A set of simulations across Europe showing the Carbon sequestration potential associated to maximized roots

The amount of soil organic carbon (SOC) in soils is a balance of the carbon input from plants and organic amendments and the carbon output due to mineralisation. Root carbon inputs have been shown to contribute 3-5 times more to soil organic carbon than aboveground plant carbon. We examined the biomass data from ten wheat varieties that were sampled at nine sites across Europe and derived allocations functions to investigate the potential of wheat variety selection on soil organic carbon on a European scale. Five versions of the widely applied SOC model RothC were applied that differed in the decomposition rates for straw and root carbon inputs: the standard RothC version, two versions calibrated for root and straw input, and two versions that were derived in Task 6.1 and take into account the observed three times higher SOC efficiency with two different dynamics in the RothC model (elevated root 1. resistance to decomposition and 2. carbon use efficiency). Each of the ten varieties’ impact on SOC after 50 years was simulated applying their straw and root carbon input compared to the standard variety (defined as the ten-variety average) carbon input. Surprisingly, the maximum and minimum root varieties showed on average over all five RothC versions similar SOC changes and these changes were negative (-0.057 and -0.031 t SOC/ha). The maximum biomass variety performed best with a mean SOC gain of 0.383 t after 50 years and per hectare of European agricultural land (1.277 t SOC/ha in monoculture). The simulation results show that focussing on root biomass alone might result in increased root-derived SOC but might overall even lose soil organic carbon compared to the standard variety due to less above ground biomass carbon input to the soils.