Simulation of biomass, carbon and nitrogen accumulation in grass to link with a soil nitrogen dynamics model

In order to represent nitrogen and carbon cycling in the soil-plant-atmosph ere continuum, a previously developed weather-driven grass growth model has been adapted to become the crop growth component of the soil nitrogen dyna mics model SOILN. This provides a means of simulating nitrogen uptake by th e grass crop, an important component of the overall nitrogen balance in gra ssland. Grass growth is represented by a photosynthesis equation adjusted to take a ccount of respiration as well as constraints due to lack of water and nitro gen in the soil. Water shortage is represented by linked simulations with t he soil water and heat model sort, and nitrogen shortage by links with the SOILN model. Accumulated biomass and the nitrogen component of biomass are allocated to leaf, stem and root pools, and flows from live biomass pools t o those representing above- and below-ground senescent material are also re presented. The model is tested by comparing simulated cut grass yields and nitrogen contents of cut material with measured data at a test site. Soil n itrogen processes in the model are tested by comparing simulated and measur ed nitrate in drainflows. Agreement is reasonable, indicating that the comb ined model gives a realistic representation of carbon and nitrogen processe s in grassland. The use of the combined model in a predictive manner has been demonstrated in a comparison of nitrogen balances with a number of alternative slurry an d mineral nitrogen fertilizer application scenarios.