Partitioning of Biomass in the Crop Submodel of WEPS (Wind Erosion Prediction System)

Abstract

A crop growth submodel (dubbed CROP) is being developed for the wind erosion prediction system (WEPS). One of the requirements of CROP is to estimate leaf and stem growth on a daily mass basis and supply these values to the appropriate subroutines. The separate effects of leaves and stems on the processes of wind erosion then can be taken into account in the model. We developed a procedure for calculating leaf and stem growth separately for six crops: corn (Zea mays L.), grain sorghum [Sorghum bicolor (L.) Moench)], soybean [Glycine max (L.) Merr.], winter wheat (Triticum aestivum L.), oat (Avena sativa L.), and rice (Oryza sativa L.). Above ground biomass was regressed on relative growing degree days (which is a ratio of the growing degree days from planting to any day, to the growing degree days from planting to physiological maturity), or relative growing days where temperature data were not available. Stem mass was regressed on above ground biomass. In both cases, the logistic (sigmoid) model was used. Differentiation of the stem mass equation in conjunction with the biomass equation enabled us to calculate the partitioning ratios of leaf, stem, and reproductive plant parts, as functions of relative growing degree days (or relative growing days). The partitioning equations were incorporated into CROP. Overall, CROP predicted leaf, stem, reproductive, and above ground masses agreed fairly well with measured data (r2 ranged from 0.60 to 0.92, slopes from 0.65 to 1.18 and intercepts from 0.15 to 0.96 t ha1).