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Impacts of acidification on ammonia emissions and crop available N supply following slurry and digestate applications

John Williams1, Dom Edwards1, Dave Chadwick2, John Langley2, Tom Misselbrook3

and Sarah Gilhespy3

1 ADAS Boxworth, Cambridge CB23 4NN UK2 Bangor University, Gwynedd, North Wales, LL57 2DG, UK

3 Rothamsted Research North Wyke, Devon EX20 3SB UK

IFS Spring Webinar Series

27 May 2020

• Policy background

• What’s the big deal?

• Sources of ammonia emission

• Mitigation options

• Current Defra funded study

• Scope and objectives

• Sites and methodologies

• Interim results

• On-farm installation

• Summary and conclusions

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Content

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Ammonia is a significant pollutant

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• About 85% of UK ammonia emissions come from agriculture with livestock systems the main contributor

• Ammonia increases particulates in air which are harmful to human health

• Over 90% of sensitive SACs and SSSIs in the UK exceed their critical loads for total nitrogen deposition

• Ammonia is a significant component (approximately 65%) of total nitrogen deposition in the UK

• Habitat recovery is slow

Source: Defra’s Clean Air Strategy N deposition critical load exceedance map

UK Ammonia emission reduction targets

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• 2017 emissions 283 kt. Ceiling for 2010-2019: 297kt

• The UK has agreed to international targets to reduce emissions from 2005 levels by 8% by 2020 and by 16% by 2030 (ceilings are currently 265 kt and 242 kt respectively) – Clean Air Strategy

Projected emissions

Source: UK Informative inventory report 2018

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Ammonia emissions from UK agriculture (2017)

Source: Misselbrook and Gilhespy 2019

Total emissions from UK

agriculture 245,000t.

Ammonia emission mitigation across the manure management continuum

• Housing:

o Building design

o Reducing area of ammonia emitting surfaces

o Scrubbers on vents of controlled ventilation systems

• Storage:

o Covers

• Land spreading:

o Precision application techniques

o Rapid soil incorporation

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Ammonia emission control is expensive

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What about acidification ?

Acidification affects the NH4+ /NH3 equilibrium:

NH3(g) + H+(aq) NH4+(aq)

• Literature suggests reducing pH to c.5.5 can reduce ammonia emissions by more than 80%

• Widely used in Denmark (10-20% of pig slurry acidified.)

• Has potential to reduce emissions from the whole manure management continuum.

• Some practical issues relating to slurry foaming after acid addition.

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Defra Slurry Acidification Project SCF0215 2018 -2021

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What do we want to know?Do applications of acidified slurry and digestate:

• Reduce ammonia emissions• Increase crop available N supply• Affect soil quality• Is it practical for UK farmers ?

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Field experiments

Site Soil type Rainfall (mm) Land use

Gleadthorpe Sandy loam 650 Arable

Boxworth Clay 550 Arable

Terrington Silty clay loam 600 Arable

High Mowthorpe

Sandy loam 950 Grass

Bangor University

Clay loam 1100 Grass

RothamstedNorth Wyke

Sandy loam 1500 Grass

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Experimental design • Livestock slurry (all sites)

• Digestate (Gleadthorpe and North Wyke)

• Concentrated sulphuric acid added to slurry/digesate tanks prior to application

• Target application rates, 35m3/ha for livestock slurry; 25m3/ha for digestate

• Different application timings (autumn/spring on arable; 1st/2nd grass cuts)

• Different application methods (broadcast/bandspread)

• Single and repeated (2 years) applications

• 3 replicates in a randomised block design

Measurements

• Ammonia emissions (Gleadthorpe and NorthWyke)

• Nitrate leaching (Gleadthorpe)

• Crop yields and N offtakes (all sites)

• Fertiliser N replacement values (all sites)

• Soil quality (all sites: pH, metals, nutrients;Gleadthorpe and North Wyke: soil biology; postharvest 2020)

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0

20

40

60

80

100

120

0 50 100 150 200

Amm

onia

loss

(kg/

ha N

)

Hours after application

45% reduction

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Ammonia emissions autumn 2018 - Gleadthorpe

Pig slurry; pH 7.1 6.5 Digestate; pH 7.7 6.3

0

20

40

60

80

100

120

0 50 100 150 200

Amm

onia

em

issio

n kg

/ha

N)

