The efficient use of fertiliser is important not only to reduce
waste and potential pollution by leaching but also keeps inputs
at an optimum level and input costs to a minimum. All fertiliser
recommendations need to be based on sound knowledge and therefore
a soil analyst would be the first port of call. Use RB209 with
your analysis to formulate your fertiliser strategy.
Nutrient requirements
Nitrogen, Potassium, Magnesium, Phosphorous, Sulphur, Manganese,
Calcium, Molybdenum and Boron.
Oilseed rape has a high requirement for many major and minor
elements.
Nitrogen.
This nutrient plays a major role in chlorophyll production and
protein synthesis. It is needed for plant development and yield.
Insufficient supply causes movement of this element from the
older leaves to the younger leaves. In the spring there may
be visible yellowing of the lower leaves which often disappears
after the first application of nitrogen. Plants will be dwarfed
and stunted through lack of leaf expansion and growth and foliage
will become pale green/yellow.
Control deficiency by applying adequate nitrogenous top dressing.
Applications up to mid season or flowering are more effective
where soil levels of nitrogen are low. Foliar sprays can be
used but these will not be cost effective.
Potassium.
This nutrient is essential in that it regulates cell water content,
and through this, the rate of cell expansion.
Deficiency normally occurs on light, acidic, poorly drained
land. The symptoms include wilting, dark green colouration and
undulation of the leaves, especially under intense sunshine.
White to yellow-brown areas are seen first on the lower and
then on the upper leaves proceeding from the leaf margins to
the centre of the lamina. If this persists single areas coalesce,
leaf margins become curled upward and the whole leaf dies. Deficiency
occurs in pH ranges below pH 5.5.
Control deficiency by applying this element in the basal fertiliser.
If a deficiency is discovered later in the season a degree of
rectification can be achieved by applying a foliar spray of
potassium sulphate. This may well cause scorch.
Phosphorous.
This nutrient is a vital component of adenosine tri-phosphate,
which is responsible for supplying energy to drive all plant
physiological processes.
Deficient plants are dull purple and later shiny red to orange
in colour. It is first seen on the older leaves, however if
the deficiency persists, the growth of the plant is restricted,
the stems will become thin and the older leaves will die prematurely.
Deficiency occurs in pH ranges below pH 6.0. Maintain soils
at index 2 for seed yield and high index 2 to deter pigeons.
Control deficiency by applying recommended amounts for that
crop using soil analyst and RB209. If deficiency is discovered
later in the season a degree of correction can be obtained by
applying a foliar spray of ammonium or potassium phosphate.
This may cause scorch.
Magnesium.
This nutrient is necessary for chlorophyll production and numerous
enzyme functions.
Symptoms of deficiency include chlorolic marbling and leaves
tinged purple, red or orange.
Deficiency normally occurs in sands and chalk soils, where pH
is low and there is restricted root development leading to poor
uptake. Deficiencies are rarely seen although the requirements
for this element are high. Where they do occur is on light and
acid soil where older leaves show interveinal clearing with
the areas near to the main veins remaining green. The cleared
area later becomes orange-red-brown in colour and necrotic.
The leaves appear to be speckled. This deficiency can cause
leaf death.
Control deficiency by addressing the problem in the autumn.
This can be achieved by applying a suitable magnesium fertiliser
e.g. Kieserite (25% MgO, 50%SO3), Calcined Magnesite (82%MgO).
Small deficiencies can be corrected with a foliar spray (Epsom
salts MgSO4.7H2O nutrient content 10Mg) - application rate 5-10kg/ha.
Magnesium fertiliser is only justified at soil index 0 when
50-100kg/ha MgO should be applied every 3-4 years.
Sulphur.
Used by the plant to construct cell components such as proteins
and mustard oils.
The low deposition of this element from the atmosphere brought
about by the recent cleaning up of industrial processes means
that it is often now only available at levels that could cause
acute deficiency. Sulphur is also a very leachable element.
The symptoms of deficiency are very similar to those seen by
nitrogen deficiency. The margins of the leaves become pale green
and then yellow to red in colour. The veins are cleared. With
continuing deficiency the plant becomes stunted and narrow brittle
erect leaves develop. Deficiency occurs on the young leaves
first. During flowering the deficiency becomes evident by pale
to white discolouration of the petals. Plants affected exhibit
pods that are reddish in colour and thickened. Seed yield will
be greatly reduced.
