Don't apply effluent to saturated soils

When the soil is saturated, the pores within it (gaps between soil particles) are filled with water.

Any effluent applied during these conditions is likely to pond and run off or leach through the soil or into tile drains, rather than being absorbed and taken up by the plants.

So, how do you know if the soil is saturated? A simple squelch test can tell you, according to Otago Regional Council.

• Step on the soil. If your boot mark fills with water, the soil is saturated.

• Check your council website to see if you have a monitoring site nearby.
  • A hand-held moisture meter is useful. However, you need to test it in the soil in a range of conditions (dry– wet) so you see what reading to use for saturation.

Ponding occurs when the effluent, solids, and liquids that are applied to land stay on the surface as a pond or puddle rather than being rapidly absorbed into the soil.

Ponding of effluent results in runoff and leaching into waterways and groundwater aquifers and is a prohibited activity in the Otago Water Plan.

What causes ponding?

• Too much effluent is applied to land, or it is applied too quickly for the soil to absorb it.

• Effluent being applied when the soil is saturated.

Once the soil is squelchy under foot or at saturation point, it’s too late to avoid ponding and runoff. Irrigate only when there is enough soil water deficit to absorb the applied effluent.

If ponding or runoff occurs when there is a soil water deficit, it means you are applying too much effluent or applying it too quickly.

Applying solids, sludge, muck and slurry to paddocks must be treated the same as liquid effluent.

The same goes for effluent being applied with irrigation water, no matter what the mix is.

Good practices include timing: Do not apply sludge, muck and slurry solids to soils that are at or near saturation. Apply it to land when the grass or crops are able to take it up quickly and use it when soil moisture levels are low, and soil temperatures are warmer. Keep the application well away (at least 50 metres) from waterways.

Apply it as thinly and as evenly as possible. Do not dump large piles of muck onto paddocks. This creates a concentrated patch of effluent, or ponding, which is prohibited.