Temporal variations in nitrous oxide fluxes from urine-affected grassland

Abstract

Fluxes of nitrous oxide (N 2O) from a permanent pasture were measured during a 1-y period using flux chambers. Intact soil cores from the same pasture were also treated with cow urine (19 g N m −2) in a laboratory incubation experiment. Diurnal variations in flux rates were determined using a mobile laboratory for continuous field measurements of N 2O fluxes at the field site. Nitrous oxide fluxes peaked after fertilizer (urea and NH 4NO 3) application, and winter fluxes were comparable to those measured during other parts of the year, with the annual N 2O flux estimated at 3.2 kg N ha −1 y −1 or 1.3% of the fertilizer-N applied. Nitrous oxide fluxes followed the same diurnal variation as soil temperature, with N 2O production peaking in late afternoon. Multiple linear regression analyses demonstrated weak relationships between N 2O flux, rainfall and soil temperature ( R 2 =0.28). There was an immediate increase in N 2O emission after urine application with rates reaching a peak of 89 mg N m −2 d −1 within 6 h, with an estimated 7% of the applied urine-N being lost as N 2O over 42 d. Results indicate that the large spatial and temporal variability in N 2O fluxes have to be assessed if accurate estimates of N 2O losses are to be derived for grazed grasslands.