Yield Losses in Tropical Rice as Influenced by the Composition of Weed Flora and the Timing of its Elimination

Abstract

Yields from 140 rice trials conducted at CIBA-GEIGY’s Agricultural Research and Development Station in Indonesia were compiled with the aim of determining yield losses in both irrigated transplanted and wet-sown rice in relation to the timing of the elimination of the annual weed flora and its composition.Relative yield losses due to weeds averaged 50% and were independent of rice production system or season. Actual yield losses were greater in wet season and transplanted rice. While all weed species present contributed to yield losses, the contribution from both grasses and sedges was more significant than that of broadleaved weeds.Yields increased irrespective of the timing of weed elimination. In particular, elimination of weeds during the period 0–9 DAT/DAS lead to significant yield gains, also when compared with the handweeded check. Such early elimination of weeds was especially beneficial in dry seasons and wet-sown rice.It is suggested that future studies on rice/weed-competition should pay particular attention to the weed group of sedges as well as to seasonal influences.