A Farmers’ Guide
Optimising grass
growth and quality
with Sulphur.
Our role in
your business.
GrowHow UK is the only British producer of True Granular Compounds
and Nitrogen fertilisers.
Our aim is to help UK grassland farmers operate profitable milk and
meat production systems, by providing the best fertiliser products
and advice to optimise grass and forage production and utilisation.
We believe that whatever system you operate, making the most of
home-grown grass and forage is a key part of your success.
Why is Sulphur important
for grassland farmers?
Sulphur is as important for grass growth and quality as Nitrogen, Phosphate and
Potash. Where Sulphur is in short supply, applying Sulphur containing fertilisers is key
to achieving grass yield with the energy and protein content required.
Along with Nitrogen, Sulphur is vital in protein synthesis within the grass plant.
Sulphur is the core component of some of the key amino acids that make up
proteins. Without enough Sulphur plant protein production is compromised, which
reduces yield. Proteins are also needed for the grass plant to make sugars.
So where Sulphur is in short supply, there is a triple-impact of reduced sugar content,
reduced protein content and reduced yields. Consequently, not only are grass yields
disappointing, but what is produced is less palatable.
Why do we need Sulphur
in fertilisers?
The grass plant requires a supply of up to half as much Sulphur as Nitrogen. Historically,
much of this Sulphur has been supplied through atmospheric deposition as a bi-product of
industrial activity. However, as anti-pollution measures were taken from the 1980s onward,
a steady decline in Sulphur emissions occurred, resulting in less Sulphur being deposited on
agricultural land.
Back in the 1960s and 70s, around 70 to 80kg S/ha (55 to 65 units S/acre) was deposited
on agricultural land from the atmosphere, making the inclusion of Sulphur in fertilisers
unnecessary. Deposition reduced to less than 5kg S/ha in the 2000s and measurements have
since ceased as rates of Sulphur falling from the atmosphere are now so low.
The content of Sulphur in manures is also variable and the availability of this source for plant
uptake is generally low. So there is a need to use Sulphur containing fertilisers in many parts of
the UK. It is important to note that Sulphur in fertilisers is expressed as sulphate (SO3), because
this is the only form of Sulphur that plants can take up from soil solution and use for growth.
Sulphur emissions in the UK
Sulphur emissions (Mt S/yr)
4
3
S emissions
Targets
2
1
0
1850 1870
1890 1990 1930 1950 1970 1990 2010
Year
How do we know if
grass needs Sulphur?
Sulphur deficiency is not always visible. Paling and then yellowing of the leaves (similar
to that observed in Nitrogen deficiency) may be seen, although it is in the younger leaves
first, whereas Nitrogen deficiency is seen in older leaves.
On grassland a substantial response to Sulphur is most likely on younger swards or on
coarser (lighter) textured soils. However, as Sulphur deposition from the atmosphere is
now so low, even older swards on heavier soils may be Sulphur deficient.
Sulphur status is normally assessed by herbage analysis. It is possible to obtain a soil analysis
for sulphate content, but this is very variable and so plant tissue testing is more reliable.
The amount of Sulphur in grass normally ranges from 0.2 to 0.4% in the dry matter
(2 to 4g S/kg DM). The most recent advice suggests that it should be at least 0.25% to
avoid deficiency.
Obtaining the Nitrogen: Sulphur (N:S) ratio of herbage is the usual way to assess whether
Sulphur is required. Samples should be taken when the grass is growing rapidly in spring,
or during aftermath growth following silage cuts. A ratio greater than 13:1 is considered
deficient, but a response may be seen down to 10:1. Care must be taken in interpreting
results as very high or very low Nitrogen contents can provide confusion. For example:
l A
Nitrogen concentration of 4.6% and a Sulphur concentration of 0.35% gives a ratio of 13:1, which appears ‘Sulphur-deficient’, but the need for Sulphur is borderline as the Sulphur content is relatively high.
l A
Nitrogen concentration of 2.5% and a Sulphur concentration of 0.21% gives
a ratio of 12:1, which appears ‘Sulphur-sufficient’, but the Sulphur percentage
is low and the sward would benefit from Sulphur applications.
Blue bags grow
better crops...
Diagnosing Sulphur-deficiency
with a N:S ratio
Above 13:1 with a Sulphur content less than 0.25%
= Sulphur-deficient
Between 10:1 and 13:1 with a Sulphur content less than 0.25%
Between 10:1 and 13:1 with a Sulphur content more than 0.25%
Below 10:1 with a Sulphur content more than 0.25%
= Sulphur-deficient
= Sulphur-sufficient
= Sulphur-sufficient
A malate: sulphate analysis of fresh herbage may also be used to assess Sulphur-deficiency.
