1. Effect of soil compaction and fertilization practise on N 2 O emission and CH 4 oxidation Sissel Hansen 1 Marina A. Bleken 2, Bishal K. Sitaula 3, 1)Bioforsk Organic Food and Farming Division 2)Norwegian Univ. of Life Sciences, Dept. of Plant & Env. Sci. 3)Norwegian Univ. of Life Sciences, Dept. of Int. Env. & Dev. Stu.

2. Outline Description of Agriculture in the region Field experiment Results N 2 O emission N 2 O of total N and mineral N applied CH 4 uptake GWP: N 2 O versus CH 4 Conclusions

5. Precipitation in mm

6. Average temperatures in °C

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

9. 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).

10. Nitrogen Input and sources: Fertilization with mineral-N (min N) and total N (tot N) in NH 4 NO 3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO) kg N per ha Year Green fodderGrassland

11. Soil compaction treatment: 5 passes each year with a 4 tonne tractor wheel by wheel

12. 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

13. Effect of soil compaction on N 2 O consentration in soil air (NH 4 NO 3 fertilized green fodder) 140 kg N ha -1 NH 4 NO 3 Compacted Uncompacted

14. Accumulated N 2 O emission early summer in green fodder year 7; fertilization with NH 4 NO 3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

15. Likely reasons for lower N 2 O emissions from cattle slurry in compacted than in uncompacted soil N2N2 N2ON2O NO 0 30 Days Ratio of NO, N 2 O and N 2 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 N 2

16. Accumulated N 2 O emission after fertilization with NH 4 NO 3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

17. N 2 O emissions during early summer in % of N added after fertilization with NH 4 NO 3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO) The average percentage fertilizer-derived N 2 O emissions was calculated as the N 2 O emission in fertilized treatments minus N 2 O 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)

18. N 2 O emissions during early summer in % of N added after fertilization with NH 4 NO 3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO) Uncompacted soilCompacted soil

19. Accumulated CH 4 uptake early summer year 7 and 9 after fertilization with NH 4 NO 3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO)

20. GWP effect of CH 4 oxidation versus N 2 O emission 720 times more CO 2 equivalents were emitted as N 2 O, than absorbed in soil through CH 4 oxidation in CSO treatment NPK (NH 4 NO 3 ) treatment 1860 times Calculations: N 2 O = 310 times CO 2, CH 4 =23 times CO 2

21. Conclusion Include effects of soil structure and soil moisture when estimates of N 2 O emissions are maid Higher N 2 O emissions per ha from conventional than organic fertilization practise Soil compaction increased the emissions, particularly after fertilization with NH 4 NO 3 Soil compaction decreased net CH 4 uptake The effect of methane oxidation on reduced GWP was negligible compared with increased GWP caused by N 2 O emission.

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23. Fertilization with mineral-N (min N) and total N (tot N) in NH 4 NO 3 (NPK), cattle slurry high (CSH) and cattle slurry organic (CSO) kg N per ha Year Green fodderBarleyGrassland

24. N 2 O emissions during early summer in % of N added with NH 4 NO 3