长期施肥对稻田土壤活性有机碳和氮的影响

土壤活性有机碳、氮是土壤有机碳、氮中最活跃的组分,在土壤碳、氮循环过程中具有重要作用。以湖南3个长期定位试验点（桃源、宁乡、桃江）为研究对象,分析测定表层土壤MBC、MBN、DOC、DON,研究长期施肥对土壤活性有机碳、氮（MBC＋DOC,MBN＋DON）的影响。结果表明,长期施用化肥及配施有机肥均能提高土壤活性有机碳、氮的含量。与对应的无肥处理（CK）相比,长期单施化肥（NPK）使土壤活性有机碳、氮的提高幅度分别为3.3%~21.0%和3.3%~27.1%,长期有机肥施用提高幅度分别为48.7%~84.8%和17.9%~105.8%,且土壤活性有机碳、氮含量随有机肥施用量的提高而增加,3个试验点活性有机碳大小顺序为桃源〉宁乡〉桃江。土壤活性有机碳与土壤有机碳（SOC）的累积速率呈显著正相关关系（P〈0.05）,而与SOC的含量关系不大。桃源土壤粘粒含量较高可能是土壤SOC累积速率快的主要原因;宁乡和桃江的粘粒含量和有机碳投入量相差不大,桃江较高的初始SOC水平影响了SOC积累速率;桃源和宁乡试验点的土壤活性氮含量相差不大,约是桃江的1.8倍。与土壤全氮（TN）相比,全氮的积累速率与土壤活性氮的关系更为密切,两者间有极显著的相关关系（P〈0.01）。

Effect of Long-term Fertilization on Active Organic Carbon and Nitrogen in Paddy Soils

Soil active organic carbon and nitrogen play important roles in soil carbon and nitrogen cycle as the most active parts of soil organic carbon and nitrogen.Soil microbial biomass carbon（MBC）and microbial biomass nitrogen（MBN）,dissolved organic carbon（DOC）and dissolved organic nitrogen（DON）were measured to investigate the effects of long-term fertilization on active soil organic carbon（MBC＋DOC） and nitrogen（MBN＋DON）from three long-term field experiments（Taoyuan,Ningxiang and Taojiang）in Hunan Province,China.Results showed that chemical fertilizer or combined with organic manure applications increased the contents of soil active organic carbon and nitrogen,as compared to non-fertilizer treatments.The applications of chemical fertilizer increased active soil organic carbon and nitrogen contents by 3.3%～21.0% and 3.3%～27.1%,respectively.Similarly,the applications of organic manure increased active soil organic carbon and nitrogen contents by 48.7%～84.8% and 17.9%～105.8%,respectively.Furthermore positive correlation between the active soil organic carbon and nitrogen contents and organic fertilizer application amounts were found in all the three sites.The contents of active soil organic carbon between three sites followed the track of Taoyuan〉Ningxiang〉Taojiang.The correlations relationship between active soil organic carbon contents and soil organic carbon accumulation rates was significantly positive（P〈0.05）,while correlation relationship between active soil organic carbon contents and soil organic carbon contents was insignificant.High soil clay contents at Taoyuan site could be the reason why SOC accumulation rates at Taoyuan site were higher than other sites.Although the clay contents and amounts of organic carbon input at Ningxiang and Taojiang sites were similar,the difference of SOC accumulation rates at the two sites was significant.Since high original SOC content at Tao-jiang site was a regulated factor of SOC accumulation rates.Comparable active soil organic nitrogen contents were gained at Taoyuan and Ningxiang sites which were about 1.8 times that in Taoijang site.The significant correlation between active soil organic nitrogen contents and total nitrogen accumulated rates（P〈0.01）was found in the study.