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- Author or Editor: Gerald E. Wilcox x
Abstract
Vegetables have high K needs because of the succulent nature of the harvested portion of the crop. The K removal is highest for leafy vegetables when the entire plant is removed, as with celery, and least for the seed crops such as peas and lima beans. The amount of K removed in the crop varies from 80 lbs/A for peas to 350 lbs/A for celery while the majority of vegetables remove in the range of 100-150 lbs/A K.
Abstract
Ripe fruit yields of ‘Campbell 17’ tomatoes at the 50% ripe fruit stage increased from 6.0 to 13.1 tons per acre in the population range of 1,815 to 7,260 plants per acre. Constant yield was obtained in the population range from 7,260 to 29,040 plants per acre in single rows and from 4,840 to 58,080 plants per acre in the twin rows.
Single harvest at the 85% ripe fruit stage resulted in a yield increase from 7.5 to 20.8 tons per acre in the population range from 1,815 to 9,680 plants per acre in single rows. A significant decrease in yield was obtained at the population of 29,040 plants per acre. The ripe fruit yield from twin rows at this harvest stage reached a nearly constant yield plateau of 19.3 to 22.8 tons per acre in the population range of 7,260 thru 29,040 plants per acre. Plant spacing of 3 inches in the row in both single and twin rows resulted in a significant yield reduction at the later harvest date.
A power form curve expressed the yield per plant—plants per acre relationship at plant spacings of 6 to 12 inches in the single rows and from 6 to 24 inches in the twin rows.
Two mechanisms that reduce water and salt stress, respectively, are an increase in root hydraulic conductivity (LP ) and reduction in Na and Cl absorption and transport to the leaf. NH4 +-N decreased muskmelon LP 55-70% while under 100 mM NaCl stress and 40-50% in the absence of NaCl stress. A decrease in LP increases the rate of water stress development as the transpiration rate increases. Although dry weight decreased about 70%, with NO- 3-N, muskmelon remained healthy green, while with NH+ 4-N they became chlorotic and necrotic with a 100% and 25% increase in leaf blade Na and Cl compared to NO- 3-N, respectively. Further investigation indicated that NH+ 4-N increased muskmelon sensitivity to NaCl through both an increased rate of net Na influx and transport of Na to the leaf. Since Na influx partitioning is controlled by mechanisms K/Na selectivity and exchange across membranes, the NH+ 4-N inhibition of K absorption may impair K/Na exchange mechanisms. Reduced K/Na selectivity or Na efflux are implicated as the source of the increased net Na influx with NH+ 4-N. The importance of K in preventing Na partitioning to the leaf was confined through removal of K from the nutrient solution thereby simulating the NH+ 4-N-induced gradual K depletion in muskmelon. Our work indicates that at a given level of water or NaCl stress, NO- 3-N reduces the level of stress experienced by muskmelon through increasing LP and reducing the net rate of Na influx and transport to the sensitive leaf blade. This avoidance mechanism should enable muskmelon plants fertilized with NO- 3-N to tolerate greater levels of stress.
Two mechanisms that reduce water and salt stress, respectively, are an increase in root hydraulic conductivity (LP ) and reduction in Na and Cl absorption and transport to the leaf. NH4 +-N decreased muskmelon LP 55-70% while under 100 mM NaCl stress and 40-50% in the absence of NaCl stress. A decrease in LP increases the rate of water stress development as the transpiration rate increases. Although dry weight decreased about 70%, with NO- 3-N, muskmelon remained healthy green, while with NH+ 4-N they became chlorotic and necrotic with a 100% and 25% increase in leaf blade Na and Cl compared to NO- 3-N, respectively. Further investigation indicated that NH+ 4-N increased muskmelon sensitivity to NaCl through both an increased rate of net Na influx and transport of Na to the leaf. Since Na influx partitioning is controlled by mechanisms K/Na selectivity and exchange across membranes, the NH+ 4-N inhibition of K absorption may impair K/Na exchange mechanisms. Reduced K/Na selectivity or Na efflux are implicated as the source of the increased net Na influx with NH+ 4-N. The importance of K in preventing Na partitioning to the leaf was confined through removal of K from the nutrient solution thereby simulating the NH+ 4-N-induced gradual K depletion in muskmelon. Our work indicates that at a given level of water or NaCl stress, NO- 3-N reduces the level of stress experienced by muskmelon through increasing LP and reducing the net rate of Na influx and transport to the sensitive leaf blade. This avoidance mechanism should enable muskmelon plants fertilized with NO- 3-N to tolerate greater levels of stress.
Abstract
Growth retardants have been used to control stem elongation of hydroponic tomato (Lycopersicon esculentum Mill.) transplants. However, the residual effect of chlormequat chloride on vegetative growth reduces yield. Therefore, the recovery rate of transplant growth was compared between treatments that reduce stem elongation (salt stress, thigmic stress, and chlormequat chloride) to determine which treatments had the best combination of a fast growth recovery rate and control of stem elongation. Tomato plants were grown hydroponically during treatment and recovery periods in a recirculating nutrient solution. Although all treatments except thigmic stress initially decreased shoot dry weight, 24 days after treatment (DAT) termination night-salt stress and thigmic stress produced plants with shoot dry weight comparable to controls. Day and 24-hr salt stress and chlormequat chloride-treated plants had shoot dry weights of 40% to 60% of control 24 DAT termination. Plants treated with chlormequat chloride were still growing slower than controls 24 DAT termination. Both night-salt stress and thigmic stress are suitable prospects for use in control of hydroponic tomato transplant vegetative growth. Oscillatory wind stress applied by the sweeping motion of a leaf blower or by brushing plants with a foam rubber mat are potential commercially feasible ways to apply mechanical stress. Chemical names used: 2-chloro-N,N,N-trimethyIethanaminum chloride (chlormequat chloride).
