Wednesday, July 6, 2022

Soil assessment important

A recent meeting of Waikato dairy farmers and technical experts highlighted the importance of getting the soil in effluent areas mapped. The meeting was held to discuss some of the issues associated with farming on peat – a challenge faced by hundreds of Waikato farmers. Soil assessment is particularly important for farmers who plan to install effluent ponds or tanks on shallow or very mineralised peat. Accurately knowing the risk status of the soils in your farm’s effluent area is important. It could save a lot of money in effluent storage pond construction or tank installation costs. A high-risk soil, which is what peat is classed as, will require roughly twice the size storage pond as low-risk soil.

If the risk status is described as “low” rather than “high”  in the dairy effluent storage calculator, the size of effluent pond/tank can be dramatically reduced if the water table is not an issue.

At what point, though, does a peat soil act more as a mineralised soil and can therefore be classed as “low risk”?

This was one of the questions discussed at the meeting, which was organised by Gordonton dairy farmer Ian Taylor and me. The technical discussion was led by AgResearch soil scientist Dr David Houlbrooke. There were also representatives from the Waikato Regional Council, Fonterra and DairyNZ.

The recommendation for farmers to get their soil assessed was made because a soil map, with a scale of 1:50,000 or greater, is not detailed enough. Added to that is that some soils classed as peat on the soil maps might not even be peat. Others might have a thin and mature or consolidated peat layer, which looks and acts more like a low-risk mineralised soil.

To consult a soil expert for independent soil mapping there are several avenues.

    • Landcare Research
    • Retired soil scientists (some are doing part-time consulting)
    • Soil science society
    • AgResearch.

Ian obtained a quote from a reputable soil scientist of about $500/farm, if the effluent areas of 10 farms were assessed at the same time.

Waikato farmers who want to know more or would like to have the soil in their effluent area assessed can contact Ian, who is co-ordinating the initial group to be assessed, at

DairyNZ’s Pocket guide to determining soil risk for dairy farm effluent application is a useful tool to help determine soil risk. For a copy phone the farmer information line on 0800 4 DAIRYNZ or visit

Phil Irvine is DairyNZ’s consulting officer for Hamilton North.

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