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26
Forage & Nutrition
Guide 2018
The importance of liming
There is nothing new about the importance of lime for soil health and
fertility. The thousands of redundant lime kilns dotted across the Irish rural
landscape bear testimony to the fact that the benefits of lime application
have been recognised by previous generations of Irish farmers
However, it is also a fact that a majority of Irish soils are
now lime deficient, resulting in sub-optimal productivity. A
paper delivered by David Wall and Ger Courtney of Teagasc
at last December's Teagasc Dairy Conference outlined the
payback for keeping lime levels maintained on grassland
farms. The key summary points in the paper included the
fact that lime is key for maintaining good soil pH and fertility
and achieving high rates of grass growth and production
targets on Irish dairy farms. Soil testing and planning of lime
applications are essential for effective maintenance of soil pH
levels on grassland farms. There is a large pay back for lime
applications on grassland farms, as 100 investment in lime
delivers 600 in extra grass.
OPTIMISING GRASS PRODUCTION
Key messages contained in this Teagasc paper on lime should
be emphasised. "Soil fertility is a key component in growing
sufficient grass to feed the herd on an annual basis. Irish
soils are acidic by nature due to our high annual rainfall. Soil
acidity (low pH) reduces the availability of major soil nutrients
such as nitrogen (N), phosphorus (P) and potassium (K). Soil
acidity will reduce the uptake and plant efficiency of applied
nutrients in fertilisers and organic manures. Soil test results
show that 90 per cent of grassland soils have a poor balance
in terms of pH, P and K to maximise grass production."
A NATIONAL LIME DEFICIT
Wall and Courtney showed that, nationally, more than 65 per
cent of grassland soils require lime to neutralise soil acidity
(ie. soils with low pH levels): "However, in some counties, in
excess of 80 per cent of soils require lime. Grassland farmers
should aim to maintain mineral soils between pH 6.3 to
6.5 and peaty soils between pH 5.5 to 5.8. This is the first
step towards increasing soil fertility and improved grass
production to meet the feed demands of the livestock over
the growing season."
THE EFFECT OF LIME ON THE SOIL
Lime is a soil conditioner and reduces soil acidity by
neutralising the acids present, allowing the micro-organisms
and earthworms to thrive and break down plant residues,
animal manures and organic matter. As the Teagasc paper
points out: "This helps to release stored soil nutrients such
as N, P, K, sulphur and micro-nutrients for plant uptake. For
example, grassland soils receiving regular lime applications
have been shown to release up to 80kg per hectare (ha)
additional N compared to soils with low soil pH. Important
grassland plant species such as ryegrass and clover will
persist for longer following reseeding where soil pH has been
maintained close to the target levels through regular lime
applications."
Recent Teagasc research at Johnstown demonstrates the
importance of lime in relation to soil P availability and the
improved efficiency from applied P fertiliser. Soil pH correction
is the first step to consider when building-up soil P levels for
high grass production systems. An application of 5 tonne (t)/
ha ground limestone can produce approximately 1 t DM/ha
additional grass and have similar grass yields compared to
the application of 40 kg/ha P fertiliser alone. However, the
addition of lime and P fertiliser in combination is shown in
Teagasc trials to produce the largest grass yield response (1.5
t/ha more grass than the control). These results show how
effective lime is for increasing the availability of both stored
soil P (from previous fertiliser and manure applications) and
freshly applied fertiliser P.
FINANCIAL RETURNS
The benefits of applying lime and P, as distinct from applying
only lime or only P were highlighted by Wall and Courtney in
their paper. In addition the paper clearly showed the return
on investment in lime: "As with any business, achieving a
positive return on investment is critical when using any input.
When the pH of grassland soils is maintained close to the
optimum range, increasing grass yield by at least 1.0t DM/
ha/year is achievable. In addition to P and K release from the
soil, N supply worth up to 80 euro may also be achieved to
boost spring growth. If this extra grass production is utilised
by the grazing livestock, it has the potential to reduce farm
feed bills by around 150/ha/year. Over a five-year liming
period, this represents a 6:1 (grass 150/t: lime 25/t) return
on investment in lime, not including the potential for reducing
fertiliser costs into the future."
CORRECT APPLICATION CRITICAL
The Teagasc paper also provided advice on the best lime
spreading strategies: "The target soil pH for grassland on
Author: Matt O'Keeffe
Editor, Irish Farmers Monthly, and dairy farmer
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