Response of Nitrogen Accrual in Various Soil Organic Matter Fractions to Different Land Uses

Land use practices are a key driver of soil nitrogen (N) dynamics, yet their influence on N accumulation within distinct soil organic matter (SOM) fractions remains insufficiently understood. This study aimed to elucidate the responses of N accrual in different SOM fractions to contrasting land uses. To achieve this purpose, soil samples were collected from seven representative land uses: forest, pasture, corn plantation, sugarcane plantation, cassava plantation, orchard, and abandoned land. Subsequently, soil samples were fractionated into free particulate SOM (fSOM), occluded light SOM (oSOM), weakly bound form SOM (wSOM), and strongly bound form SOM (sSOM) fractions, and N contents were quantified for each fraction. The results showed pronounced land use effects on both the magnitude and distribution of N among SOM fractions. The forest land use consistently promoted greater N accumulation in fSOM (0.15 g N kg−1 soil), oSOM (0.14 g N kg−1 soil), and wSOM fractions (0.29 g N kg−1 soil), reflecting high organic inputs and low disturbance intensity. The pasture land use exhibited the highest N accumulation in the sSOM fraction (1.01 g N kg−1 soil), indicating enhanced stabilization of N through strong organo-mineral associations. Intensively managed croplands and abandoned land generally displayed lower N storage across SOM fractions. Overall, these findings highlight the critical role of land use in regulating N partitioning and stabilization within SOM fractions and underscore the importance of low-disturbance, perennial vegetation systems for improving long-term soil N retention.