GREENHOUSE TOMATO RESPONSE TO LOW AMMONIUM-NITROGEN CONCENTRATIONS AND DURATION OF AMMONIUM-NITROGEN SUPPLY

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1 This article was downloaded by: [Colegio de Posgraduados] On: 22 January 2015, At: 06:43 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: Registered office: Mortimer House, Mortimer Street, London W1T 3JH, UK Journal of Plant Nutrition Publication details, including instructions for authors and subscription information: GREENHOUSE TOMATO RESPONSE TO LOW AMMONIUM-NITROGEN CONCENTRATIONS AND DURATION OF AMMONIUM-NITROGEN SUPPLY M. Sandoval-Villa a, E. A. Guertal b & C. W. Wood b a Colegio de Postgraduados, Programa de Edafología, Montecillo, Méx, 56230, México b Department of Agronomy and Soils, 202 Funchess Hall, Auburn University, Auburn, AL, , U.S.A. Published online: 14 Feb To cite this article: M. Sandoval-Villa, E. A. Guertal & C. W. Wood (2001) GREENHOUSE TOMATO RESPONSE TO LOW AMMONIUM-NITROGEN CONCENTRATIONS AND DURATION OF AMMONIUM-NITROGEN SUPPLY, Journal of Plant Nutrition, 24:11, , DOI: /PLN To link to this article: PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the Content ) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at

2 JOURNAL OF PLANT NUTRITION, 24(11), (2001) GREENHOUSE TOMATO RESPONSE TO LOW AMMONIUM-NITROGEN CONCENTRATIONS AND DURATION OF AMMONIUM-NITROGEN SUPPLY M. Sandoval-Villa, 1, * E. A. Guertal, 2 and C. W. Wood 2 1 Colegio de Postgraduados, Programa de Edafología, Montecillo, Méx., México Auburn University, Department of Agronomy and Soils, 202 Funchess Hall, Auburn University, Auburn, AL ABSTRACT High ammonium-nitrogen (NH 4 -N) concentration in solution may adversely affect greenhouse tomato (Lycopersicon esculentum Mill.) yield, but it has been reported that small NH 4 -N fractions improve yield and may increase vegetative growth and nutrient element uptake. The effects of short- or long-term supply of NH 4 -N to tomato plants is not clear, and further information is required to determine how it can affect fruit yield. The objective of this study was to determine the tomato yield response to 0:100, 10:90, 20:80, 30:70, and 40:60 NH 4 -N:NO 3 -N ratios supplied at the vegetative, vegetative plus flowering, flowering plus fruiting, and fruiting stages, and over the entire plant life cycle. *Corresponding author Copyright # 2001 by Marcel Dekker, Inc.

3 1788 SANDOVAL-VILLA, GUERTAL, AND WOOD Two experiments under greenhouse conditions were conducted with ambient light in which light intensity was 2,667 and 5,030 W h 71 m 72 for the winter ( ) and the spring (1997) experiments, respectively. In both experiments, neither the length of NH 4 -N supply nor the NH 4 -N concentration in solution affected tomato yield. Longer NH 4 -N supply increased the amount of fruit with blossom-end rot (BER) in the winter ( ) experiment, but BER incidence was unaffected in the spring (1997) experiment by duration of NH 4 -N supply. The number of fruit with BER was greatly increased by higher NH 4 - N concentrations in solution in the spring (1997) experiment. Plant height was not affected by NH 4 -N concentration in either the winter or spring experiments, and neither was fruit firmness measured for fruit at the mature green stage. Fresh and dry weights were unaffected by NH 4 -N concentration or length of supply, but in the spring (1997) experiment, fresh weight of leaves, as well as their proportion to the weight of the aerial parts, were affected by both NH 4 -N concentration and length of supply. High concentrations of NH 4 -N and long periods of NH 4 - N supply increased calcium (Ca) concentration in leaf tissue, but only for the spring (1997) experiment was there a significant relationship between Ca concentration in leaves and BER incidence. INTRODUCTION In most NH 4 -N:NO 3 -N ratio studies, NH 4 -N concentrations were widely spaced at intervals of 25 to 30%. Some researchers have concluded that for highest tomato yields, optimum NH 4 -N concentrations in hydroponic culture should be around 25% or 30% of total N in solution (1,2). However, the addition of NH 4 -N fractions as small as 4% to 8% to the nutrient solution have been found to increase yield of bell pepper (Capsicum annum L.) (3) and Irish potato (Solanum tuberosum L.) plants (4). There are few reports regarding the effect of variations in NH 4 -N supply during different plant growth stages, where concentration of NH 4 -N in solution corresponded to a small fraction of the total N at different stages of plant growth or for different lengths of NH 4 -N supply. Work dealing with different lengths of NH 4 -N supply was conducted by Sarro et al. (3). They found that the longer NH 4 -N (30%) was supplied, the lower the fruit yield of bell pepper. Fruit yield for treatment with 30% NH 4 -N applied throughout the plant growth cycle was 200 g plant 71 lower than fruit yield obtained without NH 4 -N. Low temperatures in the root zone decreased NO 3 -N and K transport to plant

