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. Introduction Conservation agriculture: –↓ Erosion –↑ SOM –↑ Soil moisture –Improved soil structure –Soil temperature moderation 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 JanFebMarMayJunJulSepAprOctNovDecAug Soybean or Control CollardsRye 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 m 2

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 ABCBCC

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 1 st yr Grass control –variable, increases in 2 nd 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/