Combined Application of Lime and a Nitrification Inhibitor (3,4-Dimethylpyrazole Phosphate) Markedly Decreased Nitrous Oxide Emissions from an Acid Soil

High nitrous oxide (N2O) emissions (2-10% of fertiliser N) were observed previously from acid soils cropped with sugarcane (Saccharum officinarum) in Australia. We assessed the impact of lime, a nitrification inhibitor (NI, as 3,4-dimethylpyrazole phosphate, DMPP), and copper (Cu) on N2O emissions from an acid sugarcane soil in a laboratory experiment using (1) urea (U), (2) U + DMPP, (3) U + CuSO4 center dot 5H(2)O (U + Cu), and (4) U + DMPP + Cu. The treatments were applied to both an un-limed soil (pH 5.1) and a limed soil (pH 6.9) and incubated at 25 degrees C and 55% water holding capacity (WHC) for 28 d, and then increased to 90% WHC for another 8 d to favour denitrification. At 55% WHC, both the addition of the NI (U + DMPP) and the liming of the acid soil significantly decreased cumulative N2O emissions, due to significantly lower net nitrifications. Liming and DMPP decreased N2O emissions by 79% and 90%, respectively. However, where lime and DMPP were applied together, N2O emissions decreased by 94% compared to those in the un-limed (acid) U-treated soil. In contrast, the addition of Cu and the increase in water content to 90% WHC had no significant effect on N2O emissions. Therefore, the combined use of lime and DMPP provides the best option to decrease N2O emissions from the acid soil.