The effectiveness of the nitrification inhibitor DCD
The on-going intensification of New Zealand agriculture has led to a demand for technologies that can minimise nitrogen (N) losses from pastoral land to air and water.
Nitrogen can be lost from soil as the gas nitrous oxide (N2O), which is a potent greenhouse gas that has a warming potential about 300 times greater than carbon dioxide (CO2). It can also be lost in drainage in the form of nitrate, which can potentially contaminant groundwater aquifers or encourage the growth of nuisance weeds and algae in streams and lakes when concentrations are high enough.
One set of technologies developed to conserve soil N or increase the efficiency of N supply to plants is the application to soils of nitrification inhibitors such as dicyandiamide (DCD). These chemicals slow or “inhibit” the conversion of N from the relatively immobile ammonium (NH4) form to the mobile nitrate (NO3) form (see image).
Between 2009 and 2012, a research collaboration between Cecile de Klein (AgResearch Invermay), Stewart Ledgard (AgResearch Ruakura) and researchers from Lincoln University and Landcare Research, has quantified the effectiveness of DCD under grazing conditions at a number of contrasting experimental sites in the North and South Islands. This research has shown that DCD can reduce N2O emissions from urine patches by about 50% on average. Reductions in nitrate leaching losses varied across the sites, with leaching losses from urine patches reduced by c. 25-70% depending on soil type and time of application. DCD reduced leaching losses from grazed pasture by up to <5 to 20%. The effectiveness of DCD for increasing annual DM production from grazed pastures also varied considerably depending on soil, climate and management factors; from 0 to 10%.