Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Corn plants were sampled from two field experiments in 1984 and 1985 to study the effects of N, P, and K fertility levels on the dry weight and nutrient composition of corn plant parts during the seed-filling period. P and K fertility variables represented previously established levels in the soil; N fertility was achieved by applications of urea prior to planting. Selected plant samples at different stages of development were chemically analyzed for several elements;Grain yields ranged from 3350 to 8640 kg/ha in 1984 and from 5640 to 11100 kg/ha in 1985, with the depressed yields in 1984 resulting from late-season moisture stress. Fertilizer N produced much larger increases in the dry weights of all plant parts during the seed-filling period and in final grain yields than did increased levels of P and K. Differences in fertility did not influence the relative proportion of different plant parts or the pattern of dry matter accumulation in the ears;Changes in nutrient concentrations varied for different elements, plant parts and positions on the plants, and with fertility levels. Of the vegetative plant parts, leaves best reflected the nutritional status of the plants. Leaf concentrations of N, P, K, and S at 75% silking in 1985 were below the lower limits of established sufficiency ranges;Fertilizer N increased the concentrations of N, P, S, Mn, Cu, and Zn in the leaves and of N, S, and Fe in the grain, but decreased the concentration of Ca in the grain. Increased soil test P levels increased leaf P, N, and Ca concentrations and grain P concentration, but decreased Zn concentrations in the leaves and grain and Cu concentration in the grain. Higher soil K levels increased K concentration and decreased P, S, Ca, Mg, Mn, and Fe concentrations in the leaves, but did not influence nutrient concentrations in the grain. Differences in nutrient concentrations due to different fertility levels generally persisted in the leaves throughout the seed-filling period and increased in the grain as it developed;Increases in the dry weights of leaves and grain in response to increased fertility were reflected in increased nutrient contents in these parts. Differences in fertility did not markedly influence the amounts of nutrients in the grain during early stages, but increased fertility progressively increased the quantity of nutrients in the grain as it developed.



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Nael M. El-Hout



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461 pages