4 GREENHOUSE TOMATO 1789 shoots, while reducing uptake of Ca and Mg by roots, which resulted in a significant decrease in the root growth. This effect may also be related to sugar depletion due to the assimilation of NH 4 -N in roots (5 7). Fruit firmness is known to be higher with nutrient solutions containing NO 3 -N plus NH 4 -N or NH 4 -N plus urea than with NO 3 -N alone (8). Ahrens et al. (9) demonstrated that fruit firmness and stability depends on the fruit development stage in which it is determined. Ahrens et al. (9) monitored whole fruit and pericarp firmness throughout ripening from immature-green to red in 12 tomato cultivars. Their results indicated that fruit firmness at the immature-green, mature-green, or breaker stage was not correlated to firmness at the red stage (table-ripe). Pericarp firmness was highly correlated with whole fruit firmness at the red stage, but only moderately at earlier ripening stages. The objective of this study was to evaluate the response of a greenhouse tomato cultivar to low NH 4 -N concentrations in solution supplied throughout the plant growth cycle, and during the vegetative, vegetative plus flowering, flowering and fruiting plus fruiting, stages of plant growth. MATERIALS AND METHODS Experimental Design A randomized complete block design with six replications was used to conduct two experiments. Treatments consisted of the combination of five NH 4 - N:NO 3 -N percent ratios (0:100, 10:90, 20:80, 30:70, and 40:60) and three periods of application for each NH 4 -N:NO 3 -N ratio. Periods of application for the winter ( ) experiment were during the vegetative, vegetative plus flowering, and for the entire plant cycle. In the spring (1997) experiment, NH 4 -N:NO 3 -N ratios were applied during fruiting, flowering plus fruiting, and during the entire cycle of plant growth. Response variables chosen were tomato yield, BER incidence, number of fruit produced by each plant, fresh and dry weight, and nutrient element concentrations in leaves and fruit. Nutrient Solution A Steiner (10) type nutrient solution with a total N concentration of 12 mm was used under hydroponic greenhouse conditions to grow the indeterminate tomato variety Max. Levels of other nutrient elements were maintained at 5 mm for Ca, 6 mm for potassium (K), 2 mm for magnesium (Mg), and 1 mm for phosphorus (P). A stock solution of iron (Fe)-DTPA (HydroGardens, Colorado Springs, CO) was prepared at 10 g L 71. One ml of the Fe stock solution was

