Carbon And Nitrogen　Accumulation And Mineralization In Aggregates Under Long-term Manure Fertilization Practices On Black Soil

Soil carbon and nitrogen are important nutrients in biogeochemical cycle.Carbon and nitrogen in agricultural soil is an important part of soil fertility, which cannot only be integrated to reflect the chemical, physical and biological properties, butalso greatly related to environmental problem such as global climate change andwater pollution. Fertilization is an effective way to increase crop yield and soilfertility, but improper fertilization also cause serious environmental risk. Based on along-term experiment under manure fertilization on black soil in northeast China, westudied the accumulation and mineralization of carbon and nitrogen in black soil anddifferent fraction size aggregates of various fertilizations with aggregate sizeseparation and laboratory imitation incubation experiment, and discussed thecharacteristic of black soil carbon source utilization efficiency of microorganisms andenvironmental risk caused by long-term manure application under the differentfertilization practices. Results are as given follows：（1）Long-term manure application significantly improved the accumulation ofsoil organic matter (calculated as soil organic carbon) and total nitrogen capacity.Compared with control, moderate manure application or combined with chemicalfertilizer could significantly increase soil organic matter and total nitrogen content by45.8%~52.2%and53.3%~78.2%, respectively. The high amount of manure combinedwith chemical fertilizer could significantly increase soil organic matter and totalnitrogen content by76.7%~110.1%and56.4%~96.6%, respectively. There was stronglinearly correlation between nitrogen applied amount and soil nitrogen accumulation,and organic nitrogen fertilizer application contributed greater nitrogen accumulationcompared to chemical nitrogen fertilizer. The soil nitrogen accumulation wasincreased31.73kg/hm2every year with100kg/hm2organic nitrogen fertilizerapplication. Morever, long-term manure fertilization could also significantly increasethe SOC and TN content in soil aggregates, which was increased by the increasinglevel manure applied.（2）Long-term manure fertilization significantly influenced soil nitrogenmineralization amount and rate. Results showed that The amounts of soil mineralized nitrogen were increased by7.2and9.2times under the moderate and high applicationrates of manure, respectively. However, the application of chemical fertilizers (N orNPK) had no effect on black soil nitrogen mineralization. After the application for32years, soil nitrogen mineralization amounts were largely enhanced with theapplication of moderate and high rates of manure alone, which were equivalent to8.2times and10.2times of that under the control, respectively. The application oforganic manure could significantly enhance soil nitrogen mineralization rate.However, compared with the manure fertilization alone, additional application ofchemical N fertilizer and NPK fertilizers obviously decreased the Nt/TN rate.（3）There were strong linearly correlations between soil mineralized nitrogenamount and soil organic matter, soil nitrogen and labile fractions, and the nitrogenmineralization amount increased1t/hm2when soil organic matter increased0.39t/hm2. The soil nitrogen mineralization rate was improved with the increase of organicmatter and total nitrogen stock, and then was stable at0.4%level. These resultsindicated that, eventhough the amount of soil nitrogen mineralization was directlyrelated to the number of organic matter, soil organic matter quality also regulated thenitrogen mineralization capacity.（4）The long-term manure fertilization colud also significantly increase boththe concentrations and ratios of dissolved organic carbon and nitrogen. Theapplication of chemical NPK fertilizers combined with organic manure significantlydecreased the ratio of soil microbial biomass nitrogen to soil total nitrogen, increasedsoil microbial biomass C/N ratio, and promoted the biological fixation of soilnitrogen. Single organic fertilizaion had no significant effect on the soil nitratecontent of soil profile, but the high amount of organic manure combined withchemical fertilizers resulted in severe nitrate leaching in soil profile, increasing therisk of environment.（5）Organic fertilization had a significant impact on carbon decomposition andnitrogen mineralization of soil aggregates. Soil carbon and nitrogen mineralizationwas respectively80.3~161.1g/kg and2.1~32.9g/kg in <53μm fraction underlong-term fertilization, which was the largest among all the different size fractions.Long-term manure fertilization could also improve soil microbial biomass carbon andsoil microbial biomass nitrogen, especially combined with chemical fertilizer (N or NPK), and soil microbial biomass carbon was increased respectively1.16,2.48, and2.35times under M60NPK compared to control. However, N applied alone got thelowest level. Long-term manure application increased SMBC/SMBN, andsignificantly decreased the CO2/SMBC, which was beneficial to the carbon andnitrogen use efficiency of microorganisms.