Effects of long-term fertilization on spring season weed community in winter fallow paddy field in red soil area under double-rice cropping system

An investigation in winter fallow field of double-rice cropping system in the red soil area was carried out in 2012 in a long-term fertilization experiment (started in 1982) site in Hengyang Red Soil Experiment Station of Chinese Academy of Agricultural Sciences to study the species, biomass and biodiversity of weed communities during spring season. The investigated long-term fertilization experiment included five fertilization treatments of application of organic fertilizer, chemical fertilizer and combined application of organic and inorganic fertilizers with the same rates of nitrogen (N), phosphorus (P) and potassium (K) in both the organic and chemical fertilizers, which were no fertilizer (CK), organic fertilizer (composted cattle manure, M), combined application of P and K inorganic fertilizer and organic fertilizer (PKM), application of inorganic N, P, and K fertilizer (NPK), combined application of N, K inorganic fertilizer and organic fertilizer (NKM), combined application of N, P inorganic fertilizer and organic fertilizer (NPM), and combined application of N, P, K inorganic fertilizer and organic fertilizer (NPKM). The results showed that the dominant weed species changed and the total density and total biomass of weed communities increased under combined application of organic and inorganic fertilizers. NKM treatment had the largest number of weed species, while the least weed species number was under NPM treatment. Species diversity index (1.118 6), evenness index (0.732 3) and dominance index (0.629 7) of weed communities under M treatment were larger than those under the other treatments. However, M treatment had the lowest total weed density (297.0 plant0.25m^-2). Also NPK treatment had the lowest total weed biomass (58.0 g0.25m^-2). Compared with other treatments, NPM treatment significantly decreased diversity, evenness and dominance indexes of weed communities, and had the highest total weed density (539.7 plant0.25m^-2) and total weed biomass (109.5 g0.25m^-2), respectively. Alopecurus japonicas was the dominant weed species, and had weed density of 428.0 plant0.25m^-2 and relative weed density of 79.31% under NPM treatment, which were significantly higher than those of dominant weeds under other treatments. It was noted in this study that total dry biomass of weeds was positively correlated with content of soil alkali-hydrolyzable N (r = 0.703), negatively correlated with soil pH (r = –0.697), and significantly positively correlated with soil available P content (rr?=?0.758). Thus soil P was considered as the main factor responsible for the characteristic changes in weed communities under long-term fertilization modes. The proper regulation of soil pH and contents of soil alkali-hydrolyzable N, soil available P and especially soil available P through different long-term fertilization schemes could effectively managed biomass, density, and biodiversity of weed communities during spring season in winter fallow paddy field in the red soil area.