How Much NPK Is in Dairy Effluent? A Real Farm Example

See real NPK results from a dairy farm in Southland, New Zealand, and how nutrient testing helped put numbers around what was being returned to the paddock.

Real NPK results from a Southland dairy farm in New Zealand

Ben Johnson and Mackenzie Priest-Johnson farm near Riversdale, in New Zealand’s Southland region. Their dairy effluent is applied at around 36,000 to 38,000 litres per hectare, or roughly 4 mm. At that application rate, their nutrient test indicated they were applying approximately:

32 kg/ha of nitrogen
4 kg/ha of phosphorus
15 kg/ha of potassium

That gives a clear picture of the nutrient being applied each time they spread effluent.

Ben-Mackenzie-Follow-up-2026-Portrait-1x1 — How Much NPK Is in Dairy Effluent? A Real Farm Example 3

Ben-Mackenzie-Two-Seasons-On-Nevada-Effluent-Tanker-PTO-Stirrer-2026-1x1 — How Much NPK Is in Dairy Effluent? A Real Farm Example 4

Why testing matters

There isn’t one standard NPK figure that applies to every farm. Nutrient concentrations can vary, and so can the amount of effluent being applied per hectare. Testing your own effluent, alongside knowing your application rate, gives you farm-specific numbers to work with when making fertiliser decisions. For Ben and Mackenzie, those numbers helped put real value around what they were returning to the farm. They now complete three full-farm effluent rounds each year and, in one season, were able to cut two full rounds of synthetic nitrogen while producing 10,000 kg more milk solids. Their results won’t be the same for every farm, but they show why knowing the nutrient value of your own effluent can be worthwhile.

Watch Mackenzie and Ben Explain the Results

In this short video, Mackenzie and Ben talk through their full-farm effluent rounds and what the nutrient testing showed.

Want to know what’s in your effluent?

Test your own dairy effluent with the Nevada DIY Effluent Nutrient Testing Kit and put real numbers around its nutrient value. View the DIY Effluent Nutrient Testing Kit

Want to see the full Ben and Mackenzie story?

Read Cutting Synthetic Nitrogen with Dairy Effluent | Southland, New Zealand, or watch their follow-up On Farm video on YouTube.

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