Research on rice paddy soil health evaluation in black soil regions based on a “core + regional” framework: A case study of the Sanjiang Plain

The Sanjiang Plain in Heilongjiang Province is a major rice-producing region in China, where long-term intensive cultivation has led to soil functional degradation. Existing research has focused primarily on the general characteristics of soil fertility and lacks a precise evaluation index system that balances both universal applicability and regional specificity. Therefore, in this study, 146 surface soil samples (0–15 cm) were collected from five typical rice-growing regions on the Sanjiang Plain, 19 indicators were measured, and principal component analysis was applied to screen the core universal indicators and regional-specific indicators. A soil health index was subsequently calculated using a weighted scoring function. The results indicate the following: 1) the soil pH, organic matter content, and sand particle content were identified as core common indicators across five typical regions, with contribution rates ranging from 38% to 48%. Among the nine region-specific indicators, available phosphorus, microbial respiration intensity, and electrical conductivity exhibited significant spatial heterogeneity; 2) the soil health index for paddy fields in the eastern Sanjiang Plain region reached 0.63, which was higher than that in the other areas, whereas the soil health index in the northeastern region was the lowest (0.50) because of its low pH (5.51) and minimal microbial respiration intensity (36.73); 3) the soil health index was significantly positively correlated with crop yields (R 2 = 0.59–0.72), indicating that the selected indicators effectively reflected soil health; and 4) in the northeastern and northwestern regions with pronounced acidification, increased application of organic and phosphate fertilizers combined with liming for acid neutralization is recommended. In the central region, which has high sand content and poor nutrient retention, straw mulching and return to fields can be implemented. The “core-regional” indicator system and corresponding zoned management plan established in this study provide a scientific basis and practical pathways for precisely enhancing soil health and sustaining productive capacity in black soil rice fields.