干旱绿洲区包气带土壤盐分分布特征及运移机制——以新疆焉耆盆地为例

Distribution characteristics and migration mechanism of soil salt in the aeration zone of zrid oasis areas——A case study of Yanqi Basin in Xinjiang

土壤盐渍化问题严重制约着我国干旱—半干旱区农业可持续高质量发展,了解包气带土壤盐分离子分布特征及垂向运移机制对科学防治土壤盐渍化具有重要意义。通过精细化采集新疆焉耆盆地2 m深度剖面土壤,测定样品机械组成和8种盐分离子含量,计算土壤颗粒分形维数,采用统计学方法分析包气带土壤盐分离子垂向分布特征,对包气带土壤质地与水盐运移间的关系进行探讨。结果表明,博湖剖面包气带土壤主要为非盐渍土,土壤盐分主要受开都河下游地下水水化学类型和矿化度控制,阴阳离子比值约为2∶5,盐分类型主要为Ca^(2+)—HCO_(3)^(2-)和Na^(+)—SO_(4)^(2-)型;焉耆剖面包气带土壤普遍为重度盐渍土,土壤盐分受到开都河下游地下水水化学类型和自身包气带盐分的综合影响,阴阳离子比值约为1∶2,盐分类型主要为Ca^(2+)—SO_(4)^(2-)型和Na^(+)—Cl^(-)型。土壤分形维数和黏粒含量之间显著正相关,与砂粒含量显著负相关,包气带土壤盐分与分形维数间相关性不明显,主要受到土壤粒径组成及其所处深度等综合作用的影响。博湖包气带土壤质地由表层至深部逐渐变粗,盐分含量呈现出在0~80 cm深度的表层和125~200 cm的底部波动大,80~125 cm稳定的变化趋势,盐分离子主要聚集在约30 cm深度粉质黏壤土与粉质黏土层的交界处。土壤盐分运移大致可划分为交互作用段(0~80 cm)、平衡段(80~125 cm)和地下水扰动段(125~200 cm)3个部分,蒸发作用影响深度约80 cm。焉耆包气带土壤质地由表层至深部逐渐变细,随深度的增加,盐分含量和波动程度均逐渐减小,盐分离子主要聚集在0~10 cm表土层。盐分运移大致可划分为盐分离子上升段(0~120 cm)和平衡段(120~200 cm)两个部分,蒸发作用影响深度约为120 cm。上细下粗型的包气带土壤质地组成是抑制土壤盐渍化较为理想的分布模式,对于焉耆剖面类型可先采取灌溉压盐,然后进行约40 cm深度的翻耕,博湖剖面类型可直接采取50 cm左右深度的深耕,一定程度上能够抑制盐渍化的发生。

Objectives:The serious problem of soil salinization restricts the sustainable and high-quality development of agriculture in arid and semi-arid regions of China.Understanding the distribution characteristics and vertical migration mechanism of soil salt ions in the vadose zone is of great significance for the scientific prevention and control of soil salinization.Methods:By conducting fine-grained sampling of the 2 m depth profile soil in the Yanqi Basin,the mechanical composition and content of eight salt ions in the samples were determined.The fractal dimension of soil particles was calculated,and statistical methods were used to analyze the vertical distribution characteristics of soil salt ions in the vadose zone.Additionally,the relationship between soil texture and water—salt transport in the vadose zone was explored.Results:The results showed that the vadose zone soil in the Bohu profile was mainly non-saline soil.The soil salinity was mainly controlled by the hydrochemical type and mineralization degree of the groundwater in the downstream of Kaidu River.The ratio of cations to anions was approximately 2∶5,and the main salt types were Ca^(2+)—HCO 2-3 and Na^(+)—SO_(4)^(2-).The vadose zone soil in the Yanqi profile is generally heavily saline soil.The soil salinity is comprehensively influenced by the hydrochemical type of the groundwater in the downstream of Kaidu River and the salinity of its own vadose zone.The ratio of cations to anions is approximately 1∶2,and the main salt types are Ca^(2+)—SO _(4)^(2-)and Na^(+)—Cl^(-).There is a significant positive correlation between soil fractal dimension and fine particle content,and a significant negative correlation with sand content.There is no significant correlation between soil salinity and fractal dimension in the vadose zone,which is mainly affected by the comprehensive effects of soil particle size composition and its depth.The soil texture of the aeration zone of the Bohu profile gradually becomes coarser from the surface layer to the deep layer.The salt content exhibits a large fluctuation in the surface layer at a depth of 0~80 cm and the bottom layer at a depth of 125~200 cm,and a stable trend of change at a depth of 80~125 cm.The salt ions are mainly concentrated at the interface between the silty clay loam and the silty clay layer at a depth of about 30 cm.The soil texture of the Yanqi profile gradually becomes finer from the surface layer to the deep layer.As the depth increases,both the salt content and the degree of fluctuation gradually decrease.The salt ions are mainly concentrated in the surface soil layer at a depth of 0~10 cm.Conclusions:The transport of soil salt in the aeration zone of Bohu can be roughly divided into three parts:the interaction segment(0~80 cm),the balance segment(80~125 cm),and the groundwater disturbance segment(125~200 cm).The depth affected by evaporation is approximately 80cm.The transport of soil salt in the aeration zone of Yanqi can be roughly divided into two parts:the salt ion ascending segment(0~120 cm)and the balance segment(120~200 cm).The depth affected by evaporation is approximately 120 cm.The soil texture composition of the vadose zone with finer particles on the top and coarser particles on the bottom is an ideal distribution pattern for inhibiting soil salinization.For the Yanqi profile type,irrigation can be used first to suppress salt,followed by plowing to a depth of approximately 40 cm.For the Bohu profile type,deep tillage to a depth of about 50cm can be directly adopted,which can suppress the occurrence of salinization to a certain extent.