Ca/K X Soil Moist. =1 ** * lValues followed by uncommon letters are significantly different at the 5% level. *Significant at the 5% level. **Significant at the 1% level. 1100 E o 1050 -H m 3’? 338 1000 Lav E 950 m o B 900 31 MIST // CONTROL 400 500 600 700 800 N LEVEL (lbs./A) Figure 3. The effect Of the interaction of environ- ment and N level on tOp fresh weight Of celery plants. 100 E 95 (D H g’7 90 >43» “V Q m 85 O E! 80 HIGH ASM // LOW.ASM 400 500 600 700 800 N LEVEL (lbs./A) Figure 4. The effect Of the interaction Of N and available soil moisture (ASM) on the dry weight Of celery tOp growth. 32 indicating that misted plants gave a greater increase in yield for increasing N level than did the control plants. The interaction Of N level X soil moisture (Fig. 4) shows that tOp dry weight decreased from the low tO the high N level under low soil moisture but increased under high moisture. The misted plants were higher than the control in total tOp fresh weight (Table 2 and Fig. 3). The interac- tion Of environment X soil moisture (Fig. 5) shows that the increase in tOp dry weight from low to high soil moisture levels was greater in misted plots than in the controls. The data in Table 2 further indicate that total and marketable fresh weight decreased with increasing Ca/K ratio in the soil. The significant interaction Of Ca/K ratio X soil moisture level (Fig. 6) pointed out a greater decrease in marketable weight from the low to the medium Ca/K ratio at the high soil moisture level than at the low level and an approximately equal decrease from the medium to the high Ca/K ratio. NO Significant differences in the wilting rat- ings were attributable to the Ca/K ratios in the soil. The interaction Of Ca/K ratio X soil moisture level for transpi— ration was significant (Fig. 7). This interaction showed that at high soil moisture, the transpiration rate decreased from the low tO the medium Ca/K ratio and was about similar at the medium and high Ca/K ratios, while at low soil mois- ture, tranSpiration increased slightly from the low tO the TOP DRY WEIGHT (gr.) Figure 5. MARKETABLE WEIGHT (gro) Figure 6. 100 95 90 85 80 33 / MIST CONTROL 1 Low High SOIL MOISTURE LEVEL The effect Of the interaction Of soil moisture level and environment on the dry weight Of the celery tOp growth. 800 700 600 500 400 HIGH ASM LOW ASM A \ Low High Medium Ca/K RATIO The effect Of the interaction Of Ca/K ratio and soil moisture level on market- able weight Of celery. 34 510!” 500' 5 HIGH ASM 0.4 fig 490% Dd F, —-—e 03 E32 - an 480 AE E» 470» m LOW ASM En ' m gCD 460b E 450 A L A Low Med. High Ca/K RATIO Figure 7. The effect Of the interaction Of Ca/K ratio and soil moisture level on the volume Of water tranSpired per gram of dry matter produced by celery. 35 medium Ca/K ratio and increased greatly from the medium to the high Ca/K ratio. High soil moisture resulted in a higher total top fresh weight (Table 2), a higher marketable weight (Table 2, Fig. 6), a higher tOp dry weight (Table 2, Fig. 5), and a lower percentage tOp dry matter (Table 2) than in the low soil moisture. It also resulted in a lower degree of wilt— ing (Table 2). The only significant difference in petiole length resulted from the soil moisture treatments. Petiole length averaged 19.6 cm. in the low soil moisture and 21.4 cm. in the high. Means Of the other treatments varied from 20.1 to 20.8 cm. The results Of the chemical analyses for those elements that were significant at the 5% level are presented in Table 3. There were no significant differences due to soil N level. However, there was a Significant interaction between soil N level and soil Ca/K ratio for P content Of the heart tissues (Fig. 8). At the high N level the P con- tent increased with increasing Ca/K ratio while at the low N level it decreased from the low to the medium Ca/K ratio and then increased to the high Ca/K ratio. There was also a significant interaction between soil N level and soil moisture level for Ca/K ratio in the heart tissue (Fig. 9). This interaction indicated that at the low soil moisture level the Ca/K ratio in the heart tissue was lower at the 36 Table 3. Mineral content of celery heart tissues related to nutrition, environment and soil moisture level Ca P B Ca/K % % ppm ratio Nitrogen Level 1 N-36O .410 a .898 a 72.7 a .086 a 2 N-720 .464 a .872 a 59.8 a .100 a Environment 1 Mist .411 b .898 a 65.9 a .088 a 2 Control .463 .872 a 66.7 a .098 a CaZK Ratio 1 Ca-O, K-600 .418 a .879 ab 65.4 .084 2 Ca-llO, K-440 .416 a .857 b 63.6 b .086 b 3 Ca—220, K-280 .477 a .919 a 69.8 .108 Soil Moisture Level 1 20—30% ASM .438 a .838 b 65.6 a .094 2 70-80% ASM. .436 a .931 a 67.0 a .092 a Interactions N level X Ca/K ratio * Envir. X Ca/K ratio ** N level X Soil moist. ** 1Values followed by uncommon letters are significantly dif— ferent at the 5% level. *Significant at the 5% level. **Significant at the 1% level. p CONTENT OF HEART TISSUE (%0 Figure 8. Ca/K RATIO IN HEART TISSUE Figure 9. B CONTENT OF HEART TISSUE (ppm) Figure 10. .960 .920 .880 .840 .800 37 t LOW N ' HIGH N Low Med. Ca/K RATIO High The effects Of the interaction of Ca/K ratio and N on the P content Of celery heart tissue. .110 .100 .090 .080 W'ASM - ~ HIGH ASM _‘ 400 500 600 700 800 N LEVEL (lbs./A) The effects Of the interaction Of N level and soil moisture on the Ca/K ratio in celery heart tissue. 70 65 60 55 r CONTROL L MIST Low Meds High Ca/K RATIO The effects Of the interaction Of Ca/K ratio and environment on the B content of celery heart tissue. 38 low soil N than it was at the high soil moisture level, but higher at the high soil N level. In the environmental treatments, the Ca content of the heart tissue was higher in the control than in the misted plants (Table 3). The interaction Of environment X soil Ca/K ratio was significant for B content Of the heart tissues (Fig. 10) indicating that in the misted plants the B content decreased from the low soil Ca/K ratio to the medium and increased from the medium to the high, while in the control plants the B content increased from the low soil Ca/K ratio to the medium and slightly decreased from the medium to the high. The soil Ca/K treatments showed a higher P content in the celery heart tissue at the highest ratio than at the medium but was not different significantly from that Of the low (Table 3, Fig. 8). The B content of the celery heart in relation to the soil Ca/K ratio is explained above in the interaction Of environment X Ca/K (Fig. 10). The Ca/K in the heart tissues showed nO difference due to the two lower soil Ca/K ratios. Both, however, were lower than the value resulting from the high soil Ca/K ratio (Table 3). The high soil moisture level resulted in a higher P content of the heart tissue Of the plants than that found in plants at low soil moisture (Table 3). 39 Midday soil, air and leaf temperatures are presented in Table 4 for mist and control plants. During the seven- day period Of August 27 to September 2 the midday soil tem- perature was 0.7 C lower at the 3-inch depth and 0.8 C lower at the l/4-inch depth in the misted plots than in the con- trols. The air temperature in the canOpy was 2.2 C lower and the leaf temperature was 5.5 C lower in the misted plants than in the controls. Leaf and canOpy temperatures in control and misted plots are shown plotted at two—minute intervals in Fig. 11. The leaf temperatures Of the misted plants dropped sharply as the mist was applied. After the mist had ceased the temperature of the leaves gradually rose as the leaf surface dried, then drOpped when the next mist application was made. This cycle was repeated continuously as the leaves were saturated about to the point Of runoff followed by evaporation Of water from the leaf surface almost to the point Of dryness. Very mild blackheart symptoms in some plants were Observed from September 2 until September 9. Statistical analysis Of the results showed no significant differences attributable tO any Of the treatments. Simple linear corre— lations Of blackheart ratings with treatment and other recorded data indicated significant correlations between the following factors: wilt rating (r = -.329), P content Of heart tissue (r = +.434), and Mg content Of heart tissue (r = +.333). 