Emission of nitrous oxide from a cracking clay soil

Graeme Schwenke, David Herridge, Guy McMullen, Bruce Haigh,

Kelly Baker

Cracking Clay Soils

Cropping in the northwest NSW grain-growing region covers up to 2.5 m ha.More than 70% of crops are grown on cracking clay soils

Tamworth N2O trial site

Shrink-swell properties Crack when dry Medium-heavy clay content Alkaline pH in nw NSW

Direct soil emissions of N2O N2O is produced directly in soils as

– a by-product of nitrification, and – an end-product of denitrification

The dominant process depends largely on soil moisture content Neither process has any regard for the source of the nitrogen

Fertiliser(e.g. urea, ammonia, ammonium sulphate,

DAP, MAP, UAN)

Fertiliser(e.g. calcium nitrate,

ammonium nitrate, UAN)

Soil organic matter,Crop residues,

Manure

NH4+ NO3

-

N2O (~0.4%)

Nitrification

N2O (~ 2.4%*)N2

Denitr

ificatio

n

Plant uptake

* in an alkaline clay soil with pH >8.0

Broadacre Options for reducing direct N2O emissions?

Use less nitrogen fertiliser– Nitrogen budgeting– Flexible nitrogen fertiliser application (increase N use efficiency)– Grow legume crops that fix their own nitrogen

• Pulses should emit less N2O during crop growth• Mineralised N from residues = a form of slow release nitrogen?• Other GHG benefits through reduced N fertiliser manufacture and

transport

Reduce the “pool” of nitrate in soil waiting for plant uptake – Split / flexible nitrogen fertiliser application– Use a nitrification inhibitor with nitrogen fertiliser– Other slow-release forms of nitrogen fertiliser– Address other nutrient / disease issues to increase yield (+ nitrogen use)

“Better match timing and amount of N supply to crop demand”

Compare soil N2O emissions during several crop types– Canola, chickpea, fababean, fieldpea, wheat, sorghum

Compare soil N2O emissions across several crop rotations– Pulse-wheat, Canola-wheat, Pulse-sorghum

Compare soil N2O emissions from pulse-derived N with fertiliser N– Pulses (chickpea, fababean, fieldpea), Fertiliser (urea)

Derive soil N2O emissions factor for pulse-derived N– Chickpea, fababean, fieldpea

Project Objectives

Project Methods 3 year Crop rotation experiment

– 4 treatments• canola+N wheat+N summer fallow barley+N• chickpea wheat summer fallow chickpea• chickpea wheat+N summer fallow barley• chickpea winter fallow sorghum+N winter fallow (+N = urea fertiliser, all applied at sowing)

– 3 replications– Zero-till, stubble-retained, chemical weed and disease control

– Automatic air-sampling chambers (50 cm x 50 cm x 20 cm)• Air samples collected 7-8 times per 24 hours, 7 days a week• Air samples analysed in our field lab using a gas chromatograph

(N2O and CH4) and an infra-red gas analyser (CO2).

Air sample chambers in newly sown wheat and winter fallow plots

Gas chromatograph inside field lab

Air sample chambers in chickpea and canola

Air sample chambers in wheat and newly sown sorghum

Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Cum

ulat

ive

N2O

em

itted

(g

N/h

a)

0

200

400

600

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1000

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1400

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Canola+N

Chickpea

WheatHarvest

Canola &ChickpeaSowing

Month / Year

Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11

Dai

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all (

mm

)

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WheatSowing Sorghum

Sowing

Canola &ChickpeaHarvest

Canola+N_Wheat+N Chickpea_Sorghum+N Chickpea_Wheat+N Chickpea_Wheat-N

Cumulative N2O emissions (year 1)

G. Schwenke, I&I NSW: unpublished data

During the 2009 crop, most N2O was likely emitted during nitrification of N from urea fertiliser. Very little N2O came from legume plots.

In the 2009/10 summer fallow, most N2O was likely emitted during denitrification of the nitrate mineralised from crop residues.

All high N2O emission events occurred in response to rainfall, but not all rainfall led to emissions.

Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Cum

ulat

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N2O

em

itted

(g

N/h

a)

0

200

400

600

800

1000

1200

1400

0

200

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600

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1000

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1400

Canola+N

Chickpea

WheatHarvest

Canola &ChickpeaSowing

Month / Year

Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11

Dai

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all (

mm

)

0

20

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0

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WheatSowing Sorghum

Sowing

Canola &ChickpeaHarvest

Canola+N_Wheat+N Chickpea_Sorghum+N Chickpea_Wheat+N Chickpea_Wheat-N

Cumulative N2O emissions

G. Schwenke, I&I NSW: unpublished data

Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11 Cum

ulat

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N2O

em

itted

(g

N/h

a)

0

200

400

600

800

1000

1200

1400

0

200

400

600

800

1000

1200

1400

Canola+N

Chickpea

WheatHarvest

Canola &ChickpeaSowing

Month / Year

Jul-09 Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Mar-10 Apr-10 May-10 Jun-10 Jul-10 Aug-10 Sep-10 Oct-10 Nov-10 Dec-10 Jan-11 Feb-11

Dai

ly r

ainf

all (

mm

)

0

20

40

60

80

0

20

40

60

80

WheatSowing Sorghum

Sowing

Canola &ChickpeaHarvest

Canola+N_Wheat+N Chickpea_Sorghum+N Chickpea_Wheat+N Chickpea_Wheat-N

Cumulative N2O emissions (year 2)

G. Schwenke, I&I NSW: unpublished data

Rainfall soon after wheat sowing led to immediate N2O loss from the urea fertiliser. No N2O emitted from fallow legume plots.

Rainfall straight after sorghum sowing led to immediate N2O loss from the urea fertiliser.

Further N2O emissions occurred after heavy rainfall

In all cases it is likely that denitrification dominated the loss pathway

Summary All N2O losses strongly linked to rainfall

– Soil moisture affects the rates of nitrification and denitrification, and determines which process dominates

In 1 year, canola plots emitted 627 g N/ha as N2O versus 134 g N/ha for chickpea. Total N lost from urea applied ~ 14 kg/ha

• N2O Emission factor for canola (+80 kgN/ha as urea)0.33% (in crop)0.77% (1 year) (one third of this emitted in 2 wet summer

weeks)

• N2O Emission factor for chickpea (fixed 41 kg N/ha during its growth)0.34% (1 year) (half of this emitted in 2 wet summer weeks)

Despite a fully wet soil profile throughout autumn-winter 2010, N2O emissions only occurred after addition of N fertiliser

So far, total N2O emissions after 1.6 years of a 3-year rotation;• canola+N wheat+N summer fallow 1,260 g N/ha• chickpea wheat summer fallow 300 g N/ha• chickpea wheat+N summer fallow 650 g N/ha• chickpea winter fallow sorghum+N 698 g N/ha(+N = urea fertiliser, all applied at sowing)

Conclusions

Growing more pulses in rotation should reduce N2O emissions and help reduce overall GHG emissions from the broadacre grains industry

Further reduction in N2O emissions can be gained through better nitrogen management; – reducing fertiliser applied– increasing fertiliser use efficiency

Our future goal: to investigate N2O mitigation by tactical N fertiliser management in crop

Thank youThank you