Effects of ice cover on soil water, heat, and solute movement: An experimental study

Abstract

In cold regions, the surface cover plays a pivotal role in understanding the soil water and energy balance during winter. Although the effects of other types of surface cover on soil freezing-thawing process have been studied for decades, the effects of ice cover derived from irrigation remain unclear. To estimate the effects of ice cover on soil water, heat, and solute movement, ice coverage and field observation data were collected for three winter periods from 2013 to 2016 in Inner Mongolia, China. The collected data was then analyzed using the principal component analysis (PCA) method. The dynamics of the water, heat, and solute transport were also investigated using in-situ plot experiments conducted in four lysimeters, which were controlled by manipulating the thickness of the ice cover. The thickness of the ice cover was controlled by the amount of water irrigation in the treatment plots, and no irrigation was performed in the control plot. The results of the field-scale survey and PCA indicated that the ice cover had positive effect on soil salinization control and moisture preservation after autumn irrigation (AI). An unique air space created during the ice formation might enhance the heat insulation effect of ice cover. Furthermore, the results of the in-situ plot experiment revealed that the freezing of the irrigated soil could be divided into the unstable freezing period (UFP) and stable freezing period (SFP) when considering the ice cover. During the UFP, the upward movement of the solute that was leached by the irrigation water was reduced as the development of the freezing front was hindered by the irrigation water. During the SFP, the penetration of the freezing front was further reduced by the combination of the ‘inherited’ thermal regime from the UFP and the input solar energy reduced by the remaining ice cover and air space, which decreased the water and solute transport. The study findings aid in achieving an improved understanding of ice cover on agricultural fields in cold regions, and have important implications for water conservation and salinization control.