Abstract: In 2005 and 2007, soil samples were collected from a 27-year experimental field in Wangcheng County of Hunan Province to study the effects of long-term application of chemical fertilizers (CF) and their combinations with pig manure (PM) and rice straw (RS) on the chemical and biochemical properties of reddish paddy soil (Typic Haplic-Stagnic Anthrosis). Under the fertilization, soil pH had somewhat decrease, and soil conductivity changed less, compared with those before the experiment was installed. The contents of soil total organic carbon (TOC), total N, available N and P, and microbial biomass C (C_mic) and N (N_mic), soil respiration rate, and activities of soil urease, acid phosphatase, invertase, and dehydrogenase were all higher in treatments CF+PM and CF+RS than in treatments CF and CK, and the C_mic/TOC ratio was higher in treatments CF+PM and CF+RS than in treatment CF. During the study period, applying CF alone induced a lower rice yield than the application of CF plus PM or RS.There were significant positive correlations (P<0.01) between soil biochemical properties and soil TOC and nutrient contents. It was concluded that long-term application of CF combined with PM and RS improved the soil chemical and biochemical properties, being an effective measure to improve the quality and fertility of reddish paddy soil.

Key words: long-term fertilization, total organic carbon, soil enzymatic activity, microbial biomass, metabolic quotient, maize, soybean, intercropping, plant density, yield, economic output value.