Critical weed-seed density to prevent yield loss of rice grown on paddy fields dominated by annual weeds

Abstract

Due to the increasing complexity of weed management, it is very important to develop a model for selecting the most effective weed management strategy. We established a method based on a weed seedbank and seedling density and estimated the thresholds of weed-seed density in which yield loss could be prevented.
The number of weed seeds and seedlings and the effect of weeds on rice yield were surveyed simultaneously at seven paddy rice fields in Ibaraki prefecture where the annual weeds dominated. The annual weeds that were found were primarily Lindernia spp., Cyperus spp., and Monochoria vaginalis (Burm. F) Kunth. The rates of established seedlings were 2.5% for Lindernia spp., 4.9% for Cyperus spp., 16.4% for Monochoria vaginalis and 5.2% for total weed seeds in 1.5cm/m² of soil. However we could assume a seedling rate exceeding 3, 000 seeds in 1.5cm/m² of soil. The loss of rice yield was negligible in rice paddy fields containing less than 3, 000 seeds in 1.5cm/m² of soil.