Long-Term Weed Dynamics and Yield Comparison of Organic and Conventional Cropping Systems in the Canadian Prairies.

The transition from conventional tillage to no-till and the introduction of new crops enabled to diversify crop rotations with both annuals and perennials in the Canadian cropping systems. Furthermore, organic agriculture is widely practiced where tillage replaces herbicides. The long-term impact of these diverse cropping systems can influence the weed dynamics indifferently due to the contrasting differences in crop management, crop rotations, and amount and type of inputs being used. A long-term study (18 years) was carried out at Scott, Saskatchewan Canada by Agriculture Agri-Food Canada to study the effect of diverse cropping systems on the weed dynamics and grain yields. The experiment is a split-split-plot design with four replicates which has three input levels; conventional tillage with high inputs (HIGH), no-till with reduced inputs (RED) and organic (ORG), and three crop diversity levels; low diversity fallow-annual grains rotation , diversified annual grains, and diversified annuals and perennials. Each rotation consisted of six crop phases. Averaged across all phases, diversified annual grains rotation had the highest weed biomass in both ORG and HIGH input systems. The lowest was observed in fallow-grains rotations in RED and HIGH systems. Organic systems had about three times higher weed density compared to other systems and had three times and twelve times higher weed biomass than RED and HIGH systems respectively. Yet, mean crop yield was only 25% and 29% lower in ORG compared to the RED and HIGH respectively. The variability in weed density over time was greatest in fallow-grains rotation. The variability in weed biomass was greatest in HIGH system and lowest in ORG systems. This study concludes that even after a long period under ORG management yields were substantially low in ORG systems compared to conventional systems and these low yields may not directly attributed to high weed abundance.

Key words- organic systems, conventional systems, weed dynamics