Impacts of organic amendments on carbon stocks of an agricultural soil — Comparison of model-simulations to measurements

Organic amendments such as straw, green manure or farmyard manure are used to mitigate the soil carbon (C) losses from cultivated soils. We investigated the role of various organic amendments with different C quality for development of soil C stocks, by simulating the Ultuna long-term soil organic matter experiment in Sweden with the Yasso07 model. The aim was to evaluate the performance of the Yasso07 soil carbon model in predicting changes in soil C stocks by comparing modeled C stocks to measurements between years 1956–1991. Uncertainty bounds were calculated from the estimated uncertainty in the C inputs and model parameters. The model performance was assessed in terms of regression coefficient (R2), root mean square error (RMSE) and model efficiency (ME). The model could very accurately predict the decrease in soil C stock in bare fallow, and in treatments receiving crop litter inputs and N fertilization. Yasso07 could also predict the increase in C stocks due to different organic matter applications, based on the varying quantity and quality of these C inputs. These results support the use of the model for testing the long-term effects of different agricultural measures aiming to mitigate soil C losses.