The effectiveness of different nitrification inhibitor formulations in limiting nitrate accumulation in a Southland pastoral soil

In pastoral dairy grazing systems, the high localised nitrogen (N) concentration in urine patches has been identified as a major source of nitrate nitrogen (NO3-N) available for leaching. Our study was initiated to investigate the effectiveness of different formulations of a nitrification inhibitor, dicyandiamide (DCD), in limiting NO3-N accumulation in a typical Southland pastoral soil. Various formulations of DCD (Super U, DCD-urea granules, DCD in zoelite granules and DCD in solution), both in the presence and absence of artificial urine, were applied to small plots in late October 2003. With the exception of Super U, all the DCD formulations evaluated were effective in limiting the nitrification of ammonium-nitrogen (NH4-N) to NO3-N in soil for in excess of 100 days. Thus, applying DCD in a granular form or in conjunction with granular fertiliser can be an effective way to limit NO3-N build-up in the soil profile. Total pasture production over the duration of the trial was increased by the DCD application in the N-fertilised treatments by between 8 and 21%, but no significant differences in pasture production were noted for treatments that included an application of artificial urine. The DCD application had the added benefit of limiting nitrate accumulation in the herbage to safe levels for ingestion by grazing animals, as well as a trend to increase herbage magnesium (Mg) and calcium (Ca) concentrations, so counteracting the possible detrimental effects of high potassium (K) concentrations where urine had been applied to a Southland pastoral soil.