Simulating trends in crop yield and soil carbon in a long-term experiment – effects of rising CO2, N deposition and improved cultivation

Summary

Measurements of crop yield and soil carbon in the Bad Lauchstädt long-term fertilizer experiment were analysed with the FASSET model. The model satisfactorily predicted yield and soil carbon development in four treatments with no fertilizer, mineral fertilizer, farm yard manure and farm yard manure plus mineral fertilizer, respectively.
An analysis of the difference between observed and simulated yield showed an increasing trend with years. This increase could be attributed to an increase in observed yields during the last six decades. Scenario analysis showed that the most probable explanation for this yield increase was new crop varieties and/or use of pesticides, while the increase in atmospheric CO2 and changes in local N deposition were of lesser importance. The rise in CO2 thus only explained between 9-37% of the yield increase.
The observed and simulated development in soil carbon was quite different in the four treatments. However, the changes within each treatment for different scenarios were much smaller than the substantial difference between treatments. Thus it was concluded that the fertilizer type was more important than the analysed anthropogenic factors for the development in soil carbon