Abstract
Muskmelon (Cucumis melo L.) ‘Harvest Queen’ was grown in sand culture to investigate the effects of NH4:NO3 ratios on melon growth and elemental composition. Plants grown at NH4:NO3 ratios of 98:14, 84:28, and 56:56 developed NH4 toxicity symptoms, whereas plants grown with 20 ppm Mn and NH4:NO3 ratios of 0:112, 14:98, 28:84, and 56:56 developed Mn toxicity symptoms. Increasing the proportion of NH4 in nutrient solution up to 1:1 with NO3 decreased Mn concentrations in plant tissues and alleviated Mn toxicity symptoms, whereas at NH4:NO3 ratios of 84:28 and 98:14 uptake of Mn was inhibited and never reached a concentration in the tissue that developed toxicity symptoms. Shoot and root growth was greatest when grown at the 14:98 NH4:NO3 ratio. Increasing NH4 in the solution beyond 14 ppm in the 112-ppm N mixture resulted in increasing limitation of growth. Increasing Mn concentration in the nutrient solution to 20 ppm restricted growth at NH4:NO3 ratios ≤1. However, Mn treatment did not influence the growth of plants grown at NH4:NO3 ratios >1 at 84:28 and 98:14.
Abstract
Muskmelon (Cucumis melo L.) ‘Harvest Queen’ seedlings were grown in sand culture at 2, 15, or 30 ppm Mn with 3 different N treatments to evaluate the effects of N form on growth, composition, and development of Mn toxicity. Nitrogen treatments consisted of NO3, NH4, and NH4 shifted to NO3 at 5 days, when Mn toxicity symptoms began to show on NO3-treated plants. Muskmelons produced the most growth with N supplied as NO3, least growth with NH4, and intermediate growth with the NH4-to-NO3 shift treatment. Plants grown with NO3-N at 15 or 30 ppm of Mn had restricted growth, developed Mn toxicity symptoms 5 days after the start of Mn treatments, and had a Mn composition of over 1500 ppm in dry shoot tissue. With NH4 the Mn treatments had no effect on growth, no Mn toxicity symptoms developed, and Mn composition of shoot tissue was <800 ppm. Shifting plants from NH4 to NO3-N resulted in the development of Mn toxicity symptoms and tissue Mn composition over 1500 ppm within 4 days after the shift.
Abstract
Muskmelons (Cucumis melo L.) ‘Harvest Queen’ were grown in sand culture to evaluate the response to Mn toxicity as affected by solution concentration of Mn and Mg. Manganese toxicity symptoms were developed as water-soaked spots, necrotic spots, and necrotic lesions, which were most severe on the lower mature leaves. Leaves developed toxicity symptoms when they contained ≥900 μ-g·g-1 Mn. Increased levels of Mg in the nutrient solution alleviated symptoms of Mn toxicity, decreased Mn concentration in shoot and root tissues, and increased growth of muskmelon plants. The reduction in Mn toxicity was brought about by reduced root absorption of Mn at high Mg supply.
Abstract
Watermelon [Citrullus lanatus (Thunb.) ‘Sugar Baby’ was grown in sand culture to evaluate Mn uptake as affected by solution concentration of Mn and Mg. Manganese toxicity symptoms were developed first on the lower mature leaves as small, distinct, blackish-brown speckling on the lower leaf surface that progressed to extensive vein browning and necrotic lesions. Leaves developed toxicity symptoms when they contained ≥1325 mg·liter−1 Mn. Growth was reduced at Mn concentrations in nutrient solution ≥22.5 mg·liter−1. Development of Mn toxicity symptoms was delayed with increasing Mg concentrations in solutions. Increasing Mg concentration in solution to 48 or 96 mg·liter-1 reduced Mn composition and Mg uptake per unit root surface at 2 and 30 mg·liter-1 Mn in solution, but had no effect at 60 mg·liter-1 Mn in solution.
Abstract
Watermelon [Citrullus lanatus (Thunb.)] ‘Sugar Baby’ seedlings were grown in sand culture leached with nutrient solution containing 2, 25, or 50 mg·liter−1 Mn in combination with NH4 or NO3-N to evaluate the effects of N form on growth, composition, and development of Mn toxicity. Nitrogen form treatments consisted of continuous NO3, continuous NH4, and a treatment in which NH4 was replaced by NO3 after Mn toxicity symptoms were first observed on NO3-treated plants. Watermelon plants produced the most growth at all Mn levels with N supplied as NO3, least with NH4, and intermediate with the NH4-to-NO3 shift treatment. Plants grown with NO3-N at 25 and 50 mg·liter−1 Mn had reduced growth and developed Mn toxicity symptoms with Mn concentrations >1700 μg·g−1 in shoot tissues. However, with NH4 the Mn treatments had no effect on growth, no Mn toxicity symptoms developed, and Mn concentrations in shoot tissue were <800 μg·g−1. Shifting plants from NH4-to-NO3 nutrition at 50 mg·liter−1 Mn in solution stimulated rapid Mn absorption and produced Mn toxicity symptoms within 3 days.