2018 saw over 1 million tonnes of ground limestone spread on Irish farms, an increase of 38% on 2017 levels. While weather conditions obviously played their part in this increase, it is clear that Irish famers, acting on strong advice from Teagasc, are increasingly utilising the benefits of lime to unlock soil fertility on their own farms.
Irish soils have a natural requirement for lime to control soil acidity generated by our high levels of rainfall. These soils require lime to neutralise this acidity and restore a more favourable soil pH for crop growth, nutrient release and soil quality. In 2016, two thirds of all soils tested had suboptimal pH levels, indicating that lime application was required. According to Teagasc, in some counties this figure was as high as 80%.
Irish soils are some of the most productive soils in the world with regards to both grass and grain production, due to our temperate climate. However, if we do not utilise lime as a key component of soil fertility, this competitive advantage can be eroded. For mineral soils, farmers should aim to maintain soils at pH 6.3 for grassland and 6.5 for tillage. Of all soils tested in 2016, less than 10% of samples were in the optimum range for pH (>6.2), Phosphorus (P) (Index 3) and Potassium (K) (Index 3 or 4). According to Teagasc, under increasingly acidic soil conditions (pH <6.3) the availability and efficiency of nutrients (N, P and K) in soils for plant uptake decreases rapidly. Additionally, in grassland swards it will reduce the persistency of productive ryegrasses and clover.
There are proven commercial benefits to utilising lime to maintain soil pH. As with any business, achieving a positive return on investment is crucial when considering inputs. Optimising the pH of grassland soils can increase the annual output of grass by at least 1tDM/ha which, according to Teagasc, is worth €181/tonne of grass dry matter (DM), thereby reducing farm feed bills. According to Teagasc, a dairy farm making a €100 investment in lime will get an annual return of approximately €725 through extra grass production. This represents a return of €7.25 for every €1 invested in lime.
Use of Ground Limestone
Ground limestone is the most cost-effective source of lime. It will start to work once it has been applied and is washed into the soil. The finer fractions of the ground limestone will adjust soil pH upwards towards the target pH level over the first three months, while the coarser components will maintain this pH adjustment over the following 12-36 month period. Contrary to many opinions, ground limestone can be applied at any time of the year. However, mid-summer and autumn are ideal as the soils are dryer and more firm, coupled with increased spreading opportunities after silage and grazing.
Grolime is the certified trademark under which companies who meet necessary criteria are authorised to promote and sell their ground limestone. All Grolime certified companies are licenced by the Department of Agriculture, Food and the Marine (DAFM) to manufacture and sell ground limestone for use as a soil conditioner in Ireland. In addition, all Grolime companies undergo independent testing bi-annually for compliance with the national specification for ground limestone. To view the full list of Grolime approved companies, click here.