Studies on Competition between Upland Crops and Weeds : I. Effects of different cropping systems on the weed community

Abstract

The experiments reported here were designed to determine the effects of different cropping systems on the weed community. The cropping systems were wheat -upland rice, -peanut, -soybean and -corn (2 years continuous cropping) which were generally put into practice as inter-cropping system in the Kanto plain. Weed community consisted of large crab-grass (Digitaria adscendens Henr.), Chufa (Cyperus microiria Steud.), common lamb's-quarters (Chenopodium album L.), Polygonum spp., common purslane (Porturaca oleracea L.) and the others. The experiments were conducted extending from 1970 to 1973. 1. As the wheat-corn and wheat-soybean plots had strong weed competitive capacity, the growth of weeds was fewer than other plots during cropping season and in bare fallow after cropping. And the ratio of weed weight to total community weight was under 10% at the time of harvesting of summer crops. The wheat-upland rice plot was strong in weed competitive capacity and the ratio of weed weight to total community weight was under 10% when upland rice grew better. But the weed competitive capacity was weak when growth of upland rice was poor. The wheat-peanut plot was weak in weed competitive capacity and the ratio of weed weight to total community weight was about 50%. 2. The ratio of weeds in each plot emerged at the first summer cropping was large crab-grass about 30%, Chufa about 30%, common purslane and the others about 40%. The ratio of large crab-grass to total weed weight at the time of harvesting was over 80% except about 40% of upland rice. The ratio of large crab-grass to total weed emerged at the second cropping was over 40% in each plot, and its ratio of weed weight at the time of harvesting was larger than that of the first cropping. The dominance of large crab-grass was larger in each plot at the bare fallow in the third year. 3. The amount of weeds remarkably increased at the condition of bare fallow in the third year. These indicated that crop husbandry and cultivation method were playing an important part to weed supression. As the large number of weed emerged next spring in the plots which produced much weed dry weight at the harvesting, the importance of removal remaining weeds by hand could be emphasized, too.