Fate of 15N labelled urine on four soil types

A field lysimeter experiment was conducted over a 406 day period to determine the effect of different soil types on the fate of synthetic urinary nitrogen (N). Soil types included a sandy loam, silty loam, clay and peat. Synthetic urine was applied at 1000 kg N ha(-1), during a winter season, to intact soil cores in lysimeters. Leaching losses, nitrous oxide (N2O) emissions, and plant uptake of N were monitored, with soil N-15 content determined upon destructive sampling of the lysimeters. Plant uptake of urine-N ranged from 21.6 to 31.4%. Soil type influenced timing and form of inorganic-N leaching. Macropore flow occurred in the structured silt and clay soils resulting in the leaching of urea. Ammonium (NH4+-N), nitrite (NO2--N) and nitrate (NO3--N) all occurred in the leachates with maximum concentrations, varying with soil, type and ranging from 2.3-31.4 mu g NH4+-N mL(-1), 2.4-35.6 mu g NO2--N mL(-1), and 62-102 mu g NO3--N mL(-1), respectively. Leachates from the peat and clay soils contained high concentrations of NO2--N. Gaseous losses of N2O were low (<2% of N applied) over a 112 day measurement period. An associated experiment showed the ratio of N-2-N:N2O-N ranged from 6.2 to 33.2. Unrecovered N-15 was presumed to have been lost predominantly as gaseous N-2. It is postulated that the high levels of NO2--N could have contributed to chemodenitrification mechanisms in the peat soil.