Decomposition of Apple ( Malus domestica ) Plant Residue and Uptake of Residue-Derived N

This study examined the decomposition dynamics of apple ( Malus domestica ) plant residue (senesced leaves and pruned branches) and the uptake of residue derived N (NDfR) in apple trees. Residue mass, nitrogen (N), and carbon (C) content were monitored over two growing seasons using a modified litter bag technique in orchard soils (Dermosol, 1.76% soil organic carbon) containing 15 N-labelled and non-labelled residues. Applying the same technique to potted apple trees, we quantified the uptake of NDfR from residue sources. Decrease of residue mass, C concentration, and 15 N atom percentage excess best fit an exponential decay model for leaf and branch residue, whilst N concentration increased exponentially. NDfR was greater and released faster from leaf than branch residue, yet total NDfR taken up by apple trees was not significantly different between leaf and branch residue. Total N of branch residue remained relatively unchanged from trial commencement, which suggested fixation of external N. Despite differences in decomposition dynamics, both residue types provide a similar amount of N for plant uptake in the short term (2 years). The contribution from residue N (approximately 1 kg N ha −1 ), although small relative to fertilizer inputs, should be considered for improving N use efficiency in tree crop growing systems.