The increase of soil organic carbon as proposed by the 4/1000 initiative is strongly limited by the status of soil development - A case study along a substrate age gradient in Central Europe

During COP 21 in Paris 2015, several states and organizations agreed on the 4/1000 initiative for food security and climate. This initiative aims to increase world's soil organic carbon (SOC) stocks by 4% annually. The influence of soil development status on SOC dynamics is very important but usually not considered in studies. We analyse SOC accumulation under forest, grassland and cropping systems along a soil age gradient (10-17,000 years) to show the influence of soil development status on SOC increase. SOC stocks (0-40 cm) and accumulation rates along a chronosequence in alluvial soils of the Danube River in the Marchfeld (eastern Austria) were analysed. The analysed Fluvisols and Chernozems have been used as forest, grassland and cropland for decades or hundreds of years. The results showed that there is a fast build-up of OC stocks (0-40 cm) in young soils with accumulation of similar to 1.3 t ha(-1)a(-1) OC in the first 100 years and similar to 0.5 t ha(-1) a(-1) OC between 100 and 350 years almost independent of land use. Chernozems with a sediment deposition age older than 5.000 years have an accumulation rate < 0.01 t OC ha(-1) a(-1) (0-40 cm). Radiocarbon dating showed that the topsoil (0-10 cm) consists mainly of >modem and modern carbon indicating a fast carbon cycling. Carbon in subsoil is less exposed to decomposition and OC can be stored at long-time scales in the subsoil (C-14 age of 3670 +/- 35 BP). In view of the '4/1000' initiative, soils with constant carbon input (forest & grassland) fulfil the intended 4%0 growth rate of SOC stocks only in the first 60 years of soil development. We proclaim that under the present climate in Central Europe, the increase of SOC stocks in soil is strongly affected by the state of soil development. (C) 2018 Elsevier B.V. All rights reserved.