The Influence Of Different Agricultural Practices On The Soil Nutrient And Weed Community Composition In Redlish Rice-cropping Ecosystems

Based on a long-term experiment, the influence of different agricultural practices on the weed community composition and biodiversity, changes of soil available nutrient in different growth stage of rice and soil available nutrient change trends, and rice yields under different agricultural practices were studied in rice-cropping ecosystems. The result showed as the follows:1. During different growth stage of rice, the soil pH and soil available nutrient content were highest under rice-rice-winter flooded fallow cropping system among three cropping systems, its soil pH was 5.11 to 5.55, while 4.93 to 5.44, 4.91 to 5.40 under rice-rice-rape and rice-rice-green manure cropping systems, respectively. The soil available N content was the lowest under rice-rice-rape cropping system, the decreased amount of 28.1 mg/kg and 21.8 mg/kg were observed in the maturity stage of early rice and maturity stage of late rice, compared with rice-rice- winter flooded fallow cropping system. The soil available P content was the lowest under rice-rice-green manure cropping system, compared with rice-rice- winter flooded fallow cropping system, it reduced by 4.3 mg/kg and 2.7 mg/kg before the early rice transplants and in maturity stage of late rice. However, the soil available K content under rice-rice-rape and rice-rice-green manure cropping systems was lower than rice-rice-winter flooded fallow cropping system. In the treatment of chemic fertilizer, the soil pH and soil available P content were the highest under different fertilization systems, while the soil available N and K content were the lowest; the soil available N and K content were the highest under high rate applying of organic manure, however, the soil available P content was the lowest. Under the treatment of chemic fertilizer, the soil available P content was high by 14.8 mg/kg and 5.4 mg/kg, the soil available N content was low by 31.0 mg/kg and 41.3 mg/kg, and the soil available K content was low by 27.8 mg/kg and 29.0 mg/kg compared with high rate applying of organic manure, respectively. Between higher and lower groundwater table, the different of the soil pH and soil available nutrient content was not found.2. During different growth stage of rice, their changed tendency was all similar about soil pH and soil available nutrient content under different agricultural practices. The soil pH and soil available nutrient content was increased from the early rice transplants to recovery stage of early rice. The soil pH was reduced from recovery stage to tillering stage of early rice, and increased from the maturity stage of early rice to tillering stage of late rice. From the tillering stage to maturity stage of early rice and from tillering stage to maturity stage of late rice, the remarkable different of soil pH was not observed. There was reduced trend of soil available N content from recovery stage to tillering stage of early rice, and no obvious change from tillering stage to maturity stage of early rice and tillering stage to maturity stage of late rice. The changed rule of soil available P showed reduced-increased trend from recovery stage to maturity stage of early rice, while there was obviously reduced trend from maturity stage of early rice to heading stage of late rice. The soil available K content gradually reduced from recovery stage to heading stage of early rice and from tillering stage to heading stage of late rice, no obvious change from heading stage to maturity stage of early rice, and a little increment was found from heading stage to maturity stage of late rice.3. The rice yield was lower under rice-rice-winter flooded fallow cropping system than other two cropping systems, and its yield of early rice and late rice were 5031kg/hm²and 6568 kg/nm² under rice-rice-winter flooded fallow cropping system, respective. There was not different of early rice yield among three fertilization systems, however, the late rice yield was lower under the treatment of chemic fertilizer than other two fertilization systems, the late rice yield was 6481 kg/hm² under the treatment of chemic fertilizer. The groundwater table did not affected the rice yield.4. The agricultural practices obviously affected the weed density and preponderant weed. The evidently different of three weed biodiversity indexes (Margalef's D_MG, Shannon's E, Shannon's H') was observed in early rice crops among different cropping systems and fertilization systems. Between the treatment of high rate organic manure and chemic fertilizer, the only different of Shannon's H' was found. The groundwater table did not affected the three weed biodiversity indexes.5. The cropping systems was the most important factor that caused the weed community composition during early rice among agricultural practices, on the other hand, the fertilization systems caused the weed community composition change in late rice crops. The influence of the different groundwater table was lowest during the rice growth.