Influence of Echinochloa crus-galli density and emergence time on growth, productivity and critical period of competition with dry-seeded rice

Abstract

Echinochloa crus-galli (L.) Beauv. is a stronger competitor of rice for resources than other weeds. An adequate knowledge of the biology, ecology and critical period of competition of E. crus-galli with dry-seeded rice (DSR) is fundamental in designing effective, sustainable and integrated weed management programs. Experiments were conducted in the 2013 dry and wet seasons to determine the effect of two E. crus-galli densities (40 and 80 plants m−2) emerging at four intervals (2, 15, 30 and 45 d after rice emergence, DARE) with and without rice interference on the growth and biomass accumulation of both rice and weed, and the productivity of rice. The E. crus-galli plant height decreased with the interference of rice plants. The maximum height of 115–130 cm and number of tillers of 477–508 m−2 in rice plants were recorded when grown alone, and these growth parameters declined to 105–109 cm and 315–352 m−2, respectively, when rice emerged simultaneously with E. crus-galli. Other rice growth parameters (stem, leaf, panicle and shoot biomass, and leaf area) and grain yield attributes (panicle density, per panicle filled spikelets and grain weight) decreased significantly with increases in E. crus-galli density at the early emergence time. A delay in E. crus-galli emergence from 0 to 45 DARE caused a significant reduction in E. crus-galli biomass, which resulted in less reduction in rice biomass and leaf area index. Rice grain yield, grain weight, and harvest index improved significantly with a delay in weed emergence up to 45 DARE. The highest grain yield was recorded when rice was grown alone (6.8–7.3 t ha−1), which was similar to the yield produced in the plots wherein E. crus-galli sown at 40 plants m−2 (6.9–7.0 t ha−1) and 80 plants m−2 (6.4–6.7 t ha−1) emerged at 45 DARE. The lowest grain yield (4.3–4.9 t ha−1) was recorded in the plots wherein E. crus-galli emerged simultaneously with rice. This study established that E. crus-galli emergence at 45 DARE could not cause an economic yield loss because of less biomass accumulation and lower survival rate.