长期外源秸秆还田调节日光温室土壤氮素保持与供应的作用及机制

The excessive fertilizer applied with furrow irrigation resulted in accumulation of soluble N in soil profile and ground water contamination through substantial N leaching in plastic greenhouse production system. The aim of the project is to study the effect and mechanism of long-term straw application on N retention and supply under the greenhouse production system, and then provide some theoretical guidance in application of straw and N fertilizer for increasing N use efficiency and decreasing its loss. Reducing N fertilizer through fertigation by micro-irrigation and increasing N retention in soil are essential means for reducing the mineral N accumulation and loss. Application of straw with high C: N ratio is a useful way for synchronizing the N retention and supply, and decreasing the loss of N in farmland. However, the temperature, humidity, and the soil management in greenhouse production system are remarkably different with the farmland, which may change the dynamic immobilization—remineralization （IM-RE）of N. Therefore, it is necessary to evaluate the dynamic of N retention, supply and leaching in the greenhouse conducted with long-term application of straw with the 15N labeled technology. Besides the amount of organic materials, the quality also affected the dynamic of IM-RE of N. Thus, we evaluate the amount of immobilized N by different straw and the effect of decomposition of cellulose, hemicelluloses and lignin on the IM-RE of N to structure a model for forecasting the N retention and supply.

解决日光温室栽培下土壤累积氮数量高，损失多的问题一方面要减少氮肥施用量，另一方面要增加土壤氮素保持和供应能力。施用碳氮比高的秸秆，调控土壤氮素保持与供应是农田中提高氮利用率、减少损失的有效手段。日光温室环境条件和土壤管理与农田差异大。日光温室中外源秸秆施用后土壤固氮机理研究较少。本项目以土壤氮素固持与释放为中心，利用15N标记微区试验研究不同水肥模式下（滴灌施肥和漫灌施肥）长期（7年）秸秆还田调节土壤氮素保持与供应的效果，同时追踪温室条件下肥料氮在土壤—作物—环境的分配数量及形态；重点探索秸秆不同组分（纤维素、半纤维素和木质素）降解对氮素固持与释放的影响机制；通过研究，揭示秸秆还田在调控日光温室氮素固持与供应的效果和机理，为合理的秸秆和氮肥施用提供理论指导，以提高氮素利用，减少损失。

日光温室中氮肥投入多、损失多，对资源与环境造成很大的压力。解决日光温室损失多的问题一方面要减少氮肥施用量，另一方面要增加土壤氮素保持和供应能力。本项目通过2个培养试验、4个田间试验研究了不同秸秆施用对土壤剖面氮素分布、淋溶损失和气态损失的影响，并揭示了其中的机理。研究结果表明配施秸秆使更多的矿质态氮保持在上层（0-100 cm）土壤，与小麦秸秆相比，玉米秸秆的保持作用更明显。传统模式下，矿质态氮的淋溶损失量可达433 kg N ha-1，占氮素投入量的24%，减少氮肥投入显著降低氮素损失，在此基础上施用小麦秸秆使氮素的淋溶损失量进一步降低，与传统相比降幅达50%以上，损失率降低至18.2%和12.0%，显著提高氮肥利用率，且未减产。不同灌溉施肥模式相比，滴灌施肥显著降低矿质态氮和可溶性有机氮的淋溶损失，在两种灌溉施肥模式下，施用秸秆使矿质氮显著降低30%以上，同时也显著降低了可溶性有机氮的淋溶损失量。施用秸秆后，矿质态氮淋溶损失量的降低与氮素的固持有关。在日光温室土壤中添加有机物料使矿质氮含量显著降低，不同质量有机物料对于氮素的固持特性不同，纤维素降解速度快，对氮素的固持量最大，在施用碳量为0.8%时，固持量可达443 mg/kg，等碳量的稻壳和玉米秸秆固持量分别为119和170 mg/kg，相对于稻壳而言，玉米秸秆对于氮素的短期固持能力更强。这使土柱淋溶试验中施用玉米秸秆处理的淋溶量较稻壳处理淋溶量降低21%。综上，在日光温室中施用秸秆由于提高了氮素的微生物固持，显著降低了氮素的淋溶损失，与小麦秸秆和稻壳相比，玉米秸秆的作用更显著。