40 Table 4. Mid-day soil, air and leaf temperatures in mist and control plots. Mean Of seven days during which mist was applied (August 27 to September 2, 1966) Mean Difference (C) (C) Soil 3-inch depth 1 Mist 22.2 0.7 2 Control 22.9 Soil l/4-inch depth 1 Mist 23.3 T 0.8 2 Control 24.1 Air i§.canOpy l Mist 26.8 2.2 2 Control 29.0 Leaf l Mist 27.1 5.5 2 Control 32.6 TEMPERATURE (C) 41 MIST -—-— — CONTROL 25 24 12: Figure 11. (’Mist Appl icat ions 5‘ A 11 A A A T\‘ g A 4T 1 46 12:54 1:02 ’ 1:10 1:18 TIME (PM) The effect of mist on leaf and canopy tempera- tures on a typical hot day (August 28, 1966). Maximum air temperature was 29.4 C: relative humidity, 41%4 pan evaporation, 4.57 mm.; wind travel, 56 Km.; sky, mostly sunny. Mist duration was approximately 60 sec. per applica- tion. 42 Discussion Misted plants Showed the same trends as in the pre- vious eXperiment when compared tO the control plants for plant weights, percentage dry matter, water tranSpired and wilting. The interaction of environment X soil moisture level indicates that mist was more effective at high than low soil moisture in increasing dry matter production (Fig. 5). The interaction Of environment X N level indicates that mist was more effective in increasing tOp fresh weight at the high than the low N level (Fig. 3). Although the mist applications reduced the volume Of water transpired per gram Of dry matter produced, the Ca/K ratio in the heart tissues indicated no significant difference from that Of the control. Freeland (13) had reported higher Ca/K ratios in bean and corn plants due to reduced tranSpiration rates. The fresh weights recorded (Table 2) showed a decrease with increasing Ca/K ratio in the soil. This was in agreement with the results Of Geraldson (18), Landry (29) and Bergman (2) in their studies using nutrient solutions. Although the tOp fresh weight decreased with increasing Ca/K ratio, the tOp percentage Of dry matter tended to increase resulting in no significant difference in tOp dry weight. The volume Of water tranSpired at high soil moisture per gram Of dry matter produced declined with increasing Ca/K ratio from the lowest to the medium level and was about the same at the medium and high levels, while at low soil 43 moisture transpiration rate increased with increasing Ca/K ratio (Fig. 7). This was in agreement with Wostmann's find- ings (54) that if the Ca/K ratio was varied the tranSpira- tion rate decreased with decreasing K. However, under con- ditions an unbalance such as a water shortage, the water loss Of Ca-treated plants exceeded that of K-treated plants. Although the Ca and K content Of the celery heart tissue was not significantly altered by the different Ca/K ratios applied tO the soil, the Ca/K ratio in the heart tissue increased with increasing Ca/K ratio. This was in agreement with the Observations Of Geraldson (18). The higher fresh and dry weights resulting from the high soil moisture treatment compared to the low (Table 2) were in agreement with the findings of Janes (23) and Wheaton et al. (52). Also, the lower percentage of dry matter at high soil moisture indicated a more succulent growth. The interaction of soil moisture level X N level (Fig. 9) indicates that Ca/K ratio increased to a greater degree from the low tO the high N level in the low soil moisture plots than it did in the high soil moisture plots. This resulted in a high Ca/K ratio occurring in the low soil moisture-high N plots.in this eXperiment. The higher Ca/K ratio would tend to decrease the incidence Of black- heart, yet, blackheart has been reported to be more severe at low soil moisture and high N levels (1, 6, 46, 49). This higher Ca/K ratio may be over balanced by other factors in 44 the ultimate occurrence Of blackheart, or, it is possible that the relationship Of moisture level and N to Ca/K ratio may change under higher temperature conditions. Cannel et al. (6) found that leaf Ca, Mg, and Mn increased while P, MO and B decreased at lower soil moisture treatments. The values in Table 3 for P agree with Cannel but the values for Ca, B and all Of the other elements determined showed no change due to soil moisture level. The blackheart symptoms that develOped in the latter part Of the growing season were very mild and showed no sig- nificant differences between any Of the treatments. There was a significant negative correlation Of blackheart rating with wilting (r = -.329). This is Opposite tO the Observa- tions Of other workers (46) who reported blackheart symptoms increased by drought. However, the treatments that resulted in lower degrees Of wilting (mist and high soil moisture level) achieved more vigorous growth which has been asso- ciated with more severe blackheart symptoms (2, 18, 46). Furthermore, the low SOil moisture-high N plants had higher Ca/K ratios (Fig. 9) associated with the higher degree Of wilting (Table 2). Since high Ca/K ratio and drought are Opposing factors in the develOpment Of blackheart symptoms, the higher Ca/K ratio may have been the deciding factor in blackheart occurrence in this instance. The higher Ca/K ratios in the higher N plots are contrary tO the findings Of Takatori et a1. (45) using nutrient solutions. 45 III. Effects 2; Soil and Environmental Treatments 2g Celery Grown Under Field Conditions (1965) Celery is grown primarily on muck soil in Michigan. It was desirable, therefore, to determine the effect of the soil and atmospheric treatments on the plant water balance and the occurrence Of blackheart in celery grown under field conditions without any restriction Of root development. Procedure Utah 52-70 celery seed was sown in muck soil. At the end of May the plants were transplanted to the field at the Michigan State University Muck Farm in Houghton muck. Row Spacing was 32 inches with plants 7 inches apart in the rows. Soon after planting, KNO3 was side-dressed at 75 pounds and NH NO at 75 pounds per acre. 4 3 Treatments were applied as outlined below using a split—Split-plot design with three replications. Main plots 1 Mist 2 Control Sub-plots 1 Control 2 140 lbs. N/A as NH NO 4 3 Sub-sub—plots 1 Control 2 3000 lbs. Ca/A as CaCl2 3 4380 lbs. K/A as KCl 4 1500 lbs. Ca plus 2190 lbs. K/A as C1 salts. 46 Misting was begun on the main plots in mid-June using a sequamatic irrigation system which applied .07 inches Of water per hour between the hours of 10:00 a.m. and 4:00 p.m. on days when the temperature rose above 29 C. The Sprinklers in the sequamatic system had 5/32 inch nozzles regulated by valves with each Of the three Sprinklers on a line Operating five minutes out Of twenty in a sequencing cycle. The mist system was Operated on 23 days. The mois- ture level on all plots was maintained above 50% Of the available soil moisture. The N treatment of the sub-plots was side-dressed in two applications, August 6 and August 12, totaling 140 pounds per acre. The salt treatments Of the sub-sub-plots were applied broadcast over the entire plot surface and worked into the surface inch Of soil. These treatments were calcu- lated to result in equal osmotic concentrations and were applied in three applications, August 6, 12 and September 2, totaling the amounts indicated above. Two-row plots 7 feet long were used. On October 2, 1965 leaves Of intermediate age were cut just below the second node and percent dry matter deter- mined. On this same date the plants were harvested. Records of total tOp weight and marketable weight were made on 14 plants from the center Of each plot. 47 Statistical analyses were made by the methods previously indicated. Results Growth Of the celery plants during the season was good with the average plant weight in excess Of 2000 g. The season was cool, with only 8 days on which the temperature was above 32 C. Total tOp fresh weight, marketable weight and percentage Of dry matter are presented in Table 5. The differences between means were not significant at the 5% level. NO blackheart symptoms were Observed during the course Of the eXperiment. Discussion The mist application showed a tendency tO have decreased the yield compared to the control (Table 5). This may have resulted from a lowering Of the plant temperature below the Optimum on several days throughout the season, thus nullifying the beneficial effects on yield that could have taken place due to misting on the hotter days. The failure Of blackheart symptoms to appear may have been due tO the lack Of periods Of sufficiently high temperatures during the growing season. Furthermore, the unbalance Of nutrients may not have been severe enough to cause blackheart to develop. 