Effects of dairy slurry application on carabid beetles in tall fescue, British Columbia, Canada

Carabid populations were assessed in relation to type and level of nutrient input in a multi-year trial on tall fescue, Festuca arundinacea. Thirteen species of carabids were recovered, Pterostichus melanarius representing 81% of all catches. In 3 m wide strip plots populations of P. melanarius increased with the rate of dairy slurry application, and the effect persisted for 2 years after applications ceased. The numerical response of P. melanarius to dairy slurry required several months, with other carabid species being largely unaffected by the treatments. Species diversity decreased with the number of years of dairy slurry application and with increasing application rates, and the effect persisted for 2 years. The decline in diversity was usually caused by changes in numbers of P. melanarius. Chemical fertilizer had no effect on carabid populations compared to controls. Earthworm biomass increased with increasing dairy slurry rate. The predatory capacity of the carabids increased with increasing dairy slurry rate, and the proportion of onion maggot pupae, Delia antiqua, consumed increased with P. melanarius numbers. The application of dairy slurry may therefore be used to improve pest control in forage grass.