Effectiveness of humic-acid-based composite amendments in mitigating soil cracking and erosion in cold black soil...

The development of freeze-thaw-induced cracks is a critical driver of composite erosion in black soil farmland of cold regions. To clarify the regulatory effects of exogenous amendments, this study employed an artificial climate chamber and rainfall simulator to examine crack morphology, fractal characteristics, and sediment yield under applications of humic acid (H) alone and in combination with lignosulfonate (L) or polyacrylamide (P). Under the bare soil treatment (CK), cracks exhibited the greatest width and sediment yield, with the multifractal spectrum showing a "low peak-narrow width" pattern. At a concentration of 1 %, H reduced crack width and erosion, whereas at 2 % it loosened soil structure, resulting in increases of 43.84 % and 28.54 % in crack intensity and sediment yield, respectively, relative to CK. Combined applications of H with L or P markedly decreased crack width by inducing fine crack networks, thereby enhancing fractal dimension and widening the multifractal spectrum. Despite larger crack areas under HL1 and HP1, sediment yield declined sharply by 96.22 % and 99.62 %, respectively. Furthermore, increasing concentrations of L or P progressively broadened the spectrum width. Principal component analysis indicated that HP3 and HP2 significantly inhibited crack expansion and erosion intensity, demonstrating the strongest synergistic regulation. Overall, H-L and H-P combinations substantially improved soil structural stability and erosion resistance compared to H alone or CK. These results provide new insights into the mechanisms of amendment-mediated freeze-thaw crack regulation and offer practical guidance for soil improvement and water-soil conservation in sloping farmland of cold regions.