48 Table 5. The effect Of environment and nutrition on the growth Of celery plants (1965) f _- t f Weight per plant (grams) TOp percent Total tOp Marketable dry matter Environment 1 Mist 2075 1376 6.69 2 Control 2215 1485 6.81 Nitrogen Level 1 Control 2125 1416 6.64 2 N - 140 2165 1444 6.86 Ion Balance 1 Control 2093 1430 7.10 2 Ca - 3000 2107 1403 6.70 3 K - 4380 2193 1444 6.79 4 Ca-1500, K-2190 2193 1439 6.42 49 IV. Effects 9: Soil and Environmental Treatments gg_Celery Grown Under Field Conditions (1966) In order to encourage the develOpment of blackheart, high N and K levels were included in the treatments in the following eXperiment carried out on muck soil in the same manner as the previous eXperiment. Procedure Utah 52-70 seedlings were grown in muck and trans- planted to the field at the Michigan State University Muck Farm on May 27, 1966. Rows were Spaced 32 inches apart and plants were set 7 inches apart in the rows. Before planting, 5-10—30 plus 2% Mn was broadcast at the rate Of 800 pounds per acre. Treatments were applied as indicated below using a split-plot design with 4 replications. Main plots 1 Mist 2 Control Sub-plots l 300 lbs. N/A as NH4N 3 plus 1000 lbs. K/A as KCl 2 300 II II II II II 2000 II II II ' II 3 3 00 II II II II II 4000 II II II II 4 600 II II II II II 1000 II II II II 5 600 II II II II II 2000 II II II II 6 600 II II II II II 4000 II II II II Misting was begun in mid-June using the Same method and apparatus as described in the previous eXperiment. The mist system was Operated on 35 days. 50 The N treatments were applied in three applications, July 16, August 1, and August 12, while the K treatments were applied in two applications, July 16, and August 12, totaling the amounts indicated above. These salts were broadcast uniformly over the surface area Of the plots. Two-row plots 10 feet long were used. The soil moisture level on all plots was maintained above 50% Of the available soil moisture. Five plants from each plot were harvested on October 3. Total weight, marketable weight and average petiole length were recorded. Statistical analyses were made by the methods pre- viously indicated. Results Growth during the season was very rapid with the average plant total fresh weight Of tOp exceeding 4000 grams. There were 11 days during which the temperature rose above 32 C. Total plant tOp fresh weight, marketable weight and petiole length are presented in Table 6. NO significant differences at the 5% level were shown between the treatment means. NO blackheart symptoms develOped during the course Of the eXperiment. 51 Table 6. The effect Of environment and nutrition on the growth Of celery plants (1966) J J Weight per plant (grams) Petiole length Total tOp Marketable (cm.) Environment 1 Mist 4339 2140 25.0 2 Control 4202 2036 24.2 Nitrggen Level 1 N - 300 4220 2143 24.7 2 N — 600 4322 2033 24.5 Potassium Level 1 K - 1000 4296 2092 25.0 2 K - 2000 4256 2094 24.6 3 K - 4000 4261 2079 24.2 52 Discussion In this eXperiment plant growth on all plots was extremely vigorous, with misted plants showing a tendency to be larger than those Of the control. This increase may be attributed to the decreased plant water stress on the hotter days. The high exchange capacity of the muck soil may have prevented the N and K treatments from having a more pro- nounced effect on the plants. The failure Of blackheart to occur in this eXperi- ment may have been due to two possible conditions: (1) the failure Of periods of extreme temperatures tO occur, and (2) the maintenance Of the soil moisture level tOO near the Optimum. It is possible that the effect Of the two condi- tions is accumulative in the development Of symptoms. That is, blackheart may not develop unless the soil moisture level is low at the same time that the temperatures are high for a prolonged period Of time. GREENHOUSE EXPERIMENTS Two greenhouse eXperiments were conducted using solution culture tO avoid the effects Of soil moisture fluctuations. With soil culture the water in the soil is depleted at a rate dependent upon the amount Of moisture stress on the plant tOp and the plant size, resulting in different soil moisture contents in plots Of different treatments at a given time. Differences in plant response or in the develOpment Of blackheart symptoms occurring between plots during a two or three-day hot period could be attributed to the soil moisture level during that period as readily as tO the treatment effects. The use of solutions instead Of soil would allow uniform root conditions, permit- ting Observed differences to be attributed tO the various treatments applied. I. Effects 2; Ca/K Ratio and Environmental Conditions 9Q.CeleryGrown‘ig Nutrient Solutions TO determine the effect of plant water balance on celery response and on the develOpment Of blackheart symp- toms, atmospheric stress was modified in this SXperiment by applying mist to decrease stress and by applying infrared radiation to increase stress, with normal greenhouse 53 54 atmosphere between these two extremes. Different Ca/K ratios were used in the nutrient solution to further affect the plant water balance and tO promote the development of blackheart symptoms tO different degrees Of intensity. Procedure Celery seed Of the variety Utah 52-70 was sown in muck and the seedlings were grown to transplanting size. On April 2, 1966 these plants were transferred tO half- strength Hoaglands NO. 2 nutrient solution (22) in two- gallon crocks on greenhouse benches. Solutions were changed each week. On May 13, 1966 the following treatments were put on in a split-plot design with four replications: Main plots 1 Mist 2 Control 3 Heat lamps Sub-plots l 50 ppm Ca/235 ppm K 2 100 ppm Ca/176 ppm K 3 150 ppm Ca/ll7 ppm K 4 200 ppm Ca/59 ppm K The treatments Of the main plots were applied every day between the hours Of 9:00 a.m. and 4:00 p.m. Mist was applied intermittently from fine mist nozzles using deionized water. A timeclock was adjusted to turn the mist on for 2 seconds every 3 or 6 minutes depending on the atmOSpheric conditions so as tO keep the leaves moist, but with no appreciable runoff. Polyethylene sheets were placed across 55 the bench on two sides Of each plot extending 12 inches above the tOp Of the foliage to limit the mist tO the appropriate plots. The control consisted Of normal green- house conditions. In the plots receiving increased radia- tion, 250 watt infrared heat lamps were placed 14 inches above the foliage with one lamp supplying heat radiation to two plants. Reflectors were used to prevent radiation from striking plants of adjacent plots. The sub-plot treatments consisted Of Hoaglands NO. 1 solution (22) with the Ca and K contents modified as indi- cated above by altering the amounts Of Ca(NO3)2 and KNO3 added. These Ca/K ratios resulted in solutions with very nearly equal osmotic concentrations (0.6 atm.). NH4NO3 was added to correct the N levels resulting from the omission Of and/or KNO portions Of the Ca(NO The pH of the solu- 3)2 3’ tions was adjusted to 6.0. Deionized water was used through- out. The solutions were changed each week. Each day the volume Of water used was measured in each plot by determining the amount Of deionized water required to bring the solution level back up to a wire marker. Periodically the plants were lifted out Of the solutions, allowed to drain for a few seconds and then weighed. Ratings Of the severity Of blackheart symptoms were also made periodically. 56 Final records were made on June 17, 1966. Weights of total tOp, root, suckers and marketable stalk were recorded. The entire heart consisting Of all leaves less than 8 inches in length and cut just above the stem plate was taken from each plant as a sample for chemical analyses. Nitrogen was determined by the Kjeldahl procedure, potassium with a flame photometer, and the other elements by a direct reading photoelectric spectrometer (24). The root and the remainder Of the tOp from each plot was dried in a forced- air oven at 65 C for the determination of the dry matter content. The volume Of water transpired per gram Of dry mat- ter (DM) produced was determined by the following formula: ml. water transpired from May 14 to June 16 ml. water/g. DM = (fresh wt. June 16——fresh wt. May 14) X %DM Analysis Of variance was performed on the resulting data as indicated by Snedecor (43) and mean comparisons made by the method described by Duncan (9). Simple linear corre- lations Of blackheart ratings with all other recorded data and with treatment were run. Correlations were also run Of nutrient solution Ca/K ratio and environmental treatments with all Of the recorded factors. 