tractor spreading agri lime

Calcium Agri Lime – The Backbone of Soil Fertility

The lime kilns dotted through the countryside are a testament to the hard work and dedication of how our ancestors cared for their soils. In an era before synthetic fertilisers – agri lime; farmyard manure, seaweed etc. were the only fertilisers available to farmers.

There was no such thing as soil sampling, but the benefits of liming soils were well regarded and considered essential to productive farming. So much so that 50 years ago we were spreading 1.6 million tons of lime. In 1983, we spread over 2 million tons. Since 1985, we have struggled to spread 1 million tons each year, until 2018, when over 1 million ton was applied. The consequence being, that over half of our soils are below the optimum pH for grassland and tillage.

In general, agri lime was spread 1 in 5, so 20% of farm was limed each year in rotation. The advent of regular soil testing has served to help us decide what we don’t need, and our decisions are based on cost and what we can get away with doing. Lime rather than being an investment, is seen as a cost and as it is a relatively low cost in comparison to synthetic fertilisers, it is seen as less beneficial and can be done without.

Lime is the backbone of any fertiliser program, a regular approach to spreading lime helps to spread the cost. €10 per acre spread over 5 years, is a small cost when the benefits are clearly visible and obvious. Low pH is usually to blame when fields are not performing as they used to or as you would expect.

In Wexford, most soils are predominately high in Magnesium, if this nutrient is in excess it has a greater bearing on the pH and will often be seen, as lime not required, as pH is deemed adequate. This soil is in fact deficient in Calcium. If your soil is deficient in Calcium, so are your crops and your animals. The direct consequence of this is more diseases and deficiencies in crops and conversely in the animals that eat them.

High Magnesium soils in Wexford are usually deficient in Calcium. Ironically, they can also be deficient in available Magnesium to the plant. We only ever worry about nutrients that are deficient. A nutrient in excess is as detrimental to crop growth, as one that is lacking. Another consequence of high Magnesium is that it blocks out Potash in the plant. On a high Mg soil, you will still need to apply Potash, even if index is showing ok.

There is only one lime needed in Wexford and that is Calcium lime (Calcium Carbonate). There are no limestone quarries in Wexford. Lime is predominately hauled from Kilkenny and Carlow. Coastal areas in south Wexford, in particular, are high in Magnesium due to presence of low-lying marine till. High levels of Magnesium in the soil cause it to stick together and become hard when it dries out. People often wonder why their light soil acts like a heavy soil, and this is the reason. Applying Calcium in the form of Calcium Carbonate or Gypsum (Calcium Sulphate) will raise the level of Calcium in the soil and conversely reduce the level of Magnesium. Even if the pH looks ok, you can still add Calcium lime in this situation. 1T acre is sufficient in this situation to add Calcium to the soil. This opens the soil, allowing it to breathe, soil biology to flourish and water to drain down through the soil profile more easily. High iron content is also a sign of a Calcium deficiency.

Wexford is one of the few areas in Ireland where liming decisions should not be based solely on pH level.

The levels of Calcium and Magnesium also need to be consulted and a course of action taken to correct them. The only way this can be done is through a comprehensive soil sample, measuring every nutrient rather than just pH P, K and Mg.

The benefits of liming land are well researched. For mineral soils, farmers should aim to maintain soils at pH 6.3 for grassland and 6.5 for tillage. 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). Using lime alone can release up to 80kg of Nitrogen/ha per year from the soil for use by grass. In monetary terms this equates to a return on investment of 7:1. Now is the time to act on your soil samples and get lime spread on your land.


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