Assessment of carbon and nitrogen stocks in soil and soil organic matter fractions in an alley cropping system under a northern temperate climate

Abstract Alley cropping, combining tree rows with wide alleys for agricultural crops, has demonstrated variable potential to store additional carbon (C) and nitrogen (N) in soil, compared to conventional cropping. Studies quantifying C and N in particulate organic matter (POM) and mineral‐associated organic matter (MAOM) are scarce, despite their importance in understanding soil C accumulation and N cycling. The study aimed to quantify differences in C and N stocks in POM, MAOM, and whole soil in the 0‐ to 80‐cm soil profile, between a 10‐year‐old alley cropping system (50 trees ha −1 ), a tree‐free agricultural control, and an adjacent mature forest, under a northern temperate climate. Spatial heterogeneity of soil C and N stocks in alley cropping was also assessed. In the 0‐ to 10‐cm soil layer, C and N stocks were lower in alley cropping than in the forest. In the 10‐ to 20‐cm layer, they were greater under alley cropping than in the control. When considering the 0‐ to 20‐cm soil layer, C stock in alley cropping was numerically 34% greater (+1.26 Mg C ha −1 year −1 ) than in the control, with 80.5% of the additional C stored as MAOM. Within the alley cropping system, C and N stocks in the 0‐ to 10‐cm soil layer were generally greater under the tree row than in the cultivated alley, with most of the additional C and N stored as POM. In these cultivated soils, where soil organic matter losses may persist for decades following deforestation and pasture‐to‐cropland conversion, implementation of alley cropping could offset C losses.