5 1790 SANDOVAL-VILLA, GUERTAL, AND WOOD utilized per final liter of nutrient solution. Micronutrients were provided as a commercial mixture of boron (B), copper (Cu), manganese (Mn), molybdenum (Mo), and zinc (Zn) (Frit Industries, Inc., Ozark, AL) at 10 g m 73. Greenhouse grade calcium nitrate [Ca(NO 3 ) 2 4H 2 O] (16-0-0, N-P-K) and potassium nitrate (KNO 3 ) ( ) were used as NO 3 sources, and ammonium sulfate [(NH 4 ) 2 SO 4 ] (21-0-0) and ammonium nitrate [NH 4 NO 3 ] (34-0-0) as NH 4 and NO 3 sources. Potassium nitrate and potassium dihydrogen phosphate (KH 2 PO 4 ) were used as K sources. Magnesium sulfate (MgSO 4 7H 2 O) (Epsom salt, 9.8% Mg, Diamond Products Co., Seffner, FL) was used as the Mg source, and reagent grade KH 2 PO 4 was the sole source for P. Hydroponic System Tomato seeds were sown on rockwool propagation blocks ( cm). Seedlings were watered as needed with tap water for five days. A 1=8-strength Steiner type nutrient solution (10) including N as NO 3 -N was then supplied to seedlings for one week, after which they were transplanted onto larger rockwool blocks (76767 cm). The Steiner type nutrient solution at half-strength was applied until the fourth blossom stage, after which full-strength Steiner nutrient solution was applied for the remainder of the experiment. Treatments were initiated by transplanting three plants equally spaced 30 cm apart onto rockwool slabs ( cm). A gravity drip irrigation system, consisting of five 756-L elevated tanks, supplied water and nutrient elements. Nutrient solutions were kept in the tanks outside the greenhouse. The tanks were heated to prevent nutrient solution from freezing. Polyvinyl chloride tubing was used to connect each nutrient solution storage tank to a six-branch manifold constructed from 19-mm diameter black polyethylene tubing. Irrigation emitters were 90 cm long, heavy wall type, with a flow rate of 0.6 L min 71. A single emitter (Watermatic, Water Town, NY) was used per rockwool slab. Plants were irrigated from one to three times per day as plant water requirements increased. Recent transplants received around 70 ml of water plant 71 day 71, but nearly fully-grown and fully-grown plants received from 1 to 2 L of water plant 71 day 71. If there was no leachate present after every fertigation event, the water volume was increased to avoid salinity problems. Nutrient solution subsamples were collected from the rockwool slabs periodically to monitor electrical conductivity (EC). The rockwool slabs were flushed weekly with tap water to remove accumulated salts. As plant transpiration increased, more water was supplied to the system until EC readings were below 4.0 ds m 71. Nutrient solution phs were adjusted to 6.0 by adding 0.5 M sulfuric acid (H 2 SO 4 ). All plants were trained on suspended strings for support, and suckers were removed to leave a single stem on each plant following

6 GREENHOUSE TOMATO 1791 recommended greenhouse production practices (11). Plants were grown in a glass, gable-roof greenhouse with ambient light intensity. Daytime temperature set points were 21 and 28 C, and night temperature set points were 17 and 18 C. Cultural Practices and Sampling Sowing, transplanting, and harvesting dates for both experiments are shown in Table 1. Plants were sampled at the end of the vegetative growing stage and when fruit from the first cluster were 2.5 cm in diameter. Plant height was determined weekly. Ripe fruit from the first cluster were sampled to determine nutrient element concentration. At the end of each experiment, remaining fruit were harvested and fresh weight of leaves and the single stem determined. For the first and second samplings, the aerial part of a plant was cut from each rockwool unit and the leaves and stem were weighed to obtain fresh weights. Only recently emerged but fully expanded whole leaves were taken from the plant for nutrient element analysis. Dry weight of leaves and stem was obtained after oven-drying at 65 C for 72 h. Plant tissue was ground in a Wiley mill to pass a 1-mm stainless steel sieve. Total N content of leaves and fruit were determined by combustion analysis using a LECO CHN-600 Analyzer (LECO Corp., St. Joseph, MI). Total P, K, Ca, Mg, Mn, Cu, Fe, and Zn in prepared digests were determined by inductively coupled argon plasma (ICAP) spectroscopy (ICAP 9000 Spectrometer, Thermo-Jarrel Ash, Table 1. Date and Days After Transplanting (DAT) of Some Cultural Practices Conducted in the Winter ( ) and the Spring (1997) Experiments Winter Spring 1997 Activity Date DAT Date DAT Sowing 21 Oct., March, Transplant 8 Nov., April, 97 0 First sampling 13 Dec., April, (leaves and stem) Second sampling 10 Jan., May, (leaves and stem) Third sampling (fruits) z 2 Feb., June, Last harvest 28 Feb., July, End of the experiment 28 Feb., July, Length of harvest 28 days 30 days Average light intensity, Auburn AL (W h 71 m 72 ) z Third sampling coincided with first harvest of ripe fruit.

