Emissions of nitrous oxide from a cracking clay soil - Graeme Schwenke

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Emissions of nitrous oxide from a cracking clay soil - Graeme Schwenke

  1. 1. Emission of nitrous oxide from a cracking clay soil Graeme Schwenke , David Herridge, Guy McMullen, Bruce Haigh, Kelly Baker
  2. 2. Cracking Clay Soils Cropping in the northwest NSW grain-growing region covers up to 2.5 m ha. More than 70% of crops are grown on cracking clay soils <ul><li>Shrink-swell properties </li></ul><ul><li>Crack when dry </li></ul><ul><li>Medium-heavy clay content </li></ul><ul><li>Alkaline pH in nw NSW </li></ul>Tamworth N 2 O trial site
  3. 3. Direct soil emissions of N 2 O <ul><li>N 2 O is produced directly in soils as </li></ul><ul><ul><li>a by-product of nitrification , and </li></ul></ul><ul><ul><li>an end-product of de nitrification </li></ul></ul><ul><li>The dominant process depends largely on soil moisture content </li></ul><ul><li>Neither process has any regard for the source of the nitrogen </li></ul>* in an alkaline clay soil with pH >8.0 Fertiliser (e.g. urea, ammonia, ammonium sulphate, DAP, MAP, UAN) Fertiliser (e.g. calcium nitrate, ammonium nitrate, UAN) Soil organic matter, Crop residues, Manure NH 4 + NO 3 - N 2 O (~0.4%) Nitrification N 2 O (~ 2.4%*) N 2 Denitrification Plant uptake
  4. 4. Broadacre Options for reducing direct N 2 O emissions? <ul><li>Use less nitrogen fertiliser </li></ul><ul><ul><li>Nitrogen budgeting </li></ul></ul><ul><ul><li>Flexible nitrogen fertiliser application (increase N use efficiency) </li></ul></ul><ul><ul><li>Grow legume crops that fix their own nitrogen </li></ul></ul><ul><ul><ul><li>Pulses should emit less N 2 O during crop growth </li></ul></ul></ul><ul><ul><ul><li>Mineralised N from residues = a form of slow release nitrogen? </li></ul></ul></ul><ul><ul><ul><li>Other GHG benefits through reduced N fertiliser manufacture and transport </li></ul></ul></ul><ul><li>Reduce the “pool” of nitrate in soil waiting for plant uptake </li></ul><ul><ul><li>Split / flexible nitrogen fertiliser application </li></ul></ul><ul><ul><li>Use a nitrification inhibitor with nitrogen fertiliser </li></ul></ul><ul><ul><li>Other slow-release forms of nitrogen fertiliser </li></ul></ul><ul><ul><li>Address other nutrient / disease issues to increase yield (+ nitrogen use) </li></ul></ul><ul><li>“ Better match timing and amount </li></ul><ul><li>of N supply to crop demand” </li></ul>
  5. 5. <ul><li>Compare soil N 2 O emissions during several crop types </li></ul><ul><ul><li>Canola, chickpea, fababean, fieldpea, wheat, sorghum </li></ul></ul><ul><li>Compare soil N 2 O emissions across several crop rotations </li></ul><ul><ul><li>Pulse-wheat, Canola-wheat, Pulse-sorghum </li></ul></ul><ul><li>Compare soil N 2 O emissions from pulse-derived N with fertiliser N </li></ul><ul><ul><li>Pulses (chickpea, fababean, fieldpea), Fertiliser (urea) </li></ul></ul><ul><li>Derive soil N 2 O emissions factor for pulse-derived N </li></ul><ul><ul><li>Chickpea, fababean, fieldpea </li></ul></ul>Project Objectives
  6. 6. Project Methods <ul><li>3 year Crop rotation experiment </li></ul><ul><ul><li>4 treatments </li></ul></ul><ul><ul><ul><li>canola+N  wheat+N  summer fallow  barley+N </li></ul></ul></ul><ul><ul><ul><li>chickpea  wheat  summer fallow  chickpea </li></ul></ul></ul><ul><ul><ul><li>chickpea  wheat+N  summer fallow  barley </li></ul></ul></ul><ul><ul><ul><li>chickpea  winter fallow  sorghum+N  winter fallow </li></ul></ul></ul><ul><ul><ul><li>(+N = urea fertiliser, all applied at sowing) </li></ul></ul></ul><ul><ul><li>3 replications </li></ul></ul><ul><ul><li>Zero-till, stubble-retained, chemical weed and disease control </li></ul></ul><ul><ul><li>Automatic air-sampling chambers (50 cm x 50 cm x 20 cm) </li></ul></ul><ul><ul><ul><li>Air samples collected 7-8 times per 24 hours, 7 days a week </li></ul></ul></ul><ul><ul><ul><li>Air samples analysed in our field lab using a gas chromatograph ( N 2 O and CH 4 ) and an infra-red gas analyser (CO 2 ). </li></ul></ul></ul>
