Litter decomposition and nutrient release dynamics in two temperate agroforestry systems

Abstract

Temperate cropland agroforestry is gaining increasing attention for its ecological benefits. In these systems, crops are expected to benefit from tree nutrient inputs, mainly as leaf litter. To better understand the spatiotemporal dynamics of tree leaf litter decomposition and nutrient release in agroforestry systems, we conducted in situ litter bag incubations on the soil surface at two study sites in Germany. Each site comprised an alley-cropping agroforestry system and adjacent open cropland without trees, managed identically to crop rows of its corresponding agroforestry system. Sampling positions were established in tree rows and at 1 m, 7 m, and 24 m from trees into crop rows, and in open cropland. Our results showed similar mass loss patterns across sampling positions, but annual differences in litter decomposition and release of C and P. N was initially immobilized and subsequently released only after about 50% of litter mass was lost. By the end of incubation period, N release was positively associated with decomposition rates at all sites and years. Overall, our findings show that trees in our cropped alleys do not strongly influence litter decomposition and nutrient release. Therefore, reducing fertilizer quantities in response to tree leaf litter inputs may become easier to implement if spatial distributions of tree litter and crop demand are known. Furthermore, our findings on the temporal dynamics of nutrient release from leaf litter may help match temporal demands of crops to tree-derived nutrient inputs.