Does alley-cropping benefit soil biodiversity and nutrient cycling functions in temperate agroecosystems?

Temperate alley-cropping is anticipated to enhance soil biodiversity, nutrient-use efficiency, and carbon sequestration on croplands. However, alley-cropping’s effects on soil biodiversity and organic matter vary among systems and the mechanistic underpinnings remain poorly understood, impeding effective design and management.

Here, alley-cropping’s impacts on two processes central to soil organic matter formation and stability were examined: litter decomposition and mineral-associated organic matter formation. As soil fauna are central to carbon and nutrient cycling, yet their contributions in alley-cropping systems are largely overlooked, this thesis also assessed how faunal biodiversity and faunal-mediated litter decomposition respond to alley-cropping.
Using field- and laboratory-based approaches, soil meso- and macro-faunal biodiversity, litter decomposition, and soil organic matter stabilisation were assessed in paired alley-cropping and sole-cropping systems at five arable farms in England, United Kingdom. Measurements taken in tree rows, crop alley edges, and crop alley centres tested whether tree-row effects extended into crop alleys.

Alley-cropping increased faunal abundance, order richness, and QBS-ar scores, and tree rows supported distinct communities with more epigeous, litter-dwelling, and disturbance-sensitive taxa. Litter decomposition was also higher in tree rows and crop alley edges relative to sole-cropping, but faunal-mediated decomposition was unaffected by alley-cropping. Greater decomposition potential did not translate into more organic matter formation. Tree-row soils accumulated less mineral-associated organic matter than those from arable production zones and experienced more litter-derived C and N losses. Soil biodiversity and functioning were also strongly influenced by soil type and agronomic management.

Findings from this thesis show that alley-cropping can enhance soil faunal biodiversity and stimulate litter decomposition, both in tree rows and adjacent crop alleys. However, increased decomposition in mature or mineral-saturated systems may promote litter-derived carbon and nitrogen losses rather than formation of stable organic matter, underscoring the importance of considering system and soil properties when evaluating the long-term benefits of alley-cropping.