DEPARTMENT OF PRIMARY INDUSTRIES

Can we reduce nitrous oxide emissions from crops?

Sally J. Officer, Gavin Kearney, Frances Phillips, Roger

Armstrong and Kevin Kelly.

N2O Network

Atmospheric gas concentrations over the past 1000 years

Atmospheric nitrous oxide is increasing in the same “hockey stick” pattern as carbon dioxide and methane.

84% of nitrous oxide emissions come

from agriculture in Australia.

75% of this nitrous oxide is generated by micro-organisms in agricultural soil, using N derived from:-

• Nitrogen fertilizer

• Soil disturbance

• Animals

Additional slide to be used at your discretion

Very large increase in emissions in July as soil reaches saturation. DCD may now be ineffective, but we will not be sure until statistical modelling is completed.

“66% of nitrogen fertiliser is used on cereals in Australia.”

“90% of the increase in N2O emissions from 1990 to 1999 was due to an increase in the rate of N fertiliser application” (Dalal et al,

2003)

TGA

Measuring N2O emissions from fertilised

crops

Automated chamber system measuring nitrous

oxide 16 times a day

Comparison of emissions from wheat cropping soils with either N fertiliser or a legume

rotation as the source of N

01020304050607080

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rai

nfa

ll (

mm

)

01020304050607080

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rai

nfa

ll (

mm

)

2007

2008

Rainfall during emissions monitoring

Annual rain

372 mm

GSR rain

205 mm

Decile 2

Annual rain

322 mm

GSR rain

183 mm

Decile 1

Drought years, good indicators of future conditions

A marked increase in N2O flux from cultivated plots immediately after

cultivation and planting. Possible early effect of the DCD (need statistical analysis.

Daily average emissions and soil moisture 2007

0

2

4

6

8

10

12

Apr-2007 Jun-2007 Aug-2007 Oct-2007 Dec-2007 Jan-2008

Flu

x N

2 O (

g N

.ha-1

.d-1

)

0

5

10

15

20

25

30

35

40

45

50

So

il m

ois

ture

co

nte

nt

(v/v

%)

Wheat, No N fertiliser Wheat and N fertiliser

Wheat and N fertiliser and irrigation Soil water

Sowing Harvest

0

50

100

150

200

250

300

No N fertiliser 50 kg N/ha 50 kg N/ha

g/ha

2007Increased Flux in 2007

23%64%

Daily average emissions and soil moisture 2008

Sowing Harvest

0

20

40

60

80

100

120

140

160

No N fertiliser No N fertiliser 50 kg N/hag/

ha

Increased flux in 2008

84%154%

O2

CO2NH4+

NO3-

N2ON2O

Nitrification cycle

(aerobic)

Soil mechanisms

NO-

O2

CO2NH4+

NO3-

N2 N2

NO

NO3-

NO2- N2O

N2

N2ON2O

N2O

Nitrification cycle

(aerobic)

Denitrification cycle

(anaerobic)

Soil mechanisms

NO-

O2

CO2NH4+

NO3-

N2 N2

NO

NO3-

NO2- N2O

N2

N2ON2O

The application of band of concentrated urea granules to an aerobic (drained) soil causes large

losses of nitrous oxide through the nitrification pathway

1) A clear increase in nitrous oxide emissions associated with the use of urea

2) No yield advantage from urea in two relatively dry years

3) Legume rotations supplied sufficient N for semiarid wheat under low rainfall and also generated less nitrous oxide

Can the humble legume help to save the planet?

Legumes can be difficult to establish and may not grow well in drier years, while a year of more reliable non leguminous grain crop has been lost.

Nevertheless, encouraging farmers to increase their use of legume rotations should reduce emissions from Australian grain crops.