The Courier & Advertiser (Fife Edition)
Digging down into basics of effective mole channels
Growers on clay soils with a costly land drainage scheme lying beneath the surface can grab a post-harvest, pre-sowing opportunity to perk it up with some well-placed mole channels to keep the water flowing.
The channels must be drawn in the right place, at the right depth and at the right gradient, at a time when the soil is in the best condition for a long-lasting channel to be formed.
“Moling carried out in ideal soil conditions will typically last five or six years, or as many as 10 years or more,” says soils and cultivations consultant Philip Wright of Wright Resolutions.
In an AHDB webinar he emphasised that soils need to be in a “plastic” state for channels to be moulded successfully and before a dry few days that allow the channels to cure and become stable.
“For a simple rule of thumb, take a lump of soil from moling depth, roll it firmly into a ball and pop it into a glass of water overnight,” he suggests.
“If in the morning the ball hasn’t started to degrade or break down to any extent, then your soil type and the condition it’s in is good for moling.”
While a simple single-leg linkagemounted mole drainer can do the job, a beam-type implement that is effectively trailed in work is immune to tractor movements and provides a more stable platform for a consistently smooth and even channel, especially when working on a rough field surface.
In ideal conditions the mole plough bullet and expander will mould a stable channel – typically 45-55cm deep at 2-3m spacing – with a multitude of cracks and fissures radiating above it that will allow water to permeate the soil profile, enter the channel and run gently away to the drainage pipes.
“On a field with a natural slope it’s easy enough to draw the mole drains with a gradient as long as it is not so steep that fast-flowing water quickly erodes the channel,” says Mr Wright.
“Equally, on undulating ground, it’s essential to avoid any low sections in the channel where the water will sit and degrade the mole drain.”
He recommends consulting farm drainage maps first to ensure the mole channels are drawn at right angles or thereabouts to the buried pipes they are intended to feed, and establish the depth they are laid and the covering of backfill.
“You need to be well above the pipes to avoid damage but still intercepting the backfill poured over them to make the connection,” he points out.
“And map your new mole channels using GPS if you can because then when it comes to renewing the scheme, new channels can be drawn between the old ones, many of which may still be working satisfactorily.”