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Abstract

The response of muskmelons (Cucumis melo L.) to Mg fertilization and soil pH was studied on a Princeton loamy sand that contained 34 kg·ha−1 available Mg at pH 4.8. Calcitic limestone was used to adjust the soil to pH 5.4 in 1984 and 5.8 in 1985. Magnesium was added for 2 years at 0, 56, 112, and 168 kg·ha−1. Lime application increased exchangeable soil Ca and decreased exchangeable Mn. Liming had no effect on exchangeable Mg, but Mg application increased exchangeable Mg linearly. Plants developed Mg deficiency in plots receiving no Mg treatment regardless of soil pH and Mn toxicity in unlimed plots at pH 4.8. Leaves developed Mg deficiency symptoms when the Mg concentration in leaf tissue was 0.30%. Magnesium application increased leaf tissue Mg and reduced leaf tissue Mn concentrations. Application of calcitic limestone increased leaf tissue Ca and reduced leaf tissue Mg and Mn concentrations. Muskmelon fruit yields were increased both by liming and Mg applications. Yield increases due to liming were attributed to reduced Mn levels in plant tissue.

Open Access

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.

Open Access

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.

Open Access

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.

Open Access

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.

Open Access

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.

Open Access

Several studies in the midwestem United States have shown that chlorophyll meter readings (Minolta SPAD 502) are useful in determining the N status of corn (Zea Mays L.), and show promise as a tool for the efficient N management of corn. Studies were conducted to evaluate the potential of the `chlorophyll meter for evaluating N deficiencies in lettuce (Lactuca sativa L.). Data for chlorophyll meter readings, midrib nitrate-N, lettuce growth rate, and marketable lettuce yield were collected in five N fertility experiments in 1993 and 1994. Chlorophyll meter readings not only varied among lettuce types (butter, cos, leaf, crisphead), but also among cultivars of the crisphead type. Chlorophyll meter readings were generally poorly correlated to midrib nitrate-N levels and marketable lettuce yield. Lettuce leaves have more color variation than corn leaves, and perhaps this variation in relation to the small sensor size on the SPAD 502 confounded readings. The observation that subtle N deficiencies in lettuce are usually manifested in growth rate reduction rather than abrupt color changes may also limit the usefulness of the chlorophyll meter for lettuce.

Free access

Tipburn is considered a major limiting factor to lettuce production in greenhouses and controlled environment agriculture facilities. Conditions which promote optimal growth also result in high levels of tipburn incidence. It has been reported that air flow directed at inner leaves of rapidly growing lettuce can prevent tipburn without a concurrent reduction of growth, assumedly due to increased transpiration with increased air movement over leaf surfaces.

Lettuce was grown in the greenhouse in nutrient film technique, with additional lighting providing total of 17 to 19 mol m-2 d-1 of PAR. Control plants developed tipburn 20 to 25 days after seeding. Plants with air supplied to inner leaves by a perforated plastic sleeve did not develop tipburn up to 35 days after seeding. Diurnal changes in physiological parameters were measured starting one week prior to harvest. Leaves of control plants had significantly higher stomatal conductance and transpiration than did those of air-supplied plants, although diurnal patterns of control and air-treated plants were similar. Air flow treatment had no significant effect on the rate of photosynthesis. However, air-supplied plants had a slightly lower percentage of dry matter than control plants. The apparent growth reduction resulting from the air flow treatment evidently reduced the demand for calcium.

Free access

Abstract

Fertilization of 2 cultivars of potato (Solanum tuberosum L.) grown in solution culture with NH4—N resulted in growth reduction, leaf roll, suppression of Ca and Mg uptake, and enhancement of P uptake compared with responses with NO3—N. Calcium and Mg decreased as time under NH4 nutrition increased. Solution pH had little affect on response to N form.

Open Access

Abstract

The N form had a pronounced effect on the levels of free amino acids. When compared to NO3, NH4 brought about a several fold increase in free amino acids (dry basis) in the roots, while smaller increases were observed in mature, fully expanded leaves, in young growing leaves, and in tomato fruit. Plants fed a combination of the 2 N forms had intermediate levels. The pattern of response to NH4 indicated that aspartic and glutamic acids as well as their amides were predominantly snythesized in the roots when the N source was NH4. The site of synthesis shifted to the leaves when the N source was NO3. The amino acids arginine, serine, alanine, and γ-aminobutyric acid were predominantly synthesized in the leaves irrespective of N form. Topical application of Ca on fruit grown with NH4 resulted in amino acid levels in the fruit similar to those of NO3 fruit. Ammonium toxicity was found to be accompanied by large increases in the levels of GABA and serine in the leaves. It is suggested that ammonium toxicity is a manifestation of intracellular Ca deficiency.

Open Access