Emission from crop residues and nitrogen fixation

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Emission from crop residues and nitrogen
fixation National methodology Denmark Steen
Gyldenkærne and Mette Hjorth Mikkelsen National
Environmental Research Institute, Denmark
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Crop residuesnon-N-fixing crops

• Crop residues incorporated straw stubble
  leaves glumes

Incorporated straw is based on annual straw yield
minus gathered straw (the annual census covers
25 of the agricultural area) Amount of stubble,
leaves and glumes are based fixed amounts per ha
for the different crops multiplied with the
actual area with crop i For perennial crops,
stubble are calculated as 1/n where n is the
number of years in the rotation
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Use of crop residues - all crops
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Straw/Kernel-ratio(Useable amounts)
Source Oversigt over Landsforsøgene, 1995 and
Statistics Denmark
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Crop residues - example
Source Djurhuus and Hansen, 2004
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N-fixing crops (1) Basic model
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N-fixing crops (2)

• Mature peas
• Green peas
• Cereals for silage with legumes
• Lucerne
• Grass with legumes in rotation
• Grass with legumes outside rotation
• Legumes for seed
• Undersown fields
• Other

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N-fixing crops (3) example data
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N-fixing crops (4)

• Development in area
• Development in N-fix share in the different crops

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N-fixing crops (5) tonnes per year
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Conclusion

• Amount of crop residues varies between years due
  to climatic factors. These are however difficult
  to handle in the emission calculations due to
  lack of data.
• Crop/Kernel relationship is probably less than 1
  in most European countries
• Crop residues are calculated as the amount of
  not gathered straw based on the annual census
• Stubble and glumes are incorporated in the model
  as crop residues and handled as constant for all
  years instead as a share of crop yield. A fixed
  factor is probably more exact as a share of crop
  yield
• Roots are at the moment not incorporated, but
  data are available
• For perennial crops, stubble are calculated as
  1/n where n is the number of years in the
  rotation
• Emissions from crop residues should not count for
  more than 5-6 of the total N2O emission
• N-fix is calculated accordingly to crop residues,
  but include roots
• The share of N-fixing crops in grass in rotation
  and cereals for silage changes between years. The
  share is based on expert judgement