Effect of rice cultural practices on emergence of Echinochloa crus-galli and Monochoria vaginalis.
Seed occurrence patterns of Echinochloa crus-galli and Monochoria vaginalis were investigated in irrigated and rainfed rice cultures growing on clay and sandy clay loam, resp. The difference in E. crus-galli seed populations between irrigated and rainfed fields was small, but M. vaginalis occurred in about 1.6-fold greater numbers in rainfed fields. Under both conditions, about 50 and 30% of E. crus-galli and M. vaginalis seeds, resp., were found in the uppermost 5 cm of soil. Under both conditions, M. vaginalis was distributed to a depth of 25 cm, but distribution of E. crus-galli was only to a depth of 15 cm. Early rice transplanting brought about greater emergence of the two weeds than optimal or late transplanting. Emergence of the weeds was significantly greater in a single cropping system of rice than in a double cropping system of rice followed by barley and/or strawberry.