English

Abstract

Field studies were conducted from 2012-13 to 2014-15 to investigate the dynamics of germinable soil seedbank, density and community composition of weeds in crop rotations of barley (Hordeum vulgare L.) + pea (Pisum sativum L.) and bread wheat (Triticum aestivum L.) in Oued Zem, semi-arid Morocco. In September 2012, the initial seedbank in 6 fields was 2354 seeds m-². When herbicide-free barley + pea forage mixture (cut for hay) was followed by bread wheat, seedbank reductions were 35% after the two years. When bread wheat was followed by herbicide-free barley + pea forage mixture, seedbank reductions were only 5% in two years. Prior to wheat harvest, weed densities were 82, 8, and 14 plants m-² in April 2013, 2014 and 2015, respectively. Prior to haying herbicide-free barley + pea, weed densities were 76, 109 and 34 plants m-² in April 2013, 2014 and 2015, respectively. Weeds identified in bread wheat fields were 49, 36 and 40 species in 2012-13, 2013-14 and 2014-15, respectively. Weeds associated with herbicide-free barley + pea mixture were 68, 51 and 36 species in 2012-13, 2013-14 and 2014-15, respectively. The seedbank prior to planting and weed density prior to harvesting were strongly influenced by the most recent crop. Integrated weed management combining glyphosate before no-till planting, post-emergence herbicide use in bread wheat, haying barley + pea mixture, within the crop rotation (barley + pea/bread wheat) reduced weed seedbank by up to 35%, species richness by up to 47%, and weed density prior to wheat harvest or forage haying by up to 83%. Such changes suggest that integrated weed management practices in no-till system must be continued for more than 3 growing seasons to drastically reduce weed seedbanks and weed densities. Key words: Weed, seedbank, wheat, barley + pea, no-till, Morocco.