Fate of urine nitrogen on mineral and peat soils in New Zealand

A field lysimeter experiment was conducted over 150 days to examine the fate of synthetic urinary nitrogen (N) applied to peat and mineral soils, with and without a water table. At the start of the winter season, synthetic urine labelled with ¹⁵N, was applied at 500 kg N ha^–1. Plant uptake, leaching losses and nitrous oxide (N₂O) fluxes were monitored. Total plant uptake ranged from 11% to 35% of the urine-N applied depending on soil type and treatment. Plant uptake of applied N was greater in the presence of a water table in the mineral soil. Nitrate-N (NO₃ ^--N) was only detected in leachates from the mineral soil, at concentrations up to 146 g NO₃ ^--N mL^–1. Presence of a water table in the mineral soil reduced leaching losses (as inorganic-N) from 47% to 6%, incrased plant uptake and doubled apparent denitrification losses. In the peat soils leaching losses of applied urine-N as inorganic-N were low (<5%). Losses of N as N₂O were greater in the mineral soil than in the peat soils, with losses of 3% and <1% of N applied respectively after 100 days. Apparent denitrification losses far exceeded N₂O losses and it is postulated that the difference could be due to dinitrogen (N₂) loss and soil entrapment of N₂.