Organic carbon in soils of Central Asia—status quo and potentials for sequestration

Abstract

Expectations have been raised that carbon sequestration in soils could provide a short-term bridge to reduce the impacts of increasing carbon emissions until low-carbon technologies are available. To assess the role of Central Asia in this regard, the organic carbon in soils of Central Asia and losses in response to land use were quantified in a spatially explicit way. Based on literature information on soil organic carbon contents and in combination with the FAO-UNESCO Soil Map of the Word, the organic carbon stocks in the upper 30 cm of native soils of Central Asia were estimated to amount to 20,17 +/- 4,03 Pg. The extent of conversion of native land into agricultural land and the degradation of rangelands was assessed by a land use land cover change map of the region. This type of land use (change) was responsible for a reduction of the soil organic carbon by about 828 +/- 166 Tg C, or on average 4.1% of the total stocks. To this reduction, degradation of rangeland (observed on 4.9 Mha) with 50 Tg contributed only 6%. Most of the losses resulted from past conversion of rangelands into rainfed or irrigated agricultural land in the north of Kazakhstan. Hotspots of high soil organic matter depletion were former wetlands, drained for cultivation during the last decades. Assuming that improved agronomic and grazing management could be put in place and that therewith SOC levels in all of Central Asia's cropland and degraded rangeland could be brought back to native levels in the next 50 years, each year 16.6 Tg C could be sequestered. This is equal to the sizeable amount of 15.5% of the 2004 annual anthropogenic C-emissions of the five Central Asian countries (107 Tg C yr(-1)). However, Central Asia contributed only 1.4% of CO2 that is set free worldwide by fossil fuel burning. Therefore, the mitigation effect on rising atmospheric CO2 levels and climate change of such ambitious sequestration plans, if put into practice, would be hardly notable. The central Asian example shows that, unfortunately, the strategy of soil C sequestration as a stand-alone measure is not a viable bridge to a future in which alternative energy source can substitute fossil fuel burning, but can only be part of a set of mitigating measures.