Earthworms, soil mineral nitrogen and forage production in grass-based hayfields

This study was designed to address how earthworm activity influences soil mineral nitrogen (N), plant N uptake and forage yield in grass-based hayfields. Earthworm populations were reduced by applying carbaryl pesticide to the experimental field plots every 2-weeks, effectively eliminating the earthworms for up to 12-weeks from May to August. Grass yields and tissue N concentrations were measured every 2 weeks, and the soil mineral N concentration determined at the final harvest. Reducing earthworm populations for up to 12-weeks did not affect grass yield or N uptake. However, regression analysis showed that plots with undisturbed earthworm populations had higher soil N by 0.8 kg N ha−1 per week, representing mineralization of about 10 kg N ha−1 during the 12-week study. This was a fraction of the fertilizer N recommendation (75 kg N ha−1) for grass-based hayfields in this region. Therefore, the increase in soil mineral N from earthworm activity was small, relative to the N requirements of the hayfield.