JULIA DUX1, LINDSEY NORGROVE2, BARBARA WICK3, RONALD F. KÜHNE4
1Institute of Vegetable and Ornamental Crops, Germany
2University of Hohenheim, Biodiversity and Land Rehabilitation in the Tropics and Subtropics,
3Humboldt-University Berlin, Division of Soil Science and Site Science, Germany
4Georg-August-Universität Göttingen, Institute for Plant and Animal Production in the Tropics, Germany
We studied the impact of leaf residue decomposition and nutrient release of two weed / fallow species - Imperata cylindrica and Chromolaena odorata -- and one pioneer tree -- Phyllanthus discoideus - on enzyme activity and nutrient turnover in soils in the humid tropical lowlands of southern Cameroon in a pot experiment. We tested (i) the impact of litter types on decomposition rate, nutrient release and enzyme activities in soil, and (ii) whether soils from different vegetation and land uses differed in their ability to support decomposition under controlled conditions. We measured mass loss, nutrient release of N and P from decomposing residues, and soil enzymes of the C cycle (ß-glucosidase), N cycle (protease) and P cycle (acid and alkaline phosphatase) over 120 days.
Faster decomposition of Phyllanthus and Chromolaena residues and greater release of nutrients of N and P from decomposing leaves compared to imperata residues concurred with differences in residue quality. After 120 days, Chromolaena and Phyllanthus residue had released nearly three times as much of its initial pools of N and P than had Imperata residue. However, rapid recycling of N and P from Imperata residues in the early stages of decomposition increases the risk of nutrients being lost from the topsoil without contributing to SOM build-up in the long-term.
Most of the variation in ß-glucosidase activity was associated with differences among residue types. Decomposition and mass loss from the plant residue triggered C mineralisation in soils and were matched by equivalent increases in ß-glucosidase activity. By contrast, litter type had no impact on activities of alkaline phosphatase and protease. The role of N and P supply in regulating activity of enzymes that mineralise N and P differed for both nutrients. Protease was more responsive to variations in N supply than were P mineralising enzymes to P supply. Increases in residue nutrient fluxes of P associated with residue decomposition were not related to acid and alkaline phosphatase activity but was positively related to protease activity.
Keywords: Resiude decomposition, soil enzyme activity, weed infestation
Full paper: http://www.tropentag.de/2006/abstracts/full/351.pdf