Impact of two centuries of intensive agriculture on soil carbon, nitrogen and phosphorus cycling in the UK

This paper describes a model that estimates carbon (C), nitrogen (N) and phosphorus (P) pools, pool changes, their balance and the nutrient fluxes exported from arable and grassland systems in the UK during 1800-2010 (at different periods: historical (1800-1950), transition (1950-70) and current (1970-2010)) using an agricultural model (Roth-CNP). The Roth-CNP model was developed as part of an Integrated Model (IM) to simulate C, N and P cycling for the whole of UK, comprising atmospheric, terrestrial, hydrological and hydro-chemical models. The model was calibrated and tested using long term experiment (LTE) data from Broadbalk (1843) and Park Grass (1856) at Rothamsted. We estimated C, N and P balance and their fluxes exported from arable and grassland systems in the UK on a 5 km x 5 km grid across the whole of UK taking into account arable and improved grass land management, crops (winter wheat, potato, oilseed rape, spring barley and fodder maize) and livestock numbers in each grid. Simulated crop and grass yields and estimated soil organic carbon (SOC) stocks and nutrient fluxes in the form of NH4-N, NO3-N and PO4-P varied spatially across the whole UK. The simulated trends of crop yields were compared to that reported by national agricultural statistics for the historical to the current period. Overall, arable lands in the UK have lost SOC by −0.18, −0.25 and −0.08 Mg C ha y−1 whereas under improved grassland SOC stock has increased by 0.20, 0.47 and 0.24 Mg C ha y−1 during 1800−1950, 1950−1970 and 1970−2010 simulated in this study. Annual mineral N and P balance is dominated by different components at different time periods under both arable and grass lands. Simulated N loss (by leaching, run off, soil erosion and denitrification) increased both under arable (−15, −18 and −53 kg N ha y−1) and grass (−18, −22 and −36 kg N ha y−1) during different time periods. Simulated P surplus increased from 2.6, 10.8 and 18.1 kg P ha y−1 under arable and 2.8, 11.3 and 3.6 kg P ha y−1 under grass lands 1800−1950, 1950−1970 and 1970−2010.