Combined use of Azolla and loach suppressed weed Monochoria vaginalis and increased rice yield without agrochemicals Weiguo Cheng & Yuka Okamoto & Miwa Takei & Keitaro Tawaraya & Hironori Yasuda Received: 14 August 2014 /Accepted: 19 January 2015 /Published online: 1 February 2015 # Springer Science+Business Media Dordrecht 2015 Abstract The primary challenge in organic rice farm- ing 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 or- ganic 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. Keywords Azolla . Loach . Monochoria vaginalis . Organic farming . Rice yield Introduction Rice (Oryza sativa L.) is one of the most important crops in the world and is the most important food in Asia, which accounts for 90 % of the total world rice production area. According to the FAOSTAT database, during the last 50 years, the world rice cultivation area increased by 41 % with an average rice yield increase of about 140 % from 1.84 t ha -1 in 1961 to 4.41 t ha -1 in 2012 (FAO 2014). The substantial increase in world rice yield, as with other crops, has mainly been achieved by use of synthetic fertilizers and pesticides, the develop- ment of new crop varieties, and improved cultivation methods. However, long-term heavy application of syn- thetic fertilizers and pesticides negatively affects the environment, induces pesticide resistance, and increases agricultural costs (Tilman et al. 2002; Brown and Funk 2008; Ando et al. 2014). The growing hu- man population requires more food supply by in- creased crop production, and agriculture must find ways to feed a growing population demanding more meat and high-calorie diets, while also de- creasing its global environmental effects. Organic farming was developed to reduce the negative Org. Agr. (2015) 5:1–10 DOI 10.1007/s13165-015-0097-3 W. Cheng (*) : Y. Okamoto : M. Takei : K. Tawaraya : H. Yasuda Faculty of Agriculture, Yamagata University, 1-23 Wakaba-machi, Tsuruoka, Yamagata 997-8555, Japan e-mail: cheng@tds1.tr.yamagata-u.ac.jp