Insights into saline soil cracking subjected to drying-wetting cycles

Soil salinization has become a global environmental issue, and soil cracking can lead to preferential flows and destabilize the developments of plant-soil system. However, little is known about saline soil cracking, especially under external drying-wetting (D-W) alternations. This study explored how soil salt and continuous D-W cycles affected water evaporation and crack development responding to soil salinity (0, 0.3, 0.6, 1.0, and 2.0%, w/w) and three D-W cycles. Observed findings showed that saline soil water evaporation was smaller than nonsaline soil. Besides, the water evaporation decreased and increased as the soil salinity increased and the D-W cycles progressed, respectively. In addition, soil salt and D-W cycle inhibited and promoted soil cracking, respectively; specifically, the crack area density decreased and increased with increasing soil salinity and number of D-W cycles, respectively. Correlations indicated that the soil salt had overall larger contributions than the D-W cycle to the variations of water evaporation and crack development. Soil salt was negatively correlated with cumulative evaporation, evaporation rate, and crack length density, but was positively correlated with soil moisture; besides, D-W cycle was negatively correlated with soil moisture, but was positively correlated with cumulative evaporation, evaporation rate, crack area density, and crack length density. Mechanism exploration suggested that the salts inhibit surface cracking by promoting inter-microaggregate cementation and clay flocculation and blocking soil macropores; and the D-W cycle promotes surface cracking through the swelling-induced crack healing in the case of hydrophilic clay minerals in contact with water.