东北黑土区农林混合利用坡面土壤水分空间异质性及主控因素

针对黑土区坡面尺度上土壤水分在土地利用结构(从坡顶到坡脚,即沿着坡长方向,不同土地利用类型的排列方式)、土地利用类型(农地和林地)及地形要素的协同作用下的空间分异规律及影响机制尚不清楚的现状,以黑龙江省黑土区的农林混合利用典型坡面(克山县)为研究对象,应用植被数量生态学中的冗余分析方法(RDA)分析0~20、20~40、40~60 cm土壤水分剖面变异特征、不同土地利用结构下(农地-农地-农地-农地-农地,农地-农地-林地-林地-农地,农地-农地-林地-林地-林地,林地-林地-农地-林地-农地)坡面土壤水分异质性及其与环境因子的定量关系。结果表明:研究区坡面土壤含水率介于5.77%~45.57%,农地土壤含水率显著高于林地(P0.05),纵向上不同土地利用类型层间土壤含水率差异均不显著;土壤水分呈中等变异,纵向上农地各土层的变异系数(35.9%~39.6%)均高于林地(30.0%~36.5%),农林混合利用加强了土壤水分的空间变异程度;4种土地利用结构下,坡面土壤水分沿坡长方向呈不同的变化趋势,与土地利用镶嵌分布规律有关;冗余分析结果显示土地利用类型是影响黑土区坡面土壤水分异质性的主控因素,坡度次之,坡位和海拔高度对坡面土壤水分异质性也有影响。对于黑龙江黑土区坡面,需要结合土地利用结构配置等土地管理措施与不同的农业措施来防止坡面土壤侵蚀、提高东北区土壤肥力,实现经济效益、生态效益的协调统一。

Spatial variability and its controlling factors of soil moisture on cropland-forestland mixed hillslope in black soil area of Northeast China

Abstract: Black soil area in Heilongjiang plays an indispensable role in safeguarding national food security as an important commodity grain base. Serious soil erosion and environment degradation restrict the sustainable development of local society and economy. Soil moisture is one of the key factors which control vegetation growth, soil erosion, hydrological and ecological processes at the hillslope, and it also exhibits a great degree of spatial variability. Understanding the spatial variability of soil moisture and its influence mechanism at the slope scale is essential for controlling soil erosion, increasing food production, and improving ecological environment. In this study, spatial variability of soil moisture under the effect of land use and topographic variables was investigated on a cropland-forestland mixed hillslope. The research area was characterized by 4 different land use structures (from top slope to toe slope): cropland-cropland-cropland-cropland-cropland (L1), cropland- cropland-forestland-forestland-cropland (L2), cropland-cropland-forestland-forestland-forestland (L3), forestland-forestland- cropland-forestland-cropland (L4). Soil moisture was collected biweekly during mid-August to mid-September (2016) at 20 sites located in Keshan County of Heilongjiang Province, China. Soil moisture was measured by oven drying method at the depth of 0-20, 20-40, 40-60 cm. The relationship between environmental factors and soil moisture variability was conducted by redundancy analysis method (RDA). The results showed that: 1) Soil moisture content varied from 5.77% to 45.57%; and the soil moisture content of cropland was found markedly higher than that of forestland (P<0.05), with the mean soil moisture content ranging from 20.13% to 22.07% in cropland, and from 13.69% to 15.96% in forestland; the differences of soil moisture content at different soil depths were not significant(P>0.05). 2) Soil moisture content showed a moderate variability in the study area, coefficient of variation (CV) in cropland (35.9%-39.6%) was higher than that in forestland (30.0%-36.5%). 3) Soil moisture variations along hillslope under the impact of 4 land use structures differed from each other. The differences of soil moisture content at middle slope and toe slope in L1 were significant (P<0.05). 4) The spatial variation of soil moisture in the single land use structure (L1, CV was 14.82%) was lower than that in other cropland-forestland mixed land use structures (CV of L2, L3 and L4 was 62.70%, 38.25% and 25.70%, respectively), which indicated that land use mosaic patterns increased the variations of soil moisture. 5) RDA ordination showed that spatial variability of soil moisture was strongly influenced by land use types, and it was also affected by slope gradient, slope position and elevation. In addition, different factors control soil moisture distribution at different soil depths. This study presents that it is necessary to optimize the planting structure and take other proper methods aiming at preventing water loss and soil erosion, in order to improve soil fertility and promote the sustainable development.