Mixing dicyandiamide (DCD) with supplementary feeds for cattle: an effective method to deliver a nitrification inhibitor in urine patches

Nitrate (NO3−) leaching and nitrous oxide (N2O) emission from urine patches in grazed pastures are key sources of water and air pollution, respectively. Numerous studies have demonstrated that broadcast application of the nitrification inhibitor dicyandiamide (DCD) can abate such losses of reactive nitrogen (N). This research explored an alternative usage of DCD. It is the first field study that investigates the feeding of powdered DCD mixed with several typical cattle feeds as a practical and effective method to deliver a nitrification inhibitor to urine patches. DCD (in its dry powdered form) was manually mixed with three typical dairy cow feed types (barley concentrate, maize silage or grass silage) before being fed to the cattle in a Latin Square design experiment. DCD delivery to the small area covered by urine patches during grazing events was then measured as a DCD equivalent application rate (in kg DCD ha−1). The absence of a significant feed type effect (P > 0.1) on the urine patch DCD equivalent application rate suggests that the ingestion of any of the three supplementary feeds mixed with DCD should be similarly effective at delivering DCD to urine patches, despite the potential differences in aspects of feed digestibility and the impact on rumen pH and rate of DCD passage through the rumen. Importantly, there was a highly significant positive relationship (P ≤ 0.0001) between excreted DCD and N in urine and urine patches, which meant that the deposition rate of DCD matched the urinary N inputs in urine patches. Additionally, less total DCD was needed than is required with broadcast application. Added to the fact that DCD and urinary N are both deposited at the same time and intimately mixed in urine patches, feeding DCD to dairy cows after mixing with different feeds could represent a more effective and practical DCD application strategy than a DCD broadcast application at a single rate.