Investigation key before spending money on drainage

The cost of drainage systems needs to offer significant benefits to farmers for it to be economically viable with there being a significant outlay of money with varying levels of success.

James O’Loughin, Co-ordinator of the Teagasc Heavy Soils Programme, who presented a stand at the Beef 2016 event at Teagasc’s Animal and Grassland Research and Innovation Centre in Grange, Co Meath warned farmers of the cost and need for investigation when it comes to drainage.

Drainage can be both an expensive and complex operation, the idea that one size fits all is definitely not the case.

“A shallow drainage system could cost around €3,500/hectare and a deep drainage system (ground water drainage) is much more expensive, costing closer to €7,000/hectare,” said James.

Approximately 50% of the total land area of Ireland, 3.4m hectares, is classified as “marginal land” which is affected by the natural limitations related to its soil, topography and climate.

One of the key limitations of marginal land in Ireland is its poor drainage status, with much of it in need of artificial drainage for its productivity to be improved.

The adverse effects excess water has on land affects farming practices across the board, grass yields reduce in these affected areas due to lack of air at rooting depth which limits plant respiration and growth.

Prolonged access of farm animals and machinery is not possible due to soil moisture content and soil strength cutting the possible number of grazing days and possibility of cutting silage on this land.

The purpose of land drainage is to remove excess water from the soil as quickly as possible and how best to achieve this will vary with soil type.

Types of land drainage systems

With there being two main types of drainage systems, a ground water drainage system and a shallow drainage system, the qualities in the soil generally dictate which system will be the most suitable.

“The key thing a farmer must do before attempting to drain land is an investigation. If you’re going to drain a piece of ground get a number of areas tested, contact your local Teagasc or agricultural adviser and ask for their advise,” said O’Loughin.

Make sure it fits in with your plan and that you can get an equal reward for your input with that reward being extra grass.

Distinguishing between the two main types of drainage systems depends on whether there is a permeable layer of soil present at a workable depth which will allow the flow of water with relative ease.

In soil test pits where there is a strong inflow of water a groundwater drainage system (piped drainage system) is advised with the potential for significant improvements high in these areas.

Where there is no obvious inflow of water at any depth in a soil test pit a shallow drainage system is advised, however this type of land is more difficult to drain.

A shallow drainage system aims to improve the capacity of the soil to transmit water by fracturing and cracking it with mole ploughs and gravel mole drainage commonly used to do this.

The success of mole drainage depends on the formation of the cracks in the soil, soils with a high clay content are more suitable to using a regular mole plough as the channels made at a shallow depth have a better chance of staying open.

A gravel filled mole plough on the other hand is used when the cracks in the soil will not stay open for sufficiently long periods of time due to the soil being unstable and having a low clay content with the gravel used to support the walls.

James also urged farmers to ensure that the cost of utilising these drainage systems offered an equal reward to them in the long run with consistent higher grass yields.

I’d urge farmers to make an informed decision and to investigate which system suits them best and whether it is economically feasible.

The outfalls also need to be regularly maintained and cleaned for land drainage systems to be effective in the long run, with it being advisable to draw a layout map of the drainage system once it is completed to help with future maintenance.