57 Results Data on the growth Of the celery plants are pre- sented in Table 7 for those measurements that were signif- icant at the 5% level. Misting increased the weight of suckers per plant and decreased the percentage Of dry mat- ter in the tOp compared to the control and heat lamp treat- ments. The interaction Of environment X Ca/K ratio was Sig- nificant for total tOp fresh weight per plant (Fig. 12). This interaction indicates that in misted plots the tOp fresh weight decreased with increasing Ca/K ratio, while it increased from the 50/235 to the 100/176 ratios, then decreased tO the 200/59 ratio in the control plots. The heat lamp treatment resulted in similar values for the 50/235 and 100/176 ratios then decreased to the 200/59 ratio. The interaction Of environment X Ca/K ratio was also signifi- cant for root fresh weight (Fig. 13). In this.interaction the misted plants showed equal root weights at the 100/176 and 150/117 ratios, but a higher weight at the 50/235 ratio and a lower weight at the 200/59 ratio, while the roots Of the control plant increased in weight from the 50/235 to the 100/176 ratio, decreased to the 150/117 ratio, then remained the same to the 200/59 ratio. Root weights Of the plants given additional radiation with heat lamps were the same at the 50/235 and 100/176 ratios, then decreased to the 150/117 ratio. 58 Table 7. Growth Of celery plants related to environment and nutrient solution Ca/K ratio Root Fresh weight per plant dry Percent dry (grams) weight matter per Total plant tOp Sucker Root (gr.) TOp Root Environment 1 Mist 1277 al 555 a 143 a 9.7 a 9.5 b 6.8 a 2 Control 1132 a 406 b 126 a 9.0 a .10.3 a 7.1 3 Heat lamps 1148 a 434 b 136 a 9.8 a 10.2 a 7.2 CazijatiO 1 50/235 1285 a 550 a 150 a 9.9 ab 9.3 c 6.6 b 2 100/176 1311 a 609 a 157 a 10.5 a 9.4 c 6.7 b 3 150/117 1123 b 395 b 123 b 9.1 be 10.2 b. 7.4 4 200/59 1025 c 307 b 111 b 8.6 c 11.2 a 7.7 Interactions Envir. X Ca/K ratio * * 1Values followed by uncommon letters are significantly dif- ferent at the 5% level. *Significant at the 5%.1evel. TOP FRESH WEIGHT (gr .) Figure 12. ROOT FRESH WEIGHT (gr .) Figure 13. 59 150° F \ MIST - - — \ CONTROL 1400 . \ HEAT LAMPS ------ 1300 ' 1200 . 1100 ' 1000 - 900 L - - . 50/235 100/176 150/117 200/59 Ca/K RATIO The effects Of the interaction Of Ca/K ratio and environment on the tOp fresh weight Of celery grown in nutrient solutions in the greenhouse. 180 F MIST - -- — ‘ CONTROL EAT P ----- 160 _ H LAM S 140 P "‘\ \. \\ 120 - c‘ \ \ ““~o 100 - f ’ 80 . 50/235 100/176 150/117 200/59 Ca/K RATIO The effect of the interaction.of Ca/K ratio and environment on the fresh weight Of celery roots grown in nutrient solutions in the greenhouse. 60 Table 7 further points out that the 50/235 and 100/176 ratios resulted in higher sucker weights per plant than did the 150/117 and 200/59 ratios. Root dry weight was highest at the 50/235 and 100/176 Ca/K ratios, and lowest at the 150/117 and 200/59 ratios with no significant difference between the 50/235 and 150/117 ratios. Tap and root percent— ages Of dry matter increased with increasing Ca/K ratio with nO difference between the two low ratios in tOp and root values and no difference between the two high ratios for root values. In the last 28 days Of the eXperiment (May 20 to June 17) the misted plants increased in fresh weight 1019 g. in 50/235 Ca/K solution; 822 g. in 100/176; 737 g. in 150/117; and 608 g. in 200/59 solution. The increases dur- ing the same period Of time for plants in normal greenhouse environment (control) were 733 g. in 50/235; 879 g. in 100/176; 643 g. in 150/117; and 531 g. in 200/59 Ca/K solution. Results Of the chemical analyses Of the celery heart tissues are presented in Table 8 for those elements that showed significant differences between treatment means. In the environment treatments the only significant difference was a lower value for A1 in the control plots than in either the mist or heat lamp plots. 61 Table 8. Mineral content Of celery heart tissue in relation to environment and nutrient solution Ca/K ratio K Ca Mg Mn B A1 A % % % ppm . ppm . ppm . . Environment 1 Mist 4.71 a .160 a .196 a 20.1 a 62.8 a 29.2 a 2 Control 4.91 .147 a .200 a 20.8 a 61.6 a 23.4 b 3 Heat lamps 4.69 .184 a .210 a 23.9 a 69.8 a 28.3 a CaZK Ratio 1 50/235 5.60 .099 c .230 a 25.2 a 49.9 c 26.5 ab 2 100/176 5.07 .181 ab .209 b 23.2 ab 52.5 be 27.7 ab 3 150/117 4.57 .160 b .186 c 18.3 c 64.1 b 21.6 b 4 200/59 3.83 .215 a .183 c 19.7 bc 92.4 a 32.2 a lValues followed by uncommon letters are significantly differ- ent at the 5% level. 62 K and Mg content Of heart tissue decreased with increasing Ca/K Of the nutrient solution while Ca and B generally increased. Mn decreased from the 50/235 ratio to the 150/117 ratio and was not different at the 150/117 and 200/59 ratios. Al was lowest at the 150/117, highest at the 200/59 and intermediate at the 50/235 and 100/176 ratios (Table 8) . Blackheart ratings, tranSpiration and Ca/K ratios in the celery heart tissues are presented in Table 9. There were no significant differences in the severity Of black? heart symptoms and Ca/K ratios in heart tissues between the means Of the environment treatments. The misted plants transpired less water per gram Of dry matter produced than did the control plants, and plants of the heat lamp treat- ment transpired more than the control plants. With increasing Ca/K ratio in the nutrient solution the severity Of blackheart symptoms decreased, the volume Of water transpired per gram Of dry matter produced increaSed and the Ca/K ratio Of the heart tissue increased (Table 9). Table 10 contains the simple linear correlation coefficients that were significant between blackheart symp- toms and other factors recorded and the corresponding cOef- ficients between treatments and the same factors. 63 Table 9. Blackheart ratings, transpiration and Ca/K ratio in celery heart tissue related to environment and nutrient solution Ca/K ratio Water transpired per gram Ca/K ratio Blackheaft dry matter in heart rating (ml.) tissue Environment 1' Mist 4.34 a2 287 c .036 a 2 Control 4.28 a 360 b .031 a 3 Heat lamps 4.09 a 417 a .041 a cazk Ratio 1 50/235 5.31 a 326 c .018 c 2 100/176 4.48 ab 344 b .036 b 3 150/117 4.17 b 348 b .035 b 4 200/59 3.00 c 403 a .056 a ll-no symptoms; 9-Severe symptoms. 2Values followed by uncommon letters are significantly dif- ferent at the 5% level. 64 Table 10. The relationship Of blackheart ratings and nutrient solution Ca/K ratio to celery plant characteristics (simple linear correlation coefficients) Ca/K ratio Blackheart in nutrient rating solution TOp fresh weight +.351 * -.584 ** TOp percent dry matter -.4l6 ** +.682 ** Transpiration (dry weight basis) -.336 * +.413 ** Sucker weight +.334 ** _.595 ** Ca content in heart -.693 ** +.490 ** K content in heart +.557 ** -.824 ** B content in heart -.49l ** +.682 ** Ca/K ratio in heart -.719 ** +.654 ** Ca/K ratio in nutrient solutions -.560 ** *Significant at the 5% level. **Significant at the h% level. 65 Blackheart severity increased with increasing top fresh weight, sucker weight and K content in the heart, while symptoms decreased in severity with increasing top percent- age dry matter, transpiration rate, Ca and B content in the hearts, Ca/K ratio in the hearts and.Ca/K ratio in the nutri- ent solutions. In each case the correlation with Ca/K ratio in the nutrient solutions showed a significant, but Opposite relationship. For example, with increasing tOp fresh weight, blackheart symptoms increased, but tOp fresh weight decreased with increasing Ca/K in the nutrient solution. The correlation Of environmental treatment with blackheart ratings was not significant at the 5% level (r = -0.070). Discussion With the exception Of the values at the 100/176 Ca/K ratio, the values Of the tOp and root fresh weights were higher in the misted plots than in the control and the heat lamp plots (Figs. 12, 13). However, the percentage Of dry matter in the tOps of the control was higher, resulting in no significant differences in the dry weights Of tops and roots between the plants Of the environmental treatments (Table 7). The increase in fresh weight in the misted plants was in agreement with the results Of other workers (4, 7, 14, 47, 53) who found increased growth due to reduced plant moisture stress. The significant increase in sucker 66 weight by the mist