Determination of litter derived C and N in litterbags and soil using stable isotopes prevents overestimation of litter decomposition in alley cropping systems

Abstract

Litter decomposition is an important ecosystem process mediated by soil organisms. It has been widely estimated by determining mass loss rates of plant residues applied in litterbags. However, catabolic degradation of litter by soil organisms is overestimated when the transfer of undecomposed or partly decomposed litter outside the litterbags is not considered. To account for these constraints, 13C and 15N recovery rates of 15N labeled maize leaf litter were analyzed in litterbags and in soil below litterbags in topsoils of four arable agroforestry alley cropping systems (ACS) and one grassland ACS in Germany after 28 weeks of incubation. Litterbags with 2 mm mesh size were buried in soils under trees and in intercropped alleyways at various distances from the trees. Recovery rates of litter derived C and N significantly differed between tree rows and alleyways in arable ACS. In the mean of three arable ACS, mass loss rates of litter applied in litterbags, corrected for litter C recovered in soil, was 78 and 67% under trees and arable crops, respectively. In the grassland ACS, litter C and N not recovered in litterbags and soil below the bags was more than 80%, revealing no differences between decomposition rates in tree rows and alleyways. In tree rows, the transfer of litter derived C to soil accounted for 10–15% of C mass loss in litterbags. We suggest that transfer rates of litter derived C to mineral soil have the potential to increase C sequestration.