Multiscale assessment of cultivated land quality across soil profile and its coordination with subsystems

Multiscale assessment of cultivated land quality (CLQ) has become a major focus in geoscience, yet most studies compare surface CLQ horizontally across scales and treat each scale independently. Systematic analyses of soil profile–based CLQ and its vertical variation across nested scales remain limited. This study developed a nested, multiscale CLQ assessment framework based on the Land Evaluation and Site Assessment (LESA) approach for four geographical scales—watershed scale (WS), county scale (CS), village scale (VS), and field scale (FS)—and the 0–60 cm soil profile. The framework was used to select appropriate assessment units, characterize spatial patterns and clustering, and evaluate coupling coordination between the land evaluation (LE) and site assessment (SA) subsystems and CLQ. Field parcels, villages, individual fields, and 110-m grids were used at the WS, CS, VS, and FS, respectively; field parcels and villages were the best-performing candidate units at the WS and CS, while individual fields were the only applicable units at the VS. The LE index decreased with soil depth at the WS and CS but generally increased at the VS and FS, whereas the SA index declined overall, although non-monotonically, toward finer geographical scales. Soil profile–based CLQ showed significant, scale-dependent positive spatial autocorrelation (p < 0.001) at all four scales. Coordination patterns also varied by scale and depth: SA–CLQ coordination was stronger at the WS, LE and SA showed relatively balanced coordination at the CS and VS, and LE–CLQ coordination was stronger at the FS. Across scales, LE–CLQ coordination was generally strongest or tied for strongest at 40–60 cm and weakest at 20–40 cm. The LE and SA subsystems also exhibited scale-specific crossover points in their coordination with CLQ. These findings provide a basis for scale-specific, profile-targeted cultivated-land management and support regional food security and sustainable agricultural development.