Simulation of dynamics in nitrogen mineralisation in the belowground food webs of two arable farming systems

Food web dynamics in a conventional (high-input) and an integrated (reduced-input) arable farming system were modelled to simulate the dynamics in N mineralisation during 1 year under winter wheat. The simulated N mineralisation rates were compared with the observed in situ N mineralisation rates. In the lower depth layers (10–25 cm) the simulated rates matched the observed rates better than in the upper depth layers (0–10 cm). Declines in N mineralisation were better matched than peaks in N mineralisation. The food web model simulated net N immobilisation in the conventional practice and net N mineralisation in the integrated practice for the period following harvest, which was combined with the addition of crop residues and tillage, and in the conventional practice also with soil fumigation. These simulated rates were in agreement with the observed rates. The results indicate that in the investigated arable soils, N mineralisation depended strongly on bacteria decomposing soil organic matter and microbivores, especially protozoans, releasing N from the bacterial biomass.