SIMULATION OF DYNAMICS IN NITROGEN MINERALIZATION IN THE BELOWGROUND FOOD WEBS OF 2 ARABLE FARMING SYSTEMS

Food web dynamics in a conventional (high-input) and an integrated (re duced-input) arable farming system were modelled to simulate the dynam ics in N mineralisation during 1 year under winter wheat. The simulate d N mineralisation rates were compared with the observed in situ N min eralisation 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 peak s in N mineralisation. The food web model simulated net N immobilisati on in the conventional practice and net N mineralisation in the integr ated practice for the period following harvest, which was combined wit h the addition of crop residues and tillage, and in the conventional p ractice also with soil fumigation. These simulated rates were in agree ment with the observed rates. The results indicate that in the investi gated arable soils, N mineralisation depended strongly on bacteria dec omposing soil organic matter and microbivores, especially protozoans, releasing N from the bacterial biomass.