Abstract: Based on a 7-year sitespecific experiment, we studied the density and biodiversity of weed seedbank with milk vetch application in paddy field, discussed the relationship between weed seed community and soil fertility factors. The results showed that yearly milk vetch application significantly reduced the density of paddy weed seedbank and main weed seed species, such as Lapsana apogonoides, Juncellus serotinus (P<0.05). In 0-20 cm soil layer, Shannon index, Simpson index and Pielou index of weed seed were in order of chemical fertilizer with milk vetch application treatment, chemical fertilizer without milk vetch application treatment, no fertilizer treatment in descending order. Yearly milk vetch application significantly improved richness and evenness of weed seedbank (P<0.05). Yearly milk vetch and fertilizer application had a significant effect on major soil fertility factors (P<0.05). The soil pH had a significant negative correlation with biodiversity index of weed seedbank (P<0.05). The increase of soil total N and available N highly significantly improved the weed seedbank biodiversity (P<0.01). There was also a positive relationship between weed seedbank biodiversity and soil available N (P<0.1).

Key words: wheat/maize intercropping, crops, photosynthetically active radiation, photosynthetically active radiation (PAR) interception, geometrical model, Hetao Irrigation District.