Managing Sulphur and Potash

Natalie Wood – Yara Country Arable Agronomist

Contents

• Sulphur− What do we get from the atmosphere?− Why is sulphur important?− Different ways plants obtain sulphur− Leeching, soil types− Timing− Rates and ROI

• Potassium− Why is potassium important?− Water Uptake− Nutrient Function and deficiency− Nutrient uptake and demand

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How Much Sulphur Do We Get from the Atmosphere?

• The map of sulphur deposition shows that the majority of the country is receiving between 0 and 12kg SO3/ha/yr.

• Crop requirements are around 45kg SO3 per year for wheat and 75kg

SO3 per year for oilseed rape

• Sulphur obtained through deposition is wholly inadequate to fulfil the

crop requirements therefore its addition is necessary to fill that short-fall

Total S deposition (2011).Source: Centre for Ecology and

Hydrology (CEH)

• Sulphur plays important roles within a plant, particularly metabolism and has similar interactions to nitrogen – meaning there is a strong relationship between these two nutrients

• Sulphur deficiency has a strong impact on the uptake of nitrogen. Sulphur is an integral part of the bonds that go towards regulating enzymatic reactions in photosynthesis; therefore an insufficient amount within the plant will decrease the activity of these important enzymes

• Sulphur has many important roles including structural, catalytic and other regulatory processes involved in protein production

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Why is Sulphur Important to Plants?

SULPHUR

CysteinePrecursor to Glutothionone,

alliins,phytochelatins which all help alleviate stress.

AMINO ACIDSCysteine

MethionineStructural importance in protein formation

PHOSPHORUS

ENERGYATP

Fuel of many biochemical reactionsPhosphorus important.

PHOTOSNTHESISLight, Water, CO2

CarbohydrateChlorohyll - central molecule is Nitrogen.

PROTEINThe Biulding Blocks of Yield

• There are 3 main ways that plants can access sulphur:

− Soil Reserves – Sulphur has a similar cycle to nitrogen within the soil, however only a small proportion of the sulphur is plant-available, making it hard to build reserves in the soil

− Organic wastes – The amount of available sulphur in organic wastes is variable and therefore not consistent enough to be a reliable source. Most organic wastes are applied in the autumn/early spring when the crop can’t utilise the sulphur. Sulphur in the soil leaches in the same way that nitrogen does, meaning that when the crop is ready to use the sulphur in April – June it has already leached

− Mineral fertilizers – This is the most reliable way to ensure plants have a supply of sulphur. To have plant-available sulphur the best form of mineral fertilizers are those containing sulphate sulphur. This means that the sulphur is readily available rather than having to convert within the soil before being taken up

• Most mineral fertilizers containing sulphur also contain nitrogen; this is not a coincidence as the two nutrients have a strong relationship within the plant, with several processes requiring both N and S

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Different Ways Sulphur Gets into the Plant

Sulphate is susceptible to leaching

• The magnitude of leaching is affected

by the S fertilizer type!

• Significant amounts of sulphur can be

lost by leaching

• Lower leaching risk from calcium

sulphate (S source in YaraBela Axan)

compared to ammonium sulphate

nitrate (ASN)

• Rothamsted : “Practices that minimise

leaching losses, like those used for

nitrate are advantageous.” 0

10

20

30

40

50

YaraBela Sulphan ASN

Hanninghof, pot trial, 20 kg/ha sulphur applied at post emergence of

ryegrass, 30 mm surplus rainfall applied after the 1st cut, loss recorded in

20 cm loamy sand soil column

% S leaching of applied S

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Examples of % leaching of Sulphur by soil type (Ref: Rahn (HRI)

% Sulphur loss Drainage (mm)

Soil Type 25 50 100

Loamy sand 15 35 85

Sandy silt loam 5 20 60

From a mid Feb application of 60 kgSO3, 51 kg SO3/ha could be leached on a loamy sand, by April/May. Thus leading to low soil reserves during this period of active growth.

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5.0

5.3

5.0

5.5

4.7

4.8

4.9

5.0

5.1

5.2

5.3

5.4

5.5

5.6

Control All early All Late Little & Often

Seed

Yie

ld (t

n ha

-1)

Sulphur Application Timing

Sulphur Timing Results on OSR (Total SO3 60 kg/ha 0.2 t/ha Oilseed yield = £63/ha (OSR @ £315/t))

LSD = 0.29t/ha

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10.3

11.7

9.5

10

10.5

11

11.5

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Straight Nitrogen YaraBela Axan

Sulphur response in wheat, at 220 kg N/ha (2016 Trial)

(1.4 t/ha yield gain = £228.2/ ha from applying YaraBela Axan)

