The Study of Migration Mechanism of Soil Water and Salinity during Freezing-thawing Process of Double Ridges Mulching

Abstract

The freezing and thawing process caused soil water and salinity migration from depth to surface that led to massive evaporation and soil salination in spring. Ridges mulching is a very efficient method not only improved soil temperature, restrain evaporation, collected precipitation, but do not affected cultivation. Soil water characteristic curves reveal the relationship of soil water and soil suction, has very important meaning to research soil water migration. The study selected two kinds side mulching methods and one control as objects, the two kinds side mulching methods was weave overlay plastic film and weave, one control was bare soil. van Genuchten (VG) and Brooks and Corey (BC) models were adopted to simulated soil water characteristic curve in the freezing-thawing process. The result showed that VG model has higher simulation accuracy, and the coefficients of determination R2 are above 0.9 and nRMSE are less than 10% for BS, W and FW simulation tests except for W and FW conditions of 5 cm. The soil temperature from 0 to 30 cm depth during freezing was highest in FW, second in W, and lowest in BS. Soil water and salinity have migrated during freezing-thawing process, compared with before freezing, soil water increased from 30 cm depth under bare soil conditions and from 15 cm under mulching cover conditions after the end of freezing-thawing, and the same pattern for soil EC, from 15cm depth under mulching conditions soil EC values increased, the EC values at 15cm depth under bare soil conditions still decreasing. The study achievement can provide a reference for the study of water-salinity migration and water characteristic curves during freezing and thawing of soils in arid and cold regions, and also provide a theoretical basis for soil water conservation, suppression of evaporation from farmland and salinity accumulation in topsoil.