黄土高原苹果园生草复合系统水分耗散特征与模拟

The Loess Plateau is one of the two main apple production districts in China, apple industry takes an important role for increasing farmer’s incomes and wealth. However, soil structure and fertility degradation is increasingly salient due to the traditional clean tillage practice in apple production. Covering forage in orchard has been proved to be an efficient way to prevent land from degradation, but its application on Loess Plateau is limited due to soil water extraction characteristic of the apple tree and forage intercropping system is not well understood. Based on above problems, this project is aimed to: 1) investigate the effects of intercropping forage on the soil water dynamics and water consumption of apple orchard under rain-fed condition; 2) quantify evapotranspiration and its partitioning among apple tree transpiration, forage transpiration and soil evaporation in the intercropping system, and 3) simulate the evapotranspiration processes and soil water balance in this system and provide suggestions for grass management in rain-fed apple orchard based on the model. Results of this project can provide evidences and guidance for manage soil water in apple tree and forage intercropping system on the Loess Plateau.

黄土高原是我国两大苹果优势产区之一，苹果产业是该区农民增收致富和实现全面小康的支柱产业。然而随着种植年限的增加，果园清耕管理导致的土壤结构和肥力退化问题日益突出。生草覆盖是防治果园土壤退化的有效措施之一，但是黄土高原水资源匮乏，苹果生产多以旱作为主，生草对果园土壤水分耗散过程的影响效应仍不确定、影响机制尚不明晰，导致该模式的大范围推广应用还存在诸多争议。本项目拟采用大田定位监测和数值定量模拟相结合的方法，阐明行间种植牧草及牧草不同刈割强度对黄土高原旱作果园土壤水分动态的影响，量化苹果园生草复合系统中蒸发蒸腾的分配关系，建立复合群体蒸发蒸腾与土壤水量平衡耦合模型，提出基于土壤水资源持续利用的旱作果园生草管理策略。该研究可为黄土高原苹果园生草复合系统土壤水分高效管理利用提供依据和参考。

项目在陇东黄土高原兰州大学试验站开展了苹果园生草系统大田试验，测定了果草复合系统土壤水分动态特征、蒸散特征、果树根系分布特征、蒸散量及其组分分配以及果园系统产量，建立和验证了苹果园生草复合系统辐射传输和分配模型，建立了结合蒸发蒸腾模型和土壤水量平衡模型的水量平衡耦合模型。结果表明黄土高原半干旱苹果园种植鸭茅后加剧了干旱季节水分的耗散，降低了土壤含水量。而在强降雨后，种植鸭茅有利于增加果园0-100 cm土层的蓄水。果园行间生草后，苹果树深层细根长密度明显受到抑制。果园种草可有效降低土壤无效蒸发，但是由于林下蒸散量的增加，果园系统蒸散量增加。在两个季节的平均值中，加强刈割和常规刈割处理复合系统中鸭茅的光截获量占总辐射的23.1%和26.5%。果园生草之后，由于牧草的蒸腾增加了大气湿度、降低了果树叶片与大气的湿度梯度，苹果树的潜在蒸腾降低。由于生草降低了土壤水分，生草果园的实际蒸腾量与清耕果园的进一步扩大。不同降雨年型模拟结果表明干旱年份果园生草促进了土壤水分的消耗，而在正常年份和湿润年份均没有使土壤大幅下降，干旱年份可通过加强生草的刈割管理减少其对果园水分的消耗。建议在陇东黄土高原苹果主产区推广果园生草，促进当地林草、草畜耦合生产模式的发展。