7 1792 SANDOVAL-VILLA, GUERTAL, AND WOOD Franklin, MA) after 0.5 g tomato samples were ashed in a muffle furnace at 550 C for 8 h, followed by dissolution of the remaining ash in 0.1 M nitric acid (HNO 3 ). The solution was heated to dryness and extracted in hot 0.1 M hydrochloric acid (HCl). Statistical Analysis Data were analyzed for statistical significance using the GLM and REG procedures (12). RESULTS AND DISCUSSION Fruit Yield and BER Incidence Neither length of NH 4 -N:NO 3 -N ratio supply nor the NH 4 -N concentration in solution affected marketable tomato yields. The number of fruit with BER increased with NH 4 -N concentration only in the spring (1997) experiment (r 2 ¼ 0.87; P 0.05). Longer periods of NH 4 -N supply increased the number of fruit with BER in the winter ( ) experiment but BER incidence was unaffected in the spring (1997) crop. However, there was no effect of applying NH 4 -N during vegetative or vegetative plus flowering periods and the number of fruits with BER for the highest incidence (application of NH 4 -N the whole cycle) was less than one fruit per plant. Length of NH 4 -N supply did not affect marketable yield in either experiment. Cao and Tibbits (4) did not find a significant response to different concentrations of NH 4 -N for 4, 8, 12, and 16% NH 4 -N. However, the dry weight of five-week-old potato plants supplied with NO 3 -N was lower than any other concentration of NH 4 -N in solution. Concentrations of 4% and 8% NH 4 -N were sufficient to trigger the mechanism responsible for increasing plant dry weight, and the low threshold for this response was likely why we could not find a significant response due to different concentrations of NH 4 -N in solution in both the winter ( ) and spring (1997) experiments. Apparently, light intensity was involved in the differential BER incidence in both experiments since it was the only factor not controlled. Longer periods of NH 4 -N supply increased the amount of fruit with BER in the spring (1997) experiment. High light intensity combined with NO 3 -N alone is recommended for growing peppers hydroponically while 10% or 20% NH 4 -N in solution is suggested for growing peppers under conditions of reduced light intensity (13). In addition, Zornoza et al. (14) found that Marlgrove tomato was sensitive to a 20% solution of NH 4 -N at high light intensity. In our experiments, tomato yield was not affected as the cultivar Max may not be as sensitive to NH 4 -N under conditions of high light intensity, or that sensitivity is not manifested in fruit yield but in BER incidence.

8 GREENHOUSE TOMATO 1793 Plant Height, Fruit Firmness, and Biomass Distribution Plant height in the winter ( ) experiment was unaffected by NH 4 - N concentration in solution as measured at different sampling times. In the spring (1997) experiment, a quadratic response (r 2 ¼ 0.24, P 0.05) was found in young plants at 20 days after transplanting (DAT). Tomato fruit firmness at the maturegreen stage was unaffected by different NH 4 -N concentrations in solution or the length of NH 4 -N supply for fruit from both experiments. Neither changes in the NH 4 -N concentration nor the length of NH 4 -N supply affected tomato dry matter distribution in plants from the winter ( ) experiment. However, in the spring (1997) experiment, fresh weight of leaves was higher as the NH 4 -N concentration in solution increased (Fig. 1). The proportion of fruit to whole aerial fresh weight was decreased as both NH 4 -N concentration in solution and length of supply increased (Fig. 1). The proportion of fruit to whole aerial part weight was decreased as the NH 4 -N concentration in solution and length of NH 4 -N supply increased. It seems that high solar radiation during the spring (1997) experiment (Table 1) influenced the response of tomato plants to NH 4 -N. Green and Holley (15) found that during periods of low solar radiation, the optimum ratio for carnations (Dianthus caryophyllus L.) was one third NH 4 -N and two thirds NO 3 -N, while during periods of higher solar radiation 100% NO 3 -N was best, which is in disagreement with our findings. Leaf Nutrient Concentration High NH 4 -N concentrations in solution significantly decreased the Ca concentration in tomato leaves collected during flowering in the winter ( ) (60 DAT) and the spring (1997) (40 DAT) experiments (Fig. 2). Calcium concentrations in fruit from both experiments were low (<1gkg 71 of dried fruit tissue) and were unaffected either by NH 4 -N concentration in solution or the length of NH 4 -N supply. Potassium, P, Mg, Fe, Cu, Mn, and Zn concentrations were not affected either by NH 4 -N or length of NH 4 -N supply for leaf samples collected at the vegetative, flowering and mature-fruit stages. Length of NH 4 -N supply did not affect the concentration of Ca in plant tissue in the winter ( ) experiment, but it did for the spring (1997) experiment; longer periods of NH 4 -N supply decreased the Ca concentration (Fig. 2). There was no correlation between Ca concentration in leaves or fruit and the number of fruit with BER in plants from the winter ( ) experiment. However, in the spring (1997) experiment, the amount of fruit with BER was inversely related to Ca concentration in tomato leaves at 40 DAT (Fig. 3). Although in both experiments the same NH 4 -N:NO 3 -N ratios were utilized, the slope of the curve in the spring (1997) was double that seen

