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Sulfur management: Product and placement• Ass. Prof. Chris Guppy (UNE)

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Standard sulfur cycle

gypsum

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Cropping responses

• A CQ example – rare– Sorghum trial at Capella, (Trevor Philp and the

Pacific Seeds team)

– No fert, N only, NP, NPK and NPKS

– Not much response to anything unless S limitation was fixed

• More typically..– Additive effects of S after P limitations are

overcome

– Courtesy – Mike Bell

0

1000

2000

3000

4000

5000

Nil 200N N + P N + P +

K

N + P +

K + S

Yie

ld (

kg/

ha

)

70% yield increase

(~ 2 t/ha sorghum)

0

1000

2000

3000

4000

5000

Nil 200N N + P N + P +

K

N + P +

K + S

Yie

ld (

kg/

ha

)

70% yield increase

(~ 2 t/ha sorghum)

8

9

10

11

12

13

14

15

Control P S PS

Yie

ld (

ba

les/

ha

)

Responses rare: critical values <3 mg S/kgsubsoil S most likely buffering S requirements

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Pasture responses

0

500

1000

1500

2000

2500

3000

DAP pastille MAP SSP MAP12

Clover yield (kg/ha)

Fertilizer

Harvest 4

Harvest 3

Harvest 2

Harvest 1

15 months legume yield in high rainfall environment

More common: Critical range 6-8 mg S/kg

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Courtesy: Jim Laycock (Incitec Pivot)

0

10

20

30

40

50

60

2008N=5896

2009N=5206

2010N=3569

2011N=4659

2012N=4904

2013N=4916

2014N=4735

2015N=4537

2016N=5431

2017N=6295

2018 JunN=4345

% o

f S

oil T

es

ts

Cropping Top-Soil S (KCl)

YearSamples

Source: Nutrient Advantage Laboratory Services

with sample depth ranges ≤10cm. 54493 SamplesIncludes soil test results from NSW

█ <4 mg/kg S (KCl)

█ 4 - 8 mg/kg S (KCl)

█ ≥8 mg/kg S (KCl)

Recent soil sulfur levels across NSW in cropping regions

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Courtesy: Jim Laycock (Incitec Pivot)

0

10

20

30

40

50

60

2008N=2194

2009N=2244

2010N=2211

2011N=2317

2012N=2494

2013N=2855

2014N=3284

2015N=3549

2016N=3254

2017N=2489

2018 JunN=1567

% o

f S

oil T

es

ts

Pasture Top-Soil S (KCl)

YearSamples

Source: Nutrient Advantage Laboratory Services

with sample depth ranges ≤10cm. 28458 SamplesIncludes soil test results from NSW

█ <4 mg/kg S (KCl)

█ 4 - 8 mg/kg S (KCl)

█ ≥8 mg/kg S (KCl)

Recent soil sulfur levels across NSW in grazing regions

Products available

Product Nitrogen (%) Phosphorus (%) Sulfate-S (%) Elemental S (%)

Granulock SS 10 17.5 4 8

SuPerfect 0 8.8 11 0

Pasture King 0 15.7 4.6 0

SuStain 0 0 0 90

GoldPhos 11 17.5 5 7

Gypsum 0 0 ~17 0

Products available – oxidation rates

Source: Degryse et al. (2016) Oxidation of elemental sulfur in granular fertilisers depends on the soil-exposed surface area. SSSAJ 80:294-305

Oxidation of elemental S from a range of fertiliser products over 40 weeks

• Oxidation of elemental S is affected by soil pH, moisture and temperature

• Rates are highest in moist, warm and neutral soil

• Oxidation is proportional to size of elemental S (the smaller the micron, the faster the oxidation)

• AND proportional to contact of elemental S with soil (co-granulation reduces contact, and decreases oxidation rates)

• Half-life for pure ES (35 d); mixed granular ES (140 d) and pastilles (>3 years)

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Sulfur placement and responses

Sulfur placement is less critical

Sulfur is mobile in soils

Subsoils often contain root accessible S

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Uniform low S profile

Band of S

Sulfur placement and co-location

Effect of S banding on cereal root proliferation response after 3 weeks

• No evidence for root proliferation in response to S

• Increasing S recovery is associated with increasing root exploration and length

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Effect of P and S placement depth and co-location on growth and S recovery of clover grown for 13 weeks

Sulfur placement and co-location

Study to investigate whether co-location of P and S important for legume pastures, particularly N fixation

Biomass and S uptake linked to P recovery not placement. Leaching had no effect – a surprising result.

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Effect of P and S placement depth on root recovery by wheat using isotopes following 6 weeks growth

Sulfur placement and co-location

Study to investigate cereal recovery of S from depth in multiple wheat varieties

No significant difference in S recovery from 10 or 40 cm suggesting roots at all depths are able to recover S (i.e age is not critical)

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Gaps in S knowledge

• Critical S values

• Sampling depths that match response

• Depletion of labile organic S reserves

• Residue management to optimise S cycling

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Recap

• S deficiency not yet widespread in cropping regions, but critical in grazing regions

• Products with elemental S important under leaching conditions

• Placement less critical due to S mobility in soil