Impacts of Land-use Change on Organic Carbon Storage in Highly Weathered Soils of Tropical Sub-sahara Africa
Maximilian Kirsten1, Cordula Vogel1, Robert Mikutta2, Carsten Müller3, Didas Kimaro4, Karl-Heinz Feger1, Karsten Kalbitz1
1Technische Universität Dresden, Institute of Soil Science and Site Ecology, Germany
Land-use change of tropical forests for agricultural production is considered as a major cause for soil organic carbon (SOC) decline. However, the extent of land-use change impact on SOC storage is highly uncertain, especially for tropical Africa. Interactions with the soil mineral phase can modify such impacts because of high contents of pedogenic oxides and clay in these highly weathered soils and their potential for C stabilisation. The aim of the study was to determine land-use change impacts on SOC storage for soils commonly found in tropical sub-Sahara Africa. For that purpose ten pedological similar soils in the Eastern Usambara Mountains (Amani Nature Reserve, NE Tanzania) under contrasting land uses were sampled down to 100 cm soil depth. Measured SOC stocks were 17.5 kg m-2, 16.8 kg m-2, 16.9 kg m-2 and 20.0 kg m-2 for forests, tea plantations, croplands and home garden, respectively. A significant decrease in mean SOC storage of 1.3 kg m-2 was detected after changing forests into croplands for the 0-10 cm depth increment. No further significant land use
impacts could be detected. All soils have a clay dominated texture and are characterised by high contents in pedogenetic oxides. No significant relationships could be detected between SOC and clay contents for the investigated soils. Statistically significant relationships were found between oxalate extractable Fe/Al and SOC contents for cropland soils only, although forest soils comprised a wider range of oxalate extractable Fe concentrations. Probably, a higher variability of fresh OC input in forests may obscure the relation between SOC and pedogenetic oxides under forests.
Keywords: Land-use change, kaolinite, pedogenic Fe- and Al-oxides, SOC stabilisation, SOC storage, Tanzania
Contact Address: Maximilian Kirsten, Technische Universität Dresden, Institute of Soil Science and Site Ecology, Pienner Straße 19, 01737 Tharandt, Germany, e-mail: maximilian.kirstentu-dresden.de