改进粒度对比法估算单次农田风蚀量

为了定量估算单次大风蚀事件的土壤风蚀量,该研究采用改进的粒度对比法对2014年春季一次大风蚀事件的农田风蚀量进行了估算。结果表明,在这次风蚀事件中,研究区农田风蚀量在0.35×106~4.11×106 kg/km2之间,平均为1.30×106 kg/km2,平均风蚀厚度0.9 mm。各采样点的风蚀量存在较大差距,翻耕耙平地的风蚀量显著大于莜麦留茬地,是莜麦留茬地风蚀量的2.85倍。这次风蚀事件使研究区2014年农田风蚀量增加了1倍,可见大风蚀事件对农田风蚀量的影响较大,一次风蚀事件产生的风蚀量可能超过多次小风蚀事件的总和。改进后的粒度对比法具有多方面的优势,取样厚度稍有变化,不可风蚀颗粒物的粒径取值范围稍有变化,都不会对公式计算结果造成显著影响。该方法方便快捷,操作简单,适用于地面平坦、不可风蚀物含量较高的农田上大风蚀事件风蚀量的估算。该研究在区域农田土壤风蚀评价和风蚀模型验证方面具有较好的应用前景。

Estimation on farmland soil loss by single wind erosion using improved particle-size distribution comparison method

Abstract: Estimations were performed using improved particle-size distribution comparison method for the severe wind-erosion event in 2014 for the principal farmland types in the Bashang area of Hebei Province. The results showed that the soil loss of farmland by wind erosion in the severe wind-erosion event was 0.35×106-4.11×106 kg/km2, average wind erosion was 1.30×106 kg/km2, and the average depth of wind erosion was 0.09 cm. In the two farmland types, the soil loss by wind erosion of ploughed and raked fields during this event was 0.85×106-4.11×106 kg/km2 with an average of 2.00×106 kg/km2, and the soil loss by wind erosion of fields of oat stubble was 0.35×106?1.50×106 kg/km2 with an average of 0.70×106 kg/km2. The soil loss by wind erosion on fields of oat stubble was clearly less than on ploughed and raked fields (i.e., only 35.11%). Therefore, the presence of stubble can be seen as an effective measure against the erosion of farmland by wind. The soil loss by wind erosion at the different sampling sites varies considerably in this wind-erosion event. In the ploughed and raked fields, the soil loss by wind erosion at sampling site 1 was the largest (4.11×106 kg/km2), followed by sampling site 2 (1.66×106 kg/km2). Sampling site 3 shows the minimum soil loss by wind erosion (0.85×106 kg/km2), which was only 20.76% of that at sampling site 1. In the fields of oat stubble, the soil loss by wind erosion at sampling site 1 was the largest (1.50×106 kg/km2), followed by sampling point 4 (0.54×106 kg/km2). The soil loss by wind erosion at sampling point 2 was the minimum (0.35×106 kg/km2), which was equal to 23.12% of that at sampling site 1.The severe wind erosion event greatly increased the soil loss of farmland by wind erosion in the study area, and the intensity of the wind erosion increased from moderate before the event to severe following it. The average soil loss of the various land types by wind erosion increased from 1.30×106 kg/km2 before the wind erosion event to 2.60×106 kg/km2 after it, i.e. it effectively doubled. The soil loss of ploughed and raked fields by wind erosion increased from 1.77×106 kg/km2 before the event to 3.67×106 kg/km2 after it (an increase of 1.07 times), and the soil loss of fields of oat stubble by wind erosion increased from 0.83×106 kg/km2 before the event to 1.53×106 kg/km2 after it (an increase of 0.85 times). Therefore, it is established that large wind-erosion events contribute significantly to the wind erosion of farmland and that the soil loss by wind erosion that occur in a severe wind-erosion event might be as great as the cumulative amount of erosion by several previous smaller wind erosion events. Generally, estimations of the soil loss of farmland by wind erosion, based on the improved particle-size distribution comparison method, matched the results obtained by other methods used in earlier research, as well as the results we obtained by field observations and wind-tunnel simulation.The improved particle-size distribution comparison method has a number of advantages. Under the premise that the sampling thickness is larger than the thickness of the wind erosion layer, slight changes in the former would not obviously affect the results calculated by this method. Furthermore, under the premise that the value of non-erodible particles is larger than the threshold value of practical erodible and non-erodible particles, slight changes in the diameter value range of non-erodible particles would also not obviously affect the calculated results. In addition, this method is also convenient, rapid, simple to use, making it suitable for estimating the soil loss by wind erosion of flat farmland with a high content of non-erodible particles, under conditions of intense wind erosion.