关中平原农田土壤水力参数空间分异与模拟

土壤水力参数是土壤水分和污染物迁移等陆面过程数值模拟的重要基础参数。为探明关中平原农田土壤水力参数空间分异特征,建立空间分布预测模型,在关中平原网格布设124个样点,采集根层0-20 cm原状和扰动土壤样品,利用van Genuchten模型拟合获取土壤水分特征曲线,获得残余含水量(θr)、饱和含水量(θs)以及系数α和n等土壤水力参数。采用经典统计学、地统计学和结构方程方法分析了θr、θs、α和n的空间变异特征及影响因子,建立了水力参数传递函数预测模型。结果表明:θr和α为强变异,θs为中等变异,n为弱变异。θr、θs、α和n半方差函数最佳拟合模型分别为球状模型、指数模型、指数模型和球状模型。θs和n具有强烈的空间依赖性,变程分别为32.7,54.3 km;θr和α具有中等程度空间依赖性,变程均为52.8 km。土壤质地、容重、pH、有机质和海拔是影响土壤水力参数空间分布的主要因子。基于土壤理化性质和海拔建立的水力参数传递函数模型具有较好的模拟效果,可用于关中地区大尺度农田生态系统土壤水力参数的模拟预测。

Spatial Variations and Simulations of Farmland Soil Hydraulic Parameters in the Guanzhong Plain

Soil hydraulic parameters are critical to the numerical simulation of land surface processes such as soil moisture and pollutant transport.This study aimed to explore the spatial variation characteristics and influencing factors of soil hydraulic parameters,and then simulated these parameters through indirect method in classic cultivated area.A total of 124 sampling sites were set up in the Guanzhong Plain area,and undisturbed and disturbed soil samples at the depth of 0-20 cm were collected separately at each sampling site.Soil retention curve was estimated by the van Genuchten(VG)model and the hydraulic parameters(i.e.θr,residual water content;θs,saturated water content;αand n,shape coefficients)of the VG model were calculated.Classical statistics,geostatistical and structural equation methods were used to determine the spatial variation characteristics and influencing factors ofθr,θs,αand n,and the prediction model of hydraulic parameter pedo-transfer functions was established.The results showed that the variability of n andθs was weak and moderate,respectively;whileθr andαhad strong variability.Semi-variance functions ofθr,θs,αand n could be best fitted by the spherical model,the exponential model,the exponential model and the spherical model,respectively.θs and n exhibited strong spatial dependence,with the range of 32.7 and 54.3 km,respectively.θr andαexhibited moderate spatial dependence,with the range of 52.8 and 52.8 km,respectively.Soil texture,bulk density,pH,organic matter and elevation were the main direct factors affecting soil hydraulic parameters.The pedo-transfer functions model of hydraulic parameters based on soil physical and chemical properties and elevation had good simulation effect,and could be used to simulate and predict soil hydraulic parameters of large-scale farmland ecosystem in the Guanzhong area.