PHOSPHORUS AND POTASSIUM UPTAKE OF FIELD-GROWN SOYBEAN CULTIVARS PREDICTED BY A SIMULATION MODEL.

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 Typoic 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.