The effect of N-serve in controlling nitrification in Australian soils was studied. In an Urrbrae soil that had previously grown pasture for 16 years, an N-serve concentration equal to 5.0 percent of the added fertilizer N was required to reduce nitrification. In a frequently cropped soil, a 0.2 percent concentration was equally effective in controlling nitrification as higher concentrations of the inhibitor. When the inhibitor was added to 16 different soils, it was shown that the extent of the reduction and longevity of the inhibitor depended on soil type. This was confirmed with N15studies.When N-serve was added with NH4+-N to two Urrbrae soils under simulated field conditions, the inhibition was greater in a wheat fallow soil than in a pasture soil.N-serve, when applied with fertilizer N to wheat on the Urrbrae soil, did not significantly increase grain yields.