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Phosphorus Application Rate and Distribution in the Soil and Phosphorus Uptake by Corn¹

ABSTRACT

Evaluation of the effect of P addition and distribution in soil on P uptake by corn (Zea mays L.) plants, requires knowledge of the relation of soil P level to corn root growth rate and morphology. This research was conducted to obtain these relationships so that they could be used with root P influx and soil supply characteristics to calculate P uptake. Corn was grown for 12 and 18 days on two soils, each with five levels of P application, in pots in a controlled climate chamber. Root growth and P uptake were measured. Except for the lowest rate, increased rate of P mixed uniformly with the soil decreased average root length per pot even though shoot growth increased. Placing a common rate of P per pot in part of the soil volume increased root growth in the P-treated soil volume as compared to root growth in the untreated soil. The difference was expressed by the relation y = x^0.68, where y was the fraction of total plant root length in x, the fraction of the total soil volume that was P treated. Separate calculation of P uptake from each soil volume showed low P uptake from the untreated soil compared to that from the treated soil. Predicted P uptake per not calculated with a mathematical simulation model was correlated (r = 0.81 and 0.78 for the two soils) with observed P uptake. Information on effect of P on corn root growth and on P influx can be used in mathematical models to investigate relative P uptake from alternate P application practices.

¹ Journal Paper no. 7867. Purdue Univ. Agric. Exp. Stn., W. Lafayette, IN 47907. Contribution from the Dep. of Agronomy. This research was supported in part by TVA.

² Former Graduate Assistant, now Assistant Professor, Federal University of Rio Grande do Sul, Porto Alegre, Brazil and Professor of Agronomy, Purdue Univ., respectively.

Received for publication December 3, 1979. Accepted for publication April 23, 1980.