Predicting the Most Efficient Phosphorus Placement for Corn

Yield increase from P fertilizer application depends on the efficiency of utilization of the added P. Placing added P in part of the soil volume rather than mixing it with all the soil may increase P uptake because of less tie-up of P by the soil, however, the degree of benefit from P placement has been difficult to predict. The objective of this paper is to use data from P placement experiments with corn (Zea mays L.) together with a simulation model to develop a procedure for estimating the P placement that will maximize P recovery and plant yield. The Claassen-Barber simulation model gave predicted P uptake by corn that compared favorably with observed P uptake and hence was used in this study. The model uses parameters describing root growth and morphology, kinetics of P uptake, and kinetics of P supply by the soil. Measurements of corn root growth as affected by P placement, of P influx into corn roots as influenced by P concentration, and of soil P supply as affected by rate of P addition to three soils were used to provide data to use in the simulation model. Predicted P uptake by corn was calculated for a range of fractions of the soil volume treated with five rates of added P per pot for two soils and with one P rate on an additional soil. Uptake of P from P-treated soil was added to uptake from untreated soil to get total P uptake. As the volume fraction of P treated soil increased from zero, calculated P uptake increased to a maximum then decreased with further dilution of added P with soil. The optimum fraction of the soil that had to be P-treated to get the greatest predicted P uptake increased with rate of application. Where one rate was applied to three soils, the greater the adsorption of P by the soil, the lower the fraction of P-treated soil needed to maximize P uptake. The principles illustrated in this paper may be useful for developing the most efficient fertilizer placement for crops grown in the field.