Decomposition and nutrient release from mango and miombo woodland litter in Zimbabwe

Litter inputs from trees are potentially important in agroforestry systems as sources of nutrients and organic matter. In the smallholder farming areas of Zimbabwe, litter from trees in natural woodlands (miombo) is applied to croplands as a soil amendment. Soils in smallholder areas are generally sandy and contain low amounts of C, N, P and S. Mango trees are planted widely on smallholder farms, but miombo litter is a preferred soil amendment to mango litter. Leaf litter from mango (Mangifera indica L.) and miombo woodland were assessed as soil amendments through decomposition and nutrient release studies in Zimbabwe. Mass loss was assessed in 7 mm mesh litter bags. Changes in lignin, cellulose, hemicellulose, polyphenols and nutrient release were also assessed. Miombo litter had higher initial concentrations of N, P, S, Mg and lignin, and lower polyphenol contents than mango litter. Mass loss was faster in miombo than mango litter, with miombo litter losing 72% of the initial mass over 18 months in comparison with a 55% mass loss for mango litter under the same conditions. Initial litter N, lignin content, and Lignin–N ratios were correlated strongly with mass loss. The rate of lignin loss was higher in miombo than in mango litter. Total polyphenols could not be detected in either litter type after 2 months. There was less N immobilization in miombo litter than in mango during the 18-month study. Net N mobilization in miombo litter accounted for 66% of the initial nitrogen. N immobilization and release correlated strongly with initial litter N, lignin content and Lignin–N. Miombo litter also released more P and S than mango litter over 18 months. More rapid nutrient release by miombo litter may be the reason for its being a preferred soil amendment to mango litter, but mango litter could be used to maintain or enhance soil C.