Studies on Competition between Upland Crops and Weeds

Abstract

Effect of shade on growth of weeds was examined in 1973 and 1974. The weeds used in this experiment were large crab-grass (Digitaria adscendens HENR.), Chufa (Cyperus microiria STEUD.), common lamb's quarters (Chenopodium album L.), Polygonum nodosum PERS. and common purslane (Portulaca oleracea L.). Upland rice was used for reference.1. Plant height of large crab-grass and Chufa increased at 75 and 84% shade condition, but was extremely inhibited at 93% shade compared with the no shade control. Main stem length of common lamb's quarters and P. nodosum PERS. was equal to the control at 75% shade, but was inhibited at 84% shade. That of common purslane was inhibited at 75% shade.2. The tillers or branches of each plants decreased in number at all shade conditions. The effect of shade was not serious to common lamb's quarters, intermediate to large crab-grass and P. nodosum PERS., and serious to common purslane and Chufa. Very few tillers or branches of each plants were produced at 93% shade.3. Top dry weight of each plants decreased at all shade conditions. This decrease was the most remarkable in common purslane and Chufa which were under 10% dry weight at 84% shade compared with the control, and P. nodosum PERS. was under 20% at same conditions. The effect of shade to large crab-grass, common lamb's quarters and upland rice was relatively small, and these plants were approximately 30% dry weight at 84% shade. At 93% shade, top dry weight of each plants was less than 2% compared with the control.4. The period of heading, flowering and ripering was delayed generally at all shade conditions. The effect of shade was not serious to large crab-grass and P. nodosum PERS., but serious to another plants, especially to common purslane at growing period shade.5. These results suggest that the amount of shade required to diminish greatly growth of common purslane and Chufa is more than 80%, that of P. nodosum PERS. is 80-90%, and that of large crab-grass and common lamb's quarters is more than 90%.