Effects of sand-mulch thickness on soil evaporation during the freeze-thaw period

Control of evaporation from seasonally frozen soil is an important method for alleviating water shortages in arid and semi-arid areas. To investigate the inhibition of soil evaporation by sand and the major factors that influence soil evaporation, a series of field experiments with five sand-mulch thicknesses (0 cm, bare soil [BS], 1 cm [T1], 2 cm [T2], 3 cm [T3] and 4 cm [T4], with an average diameter of 1 mm) were conducted during the freeze-thaw period in Northern China. Soil evaporation characteristics in the three freeze-thaw stages were revealed and the major factors influencing soil evaporation were analysed using grey correlation analysis. The results showed that the cumulative soil evaporation decreased with increasing sand-mulch thickness during the freeze-thaw period, and only small differences in soil evaporation were observed between the T3 and T4 treatments. The reduction in soil evaporation under different sand-mulch thicknesses was 19.2-62.6% in the unstable freezing stage (P1), 2.0-28.3% in the stable freezing stage (P2) and 4.8-20.4% in the thawing stage (P3). In P1, solar radiation was a major factor influencing soil evaporation in all treatments and vapour pressure was a major factor in the sand-mulch treatments, and the influence of relative humidity on soil evaporation decreased in the T4 treatment. During the coldest P2, solar radiation was lowest so that relative humidity and wind speed became the more dominant influence factors on soil evaporation in all treatments, and surface soil water content was a major factor in the sand-mulch treatments. In P3, average air temperature and solar radiation were major factor influencing soil evaporation in all treatments and vapour pressure was a major factor in the BS and T1 treatments, whereas water surface evaporation was the major factor in the T2, T3 and T4 treatments. The results suggest that the addition of sand mulch in agricultural fields may be a beneficial practice to reduce water stress in arid and semi-arid areas.