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Abstract

Long-term soil fertility depends on organic matter and nutrient return from decomposing biomass. In the case of orchards, as opposed to forests, little is known about wood decomposition rates and the effect of decomposing wood on soil quality. To learn more about wood decomposition and its effect on orchards, the ash-free dry matter loss of pruning wood mulch was quantified after 5, 10, 15, 20 weeks and one year in both the tree row and interrow of a cherry orchard in Northeast Germany. In addition, the influence of macrofauna on decomposition rates was obtained by using litter bags of different mesh sizes (2 and 5 mm). To assess possible impacts on chemical soil quality three treatments with normal, double and 10-fold pruning input rates were established. After five months of decomposition, the treatment effects on pH, soil organic carbon and total nitrogen content were compared. Physical soil quality for different pruning rates was assessed via Visual Soil Examination and Evaluation (VSEE). After one year of decomposition, 60% and 65% ash-free dry matter remained in the orchard's interrow and tree row, respectively. Compared with initial values, the increase in nitrogen led to a significant decrease of the wood C/N ratio from weeks 15 and 10 onwards in the interrow and tree row, respectively. The exclusion of macrofauna resulted in significantly less material loss as well as lower nitrogen content and higher C/N ratios in the remaining wood after 20 weeks of decomposition. After five months, soil chemistry was not affected by adding pruning mulch. Physical soil quality assessed by VSEE was best for the 10-fold pruning rate and better in the tree row than in the interrow. Compared with forests, the decomposition rates for pruning wood in this cherry orchard were relatively high, which can be attributed to habitat differences. Also, the methodology, in particular the litter bag mesh size, was shown to have a significant influence on the results. While physical soil quality changes due to high pruning rate application could be detected, chemical changes may only become apparent after longer exposure times.