Earthworms promote the transfer of 15N-urea to lettuce while limit appreciably increase 15N losing to environment

Earthworm activities not only increase nitrogen (N) uptake by crops, but also lead to N losing to environment. Thus, the present study examined the transformation of 15N-labeled urea with and without earthworms (Metaphire guillelmi) in a soil-lettuce system. We evaluated lettuce 15N uptake, 15N losses including N2O emission, NH3 volatilization and leaching, as well as 15N remaining in soil. Results showed that 15N-urea uptakes by lettuce significantly increased from 33.07% to 42.72% with earthworm presence. However, little difference was found on the total amounts of leaching and gaseous losses (N2O emission and NH3 volatilization) from 15N-urea between the treatment with and without earthworms (4.04 and 5.38%, respectively). Most of the 15N-urea remained in the soil, accounting for 48.44% and 60.65% of the 15N-urea in soil with and without earthworm presence. We conclude that earthworms enhanced the transfer of 15N-urea to lettuce without appreciably increasing the 15N-urea loss from soil to the environment.