Modeling the uptake of sulfur by crops on three alluvial soils of Louisiana: Wheat

Abstract

The Cushman and Barber mechanistic model 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 wheat (Triticum aestivum [L]) grown on Gallion very fine sandy loam (Typic Hapludalf), Mhoon silty clay loam (Typic Fluvaquenf), and a Norwood silt loam (Typic Udifluvent) under glasshouse conditions. Predicted S uptake was significantly correlated with observed uptake r2=0.85. However, the model over predicted S uptake by a factor of 10.4. The assumption that the maximum ion Influx rate (Imax ) for roots growing in soils is the same as the Imax measured in solution cultures experiments may not be appropriate. Better agreement between observed and predicted S uptake values was achieved by using an estimated Imax obtained from soil studies (Is ). Using Is , predicted vs observed S uptake had a slope of 1.5 and r2=0.93. The model predicted that when S concentration in soil solution (Clo ) at the root surface (ro ) was about 2mM or higher, this high Clo will trigger a higher ion Influx rate of about 2.6 nmol/m2sec. Plants grown on soils with Clo less than 1 mM at ro will show a lower ion Influx rate of about 0.8 nmol/m2sec, suggesting that S uptake by wheat plants is biphasic and depends on Clo at ro .