Biogeosciences (Dec 2012)
The effect of cattle slurry in combination with nitrate and the nitrification inhibitor dicyandiamide on in situ nitrous oxide and dinitrogen emissions
Abstract
A field study was conducted to determine the effect of the nitrification inhibitor dicyandiamide (DCD) on N<sub>2</sub>O and N<sub>2</sub> emissions after cattle slurry (CS) application in the presence of nitrate (NO<sub>3</sub>) fertiliser on seven different occasions (between March 2009 and March 2011). N<sub>2</sub>O emissions from CS in the presence of NO<sub>3</sub> fertiliser were very high (0.4–8.7% of applied N) over a 20-day period, under mild moist conditions. Emissions were significantly larger from the CS treatment compared to an NH<sub>4</sub><sup>+</sup>-N source, supplying the same rate of N as in the slurry. This study supports the view that organic fertilisers should not be applied at the same time as nitrate-based fertilisers, as significant increases in N<sub>2</sub>O emissions occur. The average N<sub>2</sub>O mole fraction (N<sub>2</sub>O/(N<sub>2</sub>O + N<sub>2</sub>)) over all seven application dates was 0.34 for CSNO<sub>3</sub> compared to 0.24 for the NH<sub>4</sub>ClNO<sub>3</sub> treatment, indicating the dominance of N<sub>2</sub> emissions. The rate of nitrification in CSNO<sub>3</sub> was slower than in NH<sub>4</sub>ClNO<sub>3</sub>, and DCD was found to be an effective nitrification inhibitor in both treatments. However, as N<sub>2</sub>O emissions were found to be predominantly associated with the NO<sub>3</sub> pool, the effect of DCD in lowering N<sub>2</sub>O emissions is limited in the presence of a NO<sub>3</sub> fertiliser. To obtain the maximum cost-benefit of DCD in lowering N<sub>2</sub>O emissions, under mild moist conditions, it should not be applied to a nitrate containing fertiliser (e.g. ammonium nitrate or calcium ammonium nitrate), and therefore the application of DCD should be restricted to ammonium-based organic or synthetic fertilisers.