中文摘要：

【目的】土壤有机碳物理一化学联合分组方法很好地联系了有机碳的多种稳定机制,成为深入研究土壤有机碳组分特征的有效手段。本研究旨在利用该方法研究长期施肥对黄壤性水稻土有机氮组分特征的影响,为合理施肥提供理论依据。【方法】基于南方黄壤性水稻土18年长期施肥定位试验,分析了不同施肥处理土壤有机氮组分含量及分配比例的变化。试验处理包括不施肥对照（CK）、单施化肥（NPK）、单施有机肥（M）、无机肥配施低量有机肥（0.5MNPK）和无机肥配施高量有机肥（MNPK）。【结果】单施化肥处理（NPK）水稻土总有机氮及各组分有机氮含量与不施肥对照相比无显著变化,施用有机肥处理（M、0.5MNPK、MNPK）则显著提高了土壤总有机氮、游离态粗颗粒、物理保护、化学保护及生物化学保护有机氮含量提高幅度分别为27%-51%、23%-39%、128%-274%、29%-42%和13%-28%,以有机无机肥配施最为显著,但降低了游离态细颗粒有机氮含量。在各个氮组分中游离态颗粒有机氮占总有机氮比例最高（46%-50%）物理保护有机氮比例最低（2%-6%）。与不施肥（CK）及单施化肥处理（NPK）相比,有机肥处理（M、0.5MNPK、MNPK）提高了土壤物理保护有机氮的分配比例。【结论】长期施肥土壤各组分有机氮及总有机氮两两之间均呈显著相关关系只有游离细颗粒有机氮与物理保护有机氮呈负相关关系。长期施用有机肥,极大改善土壤团聚体结构促进游离细颗粒有机氮的包裹,进而提高物理保护有机氮的相对比例,土壤有机氮的物理保护作用相对增强。因此,有机无机肥配施是提高稻田土壤有机氮含量的最有效措施。

英文摘要：

[Objectives]A physical-chemical fractionation method is an effective tool for deeply investigating soil organic carbon fractions due to its linkage of stabilization mechanisms of organic carbon in soil.In this study,the method was used for better understanding the effects of long-term fertilization on yellow paddy soil organic nitrogen soil organic nitrogen（SON） fractions and guide proper fertilization.[Methods]The soil samples were collected from a 18-years＇ field experiment in yellow paddy soil,the soil organic nitrogen fractions and their proportions in total organic N were investigated using the physic-chemical fractionation method.The treatments included：no fertilizer（CK）,chemical fertilizer alone（NPK）,organic manure alone（M）,the chemical fertilizer combined with manure at a conventional rate（0.5 MNPK） and a greater rate（MNPK）.[Results]The NPK treatment had no significant effects on total SON and its fraction contents compared with CK.Total SON,unprotected coarse particulate,physically-protected,chemically-protected and biochemically-protected organic nitrogen（ON） contents were significantly increased by 27%-51%,23%-39%,128%-274%,29%-42%and 13%-28%correspondingly under the manure treatments（M,0.5MNPK,MNPK）.Compared with CK,unprotected fine particulate ON content was decreased.Among these fractions,the unprotected ON showed the highest percentage（46%-50%）,and the physically protected ON showed the lowest percentage（2%-6%） in total SON.[Conclusions]Generally,the total SON and its fractions are significantly correlated with each other.Soil unprotected fine particulate ON is negatively correlated with physically-protected ON.The physically-protected ON proportion are higher under the manure treatments（M,0.5MNPK,MNPK） than the CK and NPK treatments.Manure application promotes the transformation of free fine particulate ON to physically-protected ON due to possibly increased aggregation,thus decreased soil unprotected fine particulate ON content and increased physica