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Soil nitrogen cycling in lowland forests converted to oil palm and rubber plantations in Sumatra, Indonesia

Kara Allen1, Marife Corre1, Edzo Veldkamp1
1 Buesgen Institute, Soil Science of Tropical and Subtropical Ecosystems, Georg-August University of Goettingen, Buesgenweg 2, Goettingen 37077 Germany

O 2.10 in Environmental controls on fluxes and processes in ecosystems

17.07.2014, 12:20-12:40, H18

Tropical lowland forests are typically characterized by high nitrogen (N) pools with high N cycling rates, which allow these systems to accumulate and recycle large amounts of N. Over the last two decades, deforestation practices in Sumatra and Kalimantan, Indonesia have resulted in a 40% decrease in lowland forest coverage. In order to supply the ever-increasing demand for products such as palm oil and rubber, agricultural development will continue to replace areas of tropical lowland rainforest in Southeast Asia. Conversion of these forests can have profound effects on soil nutrient cycling. Land-use changes can lead to lower soil N cycling rates, which in turn can lead to changes in N losses from the system (e.g. nutrient leaching and emissions of climate relevant N-oxide gases). The aim of this study was to assess changes in soil N cycling rates with land-use change. The study region was Jambi Province in central Sumatra, Indonesia—an area that was once heavily forested, but has experienced high forest conversion. Two soil landscapes were selected to represent the region: sandy loam and clay Acrisol soils. In each soil landscape, four land-use systems were examined: lowland rainforest (as reference), rubber interspersed in naturally regenerating secondary forest (referred here as jungle rubber) and monoculture plantations of rubber (7-17 years old) and oil palm (9-16 years old). Net soil N cycling rates (i.e. net N mineralization and net nitrification) were measured using an in-situ buried bag method and gross rates of N cycling (i.e. N mineralization, nitrification, and microbial N assimilation) were measured using the 15N pool dilution technique on intact soil cores incubated in-situ. In both landscapes, net N cycling rates were higher in the forest than in the land-use systems, while gross N cycling rates varied across landscapes and land-uses. Ammonium (NH4+) cycling processes (gross N mineralization and NH4+ immobilization) tended to be higher in the clay Acrisol than in the sandy loam Acrisol. Nitrate (NO3-) pools and gross nitrification rates in both landscapes were lower in the jungle rubber and rubber plantations than in the forest and oil palm plantations. This could potentially correspond to studies indicating that rubber trees limit nitrification through the production of monoterpenes. In general, microbial N pools were higher in the clay Acrisol, and were lowest in the rubber and oil palm plantations in both landscapes. Turnover rates of microbial N pools were also slower in the oil palm plantations compared to the other land-use systems. This evidence suggests that conversion of rainforest to more intensively managed monoculture systems, such as oil palm plantations, could potentially reduce the cycling of N and slow down the turnover of N in the system, which may increase losses of externally added N. 



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last modified 2014-04-03