Land drainage: ‘It’s not a one-size-fits-all operation’

10 farms across the country are currently involved in the Teagasc Heavy Soils Programme. Central to the programme is the application of a number of technologies.

These include: appropriate drainage solutions; high-quality pasture management; land improvement strategies; and efficient herd management.

Earlier this week, over 200 farmers traveled to David Brady’s farm in Co. Cavan to see the work carried out on his farm as part of the programme.

Teagasc’s Dr. Pat Tuohy spoke at the event where he said: “There’s no one-size-fits-all solution when it comes to land drainage.

“There’s huge variability in terms of soil types across the country and that’s also the case across a parish or even a farm.

“The approach taken has to be tailored to the particular soil type. At the end of the day, you’re trying to move water through or over the soil and how best to do that varies.”

Tuohy explained that no two farms, currently involved in the Heavy Soils Programme, have installed the same system. The money spent on these farms has ranged from a little over €3,000/ha right the way to over €7,000/ha.

Planning a project

The Teagasc Research Officer added that farmers need to understand how their soil is behaving before they start any drainage work.

You need to take an approach where you are tailoring the drainage system to the problem at hand.

“Under the Heavy Soils Programme, we come in with the farmer on day one to get familiar with the farm and we start talking about where we want to target.

“One of the worst fields on the farm is picked out and the process of establishing the soil type begins to help come up with a strategy to drain that field or paddock.

“We always dig a number of test pits to try and establish the soil type and to find out where the water is being held up.

“There are different aspects at play and it’s important to figure those out,” he said.

Tuohy added that these test pits are usually dug to a depth of 2-2.5m and the findings from such work allows for the drainage system required to be divided into two broad catagories. These are groundwater drainage systems and shallow drainage systems.

It’s a matter of tweaking those for the farm and there are no two drainage systems the same in terms of depth, spacing or the type of drainage system used.

Groundwater drainage systems

Tuohy added: “The groundwater drainage system does exactly what it says on the tin. It’s about moving water and it’s usually installed where water rushes into the test pit once you dig to a particular depth – usually about 4-5ft.

“If you are meeting water at 4-5ft, and it’s consistent across the field, installing a groundwater drainage system at that depth is going to carry water away and control the water table.

“You are discharging the groundwater, reducing the amount stored in the soil and are lowering the water table.

“When it rains, there’s less water stored in the ground and the rain water is capable of filtering its way down.”

Shallow drainage systems

The other scenario that Tuohy discussed was shallow drainage systems. These systems are necessary where you dig to a depth of 2-2.5m and do not meet any groundwater.

You are meeting heavy soils down along to 2-2.5m and there’s no evidence of water moving or the potential for water to move into your drainage system.

“You need to develop avenues and channels for water to move off the surface of the ground.

“Shallow drains are installed at a depth of 3ft and they are crossed with either a mole plough or gravel mole plough to create channels to carry water to those shallow drains,” he said.