Factors destabilizing the control ofMonochoria vaginalisby rice bran: its conflicting powers influence both suppression and promotion of germination in paddy soil

Organic paddy rice (Oryza sativaL.) cultivation can be negatively impacted because of the weeds growth likeMonochoria vaginalis. Although the rice bran application is useful in combating weed, its performance is not consistent. In this study, laboratory experiments were conducted to elucidate the effects of rice bran on the suppression and promotion of germination ofM. vaginalis. Suppression experiments involved incubating mixtures of flooded soil and rice bran. This was followed by a germination experiment in the collected soil solutions. A negative and significant correlation was observed between germination and the electric conductivity (EC) of the solution. None of the seeds germinated when the EC of the Gray Lowland soil was over 130 mS m(-1). Conversely, the seeds in the Andosols' solution germinated even when EC was over 130 mS m(-1). Thus, the solutions of the Andosols had different mechanisms of suppression than the Gray Lowland soils. To understand the promotion of germination, air-dried soil was prepared after the flooded incubation of rice bran and soil mixture, simulating a long-term application of rice bran. Germination was analyzed in a filtrate of the mixture of air-dried soil and distilled water. The addition of rice bran significantly promoted germination. There was a negative and significant correlation between germination and dissolved oxygen (DO) suggesting that hardly decomposable components like antioxidants in rice bran decreased O(2)and stimulated germination because the seeds ofM. vaginalisrequire very little O(2)for germination.

Automated summary

Rice bran has both inhibitory and stimulatory effects on the germination of Monochoria vaginalis seeds, with different suppression mechanisms in different soil types. Antioxidants in rice bran reduce oxygen levels, promoting germination of M. vaginalis seeds which require very little oxygen for germination.