Evaluating Changes in Soil Organic Matter with Climate Using CENTURY in England and Wales.

Soil organic C (SOC) dynamics are complex, and models have been developed for predicting future changes, validated using only individual site data. In this study, we used the CENTURY model to predict changes in SOC between 1978 and 2000 using input weather data for 1978 to 2000 from the UK Meteorological Office and soil property input data derived from the National Soil Inventory (NSI). The predicted changes in SOC from the model simulation were validated using the resampled NSI data for the period 1994 to 2000. The modeling results indicate that CENTURY gave unacceptable predictions of change for three specific soil types. When these were omitted from the accuracy assessment, model predictions were statistically acceptable for all ecosystem types with model efficiency (ME) decreasing in the order: seminatural grassland (ME = 0.63) > woodland (ME = 0.27) > arable (ME = 0.08) > managed grassland (ME = 0.02). When comparing the overall measured rates of change, CENTURY correctly predicted the direction but underpredicted the magnitude of change. Once this utility was established, CENTURY was used to predict nation-level climate change-induced changes in SOC with the UKCIP02 (UK Climate Impacts Program of 2002) scenarios for the 2020s, 2050s, and 2080s, each of which comprise four emissions scenarios. The modeling predictions suggest that the predicted changes between scenarios were small. However, within that, the greatest decrease (of 1.54% SOC) will be in seminatural grassland under the high emissions scenario. The future predicted pattern of change in SOC is greater in managed grassland (reduction of 0.27-0.39% SOC) than arable land (reduction of 0.03-0.05% SOC).