三种PTFs方法获取的侵蚀黑土水分特征曲线的比较

Comparison of Soil Water Characteristic Curves of Eroded Black Soil Obtained by Three PTFs Methods

采用3种土壤转换方程(PTFs)获取不同侵蚀程度黑土的土壤水分特征曲线(SWCC),并与实测数据进行了比较,以选择适合黑土SWCC间接获取的PTFs方法。以4种不同侵蚀程度的黑土为供试土壤,采用常用的PTFs计算机模型:Rosetta3、CalcPTF和以最大吸湿量为残余含水量(θr)发展的PTFs方法(编号:PTFs3),进行了SWCC的van Genuchten (VG)模型参数的预报。Rosetta3模型的输入参数包括土壤机械组成、土壤密度、33 kPa压力下的土壤含水率(θ33 kPa)和1 500 kPa压力下土壤含水量(θ1 500 kPa);CalcPTF模型的输入参数包括土壤机械组成、土壤密度和有机碳含量;PTFs3的输入参数包括饱和含水量(θ0)、最大吸湿量(θ97%RH)、θ33 kPa和θ1 500 kPa。将上述3种方法获取的参数带入VG模型,得出供试土壤在不同水吸力下的土壤含水量,并与实测结果进行对比。结果显示,使用3种PTFs模型输出参数的VG模型预报值与实测值都有极显著的相关性,总体计算结果与实测结果也比较接近。PTFs3预报值与实测值的差值在±0.05 cm^(3)/cm^(3)内;CalcPTF-Var模型差值在-0.08~0.05 cm^(3)/cm^(3)之间;而Rosetta3模型的差值在-0.10~0.06 cm^(3)/cm^(3)之间。在土壤含水率压力小于33 kPa情况下时,SWCC差值相对较大。Rosetta3和PTFs3因为有θ33 kPa和θ1 500 kPa两点的水分进行校正,精确性比较可控,效果优于CalcPTF-Var。预报值与实测值差异的百分比也说明了这一点。具体到每个供试土壤样本,3种PTFs对剧烈侵蚀的黑土预报偏差百分比都较大,但PTFs3表现较优于其他两种模型。CalcPTF-Var在微度侵蚀样本S1的模拟上也出现了相对较大的偏差。综上,PTFs3模型是一种比较适合预报黑土SWCC的VG模型参数的PTFs方法。Rosetta3模型误差主要来源于较严重的低估了≤1 kPa SWCC的土壤含水量,而高估了6~33 kPa的土壤含水量。仅输入土壤理化性质的CalcPTF-Var模型需注意在部分黑土样本上的较大偏差。

Three Pedotransfer functions(PTFs)were used to obtain soil water characteristic curves(SWCC)of black soil with different erosion degrees,and were compared with measured data to indirectly estimate SWCC of black soil.Four types of black soil with different erosion degrees were used as the test soil.The commonly used PTFs models,Rosetta3 and CalcPTF-Var(developed by Varallyay et al,1982),and PTFs model(Number:PTFs3)developed by using the maximum hygroscopicity as the residual water content(θr)was used to predict the parameters of the van Genuchten(VG)model.The input data of the Rosetta3 model include percentages of soil particles(sand,silt and clay),soil bulk density,and soil water content at pressures of 33 kPa and 1500 kPa(θ33 kPa andθ1500 kPa).CalcPTF input data include percentages of soil particles(sand,silt and clay),soil bulk density,and soil organic carbon content.The input data of PTFs3 include saturated water content(θ0),maximum hygroscopicity(θ97%RH),θ33 kPa andθ1500 kPa.The parameters obtained from the above three methods were incorporated into the VG model to obtain the soil water content under different water suction of SWCC,and compared with the measured values.The results showed that there was significant correlation between the simulated values and the measured values by using the VG parameters obtained from three PTFs models,with the simulated results closely aligning with measured results.The difference between the predicted and measured values of PTFs3 is generally within±0.05 cm^(3)•cm^(-3);The difference between the CalcPTF-Var model is generally between-0.08 and 0.05 cm^(3)•cm^(-3);The difference in Rosetta3 model is generally between-0.10 and 0.06 cm^(3)•cm^(-3).The differences mainly come from SWCC of≤33 kPa.The differences of 33~1500 kPa SWCC is relatively small.For the Rosetta3 and PTFs3 were corrected byθ33 kPa andθ1500 kPa,the accuracy is relatively controllable and the simulated results is better than CalcPTF-Var.For each tested soil sample,the three PTFs had significant percentage of prediction deviations for severely eroded black soil,but PTFs3 performed better than the other two models.CalcPTF-Var also showed relatively large bias in the simulation of sample S1.In summary,the PTFs3 model is a more suitable method for predicting the parameters of the VG model for black soil SWCC.The main source of the Rosetta 3 model error is the underestimation of soil water content at≤1 kPa SWCC,while overestimating soil water content at 6~33 kPa.The CalcPTF-Var model that only need soil physical and chemical properties should be pay attention to the significant deviations on some black soil samples.