Biomass shifts and suppresses weed populations under conservation agriculture
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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.

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Biomass shifts and suppresses weed populations under conservation agriculture

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-00-04-00013-00.


Introduction

Conservation agriculture:

↓ Erosion

↑ SOM

↑ Soil moisture

Improved soil structure

Soil temperature moderation

Introduction

Kip Balkcom, 2008


Ca for limited input smallholders

CA for limited-input smallholders

  • #1 problem: Weed suppression


Solution

Solution?

  • High biomass cover crops (killed mulches)

  • Mulch

Ted Kornecki, 2008


Hypothesis

Hypothesis

  • Combine cover crops and mulches

  • Improve soil quality on productive field

  • Effects on:

    • Weeds, soil C, yields


Objective

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

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

Cropping Schedule

Soybean

or Control

Rye

Collards

Rye

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

Nov

Dec

Mulch application


Methods1

Methods

  • Weed coverage

    • Transects

      • 50 count transects

      • 2x per plot

      • Classified:

        • Broadleaves

        • Grasses

        • Sedges


Methods2

Methods

  • C & N:

    • Dry combustion

  • Yield:

    • 65 DAP

    • 2.8 m2


Statistics

Statistics

  • SAS:

    • Proc Means: Means and standard errors

    • Proc Glimmix: Model variable selection

    • 95% CL for treatment comparisons


Results broadleaf coverage

Results — broadleaf coverage

  • Year 1:

    • Without mulch, broadleaf weeds problematic


Results broadleaf coverage1

Results — broadleaf coverage

  • Year 1:

    • Without mulch, broadleaf weeds problematic

  • Years 2 & 3:

    • Control effective without mulch


Results grass coverage

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

Results — sedges

  • Summer cover crop x mulch interaction

  • Year 1:

    • Mulches don’t help

  • Years 2 & 3:

    • Reasonable control


Spatial variability

Spatial variability


Soc after 3 yrs

SOC after 3 yrs

A

B

BC

C

C


Soil organic carbon

Soil organic carbon


Yields

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

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

Thank you

www.oired.vt.edu/sanremcrsp/


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