Effects of winter barley as a cover crop on the weed vegetation in a no-tillage soybean

The present study clarified the effects of winter barley as a cover crop on the weed vegetation, expressed as a multiplied dominance ratio (MDR), and emergence of summer annual weeds in a no-tillage soybean system. A 3 year field study with treatments consisting of six systems was conducted: no-tillage single cropping, no-tillage cropping following winter barley and tillage single cropping, respectively with and without herbicide application. The MDR of perennial weeds increased annually in the no-tillage fields in spring, but summer annual weeds were abundant in all fields, including the no-tillage fields in summer. Grasses, for example Digitaria ciliaris (Retz.) Koeler, were especially abundant in the no-tillage fields. The MDR of summer annual weeds, especially grasses in the barley and soybean fields, were much lower than for the no-tillage single soybean fields. Densities of D. ciliaris and Echinochloa crus-galli (L.) Beauv. var. crus-galli in the no-tillage single soybean fields were much greater than in the tilled fields, with few exceptions. In contrast, broad-leaved weeds emerged more in tilled fields than in the no-tillage fields. Winter barley suppressed emergence of summer annual weeds, especially during the first 3 years. The MDR for grasses in summer showed a good correlation with the frequency of emergence for grasses every year. These results showed that the increase in the volume of grasses in summer resulted mainly from an increase in the frequency of emergence, and that the suppression of grasses by winter barley resulted mainly from suppression of the emergence frequency. Soybean yields were higher in the barley and soybean fields for the first 2 years.