Shallow drainage job works well in Tipperary field

Effective land drainage is key to efficient utilisation of land on any farm. With proper land management practices, farmers can increase livestock numbers without necessarily increasing acreage. This week, we feature a recently drained eight-acre field in Ballyporeen, south Tipperary, which displays the shift farmers are taking in more recent times to site-specific drainage design.

Test Trenches (Picture 1 above)

Conor O’Farrell has undertaken a few drainage jobs over the past number of years. Recently, he has used Hanrahan Plant Hire. Staff at the company advised him to dig a number of test pits before beginning any work to see what type of soil he was working with. In picture one (above), we see how the soil is clearly divided into two distinct layers. The top eight inches consist of a black soil type, while there is an impermeable marl-type subsoil below. This is one of the reasons that a shallow drainage system was chosen instead of deep drainage.

Conor explained that this type of soil is fine in the summer but as the days get short and there is less drying, the top layer begins to get soft in wet conditions. Conor used deep drainage in another field prior to this and found that it didn’t work as well because the soil was impermeable at lower depths and water couldn’t reach the drains.

Dykes

The field previously had dykes on two sides. Conor owns a small track machine, which he used to clean these out to help reduce costs. Parts of these dykes were as deep as 6ft as there was a slight slope in the field which aided the whole process.

Excavating

A 13t Case excavator was the biggest machine to come on site. This was used to dig the main line drain and collector drains. The main line runs down the centre of the field feeding into the dyke at the bottom. All collector drains are connected to this line and are spaced 15m apart. In one small area of the field, the spacing is reduced to 10m as a wetter type of soil is present.

Pipe laying and filling

The main line and collector lines are dug to a depth of 3ft. These are then filled with one to two inches of stone to keep the pipe off the soil floor. Once the pipes are laid, the drains are filled up using a 6t stone cart to within 2.5in of the surface, a lot higher than usual.

“I did this last year in another field and although it nearly doubles the price, I found that it worked for us,” Conor explained. All stones used for the process were part of a 10mm/20mm round wash mix, which is only one step away from gravel.

Connections and reseeding

In picture six (right), we see an unequal tee joint connecting the six-inch diameter main pipe to one of the connecting four-inch spur lines. Finally, picture seven (below) shows the finish achieved after work was complete on the field.

Conor recently sprayed off the paddock for reseeding, but explained that he wouldn’t have got away without it anyway because the paddock was due a reseed. Conor said the drainage work has been very successful and it has made a huge difference to the performance and trafficability of the field in wet weather. Conor said: “If it rained before grazing it could be two weeks before I could use the field, now two days and it’s back in action.”

Cost-benefit analysis

With his own small track machine, Conor was able to undertake part of the work himself, such as the cleaning of outside dykes and drawing the stone to the stone cart. For the entirety of the eight-acre field inclusive of stone and pipes, Conor worked out a price of around €4,000 excluding VAT (€500/acre). If all work was to be undertaken by a contractor, this cost would be somewhere in the region of €1,000 extra.

While this cost may seem excessive to some, Conor explains that, as a dairy farmer, if he wanted to expand and buy the same number of dry acres in the morning it would cost him around €100,000.