基于USLE模型的云南省坡耕地土壤侵蚀和养分流失评价

Evaluation of soil erosion and nutrient loss of slope farmland in Yunnan Province using USLE model

定量评估区域坡耕地土壤侵蚀分布规律,是科学制定坡耕地水土流失综合治理规划、开展坡耕地质量建设的基础,然而目前针对省域尺度坡耕地土壤侵蚀和养分流失规律的研究较少。该研究基于GIS空间分析技术和通用土壤流失方程(Universal Soil Loss Equation,USLE),在模型参数率定与计算精度验证基础上,定量评价云南省坡耕地土壤侵蚀和养分流失特征。结果表明:(1)云南省坡耕地土壤侵蚀面积为421.38万hm^(2),侵蚀总量为376.57×10^(6)t/a,占全省土壤侵蚀总量的63.02%,坡耕地是区域侵蚀产沙的主要策源地;坡耕地平均侵蚀模数为7986.31 t/(km^(2).a),总体处于强烈侵蚀等级,剧烈侵蚀、极强烈侵蚀和强烈侵蚀是坡耕地侵蚀产沙的主要来源;不同分区坡耕地侵蚀模数和侵蚀量差异显著,滇西南区侵蚀强度最大,滇东南区侵蚀强度最小。(2)随着坡度增加,坡耕地侵蚀面积比例、侵蚀强度、侵蚀量均呈较快增加趋势,土壤侵蚀主要来源于15°~25°、>25°、>8°~15°3个坡度级坡耕地。(3)坡耕地流失土层厚度集中分布在0~12 mm/a之间,平均流失土层厚度为7.31 mm/a;耕层更新周期集中分布在20~200 a之间,均值为175.6 a,耕层更新周期-面积分布曲线呈先快速递增,并在某一峰值之后出现快速递减趋势。(4)坡耕地养分流失空间分布存在差异性,土壤有机碳、全氮、速效钾、有效磷流失模数分别为223.60、23.94、1.59、0.15 t/(km^(2)·a),坡耕地养分流失是区域养分流失量的主要来源。研究可为区域坡耕地水土流失治理和坡耕地质量建设提供科学依据。

Slope farmland is one of the most important parts of cultivated land resources for agricultural production in mountain and hilly areas.The type of land resource is also closely related to regional water and soil ecological protection,even food security.Among them,the soil erosion of slope farmland has been one of the most serious sources of regional erosion and non-point source pollution,due to the natural conditions and man-made unreasonable utilization.Particularly,soil erosion is generally accompanied by the loss of soil,nutrients,and water in the sloping farmland.As such,the thinner arable layer can reduce the nutrients of soil structure and the quality of cultivated land.It is a high demand for the quantitative evaluation of the distribution of soil erosion in the regional sloping farmland,particularly for the decision-making on the soil and water loss for the high-quality slope farmland.However,there are only a few studies on soil erosion and nutrient loss of slope farmland at the provincial scale at present.In this study,the Universal Soil Loss Equation(USLE)model was selected to quantitatively evaluate the characteristics of soil erosion and nutrient loss of sloping farmland in Yunnan Province of China.The GIS spatial analysis was also carried out to verify the parameters and accuracy of the model.The results showed that:(1)The soil erosion area of slope farmland accounted for only 22.95%of the total erosion area,but the amount of erosion was as high as 376.57×10^(6)t/a,accounting for 63.02%of the total erosion in Yunnan Province.The slope farmland was the main source of erosion and sediment yield in the study area.The average erosion modulus of slope farmland was 7986.31 t/(km2.a)at the level of strong erosion.Severe erosion,extremely strong erosion,and strong erosion were the main sources of erosion and sediment yield of slope farmland.(2)The average erosion modulus of slope farmland increased rapidly with the increase of slope gradient.Correspondingly,the erosion intensity grade evolved from mild to severe erosion.The 3°-5°and 5°-8°slope farmland were mild erosion,the 8°-15°slope farmland was moderate and strongly erosion,the 15°-25°slope farmland was very strongly erosion,and the>25°slope farmland was the severe and very strongly erosion.The amount of soil erosion was often from the 15°-25°,the>25°,and the 8°-15°slope farmland.(3)The thickness of the lost soil layer in the sloping farmland was concentrated between 0 and 12 mm/a,and the average value was 7.31 mm/a.The renewal cycle of the cultivated layer was concentrated between 20 and 200 a,with an average of 175.6 a.The area distribution curve of the cultivated layer renewal cycle showed a rapid increase at first,then decreased rapidly after reaching a certain peak,and finally changed slightly with the increase of the cultivated layer renewal cycle.(4)There were some differences in the spatial distribution of nutrient loss in the sloping farmland.The loss modulus of Soil Organic Carbon(SOC),Total Nitrogen(TN),Available Potassium(AK),and Available Phosphorus(AP)in the sloping farmland were 223.60,23.94,1.59,and 0.15 t/(km^(2)·a),respectively,which was 4.34-5.50 times of the whole province.Therefore,the sloping farmland can be the main source of nutrient loss in Yunnan Province of China.The research can also provide the scientific basis to control the soil and water loss for the high quality of regional slope farmland.