Advanced process level understanding of factors controlling

gaseous nitrogen partitioning to reduce N2O losses from Australian

agricultural soils Clemens Scheer, Peter Grace, Daniel Warner, Johannes Friedl

Institute for Future Environments (IFE) Queensland University of Technology

• Denitrification is a key process of ecosystem N turnover • Greenhouse gas emissions N use efficiency

NITRIFICATION

NH4+ NO3

-

N2

DENITRIFICATION

N2O N2O

• The magnitude of total denitrification losses and N2 emissions are virtually unknown for the majority of Australian agricultural systems.

• Popular models (DayCent and DNDC) show vastly different N2O/N2 partitioning when simulating identical treatments.

• Models are absolutely critical for the development and verification of practical abatement strategies to reduce N2O emissions under the CFI / ERS.

• The influence of soil moisture, pH, carbon and nitrogen availability on the N2O/N2 ratio is a major area of uncertainty when predicting N2O emissions in response to management.

Research gap

1. Soil core incubations for process understanding and model calibration.

Activities

Incubation (1) - Impact of WFPS

Field based (1) Impact of DMPP

Site Treatment Denitrification losses over 21 days [kg/ha]

N2/N2O ratio

Casino (NSW) DMPP 1.57 88

UREA 2.22 44

Kerry (QLD) DMPP 0.94 13

UREA 1.3 10

Gympie (QLD) DMPP 1.06 8

UREA 0.67 5

Kingaroy

Days after NO3- application

2 4 6 8 10 12 14

N fl

ux [k

g ha

-1]

0

1

2

3

4

N2 N2O

Kingsthorpe

Days after NO3- application

2 4 6 8 10 12 14

N fl

ux [k

g ha

-1]

0

1

2

3

4

N2 N2O

360 kg ha-1 glucose

360 kg ha-1 glucose

NO3 water

NO3 water

Soil Total N lost [kg ha-1]

N2 Flux [kg ha-1]

N2O Flux [kg ha-1]

N2/ N2O Ratio

Kingaroy 14.1 ± 0.53 11.6 ± 0.10 2.5 ± 0.42 4.6

Kingsthorpe 5.7 ± 0.92 3.5 ± 0.05 2.2 ± 0.87 1.5

Field based measurements (2) Field based (2) Ferrosol vs. Vertosol

• N2O is an important indicator of much larger, economically significant losses of fertiliser nitrogen to the atmosphere via denitrification.

• Denitrification losses reached extraordinarily high values of >> 1 kg N/ha/day which might explain the high losses of N (50% of fertiliser N) observed in the field.

• Under conditions of prolonged soil water saturation and adequate carbon, the daily loss of N2 to the atmosphere can exceed N2O emissions by > 100.

• • Gaseous losses of N via denitrification in dryland cropping systems are mainly controlled by the availability of labile C in the soil profile.

• High C soils, like pastures and sugarcane systems could be identified as cropping systems with the highest denitrification potential.

NITRIFICATION

NH4+ NO3

-

N2

DENITRIFICATION

N2O N2O

Key findings

• More data on N2 and N2O emissions for different cropping systems are needed to better understand denitrification losses and how they affect NUE and soil N2O emissions.

• Data to be used to improve existing biogeochemistry models and validate their performance

• Decision support tool to identify and optimise abatement and BMP strategies

NITRIFICATION

NH4+ NO3

-

N2

DENITRIFICATION

N2O N2O

Future research needs

• Sequestration of SOC may be negating the benefit of C sequestration by increasing N2O losses as a result of enhanced denitrification activity.

• The project showed that N2O emissions are tightly coupled to total denitrification losses (up to 50% of fertiliser N)

• Focus needs to be on increasing NUE.

NITRIFICATION

NH4+ NO3

-

N2

DENITRIFICATION

N2O N2O

CFI development