Knowing the soil

Knowing the soil

Bala Tikkisetty

Knowing the soil has always been the basis of good farming because the soil is the foundation of the production system.

For modern dairy farmers a good understanding of their property’s soils has even more importance because the soil is also the basis of the effluent treatment system. Knowing the soil conditions and how they vary during the year can help to deliver very practical benefits including maximising utilisation of nutrients in dairy effluent and preventing contamination of ground water and waterways.

Soil properties such as texture and structure determine the amount of water and nutrients that can enter and be retained within a particular soil, and the rate at which excess water goes through that soil. Infiltration rates, water retention, drainage characteristics and consequent leaching losses of nutrients in effluent are strongly dependent on these properties, and they vary over time as a result of weather and farming activities

The risk of surface runoff will be significant if application is not matched to infiltration rates or if irrigating on to already saturated soils.

Treading damage during grazing, especially in wet conditions, can affect the effluent infiltration rate. So it is best to take extra care with winter grazing in your effluent area, and avoid irrigating a paddock that has been damaged until the soil recovers. If in doubt, dig a hole before irrigating and check whether the soil is loose and open or dense and compacted.

One factor to be wary of regarding runoff is that suspended solids in farm dairy effluent can accumulate on and just below the soil surface, creating an organic layer that temporarily acts as a surface coating. Although infiltration rates are then reduced to very low levels the effect is generally transient lasting about a couple of days. Using low application rate equipment will help to reduce this risk. Once again you can check this by digging a hole and having a close look at the soil condition.

Another issue is that relatively dry soil contains large pores open at the surface. When irrigating in these conditions, effluent can be rapidly transported below the root zone through a phenomenon known as “bypass flow”. This type of bypass flow can particularly occur in soils that undergo shrinkage and fissuring during drying, especially when these soils have been previously compacted by treading. High leaching losses of nutrients can result from this. That’s one reason why the Regional Council has rules limiting effluent application depths.

Farmers should therefore protect soils from grazing damage in wet conditions, especially in the effluent block, and check the soil condition by digging a few holes as the effluent irrigation season begins. Then you can schedule effluent irrigation to suit soil and climatic conditions.

To achieve this, storage facilities with enough capacity are needed. Minimise the risks of drainage and runoff by applying small depths of effluent. Irrigators with low application rates will help reduce these risks.

There are some important rules to follow on land application of farm dairy effluent:

Untreated effluent should not be discharged or allowed to run off into any drain, stream or river.
Effluent ponds, storage facilities, feed pads and stand-off pads must be sealed to prevent seepage.
Feed pads and stand-off pads must be at least 20 metres away from surface water.
Irrigation must not exceed a depth of 25 millimetres per application or result in more than 150 kilograms of nitrogen being applied per hectare per year. Effluent must not pond on the land surface, or create odour or nuisance outside a property’s boundary.

In my experience, farmers have been taking a real interest in understanding their soils more to help them manage effluent better. We all win if they’re successful at that.

Bala Tikkisetty is a sustainable agriculture advisor at Waikato Regional Council. For more information contact him on 0800 800 401.

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