Barnyard grass interference with rice is one of the major causes of low yield. In a field experiment influence of different nitrogen levels - 0, 60, 120 and 180 kg ha-1 - on barnyard grass density - 0, 4, 8, 12, and 16 plants m-2 - was evaluated to quantify the effect of barnyard grass on rice performance at different nitrogen levels. Rice-barnyard grass competition and N application significantly effected growth, yield and quality of rice. Increase in barnyard grass density resulted in corresponding decrease in the growth, yield and quality of rice; nevertheless, increase in N application improved the growth, yield and quality. Maximum spikelets, kernel weight, yield, harvest index, normal kernels, amylose contents, kernel water absorption ratio, and minimum sterile spikelets, abortive and opaque kernels were obtained with 120 kg N ha-1 and zero barnyard grass density m-2, while maximum tillers number, productive tillers, straw yield, leaf area index, crop growth rate, net assimilation rate and kernel protein contents were recorded from 180 kg N ha-1 with 0 or 4 barnyard grass plants m-2. In nutshell, 120 kg N ha-1 was adequate and four barnyard grass plants had non-significant effect on rice grain yield, and excessive N application reduced kernel quality.
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