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

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

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

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

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

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

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

Cropping Schedule JanFebMarMayJunJulSepAprOctNovDecAug Soybean or Control CollardsRye Mulch application

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

Methods C & N: –Dry combustion Yield: –65 DAP –2.8 m 2

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

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

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

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

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

Spatial variability

SOC after 3 yrs ABCBCC

Soil organic carbon

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

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

Thank you