Fluctuations of the weed seedbank

1
Fluctuations of the weed seedbank at the
long-term Beltsville Farming Systems Project
John R. Teasdale Ruth W. Mangum Jay
Radhakrishnan Michel A. Cavigelli USDA-ARS B
eltsville, Maryland, USA
2
Farming Systems Project 1996-2002

• Systems
• Recommended inputs Two year Corn-Wheat/Soybean
• Reduced inputs Two year Corn-Wheat/Soybean
• Organic Two year Corn-Soybean (CS)
• Organic Three year Corn-Soybean-Wheat/fallow
  (CSW)
• Organic Four year Corn-Soybean-Wheat/Hay-Hay
  (CSWH)

3
Multiple Regression Model D b0 bcC bc2C2
bnN bn2N2 bcnCN where D annual seedbank
change C percent weed cover at maturity N
seedbank in spring
4
Amaranthus 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
  seedbank0.

5
Conditions with no annual seedbank
change (intersection between response surface and
plane at seedbank0)
6
Annual weed seedbank dynamics at FSP
Extreme drought in 1999 No seed production
Poor control High seed production
Implication Seedbank can be reduced rapidly by
management if no seed production
7
Seedbank of Major Weed Species
Longer, more phenologically diverse organic
rotations reduced the weed seedbank
8
Lowering the seedbank by using more diverse
rotations can improve weed control in organic corn
9
Relation between weed cover at maturity and
spring seedbank for major species in corn
10
Role of Sequence
Three Rotations - All starting Corn-Soybean Rotati
on had little influence when start with corn
11
Role of Sequence
Four Year Rotation Different starting
crops Starting rotation with hay reduced seedbank
12

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