南疆枣棉间作复合系统氮素运移特征及种间竞争机制研究

The jujube industry development rapidly in southern Xinjiang results to a series of problems such as the land-use contradiction between agriculture and forestry,and the lower young orchard comprehensive production capacity,there is little experience about large-scale multistoried cropping，especially lack of mature experience about carrying out jujube-cotton intercropping planting of the larger ecological niche differences in such bad ecological conditions which have apparently affect the sustainable development of agriculture.So reasonable agroforestry planting patterns has important guiding significance to the development of high-productivity and high-efficiency agriculture.To the issue of jujube-cotton intercropping development in the Tarim Basin such as low yield and nitrogen use efficiency,we take intercropping technology in the young jujube orchard, improve nitrogen use efficiency as the goal of composite system,take field plot test and root separation micro area test which use the 15N isotope tracer technique to study time and space distribution rule of root system and nitrogen transformation characteristics,explore the relationship between soil nitrogen supply and plant nitrogen requirement during the growth,reveal interspecific nitrogen competition mechanism in jujube-cotton intercropping system, and then excavate a way of improving nitrogen production potential in the agro-forestry compound system.The results will provide theoretical basis to promoting nitrogen use efficiency and comprehensive benefits in the young jujube orchard,meanwhile,they also provide technical support for adjustment agricultural structure, promoting great harvest of agriculture and forestry in southern Xinjiang arid areas, these experiences about reasonable fertilization can be used for reference by other agroforestry planting patterns in southern Xinjiang.

南疆红枣产业的快速发展导致农林争地矛盾突出及幼龄枣园综合生产能力低，加之大规模开展立体高效种植的经验不足，尤其是在南疆恶劣生态条件下开展生态位差异较大的枣棉间作种植尚没有成熟的经验可借鉴，影响了农业的持续发展，因此建立科学、合理的枣棉间作种植模式对实现农业高产高效具有重要的指导意义。本项目针对枣棉间作生产中存在的产量低、氮肥利用效率低等问题，在幼龄枣园采用间作种植方式，以提高复合系统氮肥利用效率为目标，采取田间小区和微区根系分隔试验，利用15N同位素示踪技术，研究枣棉间作系统根系时空分布规律及氮素迁移转化特征，探明土壤氮素供应与植株需氮的互作关系，揭示枣棉间作下种间氮素竞争的机制，进而探索提高农林间作复合系统氮素生产潜力的途径。研究结果将对幼龄枣园氮肥利用效率和综合效益的全面提升提供理论依据，为南疆干旱区农业结构调整、农林双丰收提供技术支撑，并为南疆地区其它果农间作模式合理施肥提供借鉴。

随着枣树树龄的增加，枣树与棉花水肥竞争的矛盾日益凸显，间作枣园复合系统生产力逐渐降低，本项目针对枣-棉间作生产中存在的产量低、氮肥利用效率低等问题，开展了枣-棉间作系统氮素运移特征及种间竞争机制研究，以拓展枣-棉间作的有效利用周期，提高枣园综合生产效率，促进农业健康持续发展。四年的研究工作表明：（1）距离枣树0.5-1m区域是种间养分竞争的主要区域；枣-棉间作具有氮素的补偿作用，枣树与棉花对氮素吸收利用在时间和空间生态位的分离造成间作比单作更具有氮素利用的优势，而根系空间生态位互补是枣棉间作氮素高效利用的主要原因；N-15同位素示踪的结果表明，间作系统氮的吸收量比单作高53.7-57.1%，间作棉花吸收的氮素来自肥料的比例较单作高5.9-6.5个百分点；间作棉花氮素利用率比单作平均高6.4-9.6个百分点，进而提升了整个间作体系的氮素利用率。（2）轻度水分亏缺可改善土壤环境，土壤速效磷、速效钾、多酚氧化酶和蔗糖酶活性及土壤微生物群落丰富度和多样性均显著提高。（3）间作土壤全氮、硝态氮、铵态氮较单平均分别高2.2%、0.67%、11.5%；间作系统对土壤氮素的竞争在空间分布上形成互补效应，0-40cm土层棉花对土壤氮素的吸收能力大于枣树，60-100cm土层枣树对土壤氮素的吸收能力大于棉花；枣树中间种植的棉花行数越多，对土壤氮素的竞争越为剧烈，距离枣树1.45种植2行棉花的种植方式中枣树对于土壤氮素的竞争大于棉花，距离枣树1m种植4行棉花和距离枣树0.5m种植六行棉花的种植方式表现为棉花对土壤氮素的竞争大于枣树。（4）适宜间作棉花的枣树树龄阈值为5.21年（y=-0.0543x+0.7828，R²=0.9681），明确枣树树龄为5年及以下的间作系统，枣树、棉花的田间配置均采用常规模式且间距为1m；树龄6-7年，棉花采取减小播幅、缩小株距、增加间距的田间配置（（30＋40＋30）＋60）×10cm，形成“空边挤中”的种植模式；不适宜间作棉花的枣树树龄为7.61年（y=0.0518x+0.6057，R²=0.9212），树龄8年及以后，采取“间伐稀化”等疏密改造技术进行动态调控；若不间伐，则棉花退出间作系统或枣园实行清种。