applications compared to the control (Table 7) resulted in a marketable weight not significantly different from that Of the control. The reduction in the volume of water transpired per gram Of dry matter produced by the mist applications com- pared to the control (Table 9) was in agreement with McMil— lan and Burgy (32) who found that tranSpiration was reduced prOportionally to the evaporation Of the sprinkled water. The reduction in tranSpiration was not accompanied by a reduction in the uptake Of nutrients into the heart tissues (Table 8), nor by a change in the Ca/K ratio in the heart tissues (Table 9). This did not agree with the findings of Freeland (13) in which he Observed that higher transpiration caused corn and bean plants to take up relatively less Ca and more K. Michael and Marschner (35) also found that ion uptake was affected by reduced transpiration rates but their transpiration rates were reduced much more than they were in this eXperiment. The only notable effect Of the infrared heat lamps was tO increase the volume Of water transpired per gram Of dry matter produced (Table 9). However, as for the mist application, the altered transpiration rate did not result in a marked altering Of the mineral uptake. The lower Ca/K ratios in the nutrient solutions yielded higher fresh weights but lower percentages Of dry matter (Table 7), resulting in no significant differences 67 in dry matter produced compared tO the higher Ca/K ratios. Similarly the sucker weights were higher, resulting in no significant differences in marketable weight. AS the Ca/K ratio increased in the nutrient solutions, the K content in the heart tissues decreased and the Ca content increased, resulting in an increasing Ca/K ratio in the hearts (Tables 8, 9). This was in agreement with Observations of Geraldson (18). Also, the decrease in severity Of blackheart symptoms with increasing Ca/K ratio in the nutrient solution (Table 9) was in agreement with the Observations of other workers (2, 18, 29) . The volume Of water tranSpired per gram of dry matter produced was lowest in the lowest Ca/K ratio solution and highest in the highest Ca/K ratio and approximately equal in the medium ratio solutions (Table 9). Wostmann (54) found tranSpiration to decrease with increasing Ca/K ratio in solutions. However, Wostmann (54) and Biebl (5) found that highly unbalanced K applications caused reduced transpiration which may have been the case in the low Ca/K ratio solution. On the other hand, low K could have caused an increase in transpiration (48, 54). This may have been the case in the high Ca/K ratio solution. The simple linear correlation coefficients (Table 10) indicate that blackheart increased in intensity with increas- ing tOp fresh weight, increasing sucker weight and decreasing 68 percentage Of dry matter. Since these three factors are associated with succulence or increased vigor, then it fol- lows that blackheart increased in severity with increased vigor. This has been reported by many workers (1, 2, 18, 46, 49). The correlation coefficients also show that black- heart was related tO Ca, K, B and Ca/K ratio in the heart tissue. These same trends were pointed out in Table 8 and were discussed previously. While each Of the factors men— tioned above was related tO blackheart, each was related in the Opposite direction tO the Ca/K ratio in the nutrient solution. The environmental treatments, with increasing atmOSpheric stress from mist tO control to heat lamps, showed no significant correlation with blackheart. Thus, in this eXperiment the Ca/K ratio in the nutrient solution appeared to have been the dominant factor affecting the severity of blackheart symptoms. II. Effects of Ca/K Ratio, Solution Concentration and Environmental Conditions 93 Celery Grown in Nutrient Solutions In the previous greenhouse experiment the use Of infrared heat lamps to increase plant water stress caused an increase in transpiration but did not significantly alter any Of the other characteristics recorded. In order to have a more effective means Of increasing plant water stress, different levels Of osmotic concentrations Of the nutrient 69 solutions were employed in the following eXperiment in con- junction with Ca/K ratios and mist applications. Procedure Utah 52-70 celery seed was sown in vermiculite and the seedlings grown tO tranSplanting size in a one-half muck/ one-half sand mixture. On June 25, 1966 these plants were placed in half-strength Hoaglands NO. 2 nutrient solution (22) in 2-gallon crocks. Blackheart symptoms began appear- ing on July 5. To reduce the intensity Of the symptoms the Ca(NO content in the nutrient solutions was doubled and 3)2 the KNO halved when the solutions were changed on July 6 3 and again on July 20. On July 29, 1966 the following treatments were put into effect according to a Split-split-plot design with two replications: Main plots 1 100 ppm. Ca/l76 ppm. K 2 200 ppm. Ca/59 ppm. K Sub-plots l Mist 2 Control Sub-sub-plots l 0.3 atm. concentration 2 1.2 atm. concentration 3 4.8 atm. concentration. Main plot and sub-plot treatments were carried out as described in the previous eXperiment. 70 In the sub-sub-plots the osmotic concentrations were adjusted to 0.3, 1.2, and 4.8 atm. by altering the content of each element in the solutions while maintaining the Same balance between the elements. The pH of the solutions was adjusted tO 6.0. Records were taken during the course Of the eXperi- ment as indicated in the previous eXperiment. In addition, a 16-point strip-chart recorder was set up to record temper- atures by means Of COpper-constantan thermocouples con- structed Of 24-guage wire in the air, solutions and plant hearts, and by means Of thermocouples a 40-guage wire inserted into leaf veins. On several days transpiration values were recorded throughout the day by noting the volume Of water lost from inverted containers that fed water into the crocks as it was taken up by the plants, thereby keeping the level in the crocks constant. On September 24, 1966 the plants were harvested and final records were made and statistically analyzed as indi- cated for the previous eXperiment. Results Data recorded on celery growth is summarized in Table 11. The 200/59 Ca/K ratio nutrient solution resulted in significantly lower total tOp and root fresh weights than those in the 100/176 ratio solution. The interaction Of 71 Ca/K ratio X solution concentration on marketable weight was significant (Fig. 14), indicating that the marketable weight was higher in the 200/59 ratio solutions than in the 100/176 ratio solutions at the 1.2 and 4.8 atm. solution concentra- tions but lower at the 0.3 atm. The interaction of Ca/K ratio X solution concentration was also significant for root dry weight. It may be exPlained in the same terms as the previous interaction. There was also a significant interac- tion Of Ca/K ratio X solution concentration on root percent- age dry matter (Fig. 15). In this case, the root percentage of dry matter showed a greater increase from the 100/176 ratio to the 200/59 ratio the higher the solution concentra- tion. Misting resulted in a significant increase in the total tOp fresh weight per plant above that Of the control (Table 11). The 1.2 atm. solution yielded higher total tOp fresh weight, sucker fresh weights, top dry weight and lower per- cent dry matter in the tops and roots than either the 0.3 atm. or 4.8 atm. (Table 11). In these measurements the 0.3 atm. and the 4.8 atm. solutions were not significantly dif- ferent from each other except in root percentage dry matter in which case the former was lower than the latter. Root fresh weight was lower in the 4.8 atm. nutrient solutions than in the 0.3 and 1.2 atm. (Table 11). Marketable weight was lower in the 4.8 atm. than in the 1.2 atm. but not 72 .H0>0H RA may um Damowwflcmflmss .H0>0H.xm Gnu um unmowwacmwms .Hw>wa x0 03» um ucmumwmao >HOGOUAMAcmHm mum mumuuma GOEEOUCS an owBOHHom mmSHm>H es A At .0:00 .caom x owumu M\mo cofluomumucH m 0.0 m N.0H A 0.0 A m.mh n 00 n ema n mom A man .Eud m.¢ m o H.0 A 0.0 nm 0.0 m m.0m m 50H m Nmm m mam m egaa .Eu¢ ~.H N n o.b m 0.0 m 0.0 n m.mh 0 em a hma no wmv Q own .294 m.o a .ocoo SOAOSHOm m h.0 m 0.m m N.0 m m.mm 0 mm m mom 0 mme n 000 Houucoo N m 0.0 m v.0 m m.0 m 0.Hm 0 0m 0 00m 0 How 0 mmoa and: H ucmEdOHw>cm m N.