基于氢氧同位素的黄土塬区粮豆间作系统的水分利用研究

The research of intercropping system is one of the main approaches to keep global food security and agricultural sustainable development. It is a great significance to identify the root water uptake sources and quantify the contribution of soil water at different depths to water uptake by crop for optimizing water use efficiency for agriculture in arid and semi-arid regions. The application of isotope tracer technique to study the structure characteristics of water consumption is one of the main methods that have emerged in recent years, but the underlying mechanism is not clear. In this project, a field experiment will be conducted to evaluate the effects of sowing proportion and sowing date on water use in maize-soybean intercrops on the Loess Plateau of China. The precipitation, soil water, and the stem water of maize and soybean will be sampled in different growth periods of crops, and the compositions of D and18O of samples will be measured. The difference of utilization of soil water in the different growth stages of maize and soybean will be determined by comparing the stable oxygen and hydrogen isotope compositions in plant stem water and soil water in different soil layer. The contribution of soil water in different soil layer to crop water consumption will be quantified. The evapotranspiration of farmland will be distinguished by water balance and isotope mass conservation. Further, the influence of intercrops system on the water use of maize and soybean will be explored, and finally, the water use mechanism of maize-soybean intercropping systems in arid and semi-arid regions will be obtained definitely. On the one hand, this project will help to understand the interaction and feedback mechanism of water use in different intercropping systems. On the other hand, it can provide theoretical reference for food security and sustainable development for water shortage on the Loess Plateau of China.

间作系统资源分配与高效利用研究是解决全球粮食安全和农业可持续发展问题的主要途径之一。明确间作系统农作物根系吸水的主要来源和贡献比例对于解决干旱半干旱地区水分资源高效利用具有重要意义，但是运用稳定氢氧同位素示踪技术探讨间作系统水分利用特征的机理目前尚不清楚。本项目拟在黄土塬区以玉米和大豆为研究对象，以种植比例和种植时间为主要控制因子构建不同间作系统，采集玉米和大豆生育期内的降水、土壤水、茎秆水，并对其氢氧稳定同位素组成进行测定，通过分析植物茎水和不同土层土壤水氢氧稳定同位素的动态分布规律，进而研究间作系统中作物不同生育期对土壤水分利用的差异，量化间作系统中作物的用水来源及根系吸水深度，利用水量守恒和同位素质量守恒法量化区分农田蒸散量，从而揭示干旱半干旱地区间作系统的水分利用机制。本项目有助于科学理解间作系统的水分利用特征和反馈机制；可为水资源短缺的黄土塬区的粮食安全和可持续发展提供理论参考。

明确间作系统农作物根系吸水的主要来源和贡献比例对于解决干旱半干旱地区水分资源高效利用具有重要意义。本项目在黄土塬区以玉米和大豆为研究对象，以种植比例和种植时间为主要控制因子构建不同间作系统，通过直接对比法和模型分析玉米和大豆生育期内的降水、土壤水、茎秆水的氢氧同位素的变化规律，探究间作系统中作物不同生育期对土壤水分利用的差异，量化间作系统中作物的根系吸水深度。结果表明：单作玉米在拔节期、吐丝期和成熟期分别主要水分吸收深度为0-20cm（86.8±1.2%），150-200cm（48.0±1.6%），20-70cm（37.2±2.5%）。间作玉米在拔节期、吐丝期和成熟期分别主要水分吸收深度为0-20cm（48.3±1.3%），70-150 cm（30.8±1.2%），70-200 cm（65.0±2.4%）。单作大豆和间作大豆整个生育期主要水分吸收深度为0-20cm（76.4±1.6%和87.3±1.7%）。间作系统的水分利用效率相比单作提高2.4—24.8%，其中M4S2间作的水分利用效率最高。因此，间作系统玉米和大豆吸水深度的差异即生态位分化是提高水分利用的主要原因。本项目有望进一步深化对间作系统水分利用机理的认识，从而为水资源短缺的黄土塬区的可持续发展提供理论依据。