Comparison of dicyandiamide and biochar for reducing nitrate leaching under winter forage grazing in Canterbury, New Zealand

Abstract

The presence of nitrate (NO3-) in a water body can contribute to surface water eutrophication and can be harmful to the health of humans. The objective of this study was to determine suitable mitigation options for reducing NO3- leaching losses under dairy winter forage grazing conditions using dicyandiamide (DCD) and biochar in Canterbury, New Zealand. Total NO3--N leaching losses from urine-treated soil was decreased by 38% from 379 kg NO3--N ha-1 to 237 kg NO3--N ha-1 with the addition of DCD. The addition of DCD in combination with biochar to urine-treated soil reduced the total amount of NO3--N leached by 46% to 203 kg NO3--N ha-1. However, the application of biochar to urine-treated soil did not significantly affect the total amount of NO3--N leached. In addition, the urine + DCD and urine + DCD + biochar treatments significantly reduced both the soil NO3--N concentration and ammonia oxidising bacteria (AOB) amoA gene abundance. However, the urine + biochar treatment had no effect on the abundance of AOB. The nitrification inhibitor DCD was found to be an effective mitigation tool for reducing soil nitrification rate and thus NO3- leaching losses. However, biochar was not effective in reducing NO3- leaching losses at the application rate used in this study.