Application of Phosphorus, Potassium, and Zinc to Corn Grown for Grain or Silage: Nutrient Concentration and Uptake

Although the nutrient composition of the ear leaf of corn (Zea mays L.) at tasseling or silking has been used widely in estimating the nutrient status of this crop, addition of a fertilizer to correct a discovered nutrient deficiency is very difficult, if not impossible, at this late stage of growth. Development of “critical” levels of plant nutrients in corn tissue at earlier stages of plant development should he more practical and useful. Twenty-three treatment combinations of rates of P, K, and Zn from a 5³ factorial arrangement were selected and applied annually to a sandy soil for irrigated corn that was grown for either silage or grain production from 1974 through 1978. Whole plant samples were collected when the corn was 40 to 60 cm tall. Ear leaf samples at silking and grain and whole plant samples at physiological maturity were collected. All samples were analyzed for P, K, and Zn. The P concentration in whole plants at the early growth stage increased linearly as the rates of applied P and K were increased. In general, the P concentration of the ear leaf at silking increased linearly as the rate of applied P was increased for both systems of harvest. For the whole plant samples at the early growth stage, the critical P level was 0.220% P in the silage harvest system and 0.256% P in the grain harvest system. The critical levels for the ear leaf at silking were 0.220 and 0.225% P for the respective harvest systems. Phosphorus uptake by young plants, compared to the P concentration, was more closely associated with relative yield. When corn was harvested for silage, P uptake by young plants, rather than the P concentration of the ear leaf, was more closely associated with relative yield in 3 of the 5 years. Under the grain harvest system, P uptake by young plants was more closely associated with relative yield compared to the P concentration of the ear leaf tissue in all years.