A novel concept to reduce nitrogen losses from grazed pastures by administering soil nitrogen process inhibitors to ruminant animals: A study with sheep

A cross-over sheep study examined the effects of infusion of nitrogen (N) process inhibitors into the gastrointestinal tract, on excretion in urine and subsequent N transformations in soil. The aim of the study was to test a novel approach to reduce N losses from urine-N which is recognised as the main source of N loss from grazed pastures. The study consisted of two experiments; in the first, the nitrification inhibitors dicyandiamide (DCD) or 4-methylpyrazole (4MP) were continuously infused into the abomasum, and in the second, DCD was continuously infused into the rumen. Administration of DCD or 4MP to the abomasum resulted in voided urine with a slowed rate of nitrification when added to soil compared to that for urine from untreated sheep. DCD analyses revealed that over 90% of abomasum-infused DCD was excreted in urine (99% after day 1) and markedly inhibited nitrification of urine-N in soil (>90% over 70 days; P < 0.001). Recovery of rumen-infused DCD in urine was lower at 86%, but nitrification of urine-N in soil was still markedly inhibited (>90% over 69 days; P < 0.001). Less than 2% of DCD was recovered in faeces after abomasum or rumen infusion. This study highlights the potential for using direct administration of N process inhibitors to grazing animals to reduce environmental N emissions from urine patches in pasture systems.