Control deficiency by applying sulphur at the same time as applying
nitrogen in a blended mix. A top up using a foliar spray containing
sulphur can help but would prove uneconomic as a single way
of applying this element.
Manganese.
Manganese is involved in photosynthesis and enzyme functions.
Crops grown on land with high pH values (6.0-8.0) tend to exhibit
symptoms of manganese deficiency. The foliage develops a faint
interveinal marbling which becomes more marked as a yellowish
or green mottle as the leaves get older. Symptoms will be more
severe on puffy soils in dry periods after a wet spring or as
a result of poor rooting. Manganese deficiency can often be
mistaken for symptoms caused by mosaic virus, magnesium, sulphur
or iron deficiency.
A deficiency of this trace element can be corrected by an application
of manganese sulphate, the rate of application depending on
the severity of the deficiency. Over liming, alkaline soils
or organic peaty soils can cause deficiencies of this element.
Calcium.
This nutrient is used for plant cell division and cell elongation
Although oilseed rape demands high levels of this element, deficiencies
are rarely seen. Calcium deficient plants show damage at the
ends of racemes similar in appearance to bud wilt caused by
drought or damage caused by grey mould. As
long as the soil pH is maintained at a satisfactory level (6.0+)
the supply of calcium for growth should not be limited.
Molybdenum.
The needs of the rape crop are high for this element, however
deficiencies are rarely seen. Any deficiency is most likely
seen on acid soil and is favoured by calcium deficiency. Leaves
show yellowish interveinal clearings and necroses. Another symptom
can be malformed leaves ranging from cup shaped curling of the
margins to reduced development of the lamina.
Boron.
The needs of the rape crop for this element are tremendous and
can be as much as 10 times that required by cereals with deficiencies
occurring frequently. The necessity for this element can be
established by soil analysis prior to sowing.
Boron deficiency occurs in conditions where the element may
be present but less available to the crop. Conditions of high
alkalinity e.g. after liming will inevitably lock this chemical
up. The deficiency can be enhanced by drought.
The symptoms of deficiency can be seen on the younger leaves,
which are curled and undulated with their margins curved upward
and with the lamina red to yellow-brown colour. If the deficiency
persists the leaves are stunted and thickened. The petioles
and stems show scarred longitudinal fissures. With early and
extreme deficiencies the shoot tip is necrosed and numerous
lateral branches are produced. The number of pods and the number
of seeds in each pod is decreased.
FERTILISER REQUIREMENTS AND TIMING.
Timing
of P and K applications
Except on sandy soils, P and K is not leached and therefore
if indices are 2 or above, both these elements can be applied
at any time throughout the season without subsequent yield loss.
Applications can be made to the seedbed apart from light land,
where it may be more beneficial to apply this in the early spring.
For Spring Rape, to avoid wheelings in the seedbed, it may be
preferable to apply this in the drier autumn conditions before
winter ploughing.
|
P
or K Index
|
|
|
0
|
1
|
2
|
3
|
4
and over
|
|
|
Kg/ha
|
|
Winter
OSR (3.5t/ha)
|
|
Phosphate
(P2O5)
|
100
|
75
|
50M
|
0
|
0
|
|
Potash
(K2O)
|
90
|
65
|
40M
(2-) 20 (2+)
|
0
|
0
|
|
|
|
|
|
|
|
|
Spring
OSR (2t/ha)
|
|
Phosphate
(P2O5)
|
80
|
55
|
30M
|
0
|
0
|
|
Potash
(K2O)
|
75
|
50
|
25M
(2-) 0 (2+)
|
0
|
0
|
Sulphur applications
Oilseed rape is very responsive to this element. Sulphur deficiency
can be diagnosed by analysing young fully expanded leaves sampled
at flowering stage.
There has been a massive change in the use of industrial and
domestic fuels in Europe over the last few years, and the emissions
they put into the atmosphere. This has led to the steady decline
in the deposition of sulphur from the air. It is obvious from
this reduction that crop requirements for applied sulphur will
also have changed over the same time.
