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

Abstract

In order to represent nitrogen and carbon cycling in the soil–plant–atmosphere continuum, a previously developed weather‐driven grass growth model has been adapted to become the crop growth component of the soil nitrogen dynamics model SOILN. This provides a means of simulating nitrogen uptake by the grass crop, an important component of the overall nitrogen balance in grassland.Grass growth is represented by a photosynthesis equation adjusted to take account of respiration as well as constraints due to lack of water and nitrogen in the soil. Water shortage is represented by linked simulations with the soil water and heat model SOIL, 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 to those representing above‐ and below‐ground senescent material are also represented. The model is tested by comparing simulated cut grass yields and nitrogen contents of cut material with measured data at a test site. Soil nitrogen processes in the model are tested by comparing simulated and measured nitrate in drainflows. Agreement is reasonable, indicating that the combined model gives a␣realistic representation of carbon and nitrogen processes 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 and mineral nitrogen fertilizer application scenarios.