Effect of soil compaction and fertilization practise on N2O emission and CH4 oxidation

Sissel Hansen1

Marina A. Bleken2, Bishal K. Sitaula3,

1) Bioforsk Organic Food and Farming Division2) Norwegian Univ. of Life Sciences, Dept. of Plant & Env. Sci.3) Norwegian Univ. of Life Sciences, Dept. of Int. Env. & Dev. Stu.

Outline

•Description of Agriculture in the regionField experiment

•Results N2O emission

N2O of total N and mineral N applied

CH4 uptake

GWP: N2O versus CH4

•Conclusions

Precipitation in mm

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Average temperatures in °C

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May June July August September

The soil was a well-drained sandy loam soil; the topsoil contained 2.2 % C and 0.17% N

Field experiment:•10 years •Crop rotation adapted to organic dairy farming •High frequency of legumes

Split-plot factorial design with two replicates, soil compaction on main plots and fertilization on small plots (2.8 m x 8 m).

Nitrogen Input and sources: Fertilization with mineral-N (min N) and total N (tot N) in NH4NO3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

020406080

100120140160180200

7 9

NPK CSH-min N CSH-tot N CSO-min N CSO-tot N

kg N per ha

YearGreen fodder Grassland

Soil compaction treatment:

5 passes each year with a 4 tonne tractor wheel by wheel

Gas fluxes measured by soil cover chambers Spring year 7 and 9, late summer year 9

Four parallel flux measurements taken on each day of measurement. The flux was estimated by the increased concentration 3 hours after placement

Effect of soil compaction on N2O consentration in soil air (NH4NO3

fertilized green fodder)

140 kg N ha-1 NH4NO3

Compacted

Uncompacted

Accumulated N2O emission early summer in green fodder year 7; fertilization with NH4NO3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

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1.0

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NPK CSH CSO Unfertilized

kg N

2O

-N h

a-1 Uncompacted

Compacted

Likely reasons for lower N2O emissions from cattle slurry in compacted than in uncompacted soil

N2

N2O

NO

0 30Days

Ratio of NO, N2O and N2 by

denitrifikasjon in silty sand

More nitrogen lost with ammonia volatilization

Alexander,M.1977. Introduction to soil microbiology

Dense soil increases anaerobic microsites and more N is denitrified to N2

Accumulated N2O emission after fertilization with NH4NO3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

Green fodder, Year 7, early summer

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1.02.0

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5.06.0

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NPK CSH CSO Unfertilized

kg N

2O

-N h

a-1 Uncompacted

Compacted

Grassland, Year 9, early summer

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NPK CSH CSO Unfertilized

kg

N2O

-N h

a-1

Grassland, Year 9, late summer

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NPK CSH CSO Unfertilized

kg N

2O

-N h

a-1

N2O emissions during early summer in % of N added after fertilization with NH4NO3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

The average percentage fertilizer-derived N2O emissions was calculated as the N2O emission in fertilized treatments minus N2O emission in unfertilized treatment, divided by the amount of mineral N (total-N) applied with spring fertilization in year 7 (green fodder) and year 9 (grassland)

N2O emissions during early summer in % of N added after fertilization with NH4NO3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

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33.5

44.5

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Year 7 Year 9

NPK CSH-min N CSH-tot N CSO-minN CSO-tot N

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11.5

22.5

33.5

44.5

5

Year 7 Year 9

Uncompacted soil Compacted soil

Accumulated CH4 uptake early summer year 7 and 9 after fertilization with NH4NO3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

Grassland Year 9, early summer

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NPK CSH CSO Unfertilized

g C

H4 h

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Gren fodder Year 7, early summer

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NPK CSH CSO Unfertilized

g C

H4 h

a-1

Uncompacted

Compacted

GWP effect of CH4 oxidation versus N2O emission

•720 times more CO2 equivalents were emitted as N2O, than absorbed in soil through CH4 oxidation in CSO treatment

•NPK (NH4NO3) treatment 1860 times

Calculations: N2O = 310 times CO2, CH4=23 times CO2

Conclusion

•Include effects of soil structure and soil moisture when estimates of N2O emissions are maid

•Higher N2O emissions per ha from conventional than organic fertilization practise

•Soil compaction increased the emissions, particularly after fertilization with NH4NO3

•Soil compaction decreased net CH4 uptake

•The effect of methane oxidation on reduced GWP was negligible compared with increased GWP caused by N2O emission.

Thank you for your attention

Fertilization with mineral-N (min N) and total N (tot N) in NH4NO3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

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NPK CSH-min N CSH-tot N CSO-min N CSO-tot N

kg N per ha

Year Green fodder Barley GrasslandGrassland

N2O emissions during early summer in % of N added with NH4NO3

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Gren fodder, Year 7 Grassland, Year 9

UncompactedCompacted