biomass shifts and suppresses weed populations under ca. michael mulvaney
DESCRIPTION
A presentation from the WCCA 2011 event held in Brisbane, Australia.TRANSCRIPT
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 supportof the American people through USAID Cooperative Agreement No. EPP-A-00-04-00013-00.
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
Jan Feb Mar May Jun Jul SepApr Oct Nov DecAug
Soybeanor Control
Collards RyeRye
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 m2
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
A BCB C C
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 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
Thank you
www.oired.vt.edu/sanremcrsp/