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 (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 ). Using I_s , 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 (C_lo ) at the root surface (r_o ) was about 2mM or higher, this high C_lo will trigger a higher ion Influx rate of about 2.6 nmol/m²sec. Plants grown on soils with C_lo less than 1 mM at r_o 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 C_lo at r_o .

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