Influence of land preparation and weed control methods on weed growth and yield of upland rice

Plowing 20 and 30 cm deep resulted in a decrease in weed weight 15 days after emergence (DAE) compared to plowing 1-0 cm deep. At 35 DAE and thereafter the effect of plowing depth on weed weight was no longer observed. Stand count, tiller count, panicle count, plant height, and rice grain yield were likewise not affected by depth of plowing. Pendimethalin [N-(1-ethylpropyl)-3,4 dimethyl-2,6-dinitrobenzenamine] followed by one hand weeding 35 DAE controlled weeds better than when pendimethalin was followed by two applications of 2,4-D [(2,4-dichlorophenoxy) acetic acid] or when one hand weeding was done 25 DAE and gave yield comparable to the hand weeded check. The number of weed seeds/m2 in the 0-25 cm depth in the soil was significantly greater when plowing was 30 cm deep than 10 or 20 cm deep indicating that deep plowing buried weed seeds in the soil. The number of weed seeds was lower in the handweeded check than in the other weed control treatments. The use of the stale-seedbed technique twice decreased weed weight compared to when it was used once. However, it offered no advantage in weed control when compared with the conventional method of land preparation. Stand count, tiller count, plant height, panicle count, and rice grain yield were not affected by method of land preparation. Rice grain yield was significantly higher in the hand weeded check than in the other weed control treatments because weeds which grew at later stages of crop growth in the other treatments competed with the crop and reduced grain yield. Land preparation at 20, 10, and 1 days before seeding (DBS) resulted in a decrease in weed weight 25 DAE compared to land preparation 30 day. Stand count was not affected by time of land preparation. Rice had more tillers when land preparation was at 20, 10, and 1 DBS than at 30 DBS because of better weed control. The rice plants were taller when land preparation was done at 10 and 1 DBS than at the other times because of better weed control