> m 0.0 m 0.0 m 0.00 A mm m Hma 0 05¢ a com mm\oom N m «.0 m 5.0 m H.0 m 6.0m .0 mm m mom 0 00% am 0moa 0ha\ooa a osumm x\mo uoom mos uoom mos uoom meosm mo» mou .uxz Hmboe Hmuume AmEmumv unmam AmEmHmv who ucmoumm mom unmam3 hum Osman mom unmam3 nmmum coaumuucmocoo 0cm owumn &\mo GodusHom ucmfluusc .ucmficouw>cm Ou omumaou mucmam mumamo mo £u30n0 .HH magma MARKETABLE WEIGHT (gr . ) Figure 14. ROOT % DRY MATTER Figure 15. 73 700 600 500 400 300 100/176 200;59 Ca/K,RATIO The effect Of the interaction Of Ca/K . ratio and nutrient solution concentration on marketable weight Of celery. 0.3 Atm.‘--- , L 1.2.Atm. /’/ 9-0 4.8 Atm.-----,/ ///I 8.0 . ,1 (I 7.0 - ’, -—- r " 6.0 > 5.0 n . 100/176 ZOO/59 " Ca/K RATIO The effect Of the interaction Of Ca/K ratio and nutrient solution concentration on the percentage Of dry matter in celery roots. 74 Significantly different from that in the 0.3 atm. solutions. Root dry weight was lower in the 4.8 atm. solutions than in the 0.3 atm. but not significantly different from that in the 1.2 atm. In the last 28 days Of the eXperiment (August 26 to September 24) the misted plants in the 1.2 atm. solutions increased in fresh weight 552 g. in 100/176 Ca/K ratio solu- tion and 590 g. in 200/59 solutions. The increases for con— trol plants were 482 g. in 100/176, and 524 g. in 200/59 Ca/K ratio solution. The mineral content Of celery heart tissue is pre- sented in Table 12 for elements that showed Significant dif— ferences between means. The 100/176 Ca/K ratio in the nutrient solution resulted in a higher K content in the heart tissue than did the 200/59 ratio solution. However, the interaction Of Ca/K ratio X solution concentration was significant (Fig. 16) for K content. This interaction showed a smaller decrease in K content from the 100/176 to the 200/59 ratio at the 4.8 atm. solution concentration than at the 0.3 or 1.2 atm. concentrations. The mist treatment resulted in a lower B content Of heart tissue than did the control (Table 12). From Table 12 K content Of the heart tissues was lower and Mg content was higher in the plants grown in the 0.3 atm. solutions than in the 1.2 and 4.8 atm. solutions. 75 Table 12. Mineral content Of celery heart tissue related to environment, nutrient solution Ca/K ratio and concentration K Mg P B % %, %. PPm CaZKVRatiO 1 100/176 5.43 a .314 1.63 187 2 200/59 4.51 b .247 1.44 223 Environment 1 Mist 4.87 a .256 1.57 195 2 Control 5.07 a .306 1.50 215 Solution Concentration 1 0.3 Atm. 4.21 c .400 1.44 238 2 1.2 Atm. 5.57 a .264 1.66 167 3 4.8 Atm. 5.12 b .230 1.40 268 Interaction ** Ca/K ratio X Soln. conc. l ent at the 5%.level. **Significant at the T% level. Values followed by uncommon letters are significantly differ- K CONTENT OF HEART TISSUE (‘36) 3.0 76 100/176 200/59 Ca/K RATIO Figure 16. The effect Of the interaction Of Ca/K GRAM OF DRY MATTER (ml.) WATER TRANSPIRED PER Figure 17. 500 450 400 350 300 ratio and nutrient solution concentration on the K content Of celery heart tissue. 0.3 Atm.‘ '-'— 1.2-Atm. 4.8 Atm. ----- ’J V// ..... §‘. 100/176 200/59 Ca/K RATIO The effect Of the interaction Of Ca/K ratio and nutrient solution concentration on the volume Of water tranSpired per gram Of dry matter produced. 77 The values in Table 12 also indicate that P content was higher and B content lower at 1.2 atm. than at either the 0.3 or 4.8 atm. concentration. Ca contents in the plant hearts showed no significant differences between treatments. Treatment mean values ranged from 0.331 to 0.477% Ca. Ratings Of blackheart symptoms, volume Of water transpired per gram Of dry matter produced and Ca/K ratio in heart tissues are summarized in Table 13. Although there were no significant differences attributable to Ca/K ratio of the nutrient solutions in these respects, the interaction Of Ca/K ratio in the solutions X solution concentration for tranSpiration was significant (Fig. 17). Transpiration was higher in the 200/59 Ca/K ratio solutions than in the 100/176 Ca/K ratio solutions for the 0.3 and 1.2 atm. concentrations but lower for the 4.8 atm. The mist treatment resulted in a lower volume Of water transpired per gram Of dry matter than did the control (Table 13). The 1.2 atm. concentration resulted in a higher degree Of blackheart symptoms than did the 4.8 atm. solution, but not significantly different from the 0.3 atm. (Table 13). There was a higher rate Of transpiration and a higher Ca/K ratio in the heart tissue in plants grown in the 0.3 atm. solutions than in either the 1.2 or 4.8 atm. (Table 13, Fig. 17). 78 Table 13. Blackheart ratings, transpiration and Ca/K ratio in celery heart tissue related to environment, nutrient solution Ca/K ratio and concentration ——‘ Blackheart ratings Water transpired l—nO symptoms per gram Ca/K ratio 9—severe dry matter in heart symptoms (ml.) tissue Ca/K Ratio ,1 100/176 2.9 a1 365 a .062 a 2 200/59 1.6 a 384 a .108 a Environment 1 Mist 2.0 a 316 b .083 a 2 Control 2.5 a 433 a .087 a Solution Concentration 1 0.3 Atm. 1.9 ab 421 a .115 a 2 1.2 Atm. 2.6 a 362 b .082 b 3 4.8 Atm. 1.5 b 347 b .078 b Interaction Ca/K ratio X Soln. conc. * lValues followed by uncommon letters are significantly differ- ent at the 5% level. *Significant at the 5% level. 79 Table 14 contains the simple linear correlation coefficients that were significant between blackheart symp- toms and other factors in the experiment and the correspond— ing coefficients between treatments and the same factors. The values indicate that blackheart severity increased with increasing sucker weight and K and P content in the heart tissues, while symptoms decreased in severity with increas- ing tOp percentage of dry matter, Ca, B and.Ca/K ratio in heart tissues, and Ca/K ratio in the nutrient solutions. In each case the correlation with Ca/K ratio in the nutrient solutions showed the Opposite relationship. The correlation Of environmental treatments with blackheart ratings was not significant at the 5%.leve1 (r = +0.199). The effects Of misting on temperature are summarized in Table 15. Recordings made at 8:00 a.m. prior to starting the mist indicate that leaf temperatures were 0.2 C lower in the misted plots than in the control while heart tempera- tures were 0.3 C lower, air in canOpy 0.9 C lower and nutri- ent solutions 1.0 C lower. The 2:00 p.m. recordings when the mist was in Operation indicated that leaf temperatures were 2.4 C lower, hearts 1.2 lower, air in canopy 2.6 lower and nutrient solutions 1.8 lower in the misted than in the control plots. 80 Table 14. Relationship Of blackheart rating and nutrient solution Ca/K ratio to celery plant characteris- tics (simple linear correlation coefficients) m Ca/K ratio Blackheart in nutrient rating solutions Top percent dry matter -.434 * +.306 Sucker weight +.518 ** -.408 * Ca content in heart -.436 * +.575 ** K content in heart +.534 ** -.597 ** P content in heart +.600 ** -.490 ** B content in heart -.547 ** +.287 Ca/K ratio in heart —.543 ** +.656 ** Ca/K ratio in nutrient solutions -.539 ** *Significant at the 5% level. **Significant at the 1%.leve1. 81 Table 15. Mean daily 8:30 a.m. and 2:00 p.m. leaf, heart, air and solution temperatures (C) between August 25 and September 5, 1966 8:30 a.m. 2:00 p.m. Temper- Difference Temper- Difference ature between ature between mist and mist and control control LS: l Mist 23.4 .. 27.2 ... 2 Control 23.6 0.2 29.6 2.4 E2252 1 Mist 23.1 ... 28.2 ... 2 Control 23.4 0.3 29.4 1.2 Ail; £1 canopy l Mist 22.9 ... 27.9 ... 2 Control 23.8 0.9 30.5 2.6 Nutrient solution 1 Mist 23.2 ... 28.2 ... 2 Control 24.2 1.0 30.0 1.8 82 Figure 18 shows the effect Of misting on the rate of transpiration Of the celery plants. Before the misting started the transpiration rates were approximately equal at about 30 cc./hour. AS environmental stress increased, the control plants increased in tranSpiration rate more rapidly than did the misted plants and reached a rate Of approxi- mately 33 cc./hour higher than plants in the misted plots. After misting ceased the difference gradually disappeared. Values for daily transpiration, blackheart ratings and growth rates are plotted for the period between August 17 and September 18, 1966 in Figure 19. Comparing the black- heart values tO those Of transpiration there was an indica- tion that where tranSpiration was low, blackheart symptoms tended to decline and where tranSpiration was high, black- heart symptoms either remained relatively constant or increased. In comparing the growth rate to the transpiration rate (Fig. 19), during periods Of high transpiration the growth rate in the misted plots appeared tO exceed that Of the control plots, while during periods of low tranSpiration growth rate in misted plots was as low as or lower than that Of the control plots. In like manner there was a suggested relationship between growth rate and blackheart symptoms-- symptoms increasing in severity during periods Of greater difference between growth rates Of misted plants and control plants and decreasing during periods Of smaller differences. 