| The research adopted methods of experimental plots and investigation in paddy fields, and maked a study on the physical and chemical characteristics of soil, diversity of weed communities, population dynamics for rice insect pests and diseases, and economical benefits in rice-duck ecological farming ecosystem from 2008 to 2009. The main results were as follows:1. The soil nutrient characteristics in rice-duck ecological farming during growth stage of rice(1) The content of water stable aggregate and nutrient characteristics. Compared with that of sole cropping,2-1 mm water stable aggregate were increased by 5.29% in rice-duck ecological system,<0.25 mm and>2 mm water stable aggregate were decreased by 5.17% and 0.28% respectively. The content of total N, total P, total K and organic carbon were increased markedly in 2-1 mm and 1-0.25 mm water stable aggregate,<0.25 mm water stable aggregate were decreased.(2) Nutrient characteristics of soil profile. The content of N, P and K were decreased from surfance soil to 20 cm soil profile. Ducks moving and inputed dejecta into paddy fields, which influence on the surfance soil nutrient remakedly. The content of total P, total K, available N, available K and active organic carbon were increased markedly in 0-5 cm soil profile, while the content of total N was decreased. In 5-10 cm soil profile, the content of total P, total K were hegher than sole rice cropping, and in 10-15 cm soil profile, the content of available N, available P were incereased, and in 15-20 cm soil profile the content of total K were increased.(3) Nutritional status in the root zone. Available N, available K, active organic carbon, heigh-active organic carbon and pH value of rice root surface soil were increased by 30.80 mg/kg,17.93 mg/kg,2.17 g/kg,0.56 g/kg and 0.23, and total N and available P were decreased by 0.11 g/kg,8.66 mg/kg. The soil total N, available N available K, organic carbon, active organic carbon and mid-active organic carbon in rhizosphere were decreased by 0.11 g/kg,15.13 mg/kg,7.61 mg/kg,2.39 g/kg,2.64 g/kg and 0.72 g/kg, and available P was increased by 9.66 mg/kg. (4) The correlation analysis between organic carbon and soil properties. Soil total N, total P and available N was significantly correlated with Soil total organic carbon (R=0.95, 0.95,0.96), regression equations were Y=-11.3033+18.61137X, Y=1.454846+26.23002X, and Y=-2.83889+0.181469X respectively. The concertration of total K was with active organic carbon the linear regression equation was Y=39.21046-2.02799X. Soil pH value, bulk density and total porosity were significantly correlated with Soil total organic carbon (R=-0.85,-0.77,0.77), regression equations were Y=59.51093-7.15519X, Y=24.12376-4.27418X, Y=12.79717+0.113266X, F value were 10.11,5.90,5.90.2. The biodiversity of weed and population dynamics on rice insect pests and diseases in scale rice-duck ecological farming ecosystem.(1) The composition and diversity of weed communities. The density of weed of the scale rice-duck farming in paddy fields decreased significantly compared with the sole rice cropping. Before the rice booting stage,weed was composed of Mouochoria vaginalis, Echinochhloa crausgalli, Alternanthera philoxeroides, Murdannia triquetra, Cynodon dactylon L and Alopecurus pratensis Linn; From the rice heading stage to ripe stage, weed was composed of Echinochhloa crausgalli, Alternanthera philoxeroides and Cynodon dactylon L. At the rice tillering stage species richness, Simpon index and Shannon-Wiener index of scale rice-duck farming were higher than sole cropping, while Pielou index was lower than sole cropping. From the rice booting stage to rice ripe stage, species richness, Simpon index and Shannon-Wiener index of scale rice-duck farming were lower than that of sole cropping, while Pielou index was significantly higher than that of sole cropping. During the whole rice growing stage, weed density, weed fresh weight and species diversity were not significantly different between the scale rice-duck farming and conventional rice-duck farming,but species diversity of weed had a increasing trend. The scale rice-duck farming changed the structure of weed community and decreased the weed species diversity, which effectively limited weed infestation in paddy fields.(2) Population dynamics on rice insect pests and diseases in scale rice-duck ecological farming ecosystem. In scale rice-duck farming the mean densities of rice stem borers, leaf folder, planthoppers and leafhoppers were decreased by 54.4%,48.8%,73.6% and 96.1% compared with mono-cropping, as well as the rate of diseased plant of rice sheath blights and rice planthopper were decreased by 78.9% and 48.5%; While compared with the conventional rice-duck farming, the average densities of rice stem borer, rice leaf folder, rice planthopper and rice leafhopper was reduced by 18.2%,9.5%,7.0% and 0.82%, and the rate of diseased plant of rice sheath blight were decreased by 35.5%, unfortunately the rate of diseased plant rice blast-infested was increased by 8.0%. In scale rice-duck farming ecosystem, the percentage of infected plants of rice striped stem borer and rice planthopper were 52.9% and 6.9% lower than conventional rice-duck farming. The experiment also shows that the population peak density of rice stem borer, rice leaf folder and planthopper were postponed in scale rice-duck farming field, and infestation period of rice sheath blight was shortened by 10-14 days. The characters of rice in scale_rice-duck farming field were improved in terms of larger number of spikes per plant and kernels per spike, higher 1000-kernel-weight, lower emptiness rate and the highest grain yield. Net profit of scale rice-duck farming treatment increased by 1024.32 yuan/hm2 (4.53%) and 1370.61 yuan/hm2 (71.21%) compared with the conventional rice-duck farming and mono-cropping respectively. The scale rice-duck farming has an good effect on control of rice diseases and pests, and its economic income was increased markedly.
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