Hours after application

Broadcast

Bandspread

Acidifiedbroadcast

Acidifiedbandspread

180 kg/ha total N applied190 kg/ha N total N applied

22% reduction

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Ammonia emissions spring 2019 - Gleadthorpe

0

20

40

60

80

100

120

0 50 100 150 200

Amm

onia

loss

(kg/

ha N

)

Hours after application

Broadcast

Bandspread

Acidified broadcast

Acidified bandspread

0

20

40

60

80

100

120

0 50 100 150 200

Amm

onia

loss

(kg/

ha N

)

Hours after application

180 kg/ha total N applied

74% reduction

Pig Slurry; pH 7.7 5.3 Digestate; pH 7.8 5.8

170 kg/ha total N applied

78% reduction

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Grain yields from spring application timings ADAS Gleadthorpe 2019

aa

b b

a a

b b

P<0.05; letters indicate statistically significant differences between treatments

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Grain N offtakes from spring application timings ADAS Gleadthorpe 2019

a aa a

b b b b

P<0.05; letters indicate statistically significant differences between treatments

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Calculating manure fertiliser replacement values (example 250 kg N/ha application)

Crop yield = 8 t/ha

Fertiliser N replacement value =125 kg/ha N

N use efficiency = 50% (i.e. 125/250)

Site Acidified Non-acidified

%total N applied

Boxworth 38 37

Gleadthorpe (pig slurry) 53 27

Gleadthopre (digestate) 59 30

High Mowthorpe (1st cut) 31 23

High Mowthorpe (2nd cut) 44 32

North Wyke cattle slurry (1st cut) 40 21

North Wyke cattle slurry (2nd cut) 42 22

North Wyke digestate (1st cut) 54 40

North Wyke digestate (2nd cut) 52 47

Bangor (1st cut) 29 14

Bangor (2nd cut) 20 13

Mean 42 28

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Manufactured nitrogen fertiliser replacement value of spring application timings – interim results

* No response to N at Terrington

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Acidified Non-acidified

Site Soil pH

Arable (Single application)

ADAS Terrington (N.S.) 8.48 8.53

ADAS Boxworth (N.S.) 8.04 8.07

ADAS Gleadthorpe (N.S.) 7.35 7.45

Grassland (2 applications)

ADAS High Mowthorpe (P<0.05) 6.20 6.70

Rothamsted North Wyke (N.S.) 5.95 6.19

Bangor University (N.S.) 6.67 6.87

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Changes in soil pH after one season

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Visual Overview of the typical system

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Example Layout & process flow Pigs

• A fully automated system

• Slurry is removed daily from individual chambers underneath the slatted floor into the process tank

• The slurry is put through a separator and the liquid fraction is treated with sulphuric acid until the target pH is reached

• The acidified liquid fraction is then pumped back to its corresponding chamber

• Excess daily volume is pumped to storage on each cycle

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Operational Information

Daily manpower requirement• Estimated at 30 minutes per day• Savings in slurry handling costs due automated system

Safety• Filling of acid tank is undertaken by authorised commercial suppliers • Acid is not handled at any time by the farmer / operator • The system is closed minimising exposure risk

Annual costs (6000 finisher unit)• Write off and interest cost £23,000• Acid £20,000 (9 litres/m3)• Power £6,500• Maintenance £3,000

Annual savings• Store cover £4,600• Labour £2,000• Reduced mortality £50,000• Improved pig performance £50,000• Fertiliser N £8,000

PC Main Screen

Data Logging

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Acidification:

• Reduced ammonia losses by between 25% and 80%, compared with non-acidified treatments. The reductions were greatest when slurry/digestate pH was reduced to below pH 6.0

• Increased (P<0.05) grain yields and nitrogen offtakes following spring application timings of pig slurry and food based digestate at ADAS Gleadthorpe

• Reduced (P<0.05) soil pH by 0.5 pH unit at High Mowthorpe

• Added capital and operational costs offset by benefits in system efficiencies and improved pig performance.

• Further work currently being carried out to test co-benefits of acidification on GHG emissions

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Interim conclusions

The funding of this work by Defra is gratefully acknowledged

Thanks to:

Quentin Kelly-Edwards from JH-Agro

Soren Petersen and Martin Hansen

Ryan Higginbotham, David Green, Sam Kendle and field teams at ADAS, Bangor and Rothamsted Research North Wyke

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Acknowledgements

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Thank you for your attentionJohn.Williams@adas.co.uk

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