Teagasc has produced a farmer’s practical guide to draining grassland in Ireland. Published this morning it is the latest research from the Moorepark Animal and Grassland Research and Innovation Centre into draining grasslands, which it says is key to increasing productivity.

According to the agency, Ireland’s competitive advantage in ruminant livestock production is based on low-cost grass-based systems. Teagasc outlined the main benefits it found of improved drainage to a grassland farmer:

  • An extended grazing season
  • Reduced surface damage by livestock
  • Improved trafficability/accessibility for machinery
  • Reduced reliance on supplementary feedstuffs
  • Reduced disease risk to livestock
  • Better availability of Nitrogen in soil
  • Increased yield and lower production costs

Among the highlights and recommendations include:

* No drainage work should be carried out before the drainage characteristics of the soil are established by a site and soil test pit investigation.

• Two types of drainage system exist: a ground water drainage system and a shallow drainage system. The design of the system depends entirely on the drainage characteristics of the soil.

• Distinguishing between the two types of drainage systems essentially comes down to whether or not a permeable layer is present (at a workable depth) that will allow the flow of water with relative ease. If such a layer is evident, a piped drain system at that depth is likely to be effective.If no such layer is found during soil test pit investigations, it will be necessary to improve the drainage capacity of the soil.This involves a disruption technique such as moling, gravel moling or subsoiling in tandem with collector drains.

• Drains are not effective unless they are placed in a free draining soil layer or complimentary measures (mole drainage, subsoiling) are used to improve soil drainage capacity.If water is not moving through the soil in one or other of these two ways,the water table will not be lowered.

• Outfall level must not dictate the drainage system depth. If a free draining layer is present, it must be utilised.

• Drainpipes should always be used for drains longer than 30m.If these get blocked it is a drainage stone and not a drainage pipe issue.

• Drainage stone should not be filled to the top of the field trench except for very limited conditions (the bottom of an obvious hollow).Otherwise it is an extremely expensive way of collecting little water.

• Most of the stone being used for land drainage today is too big. Clean aggregate in the 10–40 mm (0.4 to 1.5 inch approx) grading band should be used. Generally you get what you pay for.

• Subsoiling is not effective unless a shallow impermeable layer is being broken or field drains have been installed prior to the operation. Otherwise it will not have any long-term effect and may do more harm than good.

• Most land drainage systems are poorly maintained. Open drains should be clean and as deep as possible and field drains feeding into them should be regularly rodded or jetted.

The financial support for the research programme from state grants, Dairy Levy Research, European Research and Development Fund was acknowledged by Teagasc. Also the assistance of Tim Gleeson (formally Teagasc) with the heavy soils programme was also thanked.

A full copy of the report is available here.

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