FATE OF N-15 LABELED URINE ON 4 SOIL TYPES

A field lysimeter experiment was conducted over a 406 day period to de termine the effect of different soil types on the fate of synthetic ur inary 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 w inter season, to intact soil cores in lysimeters. Leaching losses, nit rous oxide (N2O) emissions, and plant uptake of N were monitored, with soil N-15 content determined upon destructive sampling of the lysimet ers. Plant uptake of urine-N ranged from 21.6 to 31.4%. Soil type infl uenced timing and form of inorganic-N leaching. Macropore flow occurre d in the structured silt and clay soils resulting in the leaching of u rea. Ammonium (NH4+-N), nitrite (NO2--N) and nitrate (NO3--N) all occu rred 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. Gaseo us losses of N2O were low (<2% of N applied) over a 112 day measuremen t period. An associated experiment showed the ratio of N-2-N:N2O-N ran ged 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 t he peat soil.