Farm Ireland
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Thursday 15 November 2018

Spreading lime now could save thousands in feed costs next year

Now is the ideal time to spread lime
Now is the ideal time to spread lime
Joe Kelleher

Joe Kelleher

Ground conditions are very good in most parts of the country at present. This presents a great opportunity for getting a few loads of lime out this autumn.

With many fields closed up in the past week or two, now is an ideal time to spread lime on these fields.

When spreading compound fertiliser in a field which has a soil pH of 5.5 you are losing two thirds of the Phosphorus and one third of the Nitrogen due to fact that these nutrients are tied up in the soil and are not made available to the growing plant.

This means that if you spread a bag of 18.6.12 in a field with a soil pH of 5.5, then the reality is that you are really only getting the benefit of 12 units of Nitrogen and 3 units of phosphorus.

This is why correcting soil pH always comes ahead of correcting Phosphorus and Potassium deficiencies. With all this in mind, trials have shown that by increasing soil pH from 5.5 to 6.3, up to an extra 2ton of dry matter per hectare can be grown.

Nationally we are spreading approximately 750,000tonnes of lime annually.

However, to rectify the fact that two thirds of our soils nationally are deficient in lime, this figure needs to be doubled. In the '70s, our parents and grandparents were spreading far in excess of 1.5 million tonnes annually.

Which lime to use?

Calcium ground limestone is most common form of lime spread. It is readily available in most parts if the country and is fast acting and gives rapid pH adjustment.

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Magnesium (Dolomitic) ground limestone is also available in many parts of the country. It is slower to react but has a higher liming value than Calcium limestone.

It is a good source of magnesium for soils with low levels or a history of grass tetany.

Basalt rock dust is also used by a small number of farmers. It is only available in parts of the country where basalt quarries are found.

It is slow releasing and acts for up to 10 years and is known to contain up to 40 trace elements.

Granulated lime in bag form is also available. It is fast acting and is good as a maintenance dressing but may be cost prohibitive as a means of increasing pH.

John Leahy from Athea in Co Limerick is one farmer who has had positive results from using lime on his farm. John's farm consists of heavy clay mineral and peat soils and he has managed to increase the pH on his farm from 5.5 to 6.3 over three years.

John has applied 100ton lime per year on 40ha costing €2,600/year which has led to an increased average grass production by 1.5t DM/ha/year (valued at €272/ha). On average John has applied 7.5ton/Ha (3ton/acre).

This represents a return on investment of €4 in extra grass for every €1 in lime in year one.

However, lime is like the gift that keeps on giving as it will continue returning on your investment for a number of years after it is initially applied.

In John's own words "I've taken an aggressive approach to liming over the last three years, making it a priority area of spending, grass growth has turned around on the farm, grass has a healthier appearance and responds more quickly to N fertiliser. I also feel it has improved drainage on the heavier soils on the farm".

Up to 60 units of free background Nitrogen will be released by spreading lime on low pH soils. 1ton of lime generally costs €23/ton (spread and delivered) or €460 for a 20 ton load.

If this load of lime was spread across 10acres, then it should grow an extra 6ton of dry matter in 2019. Replacing this 6 ton of grass with concentrate would cost €1800 approximately.

Most of the major banks are now offering loans for the purpose of improving soil fertility. Lime is the cheapest fertiliser available in this country. Perhaps we should spread more of it?

Joe Kelleher is a Teagasc advisor based in Newcastle West, Co Limerick

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