The effect of cattle slurry in combination with nitrate and the nitrification inhibitor dicyandiamide on in situ nitrous oxide and dinitrogen emissions
A field study was conducted to determine the effect of the nitrification inhibitor dicyandiamide (DCD) on N 2O and N 2 emissions after cattle slurry (CS) application in the presence of nitrate (NO 3) fertiliser on seven different occasions (between March 2009 and March 2011). N 2O emissions from CS in the presence of NO 3 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 4+-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 2O emissions occur. The average N 2O mole fraction (N 2O/(N 2O + N 2)) over all seven application dates was 0.34 for CSNO 3 compared to 0.24 for the NH 4ClNO 3 treatment, indicating the dominance of N 2 emissions. The rate of nitrification in CSNO 3 was slower than in NH 4ClNO 3, and DCD was found to be an effective nitrification inhibitor in both treatments. However, as N 2O emissions were found to be predominantly associated with the NO 3 pool, the effect of DCD in lowering N 2O emissions is limited in the presence of a NO 3 fertiliser. To obtain the maximum cost-benefit of DCD in lowering N 2O 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.