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FORA
GE AND NUTRITION

Guide 20
1
7
FORAGE AND NUTRITION
Guide 2017
14
Back to basics with lime
Over the last 45 years, the application of lime, a major soil nutrient, has declined more than two-fold resulting in Irish soils now
majorly deficient in lime
In the 1970s and early eighties, an average of 1.7 million tonnes
of lime were applied annually. Over the last 30 years we have
applied an average of 800,000 tonnes of lime annually (less
than half). In Ireland, our soils naturally have a requirement for
lime to control soil acidity generated by our high annual rainfall.
For example, from the east to the west coast, we get in the
region of 1 (40 inches) to 1.5 (60 inches) metres of rain each
year. Rainfall is the biggest driver of soil acidity and reduction in
the production power of our soils. The accumulated reduction
in lime applications over the last 30 years has resulted in a
large percentage of soils with low pH levels. Irish soils are
some of the most productive soils in the world in terms of
either grass and grain production due to our wet climate but, if
we continue to ignore lime, a key component of soil fertility, we
are slowly eroding our competitive advantage.
Soil acidity is a major limitation to the productivity of our soils
as it reduces the availability of major soil nutrients (N, P and K)
and the uptake and e ciency of applied nutrients in manures
or fertilisers. In grassland swards, it will reduce the persistence
of productive rye grasses and clovers. Some counties, for
example Kildare and O aly, have a higher percentage of soils
above pH 6.5. This is due to the underlining parent material
which is limestone. Naturally, high soil pH levels (>pH 7.0)
or fields that are over-limed will result in reduced availability
of both major (especially P) and minor nutrients (especially
manganese [Mn]). Only apply lime based on a recent soil test
report.
Effect of lime on soil fertility and grass production
Research from Johnstown Castle demonstrates the importance
of lime in relation to soil P availability and the improved
e ciency from applied P fertiliser. Figure 1 shows the change in
soil test P levels when lime is applied by unlocking stored soil
P (purple bar) and increasing the e ciency of freshly applied
fertiliser P (green bar) compared to applying high quantities
of P fertiliser alone (red bar). This clearly shows that soil pH
optimisation is the first step to consider when setting out to
build up soil P levels.
Figure 2 shows the grass yield response to lime and P fertiliser
in grassland. The application of 5t/ha ground limestone (purple
bar) produced approximately 1t/DM/ha additional grass and
had similar grass yields compared to the application of 40kg/
ha P fertiliser alone (red bar). However, the addition of lime + P
fertiliser in combination (green bar) produced the largest grass
yield response (1.5 t/ha more grass than the control). These
results show how e ective lime is for increasing the availability
of both stored soil P (from previous fertiliser and manure
applications) and freshly applied fertiliser P.
Return on investment () in lime
As with any business, achieving a positive return on investment
is critical when using inputs. When the pH of grassland soils
are maintained close to the optimum range, increased grass
production by at least 1t/DM/ha/year can be achieved. In
Mark Plunkett & David Wall
Teagasc, Crops Environment and Land Use Programme, Johnstown Castle, Wexford
Average response across two grassland sites
Treatments added to grassland
R
elative grass DM yield (%)
115
110
105
100
95
90
DP Wall, 2015
Average soil pH:
5.2
6.4
5.2
6.4
No Fert.
9.6 t/ha
10.5 t/ha
10.4 t/ha
11.01 t/ha
Lime only
P only
P + lime
Figure 2. Relative grass DM yield response in grassland treated with
Lime (5t/ha of lime), P fertiliser (40kg/ha of P), and P + lime over a full
growing season.
Sheil, Wall &
Lalor, 2015, FAI
20
18
16
14
12
10
8
6
4
2
0
Control
P Inde
x 1
P Inde
x 2
P Inde
x 3
Lime only
Treatments applied to soil
Average response across 16 soil types
Change in soil test P (mg/L)
Lime
: 5t/ha
P Fertiliser
: 100kg/ha
P only
P and lime
Figure 1. Average change in soil test P (Morgan's) across 16 soils (av.
pH 5.5) treated with Lime (5t/ha of lime), P fertiliser (100kg/ha of P),
and P + lime and incubated over 12 months in controlled conditions.