Managing and Mitigating N Gas Emissions From Cattle Feedlots and Manure Stockpiles.

We report emissions of N gases from Australian cattle feedlots measured at 2 locations in a 3-year project to quantify emissions of direct and indirect greenhouse gases, using micrometeorological techniques.   The techniques were based on the backward Lagrangian stochastic (bLs) dispersion analysis using open- and closed-path gas concentration measurements.  Feedlot numbers varied between 13,000 and 20,000 cattle.  The NH3 emissions were equivalent to losses of 4,000 to 5,000 kg urea / day.  The average emission rates of N₂O, NH₃ and NO_x were 1.7, 162 and 2.1 g N / head / d.  Allowing for a 1% conversion to N₂O of the emitted and later deposited NH₃ and NO_x, these indirect greenhouse gases increased the overall emissions of N₂O from the feedlots by 75%.  In terms of CO2 equivalents, the combined N₂O emissions were equal to 60% of the methane emissions.  We are now extending the work to emissions from manure in the pens or in stockpiles using a novel mass balance approach.  In one approach, manure from the pens is spread in rings 2 m wide on the perimeter of a 20 m diameter circle.  Measurements of the N gases and wind speeds are made at 5 levels up to 4.8 m at the centres of the circles.  This allows calculation of the flux of the gas across the centre, which in turn is equated with the emission of the gas from the manure rings.  Experiments are run with paired rings, ca. 100 m apart .  One ring is an untreated control, while the other ring is constructed from manure that has been sprayed with a urease inhibitor either in the pen or after spreading around the circle.  The paper will provide further descriptions of the circular plot layout and instrumentation as well as preliminary results.