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

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 cotton, (Gossypium hirsutum [L]) grown on Mhoon silty clay loam (Typic Fluvaquent) and a Norwood silt loam (Typic Udifluvent) under glasshouse conditions. Predicted S uptake was significantly correlated with observed uptake r²=0.71. However, the model overpredicted S uptake by a factor of 3.5. The assumption that the maximun ion Influx rate (I _max) for roots growing in soils is the same as the I_max measured in solution cultures experiments may not be appropriate. Better agreement between observed and predicted S uptake values was achieved by using an estimated I_max obtained from soil studies (I_s) with the method of Warncke and Barber. Using I, predicted vs observed S uptake had a slope of 1.00 and r²=0.93. The model predicted that S concentration in soil solution (C_lo) at the root surface (r_o) increased with time for soils with initial S concentration in solution of lmM or higher. This high C_lo, will trigger a higher I_s of about 4 nmol/m²sec, while plants grown on soils with low S content will show a lower I_s, suggesting that S uptake by cotton plants is biphasic and depends on C_lo at r_o.

Notes

Contribution from State Project 1836. Approved for publication by the Director of the Louisiana Agricultural Experiment Station as manuscript no. LAES 95–09–9009.

Former Graduate Assistant and Associate Professor, respectively, Agronomy Department, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge, LA 70803. Second Author is currently Research Soil Chemist, Intermountain Research Station, USDA‐FS, Logan, UT, 84321.