Modeling the uptake of sulfur by crops on two alluvial soils of Louisiana: Soybeans

Abstract

The Cushman and Barber mechanistic model³ was used to help elucidate the mechanisms that govern the uptake of sulfur (S) by plants. Sulfur uptake predicted by the model was compared to measured S uptake by ‘Centenial’ soybean (Glycine max L] Men.) grown on Gallion very fine sandy loam (Typic Hapludalf) and Mhoon silty clay loam (Typic Fluvaquent) under glasshouse conditions. Predicted S uptake was significantly correlated with observed uptake r ² =0.92. However, the model overpredicted S uptake by a factor of 14. Better agreement between observed and predicted S uptake values could be achieved by decreasing the maximum influx rate (/ _max ) obtained from solution culture experiments, which may not be valid for soil studies. The assumption made by the model that / _max for roots growing in soils is the same for all root surfaces and does not change regardless of plant age may not be appropriate. If the current model and assumptions are otherwise valid, an / _max appropriate for soils was fit directly to the uptake data or estimated by the method of Warncke and Barber. In this case predicted vs observed S uptake had a slope of 1.01 and r² =0.80.