This approach measures an important metabolite (malate) which is used in energy
production in the grass plant and is dependent on Sulphur to work efficiently. The test
is arguably more accurate than the N:S ratio and can be obtained by speaking with your
GrowHow crop nutrition specialist.
Grow more grass with Sulphur
It is widely recognised that where soils are Sulphur-deficient, applying Sulphur-containing
fertilisers can give a yield response of between 10% and 40% in grass dry matter (DM) yield.
This applies to a silage cutting situation and is shown in the graph overleaf. Yield responses
to Sulphur applications for grazed grass are also commonly observed and these can range
from 5% to 20%.
The example overleaf comes from trials on a sandy
loam soil in Devon. Averaged over three years,
grass with Sulphur applications yielded 12.6t
DM/ha, compared with only 9.3t DM/ha without
Sulphur (a 35% increase).
Yield response to Sulphur over three years
t grass DM/ha
7
With Sulphur
No Sulphur
6
5
4
3
2
1
0
5.4 4.9
4.1 2.9
3.1 1.5
1
2
3
Silage cuts
Improve grass quality with Sulphur
Because Sulphur is important for protein production in the grass plant, and proteins are
also critical for energy synthesis, Sulphur-deficiency can reduce grass quality both in terms
of protein and sugar content, both of which influence palatability and animal DM intake.
It is well proven that using Sulphur containing fertilisers to correct a Sulphur-deficiency
helps to restore efficiency in these processes and results in increased concentrations of
protein and sugar in cut and grazed grass.
This can be seen in the following graphs, which come from independent experiments
conducted by IGER at North Wyke in Devon (now part of Rothamsted Research).
True protein (% in DM)
Sulphur increases grass protein
With Sulphur
No Sulphur
15
10
5
0
12
9.2
1
12.8 11.3
14 11.3
2
3
Silage cuts
Soluble sugars (% in DM)
Sulphur increases grass sugar content
With Sulphur
No Sulphur
4
3
2
1
3.4
0
3
1
3.3 2.95
3.45 2.86
2
3
Ref: IGER, North Wyke
Silage cuts
Experimental trials conducted by GrowHow at Reaseheath College in 2014 also show the
effect of Sulphur applications in a grazing situation and on different soils types. The use of
Sulphur containing fertilisers increased grass crude protein (CP) content by 4%, compared
to where Sulphur was not applied.
Increasing grass protein content (CP% in DM)
on grazed swards with Sulphur fertilisers
Soil/Sward
No Sulphur
With Sulphur
% increase
Clay loam/old sward
17.3
18.0
+4.0
Clay loam/new sward
15.9
16.5
+3.8
Sandy loam/new sward
17.0
17.7
+4.1
Recommendations:
Responses to Sulphur can vary for a number of reasons including soil type, season and
winter rainfall, but suggested rates over the season should be:
Grazing: 40-70kg SO3/ha Cutting: 50-80kg SO3/ha
Some situations could well respond to higher rates, speak to your FACTS Qualified Adviser.
Capturing the grass yield and
quality benefits of Sulphur
It’s all well and good to grow more grass of a higher quality, but the modest investment
in Sulphur containing fertilisers is wasted if the advantages are not captured and utilised
within the milk or meat production system. This means planning to achieve the increased
growth and quality and understanding how this is going to benefit the system. There are
two main ways of approaching this: producing more milk and meat, and/or using the extra
grass yield and quality to reduce costs by replacing purchased feeds.
Capturing extra yield as energy
Working on the basis of producing an extra tonne of grass for silage or grazing, we can
assume that it contains 11.5 MJ ME/kg DM. One tonne of grass DM (1,000kg) therefore
contains 11,500 MJ of ME. Not all of this will be utilised; a well-managed paddock grazing or
grass silage system will capture approximately 85% of this grass. So we should plan to use 9,775
MJ ME from our extra tonne of grass dry matter.
More milk or meat
It takes 5.4 MJ ME for a cow to produce a litre of milk, so an extra 9,775 MJ ME
per ha represents 1,810 litres milk per ha.
Looking at this another way, a dairy cow takes about 70 MJ ME per day for
maintenance, so for a 100 cow herd, an extra 9,775 MJ provides for one day
of maintenance energy plus 5 litres per cow. If our 100 cows are on 40 ha of
Sulphur-deficient land, then applying Sulphur in fertiliser can bring us an
extra 40 days of maintenance plus 5 litres.
The amount of energy used in meat production can vary with species, breed and
stage of growth, but the rule of thumb is to allow for 11 MJ maintenance ME for
every 100kg liveweight of stock, plus 47 MJ ME for every 1kg of weight gain.
So an extra 9,775 MJ ME per ha represents 208kg of liveweight gain per ha.
Again, looking at this another way, 300kg liveweight beef finishers grazing at
4 per ha require 132 MJ ME per day for maintenance and 188 MJ ME to each put on
1kg/day liveweight gain. So our extra 9,775 MJ ME will provide these beef animals
with 30 days of energy.