Rates for Sulphur

• Yara would normally recommend 40-50kg SO3 for cereals and 70-80kg SO3 for oilseed− New trials from the past 2 years would suggest higher rates if you’re on a responsive site, adding up to 30kg

more SO3

• However how do you know if you’re on a responsive site?− Grain analysis is a good way to look at how your sulphur strategy worked that season− N:S ratio of <17:1 indicates sulphur sufficiency− Anything greater than 17:1 could well require higher rates of sulphur− Milling varieties require more sulphur than feed (production of protein glutenin)− There is still time now if you have grain left to send a sample off for analysis to change your strategy for next

season

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Return on InvestmentThe cost of using an NS product (YaraBela Axan 27% N 9% SO3) is ~£28/ha more than straight nitrogen

Wheat• Typically using sulphur gives a yield benefit from 0.2- 1.4t/ha – this gives an average yield benefit of 0.85t/ha

• At November wheat (feed) prices at ~£160/t this gives between £32/ha - £224/ha – average of £128/ha

• So £128/ha / £28/ha = 4.57

• Therefore the ROI for wheat when using sulphur over straight N would be 4.6:1

Oilseed• Typical yield benefit from sulphur is 0.5t/ha

• At November OSR prices at ~£326/t this gives £163/ha

• Therefore the ROI for OSR when using sulphur over straight N would be 3.5:111

Why is Potassium Important?

Potassium

• Transport of sugars, enzyme activation, synthesis of proteins

• Increases thickness of cell walls therefore helps with pest/diseases

• Promotes the storage of carbohydrates

• Regulates water balance and improves water relations & plant turgor

• Increases drought tolerance

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Potassium

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Function Deficiency Excess

Enzymatic regulation Old leaves (marginal chlorosis) Ca unbalance

Osmotic control (water balance) Reduced vigor (lodging)

Carbohydrate translocation (resistance mechanisms)

Antagonism to Mg (deficiencies)

Potassium and Water Uptake

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l Potassium supply increases water use efficiency

l The beneficial effect of K fertilisation on water use efficiency is much more evident under drought conditions

l Potassium is present in guard cells of the stomata; which control water regulation through stomatal opening

l Therefore if there is a K deficiency the guard cells won’t be able to work as efficiently and the plant will lose more water through transpiration

l This is particularly important when we are pushing N rates and getting bigger crops with increasingly dry springs

Potassium Percentage of Sufficient Levels Within Plant

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5% 10% 20% 50% 100% 150%

Potassium is vital for early root growth and branching

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0

20

40

60

80

100

120

total roots main root 2nd order roots

root

gro

wth

rela

tive

(NPK

=100

%)

NPK NP

Nutrient Uptake During Rapid Growth Phase

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Nutrient uptake during 18 days in kg/ha

Nutrient Beginning of

tillering

End of tillering Uptake

Total per day

N 86 167 81 4.5 kgP2O5 25 55 30 1.6 kgK2O 104 242 138 7.7 kg

• High rates of K are taken up in a short space

of time, especially compared to N and P

• This crop is taking up 7.7kg of K per day

during rapid growth phase

• The key timing of K is in the spring due to the

high plant demand

Nitrogen and potassium availability is important:

26.333 37.4

48.842.1 37.7

0102030405060

double ridges tofloral initiation (14

days)

floret initiation toear emergence

(14 days)

ear emergence tomaturity (7 weeks)

Gra

in n

umbe

r/ear

Application Growth Period

MEAN EFFECTS OF HIGH OR LOW NITROGEN IN THREE DEVELOPMENTAL PERIODS FROM DOUBLE RIDGES TO MATURITY ( R. H. M. LANGER & F. K. Y.

LIEW*)

Low NitrogenHigh Nitrogen

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38

43

32

34

36

38

40

42

44

Deficient Intermediate Sufficient

Gra

in n

umbe

r/ear

Potassium Supply

Effect of potassium supply on grain number per ear/spike(Ref:PDA).

Rate and Timing of Potassium

• The rate of potassium, as a minimum application in early spring, should be 35kg/ha independent of your indices due to the fresh K being plant-available whilst soil availability might be low

• If you are below Index 1 then you will require an autumn application to ensure sufficient levels in the soil for establishment, but then also still 35kg fresh K in the spring so don’t apply all the K in that first application

• The main and most important timing for K is in the spring when the crop demand is so high

• When it comes to characteristics in the soil then K is different to P which is very immobile in the soil

• K can get into the roots via mass flow as well as diffusion therefore is more mobile in the soil meaning the plant has a better chance of accessing it when compared to P which is mainly taken up via diffusion

Deficiency on clover

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Summary

Potassium

• Important for water-regulation and enzyme activation

• Particularly important in drought conditions due to stomata

• Crops require a lot of potassium, especially during tillering

• Always apply fresh K in the spring

• Rate depends on indices

YaraMila ActyvaS Compound (16-15-15+6.5%SO3)

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Sulphur

• Important for protein-building

• Necessary to get the best out of N use

• Leaches easily – dependent on soil type

• Higher rates on responsive sites only

• Yield benefit from 0.2-1.4t/ha

• Wheat ROI of 4.6:1

• OSR ROI of 3.5:1

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Thank You