黄土高原地膜覆盖冬小麦利用播前底墒的过程及调控机制

The Loess Plateau is a major dryland wheat production region in China. Because rain season does not synchronize with wheat growth, soil water at planting (SWP) is, therefore becoming the most important water source for wheat growth and yield formation. Recent years, winter wheat with plastic film mulching (PFM) is widely adopted in the region for its significantly higher yield improving potential and water use efficiency. However, the PFM significantly changes the soil moisture and thermal condition as compared with the traditional practice, and thus the quantity of SWP, soil depth at which SWP is available to wheat, and water use pattern have also been drastically altered. Hence, it is not reasonable to assess water use efficiency of wheat under PFM by techniques and methods those used in the traditional practice. It is of great scientific significance to further study SWP use dynamics during wheat growing season and to fully understand the mechanism of water use by wheat with PFM, and therefore to seek the key factors by which the SWP using pattern could be regulated to improve water use efficiency and meanwhile to achieve a desired yield. Based on field experiments, in situ monitoring, stable isotopic technique and other laboratory methods, we are going to monitor the dynamics of SWP used by winter wheat with PFM at different levels of SWP; to investigate the relative contribution of SWP and the precipitation during growing season to wheat growth; and to work on the effects of seeding rates and nitrogen management on SWP use by plastic mulched wheat and the mechanisms behind. Besides, we would also want to clarify the interaction effects of SWP, seeding rate and nitrogen management on SWP use pattern and the mechanisms underlying. The results obtained from our study will provide support to formulate the sustainable management strategies in efficient use of limited water resources in the regions of similar conditions.

黄土高原是我国重要的旱地冬麦区，由于雨季与生长季错位，播前底墒是旱地小麦非常重要的水源。近年来地膜覆盖小麦在该区迅速发展，并显著提高了小麦产量及水分利用效率。与传统种植相比，地膜覆盖改变了土壤的水热条件，小麦利用播前底墒的深度、数量或模式均随之发生了变化，采用传统的研究手段和方法估算地膜小麦的水分利用已不能真正反映地膜小麦的水分利用效率。因此，研究地膜小麦利用水分过程及其关键影响因素，搞清地膜小麦用水机制，对实现旱区水分利用的综合调控有重要科学意义。本项目采用田间试验、田间原位观测结合氢氧稳定性同位素技术等分析方法，以传统种植为对照，研究地膜冬小麦对不同水平播前底墒的利用过程、播前底墒与生育期降水对冬小麦的贡献比例；播种密度、氮素管理对播前底墒利用的影响及作用机制；播前底墒与播种密度、氮素管理对地膜小麦水分利用的交互影响及机理。研究结果为地膜小麦有限水资源可持续高效利用提供科学依据。

地膜覆盖小麦在黄土高原迅速发展, 但是地膜小麦水分利用过程及其关键影响因素研究不足。本项目采用田间试验结合氢氧稳定同位素技术，通过贝叶斯MISIAR模型等分析方法，研究了地膜覆盖小麦利用播前底墒的过程及机理、播前底墒与群体调控、氮素管理对地膜覆盖小麦利用播前底墒的影响及机制，取得了大量数据。结果表明地膜覆盖较常规种植增加了小麦利用播前底墒的深度以及比例，特别是提高了小麦对120-300cm土层的水分利用，增加比例范围6-11%。其作用机理与地膜覆盖提高土壤温度，增加储水量，进而促进小麦根系生长（增加根长和根重密度）有关。通过播前底墒与群体调控、氮素管理及其高效耦合效应研究发现，提高播种密度或增加施氮量或氮素分期调控均可以影响覆膜小麦利用土壤水分的深度，并且与播前底墒有显著的交互作用。播前底墒较好时，增加播种密度以及氮肥用量能够提高小麦花前耗水量，有提高小麦产量的趋势；播前底墒不足时，减少播量和施氮量可以降低小麦产量下降的风险。因此，覆膜小麦可以根据播前底墒调整播种量以及氮素管理策略，获得高产及水分高效利用。