PARENT SESSION
Poster Session #74: Agroecology.
Friday, August 9. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Below and above-ground weed community response to a long-term management and rotation experiment.

Smith, Richard^*,1,2, Gross, Katherine^1,2, Harwood, Richard², ¹ W. K. Kellogg Biological Station, Hickory Corners, MI² Michigan State University, East Lansing, MI

ABSTRACT- Organic management and crop rotation are two alternative agricultural strategies aimed at increasing the sustainability of cropping systems by decreasing the need for external chemical inputs such as synthetic fertilizers, pesticides, and herbicides. As these two techniques become increasingly widespread, it is important to understand the long-term consequences of these alternative management techniques on associated weed communities. In this study I examined how the soil seed bank and emergent weed communities differed across treatments in the tenth year of a long-term corn-corn-soybean-wheat rotation and management experiment at the Kellogg Biological Station (KBS) in Southwest Michigan. Direct germination of seedbank samples collected in May (prior to crop emergence) showed that weed seed densities in the soil seed bank were, on average, 26% lower in organically managed compared to conventionally managed treatments. Crop rotation tended to increase weed seed density in both management treatments, but increased species density only in the conventional treatments. Aboveground weed community biomass was 55 % higher in continuous organic corn compared to continuous conventional corn, but decreased to a level that was equal to, or lower than, conventional treatments when crops were rotated. In conventional treatments, aboveground weed species density increased under crop rotation. Weed species density tended to be lower in organic treatments regardless of whether or not crops were rotated. The results presented here indicate that contrary to conventional wisdom organic management and crop rotation can effectively control weed populations to levels at or below those achieved in conventionally managed systems.

KEY WORDS: organic management, crop rotation, weed community, soil seed bank