农林复合种植模式对红壤坡地表土水力特性及储水的影响

Effects of agroforestry planting systems on top-layer soil hydraulic characteristics and soil water storage on red soil slopes

为探讨红壤坡地不同农林模式表层土壤水力特性差异及其对土体储水量的影响,该文分析了红壤坡地“农-林-草”、“农-林+横坡耕作”、“农-林+顺坡耕作”和“纯林”4种典型农林复合模式表层土壤(0~0.30m)的土壤水力特征参数,并通过Richards方程数值求解模拟了不同表层土壤水力特性下的土壤含水率动态和土体储水量。结果表明,农林复合模式对表层土壤水力特性有较大影响,“农-林-草”、“农-林+横坡耕作”、“农-林+顺坡耕作”、“纯林”模式的表层土的土壤性质依次表现为:土壤黏性增强(土壤进气值倒数减小)、透水性减弱(饱和水力传导度减小)。饱和水力传导度、土壤进气值倒数与土壤容重的相关系数为-0.98和-0.96。当仅考虑表层土壤水力特性差异时,土体储水能力由强到弱依次为“农-林-草”、“农-林+横坡耕作”或“农-林+顺坡耕作”和“纯林”模式土壤。“农-林-草”模式表层土壤具有在蒸发期减少深层土壤水消耗、在降雨期增加深层土壤水补给的作用,该土壤储水机制为“农-林-草”复合种植模式推广提供了理论基础。

In-depth studies on soil water storage in red soil slopes in south China are of important scientific significance and practical application value for flood control,drought relief and conservation of soil and water.Agricultural cultivation under the fruit forest is an important way of development and utilization of red soil slopes in southern China,and the properties of top-layer soil would be affected by biological process,soil erosion,artificial tillage,etc.Hence,it is essential to understand difference of top-layer soil hydraulic characteristics of several agroforestry systems,which may affect soil water storage.The study area lies in Jiangxi Provincial Eco-Science Park of Soil and Water Conservation(115°42′38″-115°43′06″E、29°16′37″-29°17′40″N),which is located in De’an County,Jiangxi Province,China and belongs to Boyang River watershed of Poyang Lake Basin.A total of 4 treatments of agroforestry systems,namely,agriculture-forestry-grass,protective farm-forest,common farm-forest,and pure forest were studied.The top layer was defined as 0-0.30 m subsurface depth in this paper,and soil samples of the top-layer soil were collected by foil sampler for each plot.For each sample,the bulk density was measured by drying method,water retention curve was test by pressure membrane meter,and saturated hydraulic conductivity was measured by saturated infiltration experiment.The van Genuchten-Mualem model was used to describe water retention curve,and the other 4soil hydraulic parameters were reciprocal of air entry pressure,grain size distribution parameter,saturated soil water content,and residual soil water content besides saturated hydraulic conductivity.The one-dimensional Richards’equation based on the Darcy’s law was used to describe soil water flow due to its solid physical foundation,and the Ross method was used to solve the Richards’equation owing to the higher computational efficiency and accuracy.For the sake of simplicity,several assumptions were considered for simulation.Firstly,the difference of top-layer soil hydraulic characteristics was the only various factor of the 4 plots,and the soil profile for simulation was also divided into 2 layers,and the top layer was from soil surface to 0.30 m depth.Secondly,the simulation period was set to from August 1^st to December 31^st,2010 since runoff wasn’t observed in this period.Thirdly,the upper boundary condition was considered as atmospheric boundary condition,where the potential evaporation was calculated by Penman-Monteith model.Besides,the lower boundary was zero-flux boundary at 1.00 m depth where was impermeable bedrock.The statistical analysis results of soil hydraulic parameters showed the most significant difference between top and deep layer in agriculture-forestry-grass soil with the lowest viscosity and highest permeability,i.e.,the largest saturated hydraulic conductivity and reciprocal of air entry pressure among the 4 plots.Correlation analysis of parameters showed that absolute of correlation coefficient between saturated hydraulic conductivity and bulk density and that between reciprocal of air entry pressure and bulk density could reach to 0.96.The distribution of soil water content of each profile was simulated,and soil water storage was calculated by the simulated soil water content.The simulation results showed the order of soil water storage under the 4 treatments from high to low as followed:agriculture-forestry-grass soil,protective farm-forest soil or common farm-forest soil and pure forest soil.The simulation results during specified periods indicted the mechanism of effects of top-layer soil hydraulic characteristics on soil water storage.For agriculture-forestry-grass soil,the top-layer soil cut off the upward movement channel of soil moisture to reduce the water consumption of the deep soil during the evaporation period,while the top-layer soil increased the downward movement to enhance the water storage of deep soil.In conclusion,agriculture-forestry-grass is worth of development and promotion in red soil slopes in south China.