Farmers working off high derogation levels should soil test every year, according to the Head of Grassland Science in Teagasc Moorepark, Michael O’Donovan.

“Without annual soil tests and reacting to them, you probably would be working in the dark. If you are working off high derogation levels, you should be testing your soils every year,” O’Donovan said.

Speaking at the recent Teagasc Greenfield dairy farm open day, O’Donovan said that the farm has its soil tested every year and the management decisions are based around these results. “Without yearly soil fertility testing, we probably would have been misguided. We are up at derogation limits in terms of P and there is about 8kg of surplus P on the farm at the moment” he added. “So that yearly soil test is very important for the farm here to keep the P levels high enough. At the moment about 66% of the farm is soil index 3 and 4,” he added. He said the low index paddocks are always being identified to ensure that they get the required levels of fertiliser P. “Every year since 2012, there has been about 24kg of P being applied, 95% of that is in the chemical form”.

The Teagasc representative also said that soil pH is important for grass growth as a low soil pH can result in a 1.5t/ha loss in grass dry matter production. The current soil pH is 6.1, which he said is a little bit low to activate phosphorous (P) in the soil and to address this issue, O’Donovan said that 300t of lime will be spread on the farm this year.