Reducing Nitrate Leaching

Between 2011 and 2016 small-scale farm trials were run across three dairy regions of New Zealand (Waikato, Canterbury, Otago) to compare the performance of typical regional farm systems with farm systems implementing a combination of mitigation options most suitable to the region. The trials ran for at least three consecutive years with detailed recording of milk production and input costs. Nitrate leaching per hectare of the milking platform (where lactating cows are kept) was estimated using either measurements (suction cups), models, or soil mineral nitrogen measurements. Post-trial, detailed farm information was used in the New Zealand greenhouse gas inventory methodology to calculate the emissions from all sources; dairy platform, dairy support land used for wintering. The results indicated that reducing inputs of nitrogen fertiliser and imported feed, with a corresponding reduction in stocking rate, contributed to lower nitrate leaching while also resulting in reduced greenhouse gas emissions. However, the implementation of a wintering barn yielded lower nitrate leaching without changes in greenhouse gas emissions due to enhanced manure management. Ultimately, these changes led to an average loss of profit of approximately NZ$100 per tonne CO₂-equivalent, highlighting the economic trade-offs involved.