全膜覆土穴播对雨养小麦特征氮库生态效应研究

It makes a practical significance of raising sustainable productivity only when nitrogen pool formation was studied on the base that whole plastic film as mulch combined with bunch planting is a category of significantly water-saving cultures in rainfed wheat in loess plateau. Therefore, management characteristics in plant nitrogen and volatilization, leaching and transformation efficiency in soil nitrogen were tested and analysed in growing season and fallow period in wheat-soil ecosystem only when winter and spring wheat were sowed in conditions that whole plastic film as mulch combined with bunch planting in the whole year, whole plastic film as mulch combined with bunch planting in the whole growth period and direct seeding uncovered with film on conditions that ammonium, nitrate and amido nitrogen was basally applied and topdressed, combinning with isolation and identification of rhizosphere soil microorganism so as well as transport and transformation efficiency in endophytic fungi mycorrhiza fungi. These studies will not only master their differences in utilization, repository form and loss of nitrogen between whole plastic film as mulch combined with bunch planting and conservation tillage so as well as direct seeding uncovered with film，but also clarify regulatory mechanism of characteristic nitrogen-pool reservation by rhizosphere microorganisms and endophytic mycorrhizal fungi so as to lay a solid foundation of optimizing cultivation techniques and improving nitrogen efficiency and solve the problem that farmland ecosystem is pollutted by wastered nitrogen in rainfed wheat in loess plateau.

全膜覆土穴播是黄土高原雨养小麦的重要节水栽培技术，研究该条件下小麦土壤特征氮库储备形态与微生态调控机制对提高旱地小麦生产力具有重要现实意义。因此，本研究通过同位素示踪技术基施不同水平氮素后全年全膜覆盖、全生育期全膜覆盖和露地平播方式进行小麦栽培，检测分析小麦-土壤生态系统中生长季和休闲期小麦植株氮素运筹、土壤氮素挥发、淋溶和转化效率的测定分析研究，查明全年全膜覆盖、全生育期全膜覆盖和露地平播栽培模式下小麦-土壤生态系统氮素运筹利用、特征氮库储备形态和氮素损失途径的差异性，阐明根际微生物对全膜覆土穴播栽培方式小麦特征氮库储备的调控机制，为栽培技术模式优化和旱地小麦氮素利用率提高奠定坚实基础，以解决黄土高原雨养小麦氮素流失污染农田生态环境的生产实际问题。

氮素循环转化与利用率提高是一项复杂而漫长的生物过程。本研究利用15N同位素示踪技术研究了全膜覆土穴播旱地冬小麦田土壤氮素生物循环转化过程与氮肥利用效率的高低。结果发现：全膜覆土穴播和露地穴播旱地冬小麦0-120cm土层的全氮含量、有机质含量随着土层下移而减小；15N丰度随着土层下移呈现先降后升趋势，各层土壤的15N丰度值与肥料残留量与土层深度成反比。具体来讲：低氮浓度下全年全膜覆土穴播栽培的氮肥残留率在为9-52%,高氮浓度下全年全膜覆土穴播栽培的氮肥残留率为12%-55%；低氮浓度下全生育期全膜覆土穴播的氮肥残留率为6%-47%，高氮浓度下全生育期全膜覆土穴播的氮肥残留率为17%-50%；低氮浓度下全生育期露地穴播栽培的氮肥残留率为8%-58%，高氮浓度下全生育期露地穴播栽培的氮肥残留率为7%-40%。Illumina Miseq技术测定分析了全年全膜覆土穴播、全生育期全膜覆土穴播和露地穴播栽培方式下根际土壤细菌类群。结果表明：全年全膜覆土穴播、全生育期全膜覆土穴播和露地穴播栽培方式下根际土壤的反硝化细菌、硝化细菌优势菌群高度相似，主要分布在变形菌门、放线菌门、厚壁菌门、丙型变形菌纲、甲型变形菌纲，变形菌是最丰富的细菌类群。这一研究结果不仅有助于阐明根际微生物对不同栽培方式小麦特征氮库储备的调控机制，而且有利于优化黄土高原旱作雨养冬小麦耕作栽培方式、提高冬小麦的氮素利用率。