9 1794 SANDOVAL-VILLA, GUERTAL, AND WOOD Figure 1. Fresh weight of leaves and NH 4 -N concentration in solution relationship and fruit fresh weight ratio to total fresh weight and concentration of NH 4 -N in solution in the spring (97) experiment tomato plants. in the winter ( ) experiment which means that leaf Ca concentration was decreased at high light intensity and high NH 4 -N concentration in solution. Because both experiments were carried out under the same conditions except light intensity, it is logical to attribute the enhanced detrimental effect of NH 4 -N on Ca concentrations in tomato leaves to light intensity. Calcium depletion in plant tissue as a result of NH 4 -N nutrition is a welldocumented affect (16,17). However, lack of depletion for Mg, K, and corresponding stimulation of P uptake is not common in these types of studies. Reduction of Ca concentration is the direct effect of non-specific competition between NH þ 4 and Ca2 þ cations. Non-specific competition occurs when any ion is in solution at a high concentration and may restrain the uptake of other ions (18). Calcium deficiency has been shown to impair membrane permeability and disorganize cell membranes (19). However, Nonami et al. (20) found that fruit just showing signs of the disorder had a similar distribution of Ca as normal fruit, suggesting that Ca may not be the direct cause of the disorder in tomatoes. They also found that the disorder was not related to absorption of Ca, and suggest that BER may be related to a metabolic disorder that expresses itself under stress

10 GREENHOUSE TOMATO 1795 Figure 2. Calcium concentration in tomato leaves at flowering stage [60 and 40 DAT; winter ( ) and spring (1997), respectively] as affected by NH 4 -N concentration in solution and length of supply. Daily average solar radiation was 2667 and 5030 W h 71 m 72 for winter ( ) and spring (1997) experiments, respectively. Bars followed by the same letter are not significantly different by LSD 0.05 test. conditions. This may be the reason that in the winter ( ) experiment no relationship between Ca concentration and BER found, but such a relationship was found in the spring (1997) experiment. In the spring experiment, BER incidence and leaf Ca concentration were quadratically (P 0.001) and linearly (P 0.01) related. The incidence of BER increased as leaf Ca concentration decreased (Fig. 3). Ho et al. (21) found that temperature appears to be the major environmental factor inducing BER regardless of cultivar and salinity.

11 1796 SANDOVAL-VILLA, GUERTAL, AND WOOD Figure 3. Relationship between leaf Ca concentration at 40 days after transplant and fresh weight of fruit with blossom-end rot Max tomato plants in the spring (1997) experiment. Plants were grown at ambient light intensity (5030 W h 71 m 72 ). In our case, greenhouse temperature was controlled except for the nutrient solution temperature, which was low during the winter, especially for morning irrigation (8 9 a.m.). CONCLUSIONS Length of NH 4 -N supply had more influence on BER incidence than NH 4 - N concentration in solution in the hydroponic nutrient solution under conditions of low light intensity. The NH 4 -N concentration in solution under conditions of high light intensity increased BER incidence. Ammonium N concentration in solution and its length of supply did not affect tomato yield. Fresh weight of leaves increased as the concentration of NH 4 -

