稳定性氮肥施用与秸秆还田对土壤保氮供氮机制影响

Microbial immobilization-mineralization and minerals fixation-release processes for fertilizer nitrogen (N) were the important mechanisms of N conservation and supply in soil. The temporal coupling relationship between the availability of soil carbon and N, as well as the effects of these processes on N conservation and supply were changed, inducing by the application of stabilized N fertilizer including different inhibitors and the straw returning. However, the processes were studied separately, and not regarded as an interrelated whole process. Hence, based on the incubation and field 15N labeling experiments, this proposal was designed to investigate systematically the responses of mechanisms of N conservation and supply in soil and their mutual transformation to stabilized N fertilizer application and straw returning. The competition for NH4+ between microbial immobilization and minerals fixation and their effects on N conservation are clarified by the distribution pattern of labeled N in different N pools. The influences of the conversion processes and their inherent correlation of microbial biomass N and fixed NH4+ pools to soil N supply are explored through the analysis of the rules and the timeliness and efficiency of immobilized N mineralization and fixed NH4+ release. The mathematical N-cycling model including the biotic and abiotic processes is constructed by the quantification of the influences of stabilized N fertilizer application and straw returning on N transformation in soil. The results will provide the theoretical basis and data support for increasing N use efficiency, optimizing stabilized N fertilizer and straw resource allocation, and improving agricultural ecosystem N-cycling theory.

氮的微生物固持-矿化和粘土矿物固定-释放过程是土壤保氮供氮的重要机制。稳定性氮肥中不同类型抑制剂和秸秆还田通过改变土壤碳氮有效性在时间尺度上的耦联关系进而改变着上述过程在土壤保氮供氮中的作用。但以往研究多将这两个过程分别对待，并未视其为彼此联系的整体过程。本项目以东北典型旱田为研究对象，利用15N示踪技术，结合培养与田间试验，系统研究土壤保氮供氮机制对稳定性氮肥施用和秸秆还田的响应。通过跟踪肥料氮在不同氮库中的分配，明晰微生物固持和矿物固定对肥料氮的竞争格局及其在保氮中的作用；通过分析被固持和固定肥料氮矿化和释放规律及其时效性，明确微生物氮库与固定态铵库转化过程及其内在联系对土壤氮素供给的影响；通过量化稳定性氮肥和秸秆还田对氮素转化相关过程的影响，构建涵盖生物与非生物过程的氮素循环模型。研究结果将为提高氮肥利用效率、优化稳定性氮肥与秸秆资源配置、完善农田氮素循环理论提供基础和支撑。

肥料氮施入土壤后可通过微生物固持和粘土矿物固定保存于土壤当中，而后被固持和固定的肥料氮会逐渐矿化和释放，供作物利用。相关过程明显受氮素养分管理措施，如：抑制剂和有机碳源添加等的影响。本研究利用15N标记技术，分析了施用稳定性氮肥和碳源后，肥料氮在各氮库中的分配与转化过程，明确了肥料氮的微生物固持和矿物固定在保氮和供氮中的作用，阐明了抑制剂与碳源添加对氮肥利用效率的影响。.无碳源添加条件下，固定态铵在保氮和供氮方面的作用大于有机氮库，固定态铵保氮和供氮作用是有机氮库1.5倍和2.6倍；随着碳源添加，有机氮库在保存和供给肥料氮方面作用超过固定态铵库，后者保氮和供氮作用仅为前者的28%和38%。碳源的添加减少了肥料氮的损失，归因于更多的肥料氮保存在非微生物有机氮库中，造成肥料有效性的降低。.抑制剂可提高固定态铵在保氮和供氮中的作用，硝化抑制剂作用效果明显，且可延缓固定态铵释放，改善土壤供氮与作物需氮同步性。但随着碳源添加，硝化抑制剂进一步促进微生物对肥料氮的固持，降低肥料氮有效性，而脲酶抑制剂则减少肥料氮被固持，缓解其有效性降低问题。.通过调整碳源添加时间和用量，肥料氮固持在保氮中的作用得到提升，但并未显著影响肥料氮的矿物固定和释放在保氮和供氮中的作用，提高氮肥利用效率同时也提高了土壤氮素有效性，更有利于作物增产。肥料氮来源固定态铵具有长期有效性，第一季释放比例平均为46.4%，平均供氮10.7kg ha-1，随时间增长，肥料氮来源固定态铵释放率降低。.综上，在潮棕壤上，无碳源添加时，两种抑制剂均有助于提高生物和非生物过程在保氮和供氮中的作用，提高氮素供给时效性。碳源与氮肥同时施用，肥料氮有效性降低；硝化抑制剂使之进一步加剧，而脲酶抑制剂则可缓解了氮素有效性低的问题。通过合理调节碳源用量与施用时间，可有效提高作物产量，进一步发挥抑制剂效果，减少肥料氮损失，提高氮肥利用效率。