Coupled simulation of farmland soil moisture evaporation and desiccation cracking

Desiccation cracking is one of the most serious surface failures in farmland soils. Soil structure can be reshaped to modify evaporation pathways in the redistribution of near-surface moisture. However, existing numerical research still treat soil-water movement and crack development as weakly coupled or even separate processes, despite their significance in hydrology and engineering. It is often required to reproduce crack evolution in the fields. In this study, a modeling framework was coupled with farmland soil moisture evaporation and desiccation cracking, with particular emphasis on the dynamic feedback between moisture loss and crack propagation. A soil-water movement was linked with a three-dimensional cracking model from linear elastic fracture mechanics. A systematic simulation was also integrated with moisture variation, volumetric shrinkage, and crack development, rather than as separate stages. Farmland soil was then taken from Yinchuan, Ningxia, western China. Field observations and laboratory response tests were conducted to validate the model after optimization. In the field experiment, crack images and crack depth measurements were collected from replicated test plots during post-saturation drying. Spatial distribution of crack depth was quantified under natural evaporative conditions. A second experiment was designed to establish the response relationship between soil shrinkage rate and volumetric water content. Water content was attributed to the key transfer mechanism between the moisture and cracking sub-model, leading to shrinkage deformation and subsequent fractures. The coupled framework also included feedback from the crack surfaces to the evaporation boundary and seepage behavior, indicating the influence of the cracks on moisture transport. Model parameters were calibrated using Monte Carlo search and field observations. The performance was assessed using geometric and statistical criteria. Crack images were compared from experiments and simulations, according to Minkowski density descriptors. While crack-depth relative frequency was used to evaluate the vertical distribution of cracking. The coefficient of determination (R²), index of agreement (IA), bias (BIAS), and root mean square error (RMSE) were employed to quantify the agreement between simulated and observed values. The field data showed that crack depth was concentrated within the 3–9 cm interval, indicating that the middle layer of the soil profile dominated for crack development under the drying conditions. The coupled model accurately reproduced the key features of crack-network morphology and vertical stratification. The results demonstrate that the strong predictive performance was achieved in the planar crack geometry, with R² values no less than 0.876, IA values no less than 0.953, BIAS values no greater than 0.101, and RMSE values no greater than 0.116. The framework performed better to represent crack length, area, network topology, and especially the propagation of deeper cracks, compared with the baseline desiccation-cracking model that relied primarily on surface evaporation as the driving mechanism. The high accuracy of field-scale simulations was attributed to consider the interaction between soil-water movement and surface cracking. Overall, a practical and physically grounded framework can provide for the co-evolution of moisture evaporation and desiccation cracking in farmland soils. Soil structural degradation under drying can offer the potential value for irrigation, soil-water regulation, and the crack risks in sustainable agriculture.