INDIRECT ESTIMATION OF SOIL HYDRAULIC-PROPERTIES TO PREDICT SOYBEAN YIELD USING GLYCIM

GLYCIM, a mechanistic model of soybean (Glycine Max L.) growth and dev elopment, requires soil hydraulic parameters as input, These data are usually not readily available. The objective of this study was to comp are yields calculated with measured hydraulic properties to those calc ulated with hydraulic properties estimated from soil texture and bulk density. We reviewed estimation methods and chose two methods to estim ate a soil moisture release function and two methods to obtain saturat ed hydraulic conductivity. Both methods use soil texture and bulk dens ity as predictors. Soil water retention predicted by these methods cor related well with measured soil water retention whereas the estimation of saturated hydraulic conductivity was poor. Soybean yields were sim ulated using GLYCIM with and without irrigation for seven locations in Mississippi, USA, using seven years of weather records. Simulated yie lds were affected more by the method of estimating the moisture releas e curve than by the method of estimating saturated hydraulic conductiv ity. The average simulated yields from estimated properties were highe r than those from measured properties because estimated water retentio n provided more available water. Correlation between yields simulated using measured and estimated hydraulic properties was higher under non -irrigated conditions than with irrigation. Averaging yields over year s with different weather conditions greatly improved the correlations. Published by Elsevier Science Ltd