Drainage can be a worthy investment when farming mixed land, like East LImerick farmer Ciaran Bartley is doing – but it can be “a complete waste of money” if not done properly.
eagasc consultant Kieran Fitzgerald gave farmers plenty to think about on a recent grass walk when he dug a sod into the ground to analyze what lies beneath.
Traditional drainage systems, which cost up to €8,600/ha, can be pointless without proper analysis of soil structure to determine water flow base, he told them.
On the other hand, if effective drainage is implemented, extending the grazing season can result in a 6-7 percent weight gain of the carcass, or about €70/hr bull at slaughter.
“The most important thing is to insert the drains at the right depth. You have to go down to the layer of gravel where the water is moving, and that can vary from 2 feet to 10 feet below the surface,” Mr Fitzgerald said.
“So the first thing that should be done when thinking about drainage is call a dredge and see how much water is moving.”
Mr Fitzgerald pointed out that nothing from Ciaran’s farm – which ranges from very dry to heavier soil – could turn it into “East Cork farmland”, but drainage will improve it.
“In dry years like 2018, this type of soil can be very productive as great land for growing grass and shouldn’t be discarded entirely,” he advised.
“There’s good root structure and the roots actually go well into the soil, but we can see that it’s colder and more compacted.
“While the roots penetrate the soil well, it gives a red color. That’s iron and that’s a sure sign that water is present and the amount of water doesn’t matter, but the water can’t escape and gets trapped and sealed in the ground.
“It’s pretty fertile soil, but for about an inch and a half it’s fertile soil, and then we’re in Gley-type soil.
“You could do a great deal of damage to this soil by coming in with a deep plow and turning it up. You would basically bury fertility.
“What we want to do with this type of soil is take what we have on top and tackle the soil structure underneath.
“It won’t be ready in a day or a year, but maybe it could be changed over a longer period of 10 to 16 years. It takes about 100 years for an inch of soil to form, so anything related to soil or drainage is a long-term investment.
“One of the advantages that we have in this country is a drain and there are a lot of farms that collect water, but there’s an advantage here because there’s — a way to drain the water. “The big problem is the water conductivity of the soil. Water does not move easily through this type of soil.
“First, a percolation test must be carried out to determine at what level the water is moving in the soil. This can be 2 feet or 10 feet deep – there is no point in installing drains at a level where no water is flowing.”
Installing a drain doesn’t come cheap, so you’ll need a plan to get it right.
“Mole drainage can work very well by breaking up the soil if done at the right time of year. Around September is usually a good time, when the soil is usually the driest and there can be a lot of fractures under the soil that introduce air into the root system
“A supplement with mole drainage is to put in gravel, which keeps the drainage from flattening out again, and the result can be pretty good,” he said.
A mole and gravel system costs around €1,500/ha; Collector drainage may be required alongside mole drainage and can amount to €3,500/ha if drainage is required at a 20m spacing and back to around €1,150/ha if a 60m spacing is deemed sufficient.
For costing, he explained that the particular soil type requirement, to be effective, will determine the likely cost, and “mole drainage requires collector drains to divert the water, and they usually run perpendicular to the moles and on a lower level and the water collected by the mole is drained faster from the collector drain,” he added.
Simpler systems can be done for €600-900/ha. Deep drainage and traditional systems where water is more difficult to evacuate can cost up to €9,000/ha.
Teagasc found on the heavy soil at Solohead Research Farm that where drainage was implemented, the grazing season was extended by 30-40 days.
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