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/