Sulphur is mobile in the soil and so needs to be applied every
year to soils with a deficiency. Heavy winter rainfall can make
the situation worse. Losses through leaching are always greater
on well-drained sandy soils than the heavier types. Sulphur
deficiency can reduce yield potential and is important for the
quality of protein in cereals.
In the early days sulphur deficiency was determined using tests
based on the N/S ratio. This often proved to be unsatisfactory.
In 2002 a new method was introduced called the Malate Test.
This is based on the Malate/sulphate ratio. For those who are
interested, Malate is an organic acid present in all plants
and it counterbalances the uptake of inorganic anions, including
sulphate. For this test to give a guide to deficiency it needs
to be carried out in early spring, and if the results show a
ratio more than 1:5, the plant is deficient. Normally rape plants
would not be sampled before the end of February, as they are
unlikely to be sulphur deficient at the stage of growth expected
at or before this time of the growing season.
Application timings for sulphur are such that the product should
be in the crop by the time it grows rapidly i.e. rapid stem
extension. For spring crops it needs to be applied at an earlier
time. Its activation, and consequently its uptake, is dependent
on moisture. As much as 12-14ml of rainfall will be required
to get the sulphate form into the soil and made available for
plant uptake.
Nationally, average field responses to sulphur on rape are close
to 30%.
Sulphur recommendations are either in kgs/ha of sulphur (S)
or kg/ha of sulphur trioxide (SO3). 1kg/ha S is equivalent to
2.5kg/ha SO3 so application rates of 75-100kg/ha of SO3 are
equivalent to applying 30-40 kgs/ha S.
Always use a sulphur in a readily available form; sulphate has
good plant availability. Sulphur products in bound or chelated
forms tend to be less available to the crop.
The first dose of sulphur with the first N dose needs to go
on in late February/early March. The higher amount of sulphur
would be appropriate to very light soils, or severe cases where
deficiency has been known for some time.
Manures
and slurries are a useful source of sulphur. Where applications
are very regular you may be able to make some slight adjustment.
There are numerous forms of inorganic fertiliser (see below)
that can be applied to supply the amount of S required by the
crop. Many of these contain nitrogen, so choice of material
will depend on both the amount of N you require and the amount
of S to satisfy the crop.
|
Name
|
%N
|
%P
|
%K
|
%S
|
| Ammonium
Sulphate |
21
|
0
|
0
|
24
|
| Kieserite |
0
|
0
|
0
|
22
|
| Kainit |
0
|
0
|
12
|
5
|
| Double
Top |
27
|
0
|
0
|
12
|
| Sulphan |
30
|
0
|
0
|
7.6
|
| Sulphur
10 |
20
|
4
|
14
|
2.8
|
| M24
Light Land S |
24
|
5
|
10
|
2.8
|
| Multicut
S |
23
|
4
|
13
|
2.8
|
| Single
Top |
27
|
0
|
0
|
4.8
|
| Multicrop
S |
10
|
15
|
21
|
8
|
| Heartland
S |
24
|
8
|
8
|
3.2
|
| Sulphur
Grass |
25
|
5
|
5
|
5
|
| Multi-sulph |
26
|
0
|
0
|
4
|
Example.
Sulphur
requirement.
The amount of sulphur required by a rape crop is between 75-100
KgSo3 /Ha or 30-40 kg S/Ha.
Apply this in late February with rest of N going on in late
March or early April.
If your expected yield is going to be over 4t/ha add a further
30kg/ha N. Total applied N will be in the region 190kg N/ha.
Using
Multi -sulph, which is a 26N 35:So3 (14S) blend and assuming
we are aiming for approx. 35kgS(87.5So3) in this treatment.
| There
are 350kgs of So3 in |
1000kgs
|
of
material. |
| Therefore
there is 1kg So3 in |
1000
|
of
material. |
|
350
|
|
Therefore
1kg of So3 comes from 2.857kg of material.
|
|
Therefore
87.5 Kg So3 comes from 250kg of material.
|
|
Apply
250kg/ha Multi-sulph.
|
Nitrogen
applications
The amount of nitrogen applied will be dependent on soil reserves.
Use of RB209 will be necessary to fine tune applications.
