延河流域三种土壤可蚀性K值估算方法比较

Comparative Study of Three Different Methods for Estimation of Soil Erodibility K in Yanhe Watershed of China

土壤可蚀性因子K是表征土壤侵蚀作用的敏感指标。采用3种土壤可蚀性K值估算方法(Torri.D模型、EPIC模型、Shirazi公式法)对延河流域土壤可蚀性进行对比研究,以实测K值为依据,采用相关性分析和模型估算筛选出符合该区侵蚀特点的土壤可蚀性估算方法。结果表明:延河流域土壤中有机碳、黏粒、粉粒含量随植被覆盖度的变化由北向南逐渐增加,平均质量直径(D_(MW))表现为森林>森林草原>草原,K_(EPIC)和Kshirazi与D_(MW)呈正相关,而Torri.D模型估算K值(K_(Torri.D))与D_(MW)呈相反的变化趋势,即从草原到森林草原再到森林,土壤团聚体稳定性和抗侵蚀性逐渐增加。K_(Torri.D)的变化范围为0.068~0.147 5,高于真实K值(0.031 2~0.079 6),相比于其他两种方法,Torri.D模型平均绝对误差(MAE)、平均相对误差(MRE)和均方根误差(RMSE)更接近于0,而精度因子(Af)更接近1,具有更高的可信度,更加适用于延河流域土壤侵蚀敏感性评价和土壤流失量预测。

[Objective] Soil erodibility K is an international index of soil susceptibility to erosion, and can be used as an important quantitative parameter in evaluating soil erodibility. The Yanhe Valley is located on the Loess Plateau, where soil erosion is very severe, and also very severe in soil erosion. In this case, it is particularly important to conduct research on soil erosion models for this region. In recent years, in studies on soil erodibility of loess, soil erodibility factor K is often used as an index for evaluation of soil erosion. Though certain progress has been made in the research on using the formula method to assess soil erosion factor K in the loess area, it is still infeasible to go on doing researches on estimating K values in some parts of the Loess Plateau due to limitation of data availability and inconsistency between standard plot and observation plot. Besides, the reliability of the formula method still need to be validated. So, it is necessary to design an equation that is workable for estimating soil erodibility K even when inadequate data of soil physical and chemical properties are available. The purpose of this study is to pick out of the three methods currently available for estimating soil erodibility K one that fits the special situation of the river valley. [Method] In this study, comparison was performed between the three methods, i.e. Torri.D model, EPIC model, and Shirazi formula in applicability to estimation of K for the nine catchments of the Yanhe Valley. Collection analysis and Model-based estimation methods were used to process and analyze the data and compare predicted K with measured K, so as to screen out the most suitable one. [Result] Results show that the contents of soil organic carbon, clay and silt gradually increased from north to south with the increasing vegetation coverage. In terms of mean weight diameter （ DMw ） , the three types of vegetation in the valley followed an order of forest 〉 forest-steppe 〉 steppe, and DWM was positively related to the K predicted with the EPIC model and Shirazi formula method, but negatively to that with the Torri.D model, which means that soil aggregate increased in stability and the soil in erosion resistance as the vegetation turned from steppe to forest-steppe to forest. The three predicted Ks displayed an order of KTo,~D 〉 KEP^c 〉 K^h~z~. KTo,~D varied in the range of 0.068 - 0.1475, higher than the measured one （ 0.0312 - 0.0796 ） . Compared with the other two, Torri.D model was the lowest in uncertainly, with mean absolute error （ MAE ） , mean relative error （MRE） , root mean square error （RMSE） close to 0, and dilution of precision （Af） close to 1, suggesting that Torri.D model is more suitable than the other two for use to evaluate soil erosion susceptibility and calculate soil loss. [Conclusion] To sum up, all the findings described above indicate that Torri.D model can be used to soil erosion susceptibility and predict soil loss of a region even when data of the region are incomplete or inadequate.