Science - April 7, 2005

More fences make better grass

While sheep roaming freely in the green Irish landscape might look attractive, it is not so good for the quality of the grass. More fences are needed.

By placing more fences and moving the sheep every day to new fenced off fields the clover content of the grass rises substantially. This is good for the grass as it creates natural nitrogen fertilisation. Pieter de Wolf of Applied Plant Research and Rogier Schulte of the Irish agricultural institute Teagasc have published their findings in the Irish Journal of Agricultural and Food Research.

In their experiment the clover content rose by over thirty percent during the growing season. In the biggest fields, where the sheep stayed for a week, the content did not rise above ten percent. The explanation is that the sheep in the big fields continuously pick out the tasty clover leaves, leaving the grass. The clover stands a better chance in the smaller fields because the sheep are moved more often.

It had long been suspected that this form of ‘strip-grazing’, as it is called, is good for clover grass meadows and for the sheep-keeping productivity. But it had never been convincingly demonstrated. Extensive grazing fields are typical in Ireland. Schulte: ‘A herd of one hundred sheep will graze about a quarter of a hectare of grass a day. This is what needs fencing off, but that can be quite expensive in terms of materials. Half a hectare per herd is probably more realistic.’ The findings apply in particular to the grasslands in the valleys of Ireland. / HB