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Phosphorus and Potassium Uptake of Field-Grown Soybean Cultivars Predicted by a Simulation Model¹

ABSTRACT

Mathematical models for calculating nutrient uptake by plants grown in soil have been successfully verified in pot experiments. However, few attempts have been made to verify the models for predicting nutrient uptake under field conditions. The Cushman mathematical model was tested for prediction of P and K uptake by soybeans (Glycine max L. Merr.) grown in the field; five cultivars were grown each year for 3 years. Experimental site varied with year. The soils used were Raub silt loam (fine silty, mixed, mesic Aquic Argiudolls) and Chalmers silt loam (fine silty, mixed, mesic Typic Haplaquolls). Observed P and K uptake was obtained from plant analysis. Root system size was obtained by taking soil core samples, washing the soil from the roots, and measuring root length and mean root radius. Root kinetic parameters for P and K influx were measured in solution culture experiments conducted in a controlled climate chamber. Soil nutrient supply parameters were measured in the laboratory on surface and subsoil samples. The model accurately predicted K uptake by the different cultivars grown in both soils and P uptake from the high-P (52 µM in the soil solution) Chalmers soil. Prediction of P uptake from the low-P (7.8 µM in the soil solution) Raub soil was 30 to 35% of the observed P uptake, even though predicted uptake by root hairs was included in the calculation. The difference may have been partly due to acidification of the rhizosphere soil by root exudate, which increased P concentration in soil solution and consequently increased P uptake.

¹ Journal Paper no. 9502. Purdue Univ., Agric. Exp. Stn., W. Lafayette, IN 47907. Contribution from the Dep. of Agronomy. This paper was supported in part by a grant under the Special Research Grants Program of the USDA.

² Post-doctoral Research Associate and Professor of Agronomy, Purdue Univ., respectively. The senior author is now Lecturer, Desert Research Inst., University of Negev, Beer-Sheva, Israel.

Received for publication June 23, 1983. Accepted for publication November 28, 1983.