Abstract:

【Objective】 In order to prevent soil acidification by regulating soil carbon and nitrogen, the change of several forms of soil carbon, nitrogen and soil pH, and the corrrelations among them were studied after the application of several organic materials.【Method】 Incubation experiments were conducted at the temperature of (25±1)℃. The dynamics of NH4+-N, NO3--N, water-extracted soluble organic carbon (WSOC), water-extracted soluble organic nitrogen (WSON), soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN) and pH after application of several organic materials (rice straw, Chinese milk vetch and pig manure) were measured. 【Result】 Compared with the control treatment, soil pH, SMBC and WSOC increased after application of organic materials, and increased with the application rates. After application of pig manure, NH4+-N, NO3--N and WSON in soil increased significantly. WSON and NO3--N in soil decreased after application of rice straw and Chinese milk vetch, and decreased with the application rates, while application of rice straw and Chinese milk vetch had no significant effect on NH4+-N. Soil pH reached its maximum between the 7th and 14th day of incubation after application of rice straw and Chinese milk vetch, while increased immediately after application of pig manure, decreased thereafter, and tended to be stable. Compared with the control treatment, soil pH increased by 0.26, 0.23 and 0.09 on average in the treatments of pig manure, rice straw and Chinese milk vetch at the end of incubation for 84 d. Soil pH was positively correlated with SMBC and WSOC in the treatments of organic materials, while soil pH was negatively correlated with WSON and NO3--N after application of rice straw and Chinese milk vetch, and insignificantly correlated with WSON and NO3--N in the treatments of pig manure.【Conclusion】 Application of several organic materials could significantly increase WSOC, SMBC and pH of the soil, with the pH increasing is in the order of pig manure ＞ rice straw ＞ Chinese milk vetch. Dynamics of soil carbon and nitrogen are important in relation to the change of soil acidity after application of organic materials, and the relativity is related to the properties of organic materials.

Key words: red soil, organic materials, pH, carbon, nitrogen