INFLUENCE OF NITROGEN FORM, MAGNESIUM, AND MANGANESE ON ION ACCUMULATION AND DEVELOPMENT OF MANGANESE TOXICITY BY PLANTS (MUSKMELON, WATERMELON, TOMATO, SOIL PH)
Abstract
The response of tomato and muskmelon to Mg fertilization and soil pH was studied on a Princeton loamy sand that contained 30 kg/ha available Mg at pH 4.8. Calcereous limestone was used to adjust the soil pH to 5.8, and Mg was added at 56, 112 and 168 kg/ha. Plants developed Mg deficiency in plots receiving no Mg treatment and Mn toxicity in unlimed plots at pH 4.8. Muskmelon and tomato fruit yields were increased both by liming and Mg applications. Yield increases due to liming were attributed to reduced Mn levels in plant tissue. Muskmelon and watermelon growth, ion composition, and development of Mn toxicity as influenced by Mn and Mg concentration, N form, and N form ratio were studied in greenhouse experiments. Manganese toxicity symptoms developed as water-soaked spots, necrotic spots, and necrotic lesions in muskmelon leaves, and as small distinct blackish brown speckling, extensive vein browning, and necrotic lesions in watermelon leaves. Symptoms were more severe on the lower mature leaves than the newly expanded leaves. Toxicity symptoms developed on leaves that contained (GREATERTHEQ)900 ppm Mn for muskmelons and (GREATERTHEQ)1325 ppm Mn for watermelons. Increasing concentration of Mg alleviated symptoms of Mn toxicity, decreased Mn concentration in shoot and root tissues, and increased growth of plants. The reduction in Mn toxicity was brought about by reduced root absorption of Mn at high Mg supply. The form of N available for uptake exerts a strong influence on muskmelon and watermelon growth and Mn composition. Plants grew best when NH(,4) was applied at 14 ppm N in a 1:7 ratio with NO(,3) than with NO(,3) alone. Ammonium suppressed K, Ca, Mg, and Mn accumulation in plant tissues, and reduced Mn uptake per unit of root surface. Plants grown with NO(,3)-N at toxic levels of Mn had reduced growth and developed severe Mn toxicity symptoms, whereas with NH(,4) the Mn treatments had no effect on growth and Mn absorption was inhibited so that no toxicity symptoms developed. Furthermore, the proportion of NH(,4) in NH(,4)/NO(,3) ratio exerted an indirect proportionate influence on Mn absorption. Toxicity symptoms developed as the proportion of NH(,4) in nutrient solution increased to 1:1 with NO(,3), whereas at NH(,4)/NO(,3) ratios > 1:1, uptake of Mn was inhibited so that Mn never reached a concentration in the tissue that developed toxicity symptoms.
Degree
Ph.D.
Subject Area
Plant propagation
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