Response of weeds and rice yield to Italian ryegrass as a cover crop and planting density in organic farming

Organic farming has been receiving increased attention in the agriculture sector; however, Japanese organic farming often requires intensive labor, and the yield is lower compared with the conventional rice (Oryza sativa L.) system. In this study, we examined the effects of planting density (12.7 vs. 24.2 plant m(-1)) and cover crop (Italian ryegrass [Lolium multiflorum Lam.] vs. winter fallow) on organic rice production in central Japan. A 2-yr experiment was conducted under organic management in a paddy field at the Center for International Field Agriculture Research & Education, Ibaraki University in 2019 and 2020 using a split-plot design with four replications. Rice yields were 25 and 6.8% higher when Italian ryegrass was used as the cover crop under sparse planting conditions than under dense planting conditions in 2019 and 2020, respectively. The interaction between cover crop and planting density was significant across the 2 yr. Although there was no significant difference in weed biomass during the rice cultivation period, sparse planting and winter fallow resulted in greater weed biomass than dense planting and Italian ryegrass, respectively. The contribution of nitrogen (N) derived from Italian ryegrass showed a significant difference between 2019 and 2020 but not between sparse and dense planting. Although cover-crop-derived N contribution to organic rice production was different between the 2 yr, the use of Italian ryegrass as a cover crop at sparse planting density can improve rice yield and suppress weed growth in central Japan.

Automated summary

The study indicates that using Italian ryegrass as a cover crop and cultivating organic rice under sparse planting conditions can increase yield and suppress weed growth.