Wednesday, November 15, 2006 - 10:30 AM

Nitrogen Losses from Urine Patches; the Effects of Soil Type and Application Time.

Christy van Beek1, Jan-Willem van Groenigen1, Eduard Hummelink1, Oene Oenema1, and Wim Corré2. (1) Alterra, PO Box 47, Wageningen, 6700 AA, Netherlands, (2) Plant Research International, PO Box 16, Wageningen, 6700 AA, Netherlands


Urine patches are a known ‘hot-spot' of N losses to the environment. Prior research has shown a seasonal trade-off of urinary-N between plant uptake in spring and leaching in fall, and therefore grazing regimes may be an important tool for farmers to prevent unwanted N losses. On  smaller time-scales, i.e. within seasons, dynamics of N loss pathways from urine patches are unclear. In this paper the results of two experiments are presented to unravel urinary N loss pathways applied at different moments. A lysimeter experiment with two sandy soils and a replicated field experiment to relate observations of the lysimeter experiment to the field-scale was performed. Urine containing 1.4669% (lysimeter) and 0.5280% (field) atomic excess 15N was applied in triplicate in September 2004, October 2004, November 2004, July 2005, September 2005, October 2005 and in November 2005. Measurements (N-difference and 15N) included N2O emission, NH3 volatilization, grass uptake, soil storage and leaching (only in lysimeters). In total more than 90% of the urinary-N was retrieved, of which 28-31% in grass uptake, 35-65% in soil storage, 18-32% in leaching, 1.5% in N2O emission and 0.2% in NH3 volatilization. Leaching and crop-uptake showed some significant effects, but we were unable to derive clear seasonal trade-off mechanisms. However, gaseous emissions were lowest for the November treatment and our results demonstrate the possibilities to direct the fate of urinary-N, e.g. minimizing N2O emission by prohibiting late-autumn grazing.