Land application of farm dairy effluent for sustainable dairy farming

Abstract

Land application of farm dairy effluent (FDE) is preferred over pond treatment because of the potential reduction in environmental impacts, and recycling of valuable nutrients. Recent findings from the past 5 years of research by AgResearch and Dexcel are presented to provide an overview of the effects of applying FDE to pastures. Results indicate that significant pasture responses to applying FDE at increasing rates of N were found in both the mowing and grazing trials. There was no difference in pasture responses between FDE and urea when applied at the same rate of N. The ryegrass content of pastures increased with increasing N rates whether from effluent or urea. N and nitrate-N concentrations in the herbage showed some increases but were not excessive at rates up to 400 kgN/ha/yr. Pasture concentrations of other nutrients (except K) were unaffected by the rate or form of nitrogen applied. Both pasture K and soil K levels were significantly higher under the effluent treatments. Nitrate and calcium leaching increased significantly under the highest rate of N application (400 kgN/ha/yr). Spreading FDE over a sufficiently large area (15-20% of the farm) can reduce inputs of K to near maintenance requirements and restrict N inputs to about 80- 120 kg N/ha/yr, thereby avoiding potential animal health and environmental problems. A behavioural study showed that cows disliked grazing pastures recently treated with FDE. This study also showed that there was a significant and rapid decline in faecal coliform counts on pasture following effluent application. Keywords: faecal coliforms, farm dairy effluent, FDE, groundwater, nitrate leaching, pasture, soil