Freezing induced soil water redistribution: A review and global meta-analysis
Xiaobin Li, Xiaoyu Chen, Yanchen Gao, Jiahui Yang, Weiting Ding, Francis Zvomuya, Nasrin Azad, Jinbo Li, Hailong He
Abstract
• There is a gain in shallow total soil water content (GSTSWC) when soil freezes. • Initial soil water content is inversely proportional to the GSTSWC. • GSTSWC of rangeland > forest land > agricultural land. • Straw mulching and plastic film mulching can increase the GSTSWC.” Over 75 % of the terrestrial territory in the Northern Hemisphere is subjected to seasonally freezing and thawing cycles. The naturally occurred soil freezing processes induce the migration of soil water from unfrozen underlying depths towards the freezing front under gradients of matric potential, temperature and vapor concentration/pressure. The upward moving soil water and vapor change to ice near unfrozen-frozen interfaces, which increases the total water content in the frozen layers. Although a portion of the migrated water redistributes during soil thawing, in general, a gain in shallow total soil water content (GSTSWC). The GSTSWC can be utilized by crops in dry and cold regions, where rainfall limits agricultural and ecosystem productivity. However, there is a knowledge gap on how much water migrates to increase the total shallow soil water content under various land uses and soil conditions. To assess the amount of GSTSWC under various driving factors, a meta -analysis and structural equation model (SEM) were performed using 774 paired observations compiled from 61 studies worldwide. The results indicate a hierarchical order of GSTSWC, with bare land exhibiting the highest GSTSWC value (17 %), followed by rangeland (13 %), forest land (7 %), and agricultural land (3 %). The GSTSWC exhibits an inverse relationship with initial soil water content (SWC). The implementation of straw and plastic film mulching practices exerts a significant effect on soil insulation and water retention, causing a notable postponement and prolongation of the soil thawing process. Consequently, GSTSWC in the 50–100 cm soil layer increases by 2 % for straw mulching and 3 % for plastic film mulching. The SEM demonstrated that mean annual precipitation and initial SWC directly affect GSTSWC. It can assist in formulating recommendations for soil water management in seasonally-frozen soil regions.