Effect Of Long-Term Different Fertilizations On Organic Carbon Mineralization In Paddy Soil

In recent years,global climate changed by the increase of concentration of greenhouse gases in the atmosphere are popular questions of common interest.CO₂ and CH₄,which increased very fast during the past years,are carbonaceous gases. Agroecosystems play an important role in the budget of atmospheric greenhouse gases. Thus,Soil organic C mineralization comes to be the hottest portion of global climate change research.Dynamics of soil organic C mineralization affected by different fertiliztions and its relationship with organic C fractions in paddy soils were investigated. Soil samples were collected from the plough layer of 3 long-term experiments at Xinhua, Ningxiang and Taojiang counties of Hunan province,China.The results observe were as follows:1.NPK plus manure or straw significantly increased the contents of TOC(Total organic C),EOOC(Easily-oxidized organic C),MBC(Microbial biomass C),WSOC (Water-soluble organic C) by 12.59%～82.84%,15.33%～103.95%,35.33%～97.54% and 15.89%～73.73%as compared to CK,respectively.The percentages of TOC presented as EOOC,MBC and WSOC ranged from 49.02%～58.31%,1.93%～3.46% and 0.10%～0.15%,respectively.No significant difference was found in these percentages among different treatments.The proportion of MBC and WSOC for Taojiang was much lower than that for Ningxiang and Xinhua sites.There were highly significant correlations observed among TOC,EOOC,MBC and WSOC.2.Mineralization of soil organic C was estimated by using 58-d anaerobic incubation study at 30℃.The cumulative amounts of evolved CO₂ and CH₄ ranged from 448.64 1516.77μg·g^-1 and 15.60～33.34μg·g^-1,respectively.The total amounts of cumulative mineralized C accounted for 3.59%～5.57%of soil TOC.The rates of CO₂ production were higher during the 13-d incubation for different treatments,then decreased and afterwards a little varied.The rates of CH₄ production presented a slowly increasing at first and then rapidly declined to low constant rates.The cumulative mineralized C in NPK plus manure or straw treatments were greater than that in inorganic fertilizers treatments.Significant correlations were found between cumulative mineralized C and TOC,EOOC,MBC and WSOC.The correlations of soil TOC,EOOC,MBC,WSOC with the percentages of cumulative mineralized C in TOC were not found to be significant. 3.Mineralization of soil organic C was estimated by using 33-d aerobic incubation study under 3 temperature regimes(10℃,20℃,30℃).The rates of CO₂ production were higher during the earlier phase(0～13 d) for different treatments,then decreased and afterwards a little varied.Daily mineralization of soil organic C during incubation accords to the relationship of logarithm.With the increase in the amount of soil sample, the amounts of total mineralized C increased with each treatment for each site.The amounts of total mineralized C in NPK plus manure or straw treatments were more than that in inorganic fertilizers treatments.The Q₁₀ values in the different treatments ranged from 1.01～1.53.Significant positive correlations were observed between the Q₁₀ values and soil TOC and EOOC.The cumulative mineralized C were significantly positively correlated with MBC at 10℃and 20℃,but no significant correlation was found at 30℃. Significant correlations were found between total mineralized C and different soil C fractions.The correlations of different soil C fractions with the percentages of total mineralized C in TOC were negatively correlated at 10℃,and not significantly at 20℃and 30℃.