Starter nitrogen applied in autumn can be as justified as an
agronomic requirement in establishing a rape crop. Defra guidance
booklet RB209 supports the use of 30kg/ha N to seedbeds at SNS
index 0 ( 60kg/ha soil N), 1 (61-80 kg/ha N and 2 (81-100kg/ha
N). SNS series 0-2 will cover most soils and situations.
Total
dose rates of nitrogen of course vary with yield potential but
as a general rule of thumb are between 150 and 220kg/ha on mineral
soil. The higher end of the range (200-220kg/ha) is suitable
for crops with good standing ability and higher yield potential
(4-5t/ha) grown on mineral soils of low residual nitrogen availability.
For those soils of high fertility or where lodging is anticipated
or yield potential is lower (3t/ha), then 180-200kg/ha needs
to be applied. For soils that are highly fertile or on organic
soils, levels of 150kg/ha would be more appropriate.
If applications are less than 100kg/ha apply the whole dressing
during late February-early March at the start of spring growth.
For amounts of 100kg/ha or greater, split the dressing, 50:50
with half during late February-early March and the remainder
by late March-early April. Adjustments to the amount of nitrogen
to be applied at these splits may be necessary if sulphur is
being applied in a blend with the nitrogen. This will be acceptable
as long as at least 25% of the total dose is applied in with
the sulphur.
If
you have come through the winter with a very backward crop,
this will benefit from prompt fertiliser application in the
spring. This should be made at the onset of spring growth not
before.
Over
the last year or two there has been work looking at delaying
50% of the N application until early May (yellow bud). This
has worked well but needs sufficient moisture at that time to
facilitate uptake.
|
SNS
Index
|
0
|
1
|
2
|
3
|
4
|
5
|
6
|
|
Seedbed
kgs/ha
|
|
All
soils
|
30
|
30
|
30
|
0
|
0
|
0
|
0
|
|
|
|
Spring
kgs/ha
|
|
All
mineral soils
|
220
|
190
|
160
|
120
|
80
|
40-80
|
0-40
|
|
Organic
soils
|
|
|
|
120
|
80
|
40-80
|
0-40
|
|
Peaty
soils
|
|
|
|
|
|
40-80
|
40-80
|
It
must be appreciated that as the price of nitrogen increases
to unprecedented levels the amount used may need to be tweaked
to take into account this high price. This will be even more
relevant if the price of oilseed rape remains low. In the RB209
book the recommendations for nitrogen are based on a breakeven
ratio of 2.5.This rate may be reduced by up to 20kg/ha if the
breakeven ratio increases to 3.0 and may be increased by up
to 20kg/ha if the breakeven ratio drops to 2.0.
The
effect of economic changes.
Normally the recommendations are insensitive to changes in the
value of the crop produce per the cost of nitrogen fertiliser.
The breakeven ratio is the crop yield (kg) needed to pay for
1kg of nitrogen. Large increases in the breakeven ratio may
justify a small reduction in the nitrogen recommendation and
vice versa.
Example.
| Ammonium
nitrate (34.5%) costs £120/t |
or
|
120
x 100
|
=
|
34.78p/kgN
|
|
34.5
x 10
|
| Rape
sold for £136/t |
or
|
136
x 100
|
=
|
13.6p/kg
|
|
1000
|
| The
breakeven ratio is |
|
34.78
|
=
|
2.5kg
crop produce/kgN
|
|
13.6
|
|
Breakeven
ratio = 2.5:1
|
Nitrogen application.
There are 260kgN in 1000kg-applied material.
1 kg of applied material gives 0.26 kg of N.
Therefore if we apply 250kg material this will give 0.26 x 250
kg of N.
Therefore we will apply 65kg/ha N (52units/acre).
Nitrogen
scorch.
Large amounts of nitrogen when given in a single application
and in liquid form as urea or urea ammonium nitrate can sometimes
cause extensive chlorosis of the leaf. Subsequent new growth
will allow recovery from this damage.
If large amounts of prilled or granular urea, or nitro chalk
are applied during stem extension, similar damage can be seen
particularly if applied after cool, humid weather followed by
dry conditions. This damage could cause bud damage, which may
occur too late for the plant to be able to compensate for.
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