Drainage drive across Ireland
This is according to Owen Fenton, of Teagasc’s environment research centre in Wexford who was speaking yesterday at its Future Farming, Future Weather conference.
According to Fenton, due to the dry summer of 2013, the momentum of drainage works across Ireland increased nationwide.
“Matching global trends, Irish drainage systems will continue to be modernised and maintained on existing and new lands,” he outlined in his presentation to an audience of more than 150 people in Teagasc’s Food and Research Centre in Ashtown, Co Dublin.
Fenton said the key questions for farmers on solutions are: how do we go about diagnosing a drainage problem? What are appropriate Irish drainage solutions and costs? How do we maintain our drainage networks into the future?
“Ireland receives some of the highest annual rainfall in Europe, with only limited variations between the summer and winter seasons, which means that Irish soils are vulnerable to drainage problems, especially in winter.”
He continued: “Presently, net rainfall (rainfall – evapotranspiration), which is the amount of water that needs to be drained from land varies across the country, but typically on a wet farm is approximately 500mm. At present the average drainage scheme is designed to export this amount of water from an agricultural site. Every field and drainage situation is different and a field may suffer from a number of different drainage problems.”
Of key importance is a soil test pit investigation, the drainage expert stressed.
He explained: “Soil test pits are dug in problem versus reference areas to approximately 2.5 metres. Next the soil profile is examined and permeable versus impermeable layers are identified. Permeable layers will be indicated by seepage of water into the soil test pit and collapsing layers. The presence of stones in shallow layers is important to note, as this may hinder some shallow drainage techniques.”
Basically permeable layers allow water to be transported off-site efficiently and therefore are amenable to groundwater drainage solutions, for example corrugated pipe, clean gravel, 10 to 40mm size rang, envelope and soil back fill, he added.
The Teagasc expert also advised that the groundwater system should be installed within or at least on the upper part of the permeable layer to effectively control the position of the watertable.
“Such a system will also aid in shrinking and cracking the impermeable layers above. Spacing of groundwater drainage systems in Ireland has moved from eight metres (€6,200-€8,600/ha) to ≥15 metres (€3,700-€6,200/ha) with the depth now identified by soil test pit investigation.”
In addition, the conference heard Teagasc’s new drainage manual is proving very popular.
The manual provides a step-by-step approach by the Teagasc team to take the reader through from the fundamentals of soil structure, to soil management and then on to the various drainage options works.
Significantly, the manual also contains a detailed analysis of the economic benefits to be accrued from an effective drainage programme.