Effects of trampling of a wet dairy pasture soil on soil porosity and on mitigation of nitrous oxide emissions by a nitrification inhibitor, dicyandiamide

Urine patches in dairy pastures are major sources of nitrous oxide (N2O). Wet winters result in compaction damage to pastures because of animal trampling. The nitrification inhibitor, dicyandiamide (DCD), is effective at reducing N2O emissions from urine patches. Here, we assessed the extent of damage to the physical quality of the soil by trampling and whether this influenced the ability of DCD to mitigate N2O emissions. A field experiment was conducted where a sandy loam soil was trampled by a mechanical hoof just before urine and DCD application. Trampling reduced air permeability and pore continuity, but this had no effect on bulk density. Urine appeared to have contributed to pore collapse and blockage. Trampling increased average cumulative N2O emissions from 1.74 to 4.66% of urine-N applied. This effect was attributed to increased water-filled pore space, aggregate destruction and suppression of grass growth. DCD was highly effective in reducing N2O emissions, with the N2O emission factor of the urine-N being decreased by 58–63%. Trampling did not significantly affect the effectiveness of DCD in reducing N2O emissions.