压砂地砾石分布特征对土壤水分性质影响机制研究

Gravel mulched field in northwest China is a classical example of water saving agriculture and dry farming. Gravel content in soil plays an important role in soil physical characteristics and hydrological functions, especially in surface hydrological process, soil water movement and water holding capacity. Therefore taking gravel mulched field in Central Ningxia for research objects, this project is proposed to study soil water properties in the gravel mulched field. Firstly, the effect of environmental factors on rock fragments properties would be analyzed, including tillage years, vegetation and topography. Accordingly, we would disclose distributions of rock fragments and their influencing factors. On this basis, quantitative study on the relationship between rock fragments properties and soil moisture movement parameters with gravels is conducted by libratory tests. Meanwhile, the effect of gravels on soil structure, soil water characteristics and water holding capacity would also be explored by field situ test. Moreover, the model fitting for evaporation and infiltration of soil water with gravels would also be explored, and we could comprehensively analyze the applicability of evaporation and infiltration models. The results obtained would illuminate the impact mechanisms of gravel size, content and distribution on soil water properties. The results could provide theoretical basis for analysis of gravel mulched field degradation, improving water use efficiency, and regional ecological environment governance.

我国西北压砂地是利用砾石覆盖地表的节水旱作农业典型范例。土壤中砾石含量对土壤物理特征和水文功能产生不可忽视的作用，尤其是对地表水文过程、土壤水分运动及持水性能等有重要影响。因此本项目拟以宁夏中部压砂地为研究对象，深入开展宁夏中部旱区压砂土壤水分性质研究，分析砾石特性与耕作年限、植被和地形等环境要素间的关系，揭示研究区砾石分布规律及其影响因素。在此基础上，利用室内试验定量研究砾石特性与含砾石土壤水分运动参数之间的关系，野外原位监测试验研究自然状况下砾石对土壤结构、土壤水分特征及持水性能的影响。阐明砾石分布特征、年限和植被等因素对压砂土壤水分蒸发、入渗及持水性能的影响，借助相关模型拟合含砾石土壤水分蒸发和入渗过程，综合分析蒸发和入渗模型的适用性。项目阐明不同砾石粒径、含量及分布情况对压砂土壤水分性质产生影响的主要机制，为分析压砂地退化程度、提高压砂地水分利用效率和区域生态环境治理提供理论依据。

土壤中砾石含量对土壤物理特征和水文功能产生不可忽视的作用，尤其是对地表水文过程、土壤水分运动及持水性能等有重要影响。项目利用实地调查、野外采样、原位试验及室内模拟试验等方法对不同砾石分布条件下压砂地土壤水分运动过程及水力学参数特征进行了研究。结果表明：压砂地不同粒径砾石的空间变异系数均大于10%，属中等变异。不同粒径砾石的空间异质比变化范围大（0.26%~82.48%），受随机性因素和结构性因素共同影响。砾石空间分异的解释力由大到小依次为：种植年限>坡向>地表粗糙度>坡度>剖面曲率>平面曲率>地表起伏度，种植年限的单因子解释力明显高于其他因子。随着种植年限增加，相同时间下湿润锋和累积入渗量逐渐减小，初始入渗速率、稳定入渗速率和平均入渗速率均呈减小趋势，Horton模型对不同种植年限压砂地水分入渗过程拟合效果最佳；水力学参数中的土壤吸渗率和平均扩散率均呈逐渐减小的趋势。与种植2 a压砂地相比，5，10，20，30和40 a土壤水分进气吸力分别减小了1.22%，42.81%，46.37%，55.94%和64.97%，土壤饱和扩散率分别减小了27.83%，68.54%，85.40%，90.57%和93.15%；土壤水分入渗能力及持水能力均明显减低，土壤容重显著增大，饱和导水率显著降低。随种植年限增大土石混合程度增加，砾石覆盖层与下层土壤边界逐渐模糊，整体上随土壤深度增加剖面染色水流形态从均匀的活塞流向指流转变，基质流区域减小，优先流区域增大。综合染色特征参数和分形维数可知种植年限越长，压砂地染色形态的不均匀性越高，优先流区占比逐渐增大、发育程度增高。项目阐明不同砾石粒径、含量及分布情况对压砂土壤水分性质产生影响的主要机制，为分析压砂地退化程度、提高压砂地水分利用效率和区域生态环境治理提供理论依据。