平茬对半干旱黄土丘陵区柠条林地土壤水分的影响

半干旱黄土丘陵区多年生柠条人工林地发生土壤旱化,研究柠条林平茬对土壤水分影响对于防治土壤旱化具有重要意义。采用中子仪测定土壤水分,对未平茬和平茬柠条林地土壤水分进行测定,分析了平茬对土壤水分的影响。结果表明:未平茬和平茬柠条林地降雨补给量(R₁,R₂)同降雨量(P)显著正相关(P<0.05)。定义降雨耗损量(林冠截留量和地表径流之和)占降雨量的百分比为降雨耗损率,未平茬林地降雨损耗率(L₁)和平茬柠条林地降雨损耗率(L₂)分别与其降雨前土壤表层(0-20 cm)含水量(S₁,S₂)呈明显指数关系(P<0.05):L₁=2.54exp(0.22S₁),L₂=2.40exp(0.27S₂),表层含水量相同时,平茬林地降雨损耗率明显高于未平茬林地。平茬后,林地降雨最大入渗深度减小,土壤水分利用深度减小;短时间内(2个月左右)林地20-160 cm含水量增加,之后平茬林地土壤含水量与未平茬林地土壤含水量接近;丰水年和丰水年后的第一年,平茬林地含水量低于未平茬林地,0-400 cm土壤储水量比未平茬林地最多低45.9 mm。平茬后200-400 cm土层土壤水分有少量增加,但是0-200 cm土层土壤含水量损失更严重。平茬3a后,平茬对柠条林地土壤水分的影响减弱。

Effect of cutting management on soil moisture in semi-arid Loess Hilly region

Soil drying has been an environmental problem in perennial artificial Caragana shrub land in the semi-arid Loess Hilly region. Cutting management was expected to have an effect on improving soil moisture regulation and thus preventing the problem. In this study, soil water conditions were measured using neutron probes for a long-term investigation stand of Caragana korshinsk Kom in the Shanghuang experimental station in northwestern China, and the effect of cutting management on soil moisture was analyzed. The results showed that the depth of soil water recharge increased with the precipitation amount, and the recharge depth in cut plot was close to that of control when the precipitation was relatively low (within 45.9 mm). However, when the rainfall was heavy enough, the recharge depth in cut plot was lower than control. The amounts of water recharge in both control (R₁) and cut (R₂) plots were positively related to precipitation (P) (P<0.05), being fitted by the relationship formulae of R₁=0.70P+2.13 and R₂=0.54P+5.01, respectively. This suggests that the rain recharge rate (the percentage of rain recharge in the total amount of rainfall) in control plot is higher than in cut plot. Defining rainfall loss as the sum of interception and runoff, and rainfall loss rate as the percentage of rainfall loss in the total amount of rainfall, then the rainfall loss rates in control (L₁) and cut (L₂) plots were exponentially related to their surface soil moisture contents (S₁, S₂) before the rain as L₁=2.54exp(0.22S₁) and L₂=2.40exp(0.27S₂), respectively. When soil moisture contents in the surface layer were equal in the two plots before the rain event, the rainfall loss rate in cut plot was higher than that of control. The largest water recharge depth and the increased amount of soil water storage resulting from rain were lower in cut plot than control in a corresponding period. However, the water use depth and the decreased amount of water storage in dry months were also lower than control. These suggest that cutting can reduce the water consumption of the Caragana shrub, but at the same time, the water supply is also reduced in the cut land, which may be caused by increased surface runoff due to the lower vegetation cover. The soil moisture in 20-160 cm increased for a short period (about two months in this study) after cutting. Then the soil moisture in cut plot was close to that in control plot. In rainy year and the year after rainy year (2003-2004 in this study), soil moisture in cut land was lower than control and the soil water storage in 0-400 cm soil layer was up to 45.9 mm lower than that in control plot. Cutting recovered soil moisture in the 200-400 cm soil layer but the water loss in the upper layer of 0-200 cm was more significant. Along with the growth of the coppice and the increase in vegetation cover in the cut land, the surface runoff declined, whereas the water consumption of the coppice forest increased. Consequently, the effect of cutting on soil moisture became weak after three years.