Rice Bran Application under Deep Flooding Can Control Weed and Increase Grain Yield in Organic Rice Culture

Rice bran application just after transplanting has been increasingly practiced as a herbicide-substitute for organic rice production in Korea. However, this practice is frequently reported to be unsatisfactory in weed suppression. An experiment with five treatments that combine flooding depth (shallow and deep), rice bran application level (low and high), and herbicide application was carried out in the paddy field to evaluate whether rice bran application under deep flooding can lead to successful weed control in compensation for the single practice of rice bran. Rice bran was broadcasted on the flood water surface just after deep flooding of 8 to 10 cm that was started at seven days after transplanting. Six weed species were recorded in the shallow flooding plot without herbicide: Monochoria vaginalis, Echinochloa crus-galli, Ludvigia prostrate, Cyperus amuricus, Aneima keisak, and Bidens tripartite. Among the first four dominant weed species, deep flooding significantly suppressed the occurrence of Echinochloa crus-galli and Cyperus amuricus, while it did not suppress the occurrence of Monochoria vaginalis and Ludwigia prostrate. On the contrary, rice bran application under deep flooding significantly suppressed Monochoria vaginalis and Ludwigia prostrate, while didn't exert an additional suppression of Echinochloa crus-galli and Cyperus amuricus compared to deep flooding alone. Rice bran application and deep flooding suppressed complimentarily all six weed species to a satisfactory extent except for Monochoria vaginalis for which suppression efficacy was 31.9%. Deep flooding substantially reduced the panicle number by inhibiting the tiller production, increased the spikelet number per panicle slightly, and led to a lower rice grain yield compared to shallow flooding with herbicide. Rice bran application under deep flooding mitigated the panicle reduction due to deep flooding, increased the spikelets per panicle significantly, and thus produced even higher grain yield in the rice bran application of 2000 kg ha as compared to the shallow flooding treatment with herbicide. In conclusion, it would be advisable to implement rice bran application under deep flooding as an integral practice for an organic rice farming system.