1 TRANS P IRAT ION RATE (cc./hr.) Figure 18. 83 00 ’ CONTROL MIST -— —— 80 ' 60 r 40F 20 r 0 l L n L L L k A A 9:00 11:00 1:00 3:00 5:00 a.m. a.m. p.m. p.m. p.m. TIME The effect Of mist on transpiration rate on a typical hot day (August 26, 1966) with some cumulus cloud. Mist was in Operation from 9:00 a.m. until 4:00 p.m. 800- a, 700 Ill 04 g} 600 m E ... (£522: 500 Eon-a [-1 m 400 III E4 g 300 w o 523* go; +40 BIL” RES 020 Es on) 2:0 0 ll SF4C‘ m 5% [SJ >1 20 E .8 2%} Sggfii 15 aagéf E5 - 10 6 8 z v H 5 Figure 19. 84 (l) MIST - - ~— _ CONTROL ...—...... I rs 18 21 24 27 30 2 5 8 ll l4 17 August September DATE The relationship between tranSpiration, blackheart rating and growth rate from August 17 to September 18, 1966.; (1) Mean daily tranSpiration: (2) Mean black- heart rating; (3) Mean growth rates. 85 Discussion The effects Of the Ca/K ratios in the nutrient solu- tions and the effects Of the environmental treatments (Tables 11, 12, 13) generally follow the same trends as in the previous eXperiment. The 1.2 atm. solution resulted in higher plant tOp weights than those Of the 0.3 atm. treatment (Table 11). This could have been caused by a depletion Of one or more elements to deficiency levels in the 0.3 atm. solutions between the weekly solution changes. The plant top weights at 4.8 atm. were also lower than those at 1.2 atm. (Table 11). This could have resulted from a reduction Of growth due to plant moisture stress as has been reported by other workers (11, 21, 39). The K content Of the heart tissues was lower in the 4.8 atm. treatment compared to the 1.2 atm. treatment but the Ca contents and the Ca/K ratios were not significantly different (Tables 12, 13). This, plus a lower vigor may eXplain why the blackheart symptoms were not as severe in the 4.8 atm. solution as in the 1.2 atm. solution (Table 13). Geraldson recorded Similar results in nutrient solutions but in the field he Observed blackheart to be more severe in plants grown under high soil osmotic conditions with resul— tant lower Ca/K ratio in the heart tissues (17, 18). 86 The low osmotic concentration treatment (0.3 atm.) resulted in a lower K content and a higher Ca/K ratio in the heart tissues than was found in plants Of the 1.2 atm. con- centration treatment (Tables 12, 13). This condition tO- gether with the lower vigor may explain the trend to lower blackheart ratings in the 0.3 atm. as compared to the 1.2 atm. solutions. The correlations presented in Table 14 show generally the same relationship as found in the previous eXperiment (Table 10) in that plant vigor, plant Ca, K, B and Ca/K ratio are closely related to blackheart symptoms but that they are also closely related tO the Ca/K ratio Of the nutrient solutions. P showed a significant correlation with blackheart in this exPeriment and in outdoor experiment II but not in the previous greenhouse eXperiment. The temperature values presented in Table 15 indi— cate that there was a small carryover effect Of the mist treatments tO the following day. The lower 2:00 p.m. tem- peratures in the misted plots could account in part for the decrease in transpiration rate as shown in Figure 18. This reduction in temperature and tranSpiration rate helps ex- plain the higher growth rate Of misted plants compared to the control plants during the periods Of higher temperatures (Fig; 19). The high points in transpiration values were associated with high temperatures and appeared to coincide with the greatest differences in growth rate between control 87 and misted plants while the low points in transpiration coincided with the smallest difference in growth rate. Although the blackheart curve in Figure 19 appeared to Show some relationship to the transpiration curve, the trends were somewhat weak. The periods Of high and low stress were possibly too short to show marked rises and falls in symptom ratings. Thus, the symptoms may have maintained a middle path between extremes that could have resulted with longer atmospheric cycles. GENERAL DISCUSS ION The purpose Of this investigation was to study celery plant characteristics and the development Of black- heart under various conditions Of plant water balance as affected by altered atmospheric conditions, soil moisture levels, osmotic concentrations and ion balances. Misting generally resulted in an increase in total fresh weight with a relatively smaller increase in dry weight because of a lower percentage Of dry matter. Sucker weight was also increased by mist applications resulting in no significant gain in marketable weight attributable to misting. The increased succulence associated with the lower percentage Of dry matter may indicate a quality improvement in celery due to misting. Since nO guide-lines were available marking the point where plant moisture stress begins in celery, it is possible that mist was applied during the course Of the out— door eXperiments when the combination Of temperature, solar radiation intensity, relative humidity, wind speed and root medium stress did not add up tO a detrimental plant water stress. In such occasions misting may have caused a reduc— tion in net photosynthesis as is indicated by the growth rates during periods of low transpiration shown in Figure 19. 88 89 It is possible that greater benefits could have been gained from misting in the outdoor eXperiments had the critical point for plant stress been known. Furthermore, the higher the temperature during the growing season, the greater might have been the potential benefit from misting. Misting did not cause any marked effect on nutrient uptake. Based on the dry matter produced, misting reduced transpiration l4 and 19% in the outdoor eXperiments I and II respectively and 20 and.27% in greenhouse eXperiments I and II respectively. The decrease was lower outdoors because mist was applied only on high temperature days while it was applied every day in the greenhouse. These reductions in transpiration may not have been great enough to cause marked changes in nutrient uptake as reported by other workers (13, 35, 40). It is possible that by reducing transpiration rate for only six hours per day, ample time remained fOr the plant to regain its nutrient equilibrium. The low soil moisture level resulted in considerably lower fresh and dry weights compared to high soil moisture (Tables 1, 2). This may be attributed to the higher degree Of plant water stress as indicated by the higher wilt ratings. This was in agreement with the Observations Of other investi- gators (7, 8, 14, 23, 27, 41, 52, 53). The higher percentage Of dry matter in the plants with low soil moisture may be associated with lower quality in celery and as such would be in agreement with the Observations Of Janes (23). 90 In soil culture, the osmotic effect Of the applica- tions of 3000 pounds of Ca per acre and 4380 Of K to muck soil was not sufficient to cause any marked plant response compared to the control. The high exchange capacity Of the colloids in the muck may have minimized the effects of the salt applications. High salt applications in a predominately mineral soil, however, resulted in increased water-use effi- ciency and increased fresh and dry weights with 2190 pounds of K per acre and 1305 of Na. This was in agreement with Viets (48). The application of 1500 pounds of Ca per acre and combinations Of 750 Ca plus 652 Na and 1500 Ca plus 1305 Na resulted in the same weight Of dry matter as in control plots but higher fresh weights due to lower percentages of dry matter being produced. Despite the fact that equal volumes Of water were applied to salt—treated plots and control plots, the control plants wilted the most severely. This was in agreement with other workers (3, 10, 11, 28) who believed that a moderate stress, but no wilting, is main- tained throughout the irrigation cycle limiting growth Of the plants. From this it appears that the osmotic stress from Ca and Na caused as much plant water stress as the soil moisture tension in the control plot resulting in equal dry ' matter production but the different type Of stress as described by Slatyer (39) for high osmotic concentrations of the soil solution resulted in a higher succulence. 