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Predicting the Most Efficient Phosphorus Placement for Soybeans¹

ABSTRACT

The effect of placement of P fertilizer on P uptake and plant growth has been predicted for corn (Zea mays L.) but not soybeans [Glycine max (L.) Merr.]. The objective of this paper is to predict the effect of P placement on soybeans and compare it with predictions made earlier for corn. Data for operation of the model were obtained from a pot experiment reported in an earlier paper. Calculations were for soybeans, cv. Century, growing on Raub soil (fine silty, mixed, mesic, Aquic Argiudolls). Calculations were made for P rates of 30, 60, 120, 240, and 480 mg kg^–1 each with fractional volumes of soil fertilized ranging from 1.0 to 0.01. Predicted P uptake was converted to predicted plant weight using an experimental relation between P uptake and plant weight. The placement giving the greatest predicted P uptake interacted with P rate. At each P rate as P was mixed with an increasing volume of soil, predicted P uptake reached a maximum and decreased. The greatest predicted P uptake occurred when P was placed in 0.04 of the soil volume when the P rate was 30 mg kg^–1, 0.10 when the rate was 60 mg kg^–1, 0.20 when the rate was 120 mg kg^–1, and 1.0 when the rate was 240 mg kg^–1. The results were comparable to those obtained with corn.

¹ Journal Paper no. 10084. Purdue Univ. Agric. Exp. Stn. West Lafayette, IN 47907. Contribution of the Dep. of Agron. The first author was supported by a scholarship from EMBRAPA, Brazil.

² Former Graduate Student, now Research Agronomist EMBRAPA-CNPSoja, Brazil and Professor of Agronomy, Purdue Univ., respectively.

Received for publication October 29, 1984. Accepted for publication March 8, 1985.