A research team led by Prof. LI Xinhu from the Xinjiang Institute of Ecology and Geography (XIEG) of the Chinese Academy of Sciences (CAS) has found that soil texture controls the morphology of salt precipitation, which in turn governs the water and heat balance of the soil.

The findings were published in Agricultural and Forest Meteorology on April 15.

To reach this conclusion, the research team conducted field experiments at the Aksu National Agro-Ecological Experimental Station in Xinjiang. They compared the hydrothermal dynamics of two typical soils (silt loam and sandy soil) under saline and non-saline conditions, and developed a numerical model to simulate coupled water-heat-salt transport.

The results show that in silt loam, salts form a dense, uniform crust that efficiently clogs soil pores; in sandy soil, by contrast, salts initially precipitate as scattered crystals, only forming a continuous crust after reaching a critical threshold. This means salt's ability to block evaporation depends not just on how much salt there is, but on the structure and morphology of the precipitated salt layer.

Based on these observations, the researchers developed tailored mathematical functions to describe salt-induced evaporation resistance. For silt loam, a logarithmic function captures the rapid clogging of pores and the sharp rise in resistance as salt accumulates. For sandy soil, a sigmoid (S-shaped) function accurately reflects the three-stage evolution: initial lag, rapid transition, and final saturation.

The study confirms that saline soils stay warmer than salt-free soils both day and night. This is mainly because the salt crust strongly suppresses evaporative cooling (latent heat flux), leaving more energy to heat the soil.

More importantly, the research shows that the way salt precipitates also affects soil temperature. The faster-forming, lower-albedo salt crust on silt loam absorbs more solar radiation, making the shallow soil layer much warmer than that of sandy soil.

The researchers also gained fresh insights into how salt crusts' roughness and albedo matter. The rough salt crust on sand has a much larger actual surface area than its projected area, which partially compensates for the evaporation reduction caused by salt coverage.

Also, salt crusts on different soils vary in color and albedo, which directly affects how much radiation the surface absorbs and thus the soil's temperature. These findings offer clear directions for improving existing models.

"Our work bridges the gap between laboratory-based mechanistic understanding and real-world field conditions. This study is a milestone for understanding the evolution of saline lands in dry regions, predicting their responses to climate change, and developing targeted strategies for salinity control and water management," said Prof. LI.