Effects of Nitrogen, Seeding Rate and Weed Interference on Growth and Yield of Wheat (Shiraz Cultivar)

In order to evaluate the effect of nitrogen، plant density and weeds on growth and yield of wheat cv. Shiraz، an experiment was conducted during 2009/2010 and 2010/2011 growing seasons at Agricultural College of Shiraz University. The experimental design was split-split plot with main plots arranged as an RCBD with three replications. Treatments included weed and weed free as main factor، three nitrogen levels (50،100،150 kg ha-1) as sub factor and seeding rate (180، 225، 270 and 315 kg ha-1) as sub factor. Wheat growth and yield as well as its components (1000-grain weight، grain number per spike and ear number m-2) were affected by weeds so that grain yield was significantly reduced by 34. 23%. With increasing level of nitrogen (from 50 to 150 kg/ha)، wheat grain yield (3840 Vs 4980 kg/ha) was significantly increased by 29/83%; however weed dry weight was also increased in weedy plots indicating that additional nitrogen cannot compensate for the effect of weed competition. Increasing seeding rate recorded significantly higher yield and yield components than control and a simultaneous reduction in weed competition with the lowest weed dry weight was achieved at 315 kg ha-1 seeding rate. A rise of nitrogen rate increased (0. 57 gr m-2) weed dry weight. There was a negative and significant correlation between seed yield and weed dry weight، so that under different nitrogen levels، increasing weed dry weight decreased seed yield. Generally، it appears that compared to increased rate of nitrogen، higher seeding rate is a more effective strategy to compensate for yield losses caused by weeds. To achieve optimal wheat yield، application of 270 kg wheat seed and 150 kg nitrogen ha-1 is recommended.