Effluent management and operation


3 min read

Good irrigation decisions Effluent spreading Effluent spreading calculator Sludges and separated solids Irrigation application systems

Good effluent management on your dairy farm combines a well-designed system with proper processes to ensure the right amount of effluent gets applied to pasture at the right time. This not only saves on fertiliser costs and enhances soil health but also helps prevent animal health problems and ensures compliance with local rules. Understanding soil water deficit is crucial to prevent run-off and applying effluent to saturated soils. There are tools available, such as the DairyNZ Farm Dairy Effluent Spreading Calculator, to help manage the application of effluent nutrients with precision. Finally, regular maintenance of your irrigation application equipment is vital for optimal performance.

Good effluent management is a combination of having a well-designed effluent system and processes for people that make sure the effluent the system collects is applied to pasture in the right amount at the right time.

On-farm benefits of good effluent management include:

  • Fertiliser savings
  • Improved soil condition
  • Prevention of animal-health issues
  • Compliance with council rules or resource consent.

Making good effluent irrigation decisions

The key to good decision making is understanding the soil water deficit. It is essential to prevent ponding and run-off and to avoid applying effluent to saturated soils.

Soil water deficit is the amount of water (ie effluent) which can be applied to the soil before it reaches field capacity (which refers to the amount of water held in the soil after excess water has drained away). If effluent is added at field capacity it will likely result in ponding, runoff or leaching.

Effluent spreading

New Zealand’s dairy farm systems produce large quantities of nutrient-rich effluent which are captured from milking sheds, holding yards, feed pads, standoff pads, and animal shelters. The average dairy cow produces about $25 worth of nutrients annually as farm dairy effluent (FDE). For a 400 cow dairy herd this represents about $10,000 of nutrients annually. Using effluent to supplement fertiliser presents an opportunity to capitalise on a cost-effective nutrient resource while improving whole farm nutrient use efficiency.

Effluent is commonly grouped into three broad categories based on dry matter (DM) content: liquids (0–5%), slurries (5–15%) and solids (>15%).

Application of effluents is typically via land.

  • Effluent Application to pasture

    To get good value out of effluent and reduce environmental risk consider:

    • Timing of application – The best way to ensure that plants can take up nutrients from effluent is to only spread it when there is sufficient soil moisture deficit / capacity available in the soil. If the soil is too wet there will be leaching or run off.
    • Rate of application/depth of application – Good practice involves ensuring the effluent is applied at a rate that can infiltrate the soil and not pond or run off, drainage beyond the plant roots is avoided and it is spread evenly.
    • Where possible, leave a buffer strip next to waterways and farm boundaries and know your consent conditions and/or regional rules
  • Effluent Application to crops

    When using effluent as a nutrient source to grow high value forage and arable crops (e.g. maize, fodder beet, brassicas, cereals) see Using dairy effluent to grow crops – an update for industry, farmers and consultants. The guide summarises key aspects relating to the use of effluents to grow crops, including effluent nutrient composition, nutrient supply, chemical characterisation and application considerations.

Effluent spreading calculator

The DairyNZ Farm Dairy Effluent Spreading Calculator (app or Excel spreadsheet) allows farmers to easily calculate nutrient loadings and application rates for dairy effluent based on a number of customisable inputs. This means that farmers can manage the application of their effluent nutrients with greater precision.

There are two calculators in this app, the Quick Calculator which is for spray irrigation systems such as travelling irrigators and sprinklers, and an Advanced Calculator which is for slurry tankers and muck spreaders. It is also available as an excel spreadsheet if you prefer to use your computer.

Download this handy app to take the guesswork out of determining your effluent nutrient loadings

Spreading sludges and separated solids

Spreading effluent solids requires specialist machinery which is suited to the type of effluent being spread. For information about effluent solids spreading methods, considerations and equipment see:

Irrigation application systems

Keeping on top of maintenance tasks for irrigation application equipment is essential for good performance and many farmers like to keep a regular check on their application depths and rates.

The guides below will take farm staff through the important parts of operating and maintaining irrigation systems. They include tips, trouble-shooting advice, and an explanation of how to measure application depth and rates.

If using a centre pivot see our Guide to Good irrigation Part 1 - Irrigation practices on Farm.

Last updated: Sep 2023

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