Energy and cost comparison for using one tonne of
extra grass DM as a replacement for purchased feeds
Feed
Approx.
Dry matter
cost per
content
tonne
(%)
dry matter
(DM)
MJ ME
content
(MJ ME/kg
DM)
9,775 MJ
grass ME
would
replace
(tonnes fresh
weight)
Replacement
value of
extra tonne
DM of grass
energy
Extra grass as silage
£80 25-30%11.5
Extra grass as grazing
£40 15-25%11.5
Feed wheat
£160
86% 13.60.84£115
Feed barley
£150
86% 13.20.86£112
Concentrate (high energy)
£265
89% 14.00.78£185
Concentrate (medium energy)
£250
89% 12.50.88£198
Capturing extra quality
Modern varieties of perennial ryegrass bring the grassland farmer not only the advantage of
extra yield compared to older varieties, but also higher sugar content. It can be argued that
some of the extra yield bred into grasses in the last few decades has been at the expense of
protein content (a dilution effect). Sulphur-containing fertilisers can help with both these issues,
improving grass protein content and helping to increase sugars.
Recent work at Teagasc’s Moorepark Dairy Research facility in Ireland has shown that using high
sugar grasses (compared to standard varieties) can increase the dry matter intake of grazing cows
by around 2kg DM/cow/day – enough energy for an extra 2 to 4 litres of milk per cow per day.
Return on Sulphur investment
Financial returns to applied Sulphur will depend on responses and how the
extra grass yield and quality are used in the farm system, but a typical return
of £10 for every £1 spent on Sulphur can be expected.
Sulphur and copper lock-up
l Fertiliser Sulphur is only replacing atmospheric deposition, not applying
additional Sulphur.
l The availability of Cu can be reduced when S is supplied in excess AND
soil has a high Molybdenum (Mo) content.
l T his is a rare combination of circumstances, because Sulphur deposition is
now so low.
l Sulphur-containing fertilisers do not contain enough S to push S supply to excess.
l There
is more benefit to the system in using Sulphur fertilisers to improve grass
yield and quality and handle any Cu issues through the diet.
GrowHow Sulphur-rich
products provide the solution...
Our belief in the need for Sulphur-containing fertilisers in grassland systems has led
to GrowHow developing a full range of NS, NKS and NPKS True Granular Compound
products to meet the needs of grassland farmers.
Product
Analysis (NPKS)
SingleTop®
27-0-0 (12 SO3)
NK Sulphur
27-0-6 (6 SO3)
KayNitro® Sulphur
25-0-13 (7 SO3)
CropMaster® Sulphur
27-4-4 (7 SO3)
MultiCut® Sulphur
23-4-13 (7 SO3)
Because sulphate can travel through the soil profile like nitrate, moving out of the reach of
plant roots, the general approach should be to apply Sulphur ‘little and often’ to maximise
efficiency and optimise the effects. This is why it is best to apply Sulphur with the main
Nitrogen applications, with Sulphur used in every Nitrogen application for grazing and
large spring dressings for silage crops, split between early and mid-spring.
Using Sulphur-containing
fertilisers can help water quality
In these environmentally conscious times,
nitrate leaching is an issue for all farmers,
in particular those farming in Nitrate
Vulnerable Zones (NVZs). The Water
Framework Directive (WFD) targets for
improving the quality of water courses
means that loss of Nitrogen from our
milk and meat production systems
is under examination and will be a
continuing challenge.
Because Sulphur and Nitrogen are so integral to protein production, where Sulphur is
deficient, the Nitrogen in the plant is not converted into proteins and growth is reduced.
This leads to less Nitrogen being taken up by the grass and soil Nitrogen accumulates. This
can then leach into the environment, potentially harming water quality.
So logically, adding Sulphur to the system in Sulphur-containing fertilisers will increase
the uptake of Nitrogen, leaving less in the soil for loss to water. This has been proven in
experiments conducted in Devon and is seen in the graph below.
Cumulative nitrate leached (kg N/ha)
Nitrogen losses reduced by 57% over winter
from grassland using Sulphur fertiliser
No Sulphur
With Sulphur
40
30
20
10
0
Mid
Nov
Late
Nov
Mid
Dec
Late
Dec
Mid
Jan
Late
Jan
Mid
Feb
Early Early
Mar Apr
s
as
Re
y
gl
in
ur
it
Br
ish
Quality in. Quantity out.
For free help and advice regarding Sulphur nutrition,
contact one of our specialist advisers, today
on: 0151 357 5758
or email: [email protected]
GrowHow UK Limited, Ince, Chester, Cheshire CH2 4LB
www.growhow.co.uk
© GrowHow UK Limited 2015