Variables controlling denitrification from earthworm casts and soil in permanent pastures.

Denitrification (using the acetylene block method) was determined in earthworm casts and soils from permanent, drained or undrained pasture plots fertilized with 0 or 200 kg N ha year as ammonium nitrate. Rates of NO production from soil cores were about three times higher from the fertilized than from the unfertilized plots while drainage had a relatively small effect. Denitrification rates from casts were 3-5 times higher than those from soil irrespective of the drainage treatment. Casts generally had higher NO, NH, and moisture contents, and higher microbial respiration rates than soil. Rates of NO production were determined primarily by NOsupply, secondarily by moisture; available C did not appear to limit denitrification in these pastures. Estimates of the potential contribution of casts to denitrification ranges from 10.1% of 29.3 kg ha year from the unfertilized, drained plot to 22% of 82.5 kg ha year from the fertilized undrained plot. [ABSTRACT FROM AUTHOR]