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 fertiliser experiment were analysed with the FASSET model. The model satisfactorily predicted yield and soil carbon development in four treatments with no fertiliser, mineral fertiliser, farm yard manure and farm yard manure plus mineral fertiliser, respectively. However, there was a residual between the observed and simulated yield, which was correlated with year. This 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 the use of new crop varieties and/or 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 developments in soil carbon were 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 type of nutrient applied was more important than the analysed anthropogenic factors for the development in soil carbon.