Interaction Effects between Weed, Sowing Rate, and N Splitting on Yield of Dryland Wheat

To assess the interaction effects of weeds, sowing rate, and N splitting on dryland wheat yield, field experiments were conducted in two years (2007 and 2009) at the College of Agriculture in Shiraz University. The treatments were replicated four times and analyzed as a split- split plot in a randomized complete block. The weedy and weed free were treated as the main plots, the wheat sowing rates treated as the sub plots (100, 120, 140 and 160 kg seed ha-1) and 5 levels (0-1, 1/3-2/3, 1/2-1/2, 2/3-1/3, and 1-0) of N splitting (100 kg ha-1) as the sub- sub plots. Results showed that by interaction between weeds, sowing rates and N splitting, the maximum biological yield (699 kg ha-1 and 1449.5 kg ha-1 in the first and the second year, respectively) was obtained in weed free, 120 kg seed ha-1 sowing rate and N splitting of 1/3-2/3. In the first year by interaction between weeds, sowing rates and N splitting, the highest grain yield (440.07 kg ha-1) was obtained in weed free, 120 kg seed ha-1 sowing rate and N splitting of 1/3-2/3 and the lowest grain yield (47.7 kg ha-1) was obtained in weedy plots with 100 kg seed ha-1 and N splitting of 0-1. In this study, the highest weed dry matter (367.5 kg ha-1 and 160.38 kg ha-1 in the first and the second year, respectively) was obtained in sowing rate of 100 kg seed ha-1 and the lowest weed dry matter (247.5 kg ha-1 and 52.3 kg ha-1 in the first and the second year, respectively) was obtained in sowing rate of 160 kg seed ha-1. In 2009, unusually low temperature in reproduction stage adversely affected wheat and led to no grain yield production.