人工林对黄土高原小流域上下游不同坡面土壤水分的影响

为对比不同生态治理小流域的土壤水分,以人工刺槐小流域杨家沟及其相邻自然恢复小流域董庄沟为研究对象,2016年8月每4天在两流域的对照坡面、样点同时采样、分层测定0~120 cm剖面土壤含水量(SWC),通过经典统计学方法分析各流域不同区段、坡向、坡位、土层的SWC变化,并采用土壤水分流域变差系数指标进行流域对比。结果表明:1)董庄沟SWC上游下游,东坡西坡,坡脚坡腰坡肩,沿剖面向下先短暂降低(0~20 cm)又持续增大(20~120 cm),不同区段、坡向间差异显著(P0.05);2)在林木耗水及蒸发调节影响下,杨家沟SWC下降(P0.05)、土壤水分格局发生变化,下游与东坡土壤较湿润,SWC坡脚显著高于坡腰与坡肩(P0.05)、剖面垂向分布先持续下降(0~100 cm)后转而上升(100~120 cm);3)SWC空间变异性董庄沟(29.19%)杨家沟(23.51%),时间变异性杨家沟(10.99%)董庄沟(8.76%);4)上游、东坡、坡腰与60~120 cm土层是杨家沟土壤水分亏缺的主要区域与层次。研究结果可以作为小流域生态建设植被配置与布局的依据。

Effect of man-made forest on soil moisture of different slopes in upper and lower reaches of small watershed of Loess Plateau

Abstract: Soil moisture is a key limiting factor of agricultural production and ecological restoration on the Loess Plateau. The comparative study on the soil moisture under the influence of different ecological managements at a small watershed scale as the basic unit of ecological restoration is of great significance to evaluate ecological effects and predict soil water accurately. Most importantly, it is essential for ecological planning and layout. In order to compare the soil water content (SWC) in the artificial forest watershed and natural restoration watershed and determine the relative deficit situation of the former, soil samples within the 120 cm profile in the 2 basins named Yangjiagou (Y) and Dongzhuanggou (D) were simultaneously taken to measure SWC of 9 layers every 4 days in August 2016. Both Y and D were inside the Nanxiaohegou watershed located in the Loess Gully Area of eastern Gansu Province and the former is of Robinia pseudopodia plantation, whereas the latter was of natural restoration. Of the 2 basins, the basic conditions such as zone, slope aspect and slope position of sampling slopes and sampling points were well contrasted. The SWC of different zones, slope aspects, slope positions and soil layers in each basin was analyzed by classical statistical methods. And a new indicator, difference ratio of soil moisture (DRSM) between the 2 different basins was used to quantitatively compare the SWC in Y and D. The results showed that: 1) In D, the SWC in the upper reaches was higher than that in the lower reaches, the SWC in the eastern slope was larger than that in the western slope, its ranking in the different slope positions from highest to lowest was toe-slope (16.96%) > waist-slope (14.34%) > shoulder-slope (11.80%), and there was significant difference between the different zones and slope aspects (P<0.05). The SWC continued to increase in the 20-120 cm soil layer after a brief decrease in the 0-20 cm soil layer down the profile. 2) In Y, as the plantation consumed soil water and regulated evaporation, the SWC decreased significantly and its distribution pattern was changed compared with that in D. Specifically, the soils in the lower reaches and eastern slope were more humid than that in the upper reaches and western slope, the SWC of the toe-slope was significantly higher than that of the waist-slope and shoulder-slope (P<0.05), and down the soil profile, it decreased continuously first in the 0-100 cm layer and then increased in the 100-120 cm layer. 3) The spatial variability followed the order of D (29.19%) > Y (23.51%), while the order of time variability was Y (10.99%) > D (8.76%). 4) The upper reaches, eastern slope, waist-slope and 60-120 cm soil layers were the main areas or layers with soil water deficit in Y, and the DRSM between Y and D was bigger. All the above results revealed spatial heterogeneity in soil desiccation caused by the Grain for Green at the small watershed scale and are expected to serve as the basis for the allocation and layout of vegetation in the ecological construction on the Loess Plateau.