Critical period of Cyperus iria L. competition in transplanted rice

摘要

Field studies were conducted during the summer season of 1994 and 1995 on a sandy loam soil at Punjab Agricultural University, Ludhiana, India, to determine the critical period of Cyperus iria competition in transplanted rice. The treatments consistedof 14 periods of weed interference laid out in a randomised block design with four replications. Infestation of C. iria throughout the crop growth period caused 64 per cent reduction in paddy yield. Highest paddy yield was obtained by keeping the crop weed free throughout. Weed free conditions for first 20 days after transplanting (DAT) and weedy thereafter yielded significantly less than weed free. There was no significant advantage of keeping the crop free of C. iria beyond 30 DAT. When the crop wasweedy for the first 20 or 30 days and weed free thereafter it yielded significantly higher than weedy and on a par with weed free conditions. However, weedy conditions for the first 40 days or more had significantly less paddy yield than weed free. C. iria competition for the first 30 days caused less than one fourth (12.9%) of the total losses in yield while competition for 40 days resulted in more than half (43.5%) of the total losses due to the weed. Maximum reduction in paddy yield (35.2%) was observed by delaying C. iria removal from 30 to 40 DAT, indicating this period as the most critical period of C. iria competition in transplanted rice.