Quantitative Study Of Soil Matrix Infiltration And Preferential Flow In Short-rotation Eucalyptus Plantations

Soil infiltration is the process by which water from the soil surface enters the soil.It is an important component of the hydrologic cycle and a key link of precipitation redistribution and soil water storage.Soil infiltration in forest consists of two parts: matrix infiltration and preferential flow.Strengthening the research on soil matrix infiltration and preferential flow of forest can deepen the understanding of the hydrological process of forest regulation,which has great significance for maintaining the stability of regional ecological environment.In this study,four aged(1,2,3 and 5 years)plantations of Eucalyptus urophylla ×E.grandis of the state-owned Dongmen Forest Farm in Guangxi Zhuang Autonomous Region were research objects.The soil matrix infiltration and preferential flow in short-rotation eucalyptus plantations were successfully measured by using the surface-positioned double-ring infiltrometer.The optimal fitting models and influencing factors of matrix infiltration and preferential flow were studied.The main findings were as follows:(1)The surface-positioned double-ring had a good applicability for measuring matrix infiltration and preferential flow of short-rotation eucalyptus plantations.The sand-soil mixture as a covering material could successfully shield the preferential flow of eucalyptus plantations for measuring matrix infiltration.The method of using sand-soil mixture as the covering material could achieve the in-situ quantitative measurement of soil matrix infiltration.Moreover,the measurement and calculation theory of preferential flow was also applicable to measure the preferential flow in short-rotation eucalyptus plantations.(2)The initial infiltration rate(224±4,211±12,206,138±17 mm/h),stable infiltration rate(194±9,168±6,165±6,116±4 mm/h),and 1 h cumulative infiltration(201±11,178±10,174±4,128±10 mm)of soil matrix infiltration decreased with the increase of forest age in four aged eucalyptus plantations.The initial infiltration rate(44314±2708,4559±3504,5322±2120,8303±1978mm/h),stable infiltration rate(63±44,82±57,167±72,283±90 mm/h),and 1.5h cumulative infiltration(913±406,890±512,1470±387,2226±514 mm)of preferential flow increased with the increase of forest age in four aged eucalyptus plantations.The spatial variability of soil matrix infiltration in the same aged eucalyptus plantation was low(2.0%–12.1%),and the spatial variability of preferential flow was higher(23.1%–69.8%).(3)Soil properties and roots were the important factors affecting matrix infiltration and preferential flow in short-rotation eucalyptus plantations,respectively.The clay content,buck density,soil organic matter,soil water stable macroaggregate,and mechanical-stable macroaggregates increased with increasing forest age,thus inhibiting soil matrix infiltration.The sand content decreased with increasing forest age,and then inhibiting soil matrix infiltration.The clay content was the dominant factor affecting soil matrix infiltration.The root biomass increased with increasing forest age,thus promoting preferential flow.Similarly,lateral preferential flow was also controlled by the root and increased with increasing forest age,eventually promoting preferential flow.(4)Different infiltration models have the different fitting effects on infiltration processes of soil matrix infiltration and preferential flow in shortrotation eucalyptus plantations.The Horton model had the best fitting effect on infiltration processes of soil matrix infiltration and preferential flow,followed by Kostiakov model and the worst Philip model.Therefore,the Horton model was the most suitable model to describe the infiltration process of soil matrix infiltration and preferential flow in eucalyptus plantations.Root biomass,as the important factor,was used in predicting the parameters of the Horton model by regression analysis.Then,a unified model predicting the preferential flow infiltration process in short-rotation eucalyptus plantations was proposed and verified.The good prediction of unified model further showed that roots had a considerable effect on preferential flow in eucalyptus plantations.Above results can provide a theoretical basis for improving the efficiency of water resource management in plantation and optimizing the model of soil infiltration.