Effluent Management in New Zealand: What to Do Right – and What Can Go Wrong with Soil Scientist Dr Gordon Rajendram
Effluent is not waste – it’s a nutrient-rich fertiliser source. When used properly, it can save money on synthetic fertiliser and support healthy soils. But when mismanaged, effluent can contaminate waterways, harm stock health and result in large fines. Here’s what farmers need to know.
The Right Way to Manage Effluent
Application Rate and Depth:
Apply effluent at no more than 25 mm per application, or 150 kg nitrogen/ha/year total from effluent. This ensures nutrients are absorbed by the root zone without runoff. Use a low application rate (5–10 mm per pass) for wet soils or sloping ground.
Timing:
Only irrigate when the soil moisture deficit is suitable – the ground must have space to absorb the liquid. Never apply to waterlogged, saturated, or frozen soils. Avoid wet winter periods when grass uptake is low.
Storage:
Effluent must be stored until conditions are right for application. Ensure ponds are sealed (1x10⁻⁹ m/s permeability or better), well-maintained, and sized to hold 90+ days of effluent – especially over wet months.
Setbacks and Compliance:
Maintain at least 20 m from waterways, bores, or drainage channels when spreading. Know your regional rules. Most require no direct discharge to water and written management plans.
Record Keeping:
Keep logs of application dates, depths, paddocks, and weather conditions. Calibrate equipment annually.
What Can Go Wrong – and the Cost
Case Study 1: Waimana, Bay of Plenty (2023)
Two farms were fined a total of $77,000 for discharging effluent into a stream. A travelling irrigator had operated too close to a drain in damp conditions, with no soil moisture checks or documented system. Result: obvious ponding and discoloured stream water.
Case Study 2: Waverley, Taranaki (2018)
A faulty oxidation pond led to raw effluent entering the Moumahaki Stream. The farmer was fined $54,000. In a separate incident, ponded effluent ran off land into a creek – a $45,000 fine followed. Poor maintenance and storage management were to blame.
Final Word
Effluent is an asset – if managed correctly. Use industry calculators (like DairyNZ’s Effluent Spreading and Storage Tools), regularly maintain systems, and apply with care. The environment, your pasture, and your wallet will thank you.
Want tailored advice for your farm?
Get in touch with Dr Gordon Rajendram today to ensure your effluent management is safe, compliant, and working for your soil. Visit www.gordonrajendramsoilscientist.co.nz or contact him directly for a personalised consultation.
Sources:
Waikato Regional Council – Effluent Management: waikatoregion.govt.nz
DairyNZ – Effluent Management and Operation: dairynz.co.nz
Environment Canterbury – Benefits of Good Effluent Management: ecan.govt.nz
Bay of Plenty Regional Council – A Guide to Managing Dairy Farm Effluent PDF
NZ Herald (2018) and SunLive (2023) – court reporting on effluent discharge prosecutions.
Contact Dr Gordon Rajendram
021 466 077 | rajendram@xtra.co.nz
www.gordonrajendramsoilscientist.co.nz
Contact MediaPA
027 458 7724
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