Temporal variation in soil macropore properties and hydraulic conductivity in croplands in the dry-hot valley region of Southwest China

In the dry-hot valley region of Southwest China, cropland soil macropore properties and hydraulic conductivity may exhibit complex temporal variations due to the combined effects of dramatic seasonal dry‒wet cycles, tillage-related disturbances and crop growth. This study aims to clarify the integrated mechanisms governing the variation in soil macropore properties and hydraulic conductivity. Three treatments were applied to cropland plots, namely, continuous fallow (CF), fallow after tillage (TF), and corn sown after tillage (TC), to quantify the effect of dry‒wet cycles, tillage-related disturbances, and crop growth, respectively, on soil macropore properties and hydraulic conductivity. X-ray computed tomography (CT) analysis (a total of 48 samples) and MiniDisk Infiltrator (MDI) experiments (a total of 162) were performed during three periods: the beginning of the wet season (May), mid-wet season (August), and the beginning of the dry season (October). The temporal variation in soil indexes for the continuous fallow treatment was statistically insignificant. Tillage in the early rainy season sharply increased soil macroporosity (1.96 times higher) and hydraulic conductivity (4.88 times higher) compared with the continuous fallow treatment. Nevertheless, both parameters then decreased in the fallow after tillage treatment and finally approached the values for the continuous fallow treatment in August. On the other hand, the corn sown after tillage treatment significantly enhanced soil macroporosity and hydraulic conductivity during the experimental period. Soil macropore parameters, such as hydraulic radius, global connectivity, and macroporosity, could explain the variance in hydraulic conductivity. Among these, macroporosity was identified as the most reliable predictor, with a determination coefficient (R2) of 0.66. The results of this study clarified the temporal dynamics of soil macropore properties and hydraulic conductivity in the dry-hot valley region. We found that dry‒wet cycling alone had little impact on cropland soil macropore characteristics and hydraulic conductivity, but it gradually reduced soil infiltration capacity after tillage-related disturbances. However, corn growth optimized soil macropore properties and enhanced hydraulic conductivity. Based on these results, we established a linear equation based on macroporosity and hydraulic radius to predict local soil hydraulic conductivity (R2 = 0.81).