库布齐沙地滴灌人工林土壤水分运移及其与土壤分形特征的关系

Patterns of Soil Water Movement in Drip-Irrigated Plantations and Their Relationship with Soil Fractal Characteristics in Kubuqi Desert

以典型人工林为研究对象,基于激光粒度衍射法测得土壤粒径分布并计算单重及多重分形维数,通过大田试验明确灌水及水分再分布过程湿润锋动态变化规律,并采用通径和冗余分析等手段探究湿润锋运移与分形特征的联系。结果表明:(1)库布齐沙地滴灌人工林湿润锋水平及垂向运移可分别用对数函数(R^(2)=0.941~0.990)和幂函数(R^(2)=0.958~0.996)描述;(2)在砂粒占比高于70%、黏粒占比低于2.5%土壤条件下,利用粉粒、黏粒含量构建的多元回归模型能较好地计算停灌后二维水分运移距离(R^(2)=0.839~1.000),但对停灌前适用性较差(R^(2)=0.243~0.403);(3)单重分形维数(D)和信息维数(D_(1))、信息维数/容量维数(D_(1)/D_(0))、关联维数(D_(2))均与砂粉比呈负相关,而滴灌形成的湿润体体积与砂粉比正相关,且D较D_(0)、D_(1)、D_(1)/D_(0)、D_(2)更能解释土壤砂粉比差异对湿润锋运移的影响。滴灌下人工林水分运移满足函数定量关系,砂粒占比高于70%且黏粒占比低于2.5%时,土壤质地越粗则湿润体体积越大,可在灌溉策略制定时进行土壤粒径分析,节约决策成本。与库布齐沙地相似环境条件下,滴灌时长6 h流量3.0 L/h时,速生杨和榆树林在停灌后48 h需启动下次灌溉,沙柳和旱柳林则不需要。

Soil particle size distributions were measured in the typical plantations of in Kubuqi desert by laser particle size diffraction method,and the single fractal and multifractal dimensions were calculated.The dynamics of soil wetting front during irrigation and water redistribution periods were measured through field experiment,and the relationship between wetting front movement and fractal characteristics was explored by means of path and redundancy analysis.The results show:1) During drip irrigation,the horizontal and vertical movement distances of the wetting fronts in Kubuqi desert can be described well by the logarithm functions (R^(2)=0.941–0.990) and the power functions (R^(2)=0.958–0.996).2) When the volume fraction of sands is higher than 70%and the volume fraction of clays is lower than 2.5%in the soil,the multiple regression model based on the contents of silts and clays can better characterize the 2D water movement distance after irrigation is stopped (R^(2)=0.839–1.000),but it has poor applicability in the process of irrigation (R^(2)=0.243–0.403).3) The single fractal dimension (D) and the multifractal dimensions such as entropy dimension (D_(1)),entropy dimension/capacity dimension (D_(1)/D_(0)),correlation dimension (D_(2)) are negatively correlated with the ratio of sands/silts of the soil,while the final volume of wetting body formed by drip irrigation is positively correlated with the ratio of sands/silts of the soil.And D is better than D_(0)D_(1),D_(1)/D_(0)and D_(2)to explain the effect of the difference of the ratio of soil sands/silts on the movement of wetting front.There are some functional quantitative relationships of soil water movement in drip-irrigated plantations.When the proportion of sands is higher than 70%and that of the clays is lower than 2.5%,the lower the content of fine particles in the soil,the larger the volume of wetting body formed by drip irrigation.The soil particle size can be analyzed in the formulation of irrigation strategy to save the decision-making cost.Under the environmental conditions similar to Kubuqi desert,when the duration of drip irrigation is 6 h and the flow is 3.0 L/h,the next irrigation should be considered for the Populus popular and Ulmus pumila within 48 h after stopping irrigation,but not for Salix psammophila and Salix matsudana Koidz plantations.