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/