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