非稳态土壤最小限制水分范围模型优化研究

Least limiting water range (LLWR) is widely used in the studies assessing the effects of various field practices on the soil physical quality, but there are still great limitations for the field study. LLWR is the functions as the soil water status, aeration, penetrometer resistance with the dry bulk density. On the one hand, soil bulk density has great temporal variability under different field management. On the other hand, the overburden stress is ignored in the traditional models predicting penetrometer resistance. Therefore, the models for soil water characteristic curve (SWCC) and penetrometer resistance (PR) developed based on both the assumption that soil is a rigid porous medium and lab data are hard to determine accurately the LLWR of the soil profile. In this study, we firstly try to reset a new SWCC-PR models group for calculating LLWR. Then, the new models for simulating SWCC and PR contained void ratio variable are developed, based on the observations of temporal variability of soil void ratio, SWCC, and PR curve after a series of drying and wetting processes. Finally, the improved LLWR model will be applied to assessment of the effects long-term conservation tillage on the black soil physical quality. The results are helpful to improve the practicability of LLWR, and can be used for study the water movement and crop growth modeling in the nonrigid soils.

最小限制水分范围模型被广泛应用于农田管理方式对土壤物理质量影响的综合评价，但在田间应用中面临很大的局限性。最小限制水分范围是土壤水分、充气孔隙、穿透阻力与容重的函数。一方面，农田管理方式使土壤容重具有很大的时间变异性；另一方面，传统的穿透阻力预测模型忽略了土壤剖面上层对下层的应力作用，导致基于“刚性土壤结构”和实验室数据建立的水分特征曲线和穿透阻力模型难以准确地确定最小限制水分范围。本项目将改进最小限制水分范围的水分特征曲线和穿透阻力模型；在此基础上，分析干湿交替过程中土壤孔隙率、水分特征曲线、穿透阻力曲线的时间变异特征，建立包含土壤孔隙率为函数的水分特征曲线和穿透阻力模型，对最小限制水分范围模型进行改进，并应用改进后的模型对长期保护性耕作后的黑土土壤物理质量进行评价。研究结果不仅有利于提高最小限制含水量方法的实用性，而且对研究非稳态土壤水分运动和作物生长模拟有重要的理论意义和应用价值。

最小限制水分范围是评价农田管理方式对土壤结构影响的综合指标。土壤穿透阻力模型和水分特征曲线模型是估算最小限制水分范围的两个关键模型。目前使用的土壤穿透阻力模型忽略了上层积土压力对下层穿透阻力的影响；土壤水分特征曲线模型无法考虑土壤容重的动态变化，且应用的并不广泛。农田土壤容重具有较高的时空变异性，因此在估算土壤最小限制水分范围过程中会产生一定的误差。本项目基于Gao et al (2016)穿透阻力模型和经典的van Genuchten（1980）水分特征曲线模型，利用室内和田间试验对非稳态条件下土壤最小限制水分范围模型进行优化。主要研究成果包括：首先，明确了土壤容重与van Genuchten（1980）水分特征曲线模型参数（θr、θs、 α、m、n）的关系，建立了适用于预测土壤容重变化下的水分特征曲线新手段；其次，利用不同质地土壤田间穿透阻力数据，引入相对土壤容重参数，建立了即考虑上层积土应力，又更加简化的土壤穿透阻力模型；最后，利用最小限制水分范围为手段表明免耕更有利于土壤长期保持对作物生长有利的水分条件，但也要考虑土壤大孔隙对作物根系生长的作用。研究结果对研究非稳态土壤水分运动和作物生长模拟有重要的理论意义和应用价值。