91 In nutrient solutions, 0.3 atm. and 4.8 atm. con- centrations with equal nutrient balance resulted in inferior growth compared tO 1.2 atm. Deficiencies Of some elements could have occurred because of low supply due to depletion in the 0.3 atm. solutions. This could also eXplain the reduced water-use efficiency Of this treatment. The high osmotic concentration could have resulted in lower growth because Of a plant moisture stress as has been reported by other workers (3, 10, ll, 38). Celery plant fresh weight decreased with increasing Ca/K ratio, with the exception Of the lowest Ca/K ratio where low Ca may have been a limiting factor. However, since the percentage Of dry matter increased with increasing Ca/K ratio, the net weight Of dry matter produced was not generally affected significantly by Ca/K ratio, but tended to be somewhat lower at the high Ca/K ratio. Water-use efficiency was approximately Similar at the intermediate Ca/K ratios but was lower at the high ratio possibly due to low K, and higher in the low ratio possibly due tO high K. The low K situation follows the thinking Of Viets (48) in that any fertilizer that increases yield also generally increases water-use efficiency. The high K effect agreed with the findings Of Wostmann (54) and Biebl (5) who found that with highly unbalanced K applications tO the soil, transpiration rates were lower due to the K. However, it 92 was contrary tO Wostmann's (54) findings that transpiration rate increased with decreasing Ca/K ratio in solutions. Blackheart symptoms were not significantly different on misted and control plants. Nevertheless, the mist appli- cations prevented an increase in the severity Of the symp- toms that should have been associated with the increase in plant fresh weight and succulence resulting from the mist treatment. Blackheart was most markedly affected by the Ca/K ratios in the nutrient solutions. Symptoms decreased with increasing Ca/K ratio. Also, blackheart was positively correlated with tOp fresh weight, sucker weight, K content in the heart tissues, and negatively correlated with tOp percentage Of dry matter, Ca, B and Ca/K ratio in the heart tissues. Yet, each Of these plant characteristics was correlated with the Ca/K ratios supplied in the nutrient solutions. Therefore, the nutrient solution Ca/K ratio appeared to have been the dominating factor in blackheart eXpression. Geraldson (17, 18) found the Ca levels in young leaves Of plants with blackheart symptoms to be from 0.1 to 0.4% while levels were 0.5 to 1.0% in young leaves from healthy plants. In greenhouse eXperiment I, carried out between May 13 and June 17, 1966 the Ca contents of the celery heart tissues varied from means Of 0.099 tO 0.215% (Table 8). Blackheart symptoms were present in most Of the 93 plants and to a greater degree than in the other experiments. In greenhouse eXperiment II carried out between July 29 and September 24, 1966 the Ca contents varied from means Of 0.331 to 0.477%.and.blackheart symptoms were not as pro- nounced as in greenhouse experiment I. In field eXperiment II carried out between May 28 and September 14, 1966 the Ca contents varied from means Of 0.410 to 0.477% (Table 3). These Ca values agree closely with Geraldson's values given above, showing that in greenhouse eXperiment I Ca contents were conducive to blackheart, in greenhouse eXperiment II Ca contents were borderline and in field eXperiment II Ca contents were just above the values conducive to blackheart. One reason for the difference in Ca content Of heart tissue and associated blackheart symptoms between the two greenhouse eXperiments could be the difference in growth rates. In the last 28 days Of greenhouse experiment I plant fresh weight in the control increased 879 9. while in exper— iment II in the same length Of time and with reasonably comparable treatments the increase in weight was only 482 9. Thus the higher blackheart ratings Of eXperiment I could have been due to a more rapid rate Of growth with Ca uptake falling behind the demands Of the plant to a greater extent. This was a reason suggested by Geraldson (20) for blackheart development. 94 Higher greenhouse minimum and maximum air and root) medium temperatures may eXplain the presence Of blackheart symptoms in the greenhouse and virtual absence in the field. Geraldson (l7, 18) found that the Ca content in the young tips Of tomato and celery plants varied inversely with the temperature. Blackheart occurrence may depend on the additive effects Of temperature, soil moisture level and nutritional status. In outdoor eXperiments III and IV with plants grown in muck soil, the adequate soil moisture level may have pre- vented blackheart from develOping. Geraldson (20) was Of the Opinion that low soil moisture could bring about a decreased.Ca uptake. However, in outdoor eXperiments I and II with plants grown in predominantly mineral soils, the soil moisture levels did fluctuate widely and plants did wilt, but the one or two days at high soil moisture stress may not have been a sufficiently long period for the plant Ca level in the heart tissues to be exhausted to the crit- ical level. On the other hand, with a continuously adequate soil moisture level or with short fluctuating cycles, a prolonged period of higher than usual air and soil temper— atures may be necessary for blackheart development. C ONC LUS IONS The application Of low rates Of irrigation (misting) to reduce plant water stress resulted in an increase in total fresh weight Of celery plants compared tO the control and a relatively smaller increase in total dry weight. Sucker weight was higher in the misted plants than in the control resulting in no significant gain in marketable weight but the marketable product was more succulent. Mist- ing during periods Of low temperature resulted in decreased rate Of growth. Misting reduced transpiration from 14 to 27%.but did not appreciably alter nutrient uptake. Increased radiation by means Of infrared heat lamps increased transpiration but did not markedly alter any other conditiOns Of the plant. Low minimum soil moisture (20-30% ASM) resulted in lower fresh and dry weights Of celery and a higher percent- age Of dry matter compared to high moisture (70-80%.ASM). Water-use efficiency was not consistently affected by soil moisture. The application of Ca plus Na to mineral soil tO increase the soil solution Osmotic concentration resulted in higher fresh weights, lower percentages of dry matter, simi- lar dry weights and water-use efficiencies and lower degrees 95 96 of wilting than the control using the same amount Of water. High (4.8 atm.) and low (0.3 atm.) osmotic concentrations in nutrient solutions generally resulted in lower plant fresh and dry weights but higher percentages Of dry matter com- pared tO those Of intermediate osmotic concentration (1.2 atm.). Water-use efficiency was lowest at the low concen- tration but not different at the intermediate and high. In soil and nutrient solutions fresh weight generally increased with decreasing Ca/K ratio and dry weight increased to a relatively smaller degree. The large increase in fresh weight with decreasing Ca/K ratio was Offset by a large increase in the sucker weight, which resulted in no differ- ence in marketable weight. In soil and solution culture very low Ca/K ratios resulted in a higher water-use effi- ciency, while moderate Ca/K ratios resulted in nO differ- ences. High Ca/K ratios.in nutrient solutions resulted in lower efficiency. Blackheart symptoms increased in severity with increasing plant tOp fresh weight, sucker weight, and K content Of heart tissue, but decreased with increasing per- centage Of dry matter, Ca, B and.Ca/K ratio in heart tissue. Blackheart severity was the same in misted as.in control plants. HOWever, the greater fresh weight and succulence Of the misted plants was not accompanied by an increase in blackheart severity. 97 Blackheart symptoms were highest in 1.2 atm. concen- tration solutions compared to 0.3 and 4.8 atm. solutions with the same nutrient balance, and were not different at the latter twO concentrations. The symptoms Of blackheart increased in severity with decreasing Ca/K ratio in the nutrient solutions. 10. LITERATURE CITED Beckenback, J. R., and E. L. 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