陕北不同沟道土地盐碱化现状及影响因素

Situation and impact factors of soil salinization in different dammed farmlands in the valley area of the Northern Shaanxi Province

沟道土地是陕北黄土丘陵沟壑区重要的土地资源。然而,当前对黄土高原沟道土地的盐碱化问题关注不够,对盐碱化的现状、发生机制和防治措施也缺乏深入系统的认识,知识储备不能满足生产实际的需要。本文以陕北黄土丘陵沟壑区自然和人为形成的沟道土地为研究对象,分别是延安顾屯新造耕地(治沟造地)、延川马家湾淤地坝土地和子洲黄土洼天然古聚湫土地,在这些流域内沿沟道采集土壤样品,测定土壤的电导率(EC)、p H值、含水量及粒度,分析土壤盐碱化的现状和影响因子。结果表明:马家湾淤地坝土地盐碱化最为严重,流域中游至上游均出现不同程度的盐碱化;顾屯新造地上游出现盐碱化,盐碱化程度较马家湾轻,而黄土洼古聚湫全流域未出现盐碱化。地下水位较浅是沟道土地发生盐碱化的主要影响因素,因此陕北沟道土地盐碱化防治应着力控制地下水位,建设良好的排水系统,加强排水。

Background,aim,and scope Soil salinization is one of the most important types of land degradation,which receives highly attention by scientists and governments around the world.During the past 50 years,China has achieved great success in controlling soil salinization,while it is still a serious problem of land degradation in many areas of China,e.g.the Yellow River Basin.The Chinese Loess Plateau(CLP)locates the middle reaches of the Yellow River,where is an area prone to soil salinization with low precipitation,high evaporation,and alkaline soil.The valley area on the CLP is the place where has high risk of soil salinization being high groundwater table and poor drainage system.However,the valley on the CLP has a large area of farmlands,e.g.the dammed farmlands formed through human and natural factors in the hilly-gully regions of the Northern Shaanxi Province.Currently,we lack a comprehensive understanding of the situation,mechanisms and prevention measures of soil salinization in these dammed farmlands in the valley of the loess hilly-gully regions,which has substantially constrained the knowledge demands of agricultural practice on the CLP.Thus,three kinds of dammed valley farmlands in the Northern Shaanxi Province were selected to examine the status and impact factors of soil salinization in the valley area of the CLP.Materials and methods The dammed farmlands included the man-made farmlands in the valley of the Gutun watershed,Yan’an City(formed through gully land consolidation),the seminatural farmlands behind the fulfilled check dams in the valley of the Majiawan watershed,Yanchuan County,and the natural farmlands formed through the ancient landslide-dammed lake in the valley of the Huangtuwa watershed,Zizhou County.Soil samples were collected in the three kinds of farmlands,and soil electric conductivity(EC),pH value,soil moisture and soil texture were measured.Moreover,based on the measured soil moisture content in the profile,groundwater levels in the three kinds of farmlands were estimated through an empirical equation.Results According to the determined soil physical and chemical parameters and the estimated groundwater levels,the situation and impact factors of soil salinization in the three kinds of farmlands were evaluated.Results showed that:(1)soil salinization both occurred in the Gutun and Majiawan watersheds,and Majiawan showed the most serious situation of soil salinization among the three valley sites;(2)in the Guntun watershed,soil salinization occurred in the upper reaches of the valley;while in the Majiawan watershed,soil salinization extended to the middle reaches of the valley;(3)in the Huangtuwa watershed,no soil salinization was found in the valley farmlands.Discussion Majiawan watershed showed the most serious situation of soil salinization due to a shallow water table,where profile soil moisture demonstrated the highest average content(28.4%)among the three kinds of farmlands.Moreover,the estimated average water table depth was 1.23 m,which demonstrated a very shallow groundwater level.In the Guntun watershed,the average groundwater level was 2.85 m and the middle and lower reaches of the valley showed a relatively deep groundwater table;while in the upper reaches of the valley,the groundwater table was shallow.Therefore,obvious soil salinization occurred in the upper reaches of the valley in the Gutun watershed.The ancient landslide-dammed farmlands in the valley of the Huangtuwa watershed demonstrated no salinization mostly being a deep groundwater table.The Huangtuwa watershed locates in a high platform,and the estimated groundwater level was 4.77 m.Moreover,the profile soil moisture content showed a moderate level and demonstrated a decreasing trend with the increase of soil depth,which indicates that soil water is well drained at the bottom of the farmland.Therefore,no soil salinization occurred in the valley farmlands.Conclusions Shallow groundwater table was the critical reason of soil salinization in the dammed farmlands in the valley of the loess hilly-gully regions of the Northern Shaanxi Province.Recommendations and perspectives Strengthening the drainage system and suppressing the groundwater table are the core issues in deal with the problems of soil salinization in the dammed farmland in the valley of the Northern Shaanxi Province.The results of this study can provide scientific basis for soil salinization control on the CLP.