Development and application of oxadiazon-fertilizer slow-release granule for synchronous application in mechanical transplanting rice

Weed infestation is a serious problem in mechanical transplanting rice in China. Developing pre-emergent (PRE) herbicide-fertilizer slow-release granule and its assorted application technology is one of the most effective way to improve the efficiency. In this work, three types of slow-release oxadiazon-fertilizer granule (SROG) coated with poly-lactic acid with a core-shell structure were developed (contained 0.25% oxadiazon active ingredient). The efficacy and rice safety of SROG were evaluated in mechanical transplanting rice fields. The results indicated that, when transplanting was applied in the same time at 180 kg/hm² (450 g a.i./hm² of oxadiazon), the three types of SROG (with different concentration of coating material) disintegrated 3 to 7 days after the application, and had over 90% control efficacy against Echinochloa spp. and Monochoria vaginalis 35 days after transplanting, which were similar to regular PRE application (combined with fertilizer) of oxadiazon EC and pyrazosulfuron-ethyl + simetryne + prometryn WP 5 days after the transplanting. The plant height, aboveground fresh weight and tiller number were greater for the three SROG treatments compare with treatments of the two regular PRE herbicides 35 days after transplanting. Similar weed control efficacy was obtained when the dosage of SROG declined to 80% (144 kg/hm² or 360 g a.i./hm²). No herbicide injury was observed in all the experiments. The mechanical application of SROG synchronized with the improved side deep fertilizing rice transplanter (just broadcast the SROG on the soil surface) was also systematically investigated. The mechanical transplanting synchronized with SROG application technology could be an effective tool for rice cultivation systems to reduce labor input and herbicide application in the future.