SOC sequestration as affected by historic and present management

In 1978, after >70 years of continuous management of the long-term fertilization experiment in Bad Lauchstädt, a general change of soil management was implemented for several treatments. Experimental plots which had previously received a high input of organic matter (OM) now received only low OM input and vice versa. The resulting changes of SOC concentrations on different treatments vary from −0.1 to +0.1 g kg−1 yr−1. These trends were analyzed in order to explain the observed variations with the mean carbon input together with the quality of the different sources to build up new SOC. The results showed that this quality related carbon flux from fresh organic matter (FOM) into SOC, here defined as “carbon reproduction flux” (Crep), is a useful indicator to explain changes in SOC trends. Moreover, it can be used to predict the amount of FOM carbon input that is needed to achieve a given sequestration rate. The results revealed that carbon sequestration requires less effort on plots that had already higher carbon input rates in the past because the SOC storage, still far from the equilibrium state, had already a positive trend. Therefore, it is important to consider not only SOC stock but also the direction of the current trend when selecting measures that increase SOC to achieve the goal of the “4‰ Initiative: soils for food security and climate” which was launched during the COP21 conference.