Abstract:
Objective The study aimed to reveal the spatial variation pattern of the cultivated topsoil yellowing risk and its influencing factors in Heilongjiang Province, in order to provide a basis for the protection of Mollic horizon in cultivated lands in Northeast China.
Method Based on thickness data from 657 Mollic horizon and 1,088 Ap horizon sampling points, combined with environmental covariates, the Residual Random Forest (RRF) model was employed to predict spatial distribution. The Cultivated-layer Thickness Stress Index (CTSI), defined as the ratio of Ap horizon thickness to Mollic horizon thickness, was proposed to assess spatial pattern and influencing factors.
Result The average thicknesses of the Mollic horizon and Ap horizon in the study area were 57.7 cm and 23.8 cm, respectively. The average CTSI was 0.43, indicating a moderate to low risk level. High-risk areas (CTSI > 0.6) accounted for 5.93% of the cultivated land, primarily distributed in regions with thinner Mollic horizons. The thinning of the Mollic horizon and excessive deep tillage were the main drivers of the risk. Topography and human activities contributed to the variation in CTSI for 52.89% and 32.30%, respectively,
Conclusion The key to mitigating the topsoil yellowing risk lies in controlling soil erosion at the source, vigorously promoting conservation tillage systems centered on straw mulching and minimal or no-tillage, while protecting and cultivating the Mollic horizon based on local conditions, controlling deep tillage depth, and appropriately designing differentiated Ap horizon thickness based on the principle of "Three Adaptations and Five Coordinations".
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