Effects Of Fertilization On Microbial Biomass In Paddy Soils Of Subtropical China

In soil ecosystem, microorganisms is the major power to decompose and transform the soil organic matters and nutrients. The biological and biochemical index could be sensitive indicators for the change of soil quality. Investigation on the changes of soil biochemical properties under intensive agricultural management would be of practical significance to understand deeply the mechanism of soil degradation, and then propose rational measures for sustainability of soil ecosystem.In this paper, effects on microbial biomass, basal respiration and biomass yield in red paddy soils of Jiangxi province under different fertilities were investigated through potted experiment, field sampling and incubation experiment. Dynamical mineralization of microbial biomass in different soil fertility levels and treatments were also observed. Factors influencing microbial biomass N mineralization and its contributions to soil total N were discussed.The results from potted experiment showed that soil available nutrients increased with fertilizer application. But microbial biomass didn't increase constantly, change of which also related to original soil and fertility level. Soil microbial biomass C changed irregularly in different levels of fertilization. Microbial biomass N in different soils changed similarly, which all decreased after 1.5 times of conventional fertilizer application. Changes in different soils were: Quaternary red clay with high fertility level(CH)> Tertiary sandstone weathering product with high fertility level(SH)> Quaternary red clay with low fertility level(CL)> Tertiary sandstone weathering product with low fertility level(SL).Soil basal respiration increased with soil organics in no fertilization treatment. In fertilization treatment, basal respiration in paddy soils of subtropical China decreased after 1.5 times of conventional fertilizer application. Metabolic quotient in different soils changed irregularly.Researches on microbial biomass under different fertilizations and crop residue cycling demonstrated that microbial biomass C increased significantly in fertilization + crop residue cycling treatment. And microbial biomass C in only fertilization even increased more quickly. Crop residue cycling in different fertilizations could significantly increase the content of microbial biomass N. Microbial biomass N increase in fertilization+1/2 crop residue cycling treatment had no significant difference with control treatment. In different fertilization treatments, trends of grain and traw yield were: NPK+C > NPK+1/2JG > NPK > NP > N+C > C > NK > CK > N. The grain and traw yield in crop residue cycling treatment was higher than non-cycling treatment. Crop residue cycling on fertilizations could significantly promote the grain and traw yield, which had extremely significant relationships with soil nutrient and microbial biomass N.In the aerobic leaching incubation experiment, microbial biomass N mineralization could be divided into two parts: quick mineralization(first 4 weeks)and relatively slow mineralization(later 8 week). Mineralization rate of microbial biomass N in first 4 weeks was almost fourfold the rate in 10-12 weeks. The mineralization amount and rate increased with soil fertility. The proportion of microbial biomass N mineralization in total N mineralization increased with incubation time and soil organics.Fertilization evidently increased the amount and rate of microbial biomass mineralization. The amount of microbial biomass mineralization were: NPK > C > NPK+C > CK, and 167.71mg/kg, 123.22mg/kg, 117.18mg/kg, 40.75mg/kg, separately. Microbial biomass N in NPK+C treatment is 37.45mg/kg, which was relatively higher than other treatments. Fertilization only and crop residue cycling could significantly increase microbial biomass C.In conclusion, fertilization application and crop residue cycling on high fertility soil would not always increase microbial biomass and basal respiration. Fertilization treatment should be made based on different soils. Fertilization with crop residue cycling treatment would make soil keep high fertility and increased microbial biomass N and crop yield. Microbial biomass had high mineralization efficience. Its contributions to soil total N mineralization increased with fertility level. Microbial biomass N mineralization amount in high fertility soil was high.