黄土丘陵区苹果园深层水分补给消耗过程、驱动机制与调控

The Loess Plateau is one of the optimal planting zones of apples and had the biggest planting areas of apple trees. In recent years, apple orchards have been increasing fast on the Loess Hilly Region owing to the policy of “Expansion into West and North”. However, the fast expansion of apple orchards can result in excessive use of deep soil water and soil desiccation due to water scarcity and strong evapotranspiration. This in turn could undermine the sustainable development of apple orchards. Therefore, this project is first to investigate the specific processes of soil water recharge and consumption by integrating in situ measurements of deep-profile soil moisture at high temporal resolution and deep-layer deuterium labeling. Then several mathematical methods are used to probe the related mechanisms based on environmental factors monitoring. Finally, this project is going to raise an effective approach of regulating deep soil water through deep infiltration by collecting rainwater and pruning. Based on the above studies, this project aims to alleviate the degree of soil desiccation due to excessive use of deep soil water, and finally realize the co-improvement of ecology and production of apple orchards. This project can provide scientific insights into the retaining of deep soil water and sustainable development of rainfed apple orchards in the hilly region of the Loess Plateau where precipitation is limited.

黄土高原是世界上的苹果优生区和最大的连片栽植区，近年来在“西进北扩”发展布局推进下黄土丘陵区苹果发展迅猛，但干旱缺水和果树蒸腾耗水强烈导致果园深层水分过度消耗而引起土壤干燥化，危害果园的持续健康发展。本研究立足于区域降水和生产实际，以旱作苹果园盛果期果树为对象，采用深剖面土壤水分高频率连续定位观测、氘同位素深层标记、果树蒸散与生理生长监测等试验手段，结合理论分析，揭示深层土壤水分补给消耗具体发生发展过程，探明其驱动机制，从“开源”和“节流”两方面提出深层土壤水分的有效调控策略，缓解果园深层土壤水分过度消耗引起的土壤干燥化，实现旱作果园生产与生态的协同发展。以为黄土丘陵区有限降水条件下旱作苹果园深层土壤水资源保育和持续健康发展提供科学依据。

针对黄土丘陵区旱作苹果园深层土壤水分过度消耗导致土壤干燥化问题，项目以黄土丘陵区苹果园深层水分补给消耗过程、驱动机制与调控为目标，采用定位监测、氢氧稳定同位素、模型模拟的方法，重点研究土壤水分和水汽通量时空变化过程及其机制，果树水分来源及其利用机制，以及不同界面土壤水分调控策略，取得如下进展：（1）揭示了黄土丘陵区旱作苹果园深层土壤水分补给消耗的过程，发现降水难以对3m以下土壤水分形成有效补给，3m以下深层土壤水分在研究期间逐年降低，且每年主要发生在5-7月关键需水期，蒸腾耗水量增加是深层土壤干燥化的主要驱动因素。（2）探明了等温和非等温两种情景下苹果园土壤液态水和水汽动态过程，发现不同典型次降雨下汽态水通量比液态水通量整体上小2个数量级，但液态水通量和汽态水通量对深层土壤的最大补给深度分别为100 cm和160 cm，表明土壤水通过向下的汽态水能够运移至更深层土壤，汽态水通量可能是黄土深层土壤水补给的重要组成。（3）阐明了不同林龄果树水分利用机制，11龄和17龄苹果树均表现出灵活的水分利用策略，11龄对浅层（0-40cm）土壤水的利用比例显著高于17龄果树，但是17龄苹果树比11龄利用了更多的2 m和3 m土层的土壤水。（4）构建促渗抑蒸多界面联合调控体系。在根土界面，研发出雨水集聚深层入渗技术（RWCI），探明了RWCI系统在不同年份均能显著缓解剖面土壤水分亏缺；在土气界面，建立果树与绿肥间作的复合系统，发现在间作期降低了土壤含水量，但在刈割覆盖期显著增加土壤含水量；在气植界面，确定出去除20%侧枝能够有效降低蒸腾耗水量，并且提升了产量和水分利用效率。研究成果将为黄土高原旱作苹果园水土资源高效利用与可持续发展提供科学依据。