Effect of winter weeds on growth and yield of direct-seeded rice in no-tillage dry paddy field

The effects of winter weeds on the growth and yield of direct-seeded rice (Oryza saliva L, cv. Akebono) were evaluated in a no-tillage dry paddy field where Alopecurus aequalis Sobol. var. amurensis (Komar.) Ohwi was Uniformly dominant, in Kurashiki, Okayama, Japan, in 1994 and 1995. Winter weeds significantly inhibited the growth and spikelet production of rice plants as compared to those in the control plots, which were established by herbicide application. The reduction in the spikelet number finally resulted in a 12.6 to 15.6%, yield reduction, although the percentage of ripened grains of rice increased somewhat because of the inhibition of the spikelet number by winter weeds. Rice yields in the weedy and control plots increased in different ways according to the increase in straw weight. The number of spikelets on the rice plants in the control plots increased as straw weight increased. In contrast, the percentage of ripened grain on the rice plants in weedy plots increased as straw weight increased. A higher rate of fertilizer greatly recovered the growth and yield of rice in weedy plots. This result suggests that the basal dressing of fertilizer at a higher volume would reduce the frequency of herbicide application for winter weeds.