  7. 7. Air sample chambers in newly sown wheat and winter fallow plots
  8. 8. Gas chromatograph inside field lab
  9. 9. Air sample chambers in chickpea and canola
  10. 10. Air sample chambers in wheat and newly sown sorghum
  11. 11. Cumulative N 2 O emissions (year 1) <ul><li>During the 2009 crop, most N 2 O was likely emitted during nitrification of N from urea fertiliser . Very little N 2 O came from legume plots. </li></ul><ul><li>In the 2009/10 summer fallow, most N 2 O was likely emitted during denitrification of the nitrate mineralised from crop residues. </li></ul><ul><li>All high N 2 O emission events occurred in response to rainfall, but not all rainfall led to emissions. </li></ul>G. Schwenke, I&I NSW: unpublished data
  12. 12. Cumulative N 2 O emissions G. Schwenke, I&I NSW: unpublished data
  13. 13. Cumulative N 2 O emissions (year 2) <ul><li>Rainfall soon after wheat sowing led to immediate N 2 O loss from the urea fertiliser. No N 2 O emitted from fallow legume plots. </li></ul><ul><li>Rainfall straight after sorghum sowing led to immediate N 2 O loss from the urea fertiliser. </li></ul><ul><li>Further N 2 O emissions occurred after heavy rainfall </li></ul><ul><li>In all cases it is likely that denitrification dominated the loss pathway </li></ul>G. Schwenke, I&I NSW: unpublished data
  14. 14. Summary <ul><li>All N 2 O losses strongly linked to rainfall </li></ul><ul><ul><li>Soil moisture affects the rates of nitrification and denitrification, and determines which process dominates </li></ul></ul><ul><li>In 1 year, canola plots emitted 627 g N/ha as N 2 O versus 134 g N/ha for chickpea. Total N lost from urea applied ~ 14 kg/ha </li></ul><ul><ul><ul><li>N 2 O Emission factor for canola (+80 kgN/ha as urea) </li></ul></ul></ul><ul><ul><li>0.33% (in crop) </li></ul></ul><ul><ul><li>0.77% (1 year) (one third of this emitted in 2 wet summer weeks) </li></ul></ul><ul><ul><ul><li>N 2 O Emission factor for chickpea (fixed 41 kg N/ha during its growth) </li></ul></ul></ul><ul><ul><li>0.34% (1 year) (half of this emitted in 2 wet summer weeks) </li></ul></ul><ul><li>Despite a fully wet soil profile throughout autumn-winter 2010, N 2 O emissions only occurred after addition of N fertiliser </li></ul><ul><li>So far , total N 2 O emissions after 1.6 years of a 3-year rotation; </li></ul><ul><ul><ul><li>canola+N  wheat+N  summer fallow 1,260 g N/ha </li></ul></ul></ul><ul><ul><ul><li>chickpea  wheat  summer fallow 300 g N/ha </li></ul></ul></ul><ul><ul><ul><li>chickpea  wheat+N  summer fallow 650 g N/ha </li></ul></ul></ul><ul><ul><ul><li>chickpea  winter fallow  sorghum+N 698 g N/ha </li></ul></ul></ul><ul><ul><ul><li>(+N = urea fertiliser, all applied at sowing) </li></ul></ul></ul>
  15. 15. Conclusions <ul><li>Growing more pulses in rotation should reduce N 2 O emissions and help reduce overall GHG emissions from the broadacre grains industry </li></ul><ul><li>Further reduction in N 2 O emissions can be gained through better nitrogen management; </li></ul><ul><ul><li>reducing fertiliser applied </li></ul></ul><ul><ul><li>increasing fertiliser use efficiency </li></ul></ul><ul><li>Our future goal: to investigate N 2 O mitigation by tactical N fertiliser management in crop </li></ul>
  16. 16. Thank you

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