At each farm the grassland with the highest organic matter content contained the largest number of earthworms (up to 858 worms m−2), (r = 0.286 (p = 0.036)). These grasslands also had the highest root biomass (r = 0.504 (p = 0.0001). With an increase in organic matter in the soil (from 5 to 10.2 % ), potential nitrogen mineralization increased from 138 to 310 kg N−1 ha 6 months−1. No relationships between the calculated amount of nitrogen mineralized by earthworms and the potential and actual nitrogen mineralization were found.
Nitrogen mineralization due to earthworm activities, calculated using production ecological formulas, ranged from 4 to 24 kg N ha−1 month−1.