| Effects of fertilization on soil microbial activity and N2O emission of Purple Soil in Central Sichuan Hilly Areas were studied, which aimed to establish the best fertilization system in central Sichuan hilly area, improve fertilizer use efficiency, reduce the purple soil N2O emission and accurately assess the N2O emission in the purple soil agro-ecosystem.Six different treatments, including pig manure (OM), pig manure+N, P, K fertilizers(OMNPK), straw+N, P, K fertilizers (RSDNPK), and the treatment of N, P, K fertilizers (NPK), N fertilizer (N) and no fertilizers (CK), were applied to the purple soil of wheat- maize rotation cropland in central Sichuan hilly areas. Soil microbial quantity, soil microbial biomass, soil respiration intensity, metabolic quotient, soil enzyme activities and N2O emission at different maize growth stages (from May to September,2010) were studied. The main results were as follows:(1)The quantities of soil microbes (bacteria, fungus, ammonia-oxidizing bacteria,actinomycetes, nitrifying bacteria and denitrifying bacteria) were improved significantly by OMNPK, OM, RSDNPK and NPK treatments at different maize growth stages. OMNPK treatment had the best effect, and increased the quantities of bacteria, fungus, actinomycetes and ammonia-oxidizing bacteria by 93.62%,98.71%,121.42% and 275.64% respectively, compared with CK. The quantities of ammonia-oxidizing bacteria, nitrifying bacteria and denitrifying bacteria were increased at some extent, while the quantities of bacteria and actinomycetes were reduced by 11.92% and 36.61% compared with CK. The change of soil microbes quantity showed the same trendency in different treatments at the whole maize growth stage, the maxima of actinomycetes quantity were appeared in maize jointing stage, and the maxima of the other soil microbes quantity were appeared in maize filling stage.(2) In the whole maize growth stages, soil microbial biomass C and N showed the same chang trendency in all the treatments, and the maxima of soil microbial biomass C and N were all in the maize filling stage. OMNPK, OM, RSDNPK and NPK treatments significantly increased the soil microbial biomass C and N in maize growth stages, and the OMNPK treatment had the best effect, then followed by the RSDNPK treatment, while the N treatment had the minimun value.(3) Fertilization treatments significantly affected the soil respiration intensity, and the soil respiration intensity order was OMNPK>OM>RSDNPK> NPK>N>CK, the maxima of the soil respiration intensity were all in the maize filling stage, while all the treatments significantly decreased the soil metabolic quotient, the soil metabolic quotient order was CK>N>OM>RSDNPK> NPK>OMNPK, and the maxima of the soil metabolic quotient of all the treatments appeared in the maize jointing stage.(4) Fertilization treatments significantly increased the activities of the soil urease, alkaline phosphatase, invertase, protease, hydroxylamine reductase, nitrite reductase and nitrate reductase. The OMNPK had the best effects, followed by the RSDNPK. While all the treatments reduced the catalase activity, the best decreasing effects were the OM and OMNPK, while the N treatment reduced the catalase activity least. In all the maize growth stages, the maxima of soil urease, alkaline phosphatase, hydroxylamine reductase and catalase activities appeared in the maize filling stage,but the maxima of soil invertase and nitrate reductase activities appeared in the jointing stage, and the maxima of the soil protease and nitrite reductase appeared in the seedling stage.(5) Fertilization treatments significantly increased the soil ammonium nitrogen and nitrate nitrogen contents, and then increased the soil N2O emission flux and total contents in the maize growth stages as well, and the maximum ammonium nitrogen and nitrate nitrogen contents appeared in the OM, and the minimum apperared in the RSDNPK. In all the treatments, the average soil N2O emission fluxs were 40.86-156.43ug.m-2.h-1, and the average soil N2O emission total contents were 0.46-1.75 kg.hm-2, which were 0.91%-1.17% of the fertilizing amount of the current season. The soil ammonium nitrogen and nitrate nitrogen contents showed the same change tendengcy as the soil N2O emission flux, which indicated that soil ammonium nitrogen and nitrate nitrogen were the main limiting factors of the soil N2O emission in the maize growth stages in hilly areas of the central Sichuan.(6) Fertilization treatments significantly increased the maize yields. OMNPK and RSDNPK treatments both had higher yields than the NPK, OM, N and CK. And the order of the maize yields in all the treatments was OMNPK>RSDNPK>NPK>OM>N>CK. Compared with the CK,the maize yields of the OMNPK, RSDNPK, NPK, OM and N increased by 1843.54%, 1841.19%,1660.43%,1506.59% and 663.41% respectively. |
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