biomass shifts and suppresses weed populations under conservation agriculture michael j. mulvaney,...
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Biomass shifts and suppresses Biomass shifts and suppresses weed populations under weed populations under conservation agricultureconservation agriculture
Michael J. Mulvaney,Michael J. Mulvaney, Virginia Tech, USAVirginia Tech, USA
C. Wes Wood,C. Wes Wood, Auburn University, USAAuburn University, USA
Andrew J. Price,Andrew J. Price, USDA ARS National Soil Dynamics Lab, USAUSDA 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.
IntroductionIntroduction• Conservation agriculture:
– ↓ Erosion– ↑ SOM– ↑ Soil moisture
– Improved soil structure – Soil temperature
moderation
Kip Balkcom, 2008
CA for limited-input smallholdersCA for limited-input smallholders
• #1 problem: Weed suppression
Solution?Solution?
• High biomass cover crops (killed mulches)
• Mulch
Ted Kornecki, 2008
HypothesisHypothesis• Combine cover crops and mulches
• Improve soil quality on productive field
• Effects on:– Weeds, soil C, yields
ObjectiveObjective 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
MethodsMethods• 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 ScheduleCropping Schedule
Jan Feb Mar May Jun Jul SepApr Oct Nov DecAug
Soybeanor Control
Collards RyeRye
Mulch application
MethodsMethods• Weed coverage
– Transects• 50 count transects• 2x per plot• Classified:
– Broadleaves– Grasses– Sedges
MethodsMethods• C & N:
– Dry combustion
• Yield:– 65 DAP– 2.8 m2
StatisticsStatistics• SAS:
– Proc Means: Means and standard errors– Proc Glimmix: Model variable selection– 95% CL for treatment comparisons
Results Results — broadleaf coverage — broadleaf coverage
• Year 1:
• Without mulch, broadleaf weeds problematic
Results Results — broadleaf coverage — broadleaf coverage
• Year 1:
• Without mulch, broadleaf weeds problematic
• Years 2 & 3:
• Control effective without mulch
Results Results — grass coverage — grass coverage
• Year 1:
• Mulches don’t help
• Year 2:
• Weeds shift toward grasses
• But mulching helps
• Year 3:
• Same as year 2?
Results Results — sedges— sedges
• Summer cover crop x mulch interaction
• Year 1:
• Mulches don’t help
• Years 2 & 3:
• Reasonable control
Spatial variabilitySpatial variability
SOC after 3 yrsSOC after 3 yrs
A BCB C C
Soil organic carbonSoil organic carbon
YieldsYields• 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
ConclusionsConclusions• 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 youThank you
www.oired.vt.edu/sanremcrsp/