12 GREENHOUSE TOMATO 1797 N in solution increased but the proportion of fruit to whole aerial part was decreased as NH 4 -N concentration in solution increased. The proportion of leaves to aerial part and fruit to aerial part weight increased with longer NH 4 -N application periods. Plant height was not influenced by NH 4 -N concentration in solution. Calcium concentration was the only ion affected by low NH 4 -N concentrations in solution (10% to 40% NH 4 -N) when tomato plants were grown at ambient light intensity during the winter and the spring experiments. ACKNOWLEDGMENTS First author is grateful to the Mexican National Council for Science and Technology (CONACYT) and Colegio de Postgraduados en Ciencias Agrícolas, México for financial support. REFERENCES 1. Ganmore-Neuman, R.; Kafkafi, U. Root Temperature and Percentage NO 3 =NH þ 4 Effect on Tomato Plant Development. I. Morphology and Growth. Agron. J. 1980, 72, Hartman, P.L.; Mills, H.A.; Jones, Jr., J. B. The Influence of Nitrate: Ammonium Ratios on Growth, Fruit Development, and Element Concentration in Floradel Tomato Plants. J. Am. Soc. Hortic. Sci. 1986, 111, Sarro, M.J.; González, L.; Peñalosa, J.M. Response of Pepper Plants to Different Periods of Nitrate and Ammonium Fertilization. Acta Hortic. 1995, 412, Cao, W.; Tibbits, T.W. Study of Various NH þ 4 =NO 3 Mixtures for Enhancing Growth of Potatoes. J. Plant Nutr. 1993, 16, Ganmore-Neuman, R.; Kafkafi, U. Root Temperature and Percentage NO 3 =NH þ 4 Effect on Tomato Plant Development. II. Nutrient Composition of Tomato Plants. Agron. J. 1980, 72, Ganmore-Neuman, R.; Kafkafi, U. The Effect of the Root Temperature and NO 3 =NH þ 4 Ratio on Strawberry Plants. I. Growth, Flowering, and Root Development. Agron. J. 1983, 75, Salsac, L.; Chaillou, S.; Morot-Gaudry, J.F.; Lesaint, C.; Jolivet, E. Nitrate and Ammonium Nutrition in Plants. Plant Physiol. Biochem. 1987, 25, Gunes, A.; Aktas, M. The Effect of Various NO 3 =NH þ 4 =Urea Rates on the Yield and Quality of Tomato. Turkish J. Agric. For. 1996, 20,

13 1798 SANDOVAL-VILLA, GUERTAL, AND WOOD 9. Ahrens, M.J.; Huber, D.J.; Scott, J.W. Firmness and Mealiness of Selected Florida-Grown Tomato Cultivars. Proc. Fla. State Hortic. Soc. 1988, 100, Steiner, A.A. The Universal Nutrient Solution. In Proceeding Sixth International Congress Soilless Culture, Wageningen, Netherlands, 1984; Snyder, R.G. Greenhouse Tomatoes, Mississippi State University Publication Cooperative Extension Service, Mississippi State University: Crystal Springs, MS, SAS. SAS=STAT User s Guide, Release 6.12; SAS Institute: Cary, NC, Jung, H.; Ito, B.; Maruo, T. Effects of Shading and NO 3 :NH 4 Ratios in the Nutrient Solution on the Growth and Yield of Pepper Plants in Nutrient Film Technique Culture. J. Japan. Soc. Hortic. Sci. 1994, 63, Zornoza, P.; Gonzalez, M.; Carpena, O.; Caselles, J. Response of Two Tomato Plant Cultivars to NO 3 :NH 4 Ratios and Light Intensity. Acta Hortic. 1995, 412, Green, J.L.; Holley, W.D. Effect of the NH þ 4 =NO 3 Ratio on Net Photosynthesis of Carnation. J. Amer. Soc. Hortic. Sci. 1974, 99, Kirkby, E.A.; Mengel, K. Ionic Balance in Different Tissues of the Tomato Plant in Relation to Nitrate, Urea, or Ammonium Nutrition. Plant Physiol. 1967, 42, Cox, W.J.; Reisenahuer, H.M. Growth and Ion Uptake by Wheat Supplied Nitrogen as Nitrate, or Ammonium, or Both. Plant Soil 1973, 38, Mengel, K.; Kirkby, E.A. Principles of Plant Nutrition; International Potash Institute: Bern, Switzerland, Van Goor, B.J. The Role of Calcium and Cell Permeability in the Disease of Blossom-End Rot of Tomatoes. Physiol. Plant. 1968, 21, Nonami, H.; Fukuyama, T.; Yamamoto, M.; Yang, L.; Hashimoto, Y. Blossom-End Rot May Not Be Directly Caused by Calcium Deficiency. Acta Hortic. 1995, 396, Ho, L.C.; Belda, R.; Brown, M.; Andrews, J.; Adams, P. Uptake and Transport of Calcium and the Possible Causes of Blossom-End Rot in Tomato. J. Exp. Bot. 1993, 44,

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