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Biomass shifts and suppresses weed populations under conservation agriculture

Biomass shifts and suppresses weed populations under conservation agriculture. Michael J. Mulvaney, Virginia Tech, USA C. Wes Wood, Auburn University , USA Andrew J. Price, USDA ARS National Soil Dynamics Lab , USA.

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Biomass shifts and suppresses weed populations under conservation agriculture

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  1. Biomass shifts and suppresses weed populations under conservation agriculture Michael J. Mulvaney,Virginia Tech, USA C. Wes Wood,Auburn University, USA Andrew J. Price,USDA ARS National Soil Dynamics Lab, USA SANREM CRSP is made possible by the United States Agency for International Development and the generous support of the American people through USAID Cooperative Agreement No. EPP-A-00-04-00013-00.

  2. Conservation agriculture: ↓ Erosion ↑ SOM ↑ Soil moisture Improved soil structure Soil temperature moderation Introduction Kip Balkcom, 2008

  3. CA for limited-input smallholders • #1 problem: Weed suppression

  4. Solution? • High biomass cover crops (killed mulches) • Mulch Ted Kornecki, 2008

  5. Hypothesis • Combine cover crops and mulches • Improve soil quality on productive field • Effects on: • Weeds, soil C, yields

  6. Objective Quantify weed suppression of a summer cover crop and organic mulches under no-till collard (Brassica oleracea L.) production during conversion to CA: • Weed populations • SOC • Collard yield

  7. Methods • Previous fallow (3 years) • 3 years: 2005–2008 • Central-Eastern AL, USA • 2x4 RCB: • 2 summer cover crops: • Forage soybean, weed fallow • 4 organic mulches: • Lespedeza, mimosa, oat straw, control • 6.7 Mg ha-1 yr-1

  8. Cropping Schedule Soybean or Control Rye Collards Rye Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mulch application

  9. Methods • Weed coverage • Transects • 50 count transects • 2x per plot • Classified: • Broadleaves • Grasses • Sedges

  10. Methods • C & N: • Dry combustion • Yield: • 65 DAP • 2.8 m2

  11. Statistics • SAS: • Proc Means: Means and standard errors • Proc Glimmix: Model variable selection • 95% CL for treatment comparisons

  12. Results — broadleaf coverage • Year 1: • Without mulch, broadleaf weeds problematic

  13. Results — broadleaf coverage • Year 1: • Without mulch, broadleaf weeds problematic • Years 2 & 3: • Control effective without mulch

  14. Results — grass coverage • Year 1: • Mulches don’t help • Year 2: • Weeds shift toward grasses • But mulching helps • Year 3: • Same as year 2?

  15. Results — sedges • Summer cover crop x mulch interaction • Year 1: • Mulches don’t help • Years 2 & 3: • Reasonable control

  16. Spatial variability

  17. SOC after 3 yrs A B BC C C

  18. Soil organic carbon

  19. Yields • Collard Yields: • No treatment differences • Ave in SC (2001) 13,450 kg/ha • Ave: 17,900 kg/ha • Assuming 25% waste & 1.1 lbs/bunch: • ATL market, Nov. 18, 2009: • 25 lbs/ctn: US$12/ctn • US$14,222/ha • No premium assumed

  20. Conclusions • Forage soybean does not effectively suppress weeds • Broadleaf and sedge control • suppressed under high biomass CA after 1st yr • Grass control • variable, increases in 2nd yr • Population shifts from broadleaves and sedges toward grasses • Conversion from fallow to CA increased SOC • Yield not affected by mulching or forage soybean

  21. Thank you www.oired.vt.edu/sanremcrsp/

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