This paper reports the results of experiments to determine whether ammonia (NH 3) loss can be reduced and nitrogen (N) use efficiency improved by using two relatively new commercial urea formulations rather than granular urea and urea ammonium nitrate. Four nitrogen treatments were applied at a rate of 40 kg N ha-1 : granular urea, "Green Urea 14™" [containing 45.8% nitrogen (N) as urea and "Agrotain®" (N-(n-butyl) thiophosphoric triamide) @ 5 L t-1 of urea as a urease inhibitor], "Nhance", a fine particle spray [containing 46% N as urea, "Agrotain" @ 1 L t-1 of urea and gibberellic acid (applied at a rate of 10 g ha-1)] and urea ammonium nitrate in solution (UAN) surface applied. Ammonia loss was determined in autumn and spring using a micrometeorological method. In autumn, use of the Green Urea and Nhance reduced NH 3 loss from the 30% of applied N lost from the granular urea to 9% and 23% respectively. Loss from all treatments in spring was very small (less than 2% of applied N), because 4 mm of rain fell within 24 hours of application onto an already wet site. The use of the Nhance and Green Urea instead of granular urea did not result in increased agronomic efficiency or recovery efficiency of the applied N, and this is most likely due to the presence of sufficient available N from both fertiliser application and the soil. A 15 N study recovered 72.8% of the applied N in the plants and soil, and showed that 30% of the total N taken up by the plant was derived from the fertiliser, and 70% from the soil.
The ability to accurately measure greenhouse gas (GHG) emissions is essential to gauge our ability to reduce these emissions. Enteric methane from ruminants is an important but often difficult source to quantify since it depends on the amount and type of feed intake. Unfortunately, many of the available measurement techniques for estimating enteric methane emissions can impose a change in feed intake. Our study evaluates a nonintrusive technique that uses a novel approach (point-source dispersion with multiple open-path concentrations) to calculate enteric methane emissions from grazing cattle, reported as the major source of GHG in many countries, particularly Australia. A scanner with a mounted open-path laser was used to measure methane concentration across five paths above a paddock containing 18 grazing cattle over 16 d. These data were used along with wind statistics in a dispersion model (WindTrax) to estimate an average herd methane emission rate over 10-mm intervals. Enteric methane emissions from the herd grazing a combination of Rhodes grass (Chlotis gayana Kunth) and Leucaena [Leucaena leucocephala (Lam.)] averaged (+/- SD) 141 (+/- 147) g animal(-1) d(-1). In a release-recovery experiment, the technique accounted for 77% of the released methane at a single point. Our study shows the technique generates more reliable methane emissions during daytime (unstable stratification).
Understanding spatial variability of emissions of nitrous oxide (N 2 O) is essential to understanding of N 2 O emissions from soils to the atmosphere and in the design of statistically valid measurement programs to determine plot, farm and regional emission rates. Two afternoon, 'snap-shot' experiments were conducted; one in the summer and one in the autumn of 2004, to examine the statistics and soil variables affecting the spatial variability of N 2 O emissions at paddock scale. Small, static chambers (mini-chambers) were placed at 100 locations over an 8,100 m 2 area of irrigated dairy pasture in northern Victoria, Australia. Chamber headspace was sampled for N 2 O and soil samples taken below each mini-chamber were analysed for soil nitrate (NO 3 -), ammonium (NH 4 + ) and other chemical and physical properties known to affect N 2 O emissions. The experiments took place immediately after the sequence of grazing, urea application and irrigation. Nitrous oxide emissions and soil variables were analysed using classical statistics to investigate the effect of soil variables on N 2 O emissions. Geostatistics were used to investigate spatial patterns of N 2 O emissions and soil variables over the measurement area. Nitrous oxide emissions were extremely variable; 45-765 ng N 2 O-N m −2 s −1 and 20-953 ng N 2 O-N m −2 s −1 for the two experiments with corresponding averages of 165 and 138 ng N 2 O-N m −2 s −1 . Nitrous oxide emissions showed spatial dependence up to 73 and 51 m for the two experiments. Nitrous oxide emissions showed significant correlation with soil nutrients in decreasing order of NO 3 -, NH 4 + and available-P concentrations. There was no significant correlation of N 2 O emissions with measured soil physical properties.
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