One of the main messages at the Moorepark Open Day last week was the importance of lime – the forgotten fertiliser. At the grass board, Teagasc researchers Michael O’Donovan and Mark Plunkett explained to the crowds that 88% of soil samples analysed from dairy farms are sub-optimum for one or more nutrients.

“In a study of soils with index 2 for phosphorus, it was found that when 32 units per acre of phosphorus was applied without any extra lime, grass growth increased by 0.8t/ha. When 2t per acre of lime was applied, without any extra phosphorus, growth increased by 0.9t/ha, but when lime and phosphorus was applied together growth increased 1.4t/ha.”

This shows the importance of lime to correct pH and release phosphorus and potassium, said Mark.

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“In 1980, 1.3m tonnes of lime was spread in Ireland,” said Michael O’Donovan.

“In 2014, only 750,000t of lime was spread. During the quota era, we completely took our eye off the ball when it came to lime and this is something that must change, if we are to grow more grass,” said Michael.

He said that the target for all farmers should be to grow 15t per hectare and utilise 12t of this. He says that for every extra tonne of grass utilised, net profit increases by €267/tonne. By improving soil fertility from an index 1 to an index 3, an extra 2t/ha of grass could be grown and this would equate to an extra profit of €400/ha per year, giving a four-to-one return on the investment in the lime and fertiliser required to improve the soil fertility.

He said grass utilisation was optimised when grass was grazed at the three-leaf stage, so between 1,300 and 1,600kg per hectare as good quality and fast re-growths are achieved at this level. To attain this, regular weekly measurements must be carried out, he said.

Michael also stressed the importance of having a high perennial ryegrass content and a high clover content in the swards, both from an animal performance and grass growth perspective. He said that an extra 1.5t/ha of grass is grown where the percentage of perennial ryegrass is high and 30 to 40% of the sward is white clover.

Pre-mowing

Answering a question from the crowd on pre-mowing, Michael said that there are very few incidences where pre-mowing will be of benefit, citing a reduction in subsequent growth after mowing as being a big drawback.

“Most people pre-mow when paddocks get too strong. If a paddock is too strong to graze, it’s also too strong to pre-mow. Some people say that their protein percent rises when they pre-mow, but protein rises at this time of the year anyway. In studies we did years ago, we found no benefit with pre-mowing, only a reduction in subsequent grass growth.

The message here is to walk and measure your farm, graze down to 4cm and take out surpluses for silage when they arise – not spend time and money topping and pre-mowing.”