Combined use of Azolla and loach suppressed weed Monochoria vaginalis and increased rice yield without agrochemicals

Abstract

The primary challenge in organic rice farming in Japan and other Asian countries is to control Monochoria vaginalis, one of the most common and troublesome broadleaved weeds. Azolla is a genus of floating aquatic ferns, used for many centuries as a green manure in traditional rice production. Loach (Misgurnus anguillicaudatus) is a freshwater fish that was once widely spread in Asian rice paddies, but has disappeared in modern conventional rice paddies due to use of synthetic agrichemicals. The objective of this study was to assess the effects of individual and combined use of Azolla filiculoides and loach to suppress M. vaginalis emergence and increase rice yield in organic rice farming. This study was designed with four treatments—control (with neither Azolla nor loach), Azolla (Azolla alone), loach (loach alone), and Az + Lo (combined Azolla and loach)—with three replications each. The results showed a partial suppression of M. vaginalis and improved rice yield with Azolla and loach. The combined use of Azolla and loach had more positive effect on weed suppression and 131 % increase in rice yield over the control treatment. This study indicated that combined use of Azolla and loach as a valuable approach in organic rice farming, especially in organically farmed rice paddies with high densities of M. vaginalis seeds. This combined use of Azolla and loach provides dual benefit of weed control and N supply without the use of synthetic N fertilizer.