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

2. Systems Recommended inputs– Two year Corn-Wheat/Soybean Recommended inputs– Two year Corn-Wheat/Soybean Reduced inputs– Two year Corn-Wheat/Soybean Reduced inputs– Two year Corn-Wheat/Soybean Organic – Two yearCorn-Soybean (CS) Organic – Two yearCorn-Soybean (CS) Organic – Three yearCorn-Soybean-Wheat/fallow (CSW) Organic – Three yearCorn-Soybean-Wheat/fallow (CSW) Organic – Four yearCorn-Soybean-Wheat/Hay-Hay (CSWH) Organic – Four yearCorn-Soybean-Wheat/Hay-Hay (CSWH) Farming Systems Project 1996-2002

3. Multiple Regression Model D = b 0 + b c C + b c2 C 2 + b n N + b n2 N 2 + b cn CN whereD = annual seedbank change C = percent weed cover at maturity N = seedbank in spring Speciesb 0 b c b c2 b n b cn R 2 A. hybridus 902911-5.84-0.702-0.01590.629 C. album1259245+3.15-0.347-0.00510.613 An. grasses1054371+1.78-0.541-0.04040.809

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 seedbank=0.

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

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. Mean over 1997-2002 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. YearA. hybridusC. albumGrass 19970.0810.3920.053 19980.5720.5320.502 20000.0410.4680.002 20010.7570.0140.700 Regression R-squared Relation between weed cover at maturity and spring seedbank for major species in corn

10. Role of Sequence: Three Rotations - All starting Corn-Soybean Rotation 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 Fluctuated according to level of seed inputs Rapid decline with no seed inputs suggests can reduce seedbank quickly through management Rapid decline with no seed inputs suggests can reduce seedbank quickly through management Rotations with higher phenological diversity can reduce seedbank Rotations with higher phenological diversity can reduce seedbank Rotation sequences beginning with hay are better than sequences beginning with corn Rotation sequences beginning with hay are better than sequences beginning with corn Lower initial seedbank can increase success of weed control in corn Lower initial seedbank can increase success of weed control in corn