MODEL ANALYSIS OF A STRAW MULCH SYSTEM FOR CONTINUOUS WHEAT IN AN ARID CLIMATE

Wheat (Triticum aestivum L.) production in some dryland regions is sev erely limited by the cereal cyst nematode (Heterodera avenae Well.). C onventional fallow management during a wet period has been shown to al low hatching of the cysts during the fallow season and thereby sanitiz e the soil for the subsequent wheat crop. Recently a straw mulch (SM) management has been introduced into a long-term experiment in the Nege v region of Israel. This management ameliorated the nematode damage an d allowed continuous wheat production. Only three seasons of successfu l experimentation exist with the SM system so questions remain about i ts performance over seasons with differing weather conditions. A simpl e, mechanistic, wheat model was extended to simulate wheat development and growth when the crop is grown on nematode-infested soils. Incorpo rating statements describing inhibition of rooting depth as a result o f nematode activity resulted in good agreement between simulations and 16 seasons of yield observations on continuous wheat. The effect of S M was simulated simply by decreasing soil evaporation and this resulte d in higher levels of soil water and decreased nematode inhibition of rooting. Good agreement was obtained between the three seasons of expe rimental data and simulations of the SM system, with predicted grain y ield within 10% of observations. Over 16 seasons, simulations of the S M system indicated substantial grain yield increases over continuous w heat in all but the highest-yielding season. Simulations in 14 seasons with conventional fallow management revealed that annual yields of SM were equivalent to biennial yields of the fallow system, resulting in a predicted doubling of wheat production for this dryland region of t he Negev.