Half of the soils in Ireland could do with a certain amount of drainage, according to Teagasc’s Dr. Pat Touhy.
Speaking recently at Moorepark ’17, Touhy discussed the importance of matching the soil drainage system to soil type.
“A bit of thought and planning needs to go into the whole process. Farmers must understand what type of soil they have and what the best approach is for that type of ground.
“How best to discharge water out of soil is going to vary with soil type,” Touhy said.
It’s a matter of knowing what [soil] you have and knowing what the problem is before going ahead with any kind of intensive.
The soil drainage expert explained that deeper ground water systems are installed when you dig a test pit and meet ground water at a particular depth. These systems are installed to drain water away.
Shallower systems, such as mole drainage / gravel mole drainage, he said, are for where you don’t have any ground water movement and you’re creating avenues for water to move closer to the surface.
“Farmers need to know what the best option is for their particular soil type,” Touhy reiterated.
Return on investment
The Teagasc research officer added: “You can spend any amount of money on drainage; any football field in the country will show you that.
“How limited the field is will dictate how much the payback is,” Touhy explained.
When considering draining, Touhy said, it’s important to think about what condition the field is in.
“Is the field grazable at all? Are you getting one or two grazings out of it in a typical year? Are you able to access the field to spread fertiliser or slurry?
It’s better to target what would be the worst field on the farm because it’s growing nothing. It’s constantly wet; even in a relatively dry year it’s not accessible.
“To drain that you’re going to get an advantage in every year,” Touhy said.
Planning to drain
The first step always is to dig test holes, he said, to the point where you’re seeing one every hectare.
They should be 6ft or 2m deep. These test holes will allow you judge the soil profile and see where water is being held up and if there are avenues for water to move, he explained.
Deep drainage systems cost approximately €8/m. Shallower drains are priced at €5-6/m. But the Teagasc expert said: “It’s not on the basis of cost obviously; it’s on the basis of what particular system is going to work for a particular soil type.
The deeper drainage system isn’t going to have any value in the wrong type of soil or vice versa. It’s about matching your system to your soil type.