Fluctuations of the weed seedbankFluctuations of the weed seedbank at the long-term at the long-term

Beltsville Farming Systems ProjectBeltsville Farming Systems Project

John R. TeasdaleJohn R. TeasdaleRuth W. MangumRuth W. MangumJay RadhakrishnanJay RadhakrishnanMichel A. CavigelliMichel A. Cavigelli

USDA-ARSUSDA-ARSBeltsville, Maryland, USABeltsville, Maryland, USA

SystemsSystems

• Recommended inputsRecommended inputs – Two year Corn-Wheat/Soybean– Two year Corn-Wheat/Soybean• Reduced inputsReduced inputs – Two year Corn-Wheat/Soybean– Two year Corn-Wheat/Soybean

• Organic – Two yearOrganic – Two year Corn-Soybean (CS)Corn-Soybean (CS)• Organic – Three yearOrganic – Three year Corn-Soybean-Wheat/fallow (CSW)Corn-Soybean-Wheat/fallow (CSW)• Organic – Four yearOrganic – Four year Corn-Soybean-Wheat/Hay-Hay (CSWH)Corn-Soybean-Wheat/Hay-Hay (CSWH)

Farming Systems ProjectFarming Systems Project1996-20021996-2002

Multiple Regression ModelMultiple Regression Model

D = bD = b00 + b + bccC + bC + bc2c2CC22 + b + bnnN + bN + bn2n2NN22 + b + bcncnCNCN

wherewhere D = annual seedbank changeD = annual seedbank changeC = percent weed cover at maturityC = percent weed cover at maturityN = seedbank in springN = seedbank in spring

SpeciesSpecies bb00 bbcc bbc2c2 bbnn bbcncn RR22

A. hybridusA. hybridus 902 902 911911 -5.84-5.84 -0.702-0.702 -0.0159-0.0159 0.6290.629

C. albumC. album 12591259 245245 +3.15+3.15 -0.347-0.347 -0.0051-0.0051 0.6130.613

An. grassesAn. grasses 10541054 371371 +1.78+1.78 -0.541-0.541 -0.0404-0.0404 0.8090.809

SeedbankChange

30,000

15,000

0

-15,000

05,000

10,00015,000

20,000Initial

Seedbank15

3045

60

PercentCover

Amaranthus hybridus annual seedbank changeAmaranthus hybridus annual seedbank change

• High weed cover leads to large seedbank increase at low initial seedbank.• High initial seedbank leads to potential large seedbank decrease.• Equilibrium defined by horizontal plane through seedbank=0.

0 10 20 30 40

0

5,000

10,000

15,000

20,000

25,000

30,000C. albumA. hybridusAnnual grass

Initi

al S

ee

db

an

k (n

o. m

-2 )

Percent Cover

Conditions with no annual seedbank changeConditions with no annual seedbank change(intersection between response surface and plane at seedbank=0)(intersection between response surface and plane at seedbank=0)

Annual weed seedbank dynamics at FSPAnnual weed seedbank dynamics at FSP

1996 1997 1998 1999 2000 2001 2002

Year

0

5000

10000

15000

Sm

oo

th p

igw

eed

see

d m

-2 Soybean-Wheat-CornWheat-Corn-SoybeanCorn-Soybean-Wheat

Organic Three-Year System

Extreme drought in 1999Extreme drought in 1999No seed productionNo seed production Poor controlPoor control

High seed productionHigh seed production

Implication:Implication:Seedbank can be Seedbank can be reduced rapidly reduced rapidly by management by management if no seed if no seed productionproduction

0100020003000400050006000700080009000

10000

A. hybridus C. album

CSCSWCSWH

Mean over 1997-2002

Seedbank of Major Weed SpeciesSeedbank of Major Weed Species

Longer, more Longer, more phenologically phenologically diverse organic diverse organic rotations reduced rotations reduced the weed seedbankthe weed seedbank

Lowering the seedbank by using more diverse Lowering the seedbank by using more diverse rotations can improve weed control in organic cornrotations can improve weed control in organic corn

0

10

20

30

40

50

Rel

ativ

e sc

ale

Spring seedbank Weed cover at maturity

Example: 1998 common lambsquarters in organic corn

CS CSW CSWH

YearYear A. hybridusA. hybridus C. albumC. album GrassGrass

19971997 0.0810.081 0.3920.392 0.0530.053

19981998 0.5720.572 0.5320.532 0.5020.502

20002000 0.0410.041 0.4680.468 0.0020.002

20012001 0.7570.757 0.0140.014 0.7000.700

Regression R-squaredRegression R-squared

Relation between weed cover at maturity and Relation between weed cover at maturity and spring seedbank for major species in cornspring seedbank for major species in corn

1996 1997 1998 1999 2000 2001 20020

5000

10000

15000

20000

25000

La

mb

squ

art

ers

Se

ed

(n

o. m

-2 )

CSCSCSCSWCSWCSWHCS

Role of Sequence:Role of Sequence:Three Rotations - All starting Corn-SoybeanThree Rotations - All starting Corn-SoybeanRotation had little influence when start with cornRotation had little influence when start with corn

1996 1997 1998 1999 2000 2001 2002

Year

0

5000

10000

15000

20000

25000

La

mb

squ

art

ers

Se

ed

(n

o. m

-2 )

CSWHCSHHCSWH- HHCSW

Role of Sequence:Role of Sequence:

Four Year Rotation – Different starting cropsFour Year Rotation – Different starting cropsStarting rotation with hay reduced seedbankStarting rotation with hay reduced seedbank

Seedbanks in organic systemsSeedbanks in organic systems

• Fluctuated according to level of seed inputsFluctuated according to level of seed inputs• Rapid decline with no seed inputs suggests can Rapid decline with no seed inputs suggests can reduce seedbank quickly through managementreduce seedbank quickly through management• Rotations with higher Rotations with higher phenological diversity phenological diversity can reduce seedbankcan reduce seedbank• Rotation sequences beginning with hay are Rotation sequences beginning with hay are better than sequences beginning with cornbetter than sequences beginning with corn• Lower initial seedbank can increase success of Lower initial seedbank can increase success of weed control in cornweed control in corn