## 4 Discussion
### Analysis of Cultivated Land Degradation Risks  
This study found that the southern area of the SNP faces higher degradation risks for cultivated land. Long-term intensive farming has resulted in a thinner black soil layer and reduced soil organic matter content in this region [11], increasing the risk of soil erosion and nutrient depletion. In the western regions, the area of saline-alkali soil has expanded, and the pH value of other soils except saline-alkali soil has dropped to 5.5-6.5 [63], further exacerbating the degradation risk of cultivated land. It is recommended to promote conservation tillage techniques, such as no till or reduced tillage, to minimize surface soil disturbance. Additionally, increasing the straw return and the application of organic fertilizers can help enhance the soil organic matter content. In the northern part of the SJP, the albic layer is close to the surface and relatively thick. Xu [9] indicated that the albic soil in the SJP accounts for 51.91% of the total albic soil area in the BSNC, with the thickness of the black soil layer being only one-third to one-quarter that of normal black soil. The low soil organic matter content leads to obstructive soil layers and nutrient decline, posing a high degradation risk to cultivated land. In the LHP, most of the cultivated land has a soil organic matter content of less than 2% [64]. Mechanical tillage has increased the soil bulk density and decreased the nutrient supply capacity [65], resulting in a high degradation risk for cultivated land in this area. It is recommended to improve the aeration and nutrient supply capacity of the albic layer through subsoiling and the application of organic fertilizers. Additionally, increasing the proportion of straw return, combined with the effective application of NPK compound fertilizers, can help replenish soil nutrients. DXXXL has the lowest effective accumulated temperature among the six regions, which is unfavorable for crop growth. The southern part of this region has thin black soil layers, low soil organic matter content, a high proportion of topsoil thickness less than 20 cm, and weak agricultural infrastructure, leading to a high risk of land degradation. CBMEL has generally higher altitudes, with cloudy and less sunny conditions in mountainous areas, affecting crop growth and yield [52]. The soil pH of cultivated land in this area is around 7, slightly acidic in the central and southern parts, with low soil organic matter content, resulting in a lower degradation risk. It is recommended to plant green  
Figure 8: Spearman rank correlation coefficient among cultivated land functions. A correlation coefficient greater than 0 indicates a positive correlation, one less than 0 indicates a negative correlation, and one equal to 0 indicates no correlation. a represents the Songnen Plain, b represents the Sanjiang Plain, c represents Changbai Mountain and Eastern Liaoning, d represents the Liaohe Plain, e represents Western Sandy, and f represents Daxing’an and Xiaoxing’anling. The asterisks indicate significance levels: * \(p<0.05\) indicates a difference, **\(p<0.01\) indicates a significant correlation, and ***\(p<0.001\) indicates a highly significant correlation. Red diagonal lines denote self-correlations, which are not displayed as they are always equal to 1.  
manure crops (such as alfalfa) to improve soil structure and increase organic matter content. For areas with severe compaction, regular subsoiling should be conducted to enhance soil aeration. Additionally, precise control of chemical fertilizer application, combined with the use of organic fertilizers, can improve soil nutrient use efficiency. The WS region is mainly composed of eolian sandy soil, meadow soil, and brown soil, with relatively high soil pH and sodium-alkali levels, posing risks of soil salinization and alkalization. It is recommended to promote grassland restoration and windbreak sand fixation measures, such as planting drought-resistant shrubs (e.g., Caragana and Salix psammophila).