Tips: Drainage is expensive business (best get it right)

The mean cost of the drainage systems installed to date as part of the Teagasc Heavy Soils programme has come in at €5,740/ha.

“It’s expensive business,” said Programme Coordinator James O’Loughlin.

“Investment on this scale must make sense from a farm business perspective.”

According to O’Loughlin if drainage work  can consistently increase grassland output there is a real return on investment.

O’Loughlin said Teagasc approaches drainage work  on the basis that 30% of the milk production in the country comes from farms with heavy soils or farms on which trafficking issues arise  at certain times of the year.

The Heavy Soils programme aims to improve the profitability of dairy farms on heavy soils through the adoption of key technologies including: high quality pasture management, land improvement strategies and efficient herd management.

The Heavy Soils Dairy Programme was created in partnership with Kerry Agribusiness, Dairygold Co-Op and Tipperary Co-Op and is a collaboration between Teagasc Research and Advisory personnel.

“There are wet patches in every county,” said to O’Loughlin.

Under the programme a total of nine grassland farms have been selected, based on soil type and location. A site-specific drainage system has been installed on a site (approx. 2 ha) in each of the participating farms.

Additionally, various soil fertility programmes, soil and pasture renovation techniques and grazing farm infrastructures are being evaluated.

In each of the participating farms, all inputs (fertilizer, concentrates, purchased forages, etc.) and outputs (grass, milk and meat production) are being monitored.

When it comes to drainage systems on farms the most important step is figure out the cause first.

“There is no one size fits all solution. There needs to be a targeted approach that’s often site specific. Often, one test hole in a 5ha field is often is not sufficient: two or three different approaches may be need to solve the drainage issues of any one field,” said O’Loughlin.

“Thats why its so crucial to figure out what’s causing the problem first.”

Farmers usually react to a wet year 

O’Loughlin said that quite a bit of drainage work has been carried out on Irish farms over the last number of years.

Farmers usually get interested in drainage as a reaction to a wet year. There was certainly the case in 2012 and spring of 2013.”

Clean existing drains first

According to O’Loughin a lot of good drainage work has been done on farms over the years. In many cases the existing drainage infrastructure may be fine. Often poorly maintained open drains can cause perfectly fine drainage systems to appear defunct.

“We are asking farmers to clean their existing drains first, they have been severely neglected over the years,” he said

“In many cases when this is done farmers can see a significant improvement in the drainage of their fields.”

Tips with drainage

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 groundwater 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 is likely to be effective, at this depth.
  • 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 mole drainage, gravel mole drainage or sub-soiling in tandem with field drains.
  • Drains are not effective unless they are placed in a permeable soil layer or complimentary measures (mole drainage, sub-soiling etc.) are used to improve soil drainage capacity. If water isn’t moving through the soil in one or other of these two ways, the watertable will not be lowered.
  • Outfall level must not dictate the drainage system depth. If a permeable layer is present, it must be utilised.
  • Drain pipes 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.
  • Sub-soiling 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.

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