Crop Residue Returns and Equilibrium Soil Organic Carbon in England and Wales

Increased temperatures caused by climatic change may increase the turnover of soil organic matter (SOM) and hence reduce soil organic C (SOC). This effect may be exacerbated if crop yields decrease in consequence of policies that limit fertilizer-N applications to reduce N pollution from agriculture. Model simulations were made of changes in SOC over 140 yr under three fertilizer-N regimes to examine the effects of changes in fertilizer-N use on SOC in arable soils in England and Wales (E&W). The RothC model was used in preference to CENTURY as the input fertilizer-N could be changed in RothC and could not in CENTURY. Results indicate that decreasing annual fertilizer-N use to 50 or 100 kg ha-1 less than is currently applied to cereals in E&W will have a negligible impact on SOC in arable soils over the next 140 yr. Soils with >180 g kg-1 clay with 16 to 27 g kg-1 SOC at the beginning of the model runs, were predicted to have about 21 to 23 g kg-1 SOC after 140 yr, while soils with <180 g kg-1 clay and about 12 g kg-1 SOC would change little over 140 yr. Increases in temperature because of climate change were predicted to reduce SOC concentrations to about 18 to 20 and 11 g kg-1 respectively.