New option for dairy effluent disposal

Thursday 27 October 2005

Bay of Plenty farmers in low-lying areas may have a new option for disposing of dairy effluent in a way that minimises the effect on the environment.

A study by Massey University has shown that a system called deferred irrigation could work well at Pongakawa, near Te Puke.

Environment Bay of Plenty has encouraged farmers to spray dairy shed effluent over their paddocks for the past 15 years. This benefits pasture growth while keeping waterways safe from pollution. However, the method does not always work in areas such as Pongakawa because groundwater is so close to the surface. After heavy or prolonged rainfall, the effluent cannot soak down into the soil and will often wash overland into drains or streams.

Last year, Environment Bay of Plenty contracted Dr Dave Horn, a senior lecturer in soil science at Massey University, to investigate another option for dairy shed effluent disposal. With deferred irrigation, farmers hold effluent in storage ponds and do not spray until they know the soil conditions are right for it.

Dr Horn’s research has shown that deferred irrigation is a feasible option for Pongakawa, and probably many other parts of the region. Going by historic rainfall figures, he calculates that a Pongakawa farm carrying 550 cows would need an effluent storage capacity of about 1000 cubic metres.

However, successful deferred irrigation involves careful management, Dr Horn says. A farmer would need to make sure application rates do not exceed the soil’s infiltration capacity, he told Environment Bay of Plenty councillors at a recent regulation and monitoring committee meeting.
Environment Bay of Plenty is also looking at techniques for reducing the amount of water used in dairy sheds. This would result in smaller sizes needed for storage tanks.

Dr Horn has also presented the results of his research to Pongakawa farmers and other interested farmers.

ENDS

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