Alley-cropping and soil-dwelling fauna promote litter decomposition in temperate agroecosystems

Temperate alley-cropping is anticipated to enhance soil fertility and carbon sequestration on croplands, with litter decomposition forming a major pathway for organic matter accumulation. Despite this, alley-cropping’s impacts on litter decomposition, and particularly soil faunal contributions to litter decomposition, remain poorly understood. This study evaluated how alley-cropping, soil-dwelling fauna, and their interactions influence Phleum pratense decomposition across five arable farms in England, United Kingdom. P. pratense decomposition over 16 weeks was compared between litter bags, with and without holes permitting access to soil meso- and macro-fauna, buried in paired alley-cropping and sole-cropping systems at three locations: in tree rows, the tree row-crop alley interface, and crop alley centres. Alley-cropping significantly altered litter decomposition rates, but not those of soil dwelling fauna. Litter decomposition was 4.8 % (± 1.5) higher in alley-cropping thansole-cropping systems (p = 0.002). The effect varied with proximity to tree rows: relative to sole-cropping, the increase was 7.2 % (± 1.8; p = 0.001) in tree rows, 5.3 % at the edge of crop alleys (± 1.8; p = 0.010), and non-significant in crop alley centres. Soil-dwelling fauna increased litter decomposition by 4.8 % (± 1.0) (p < 0.001), but faunal-mediated decomposition was unaffected by alley-cropping. Alley-cropping enhanced microorganism-mediated litter decomposition on arable farmland, both in tree rows and at crop alley edges. Incorporation of litter-derived carbon and nutrients into soil organic matter could increase carbon sequestration and fertility. However, alley-cropping’s impacts are context-dependent, with more research needed to understand under what circumstances alley-cropping enhances litter decomposition.