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。

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.