The Selective Memory of Weed Seedbanks after 18 Years of Conservation Tillage

Abstract

A conservation tillage study provided the opportunity to test whether tillage effects on the germinable weed seedbank would be consistent across different crop rotations and to investigate the potential residual effects of herbicide treatments terminated 12 yr earlier. Our objective was to measure the effects of tillage (moldboard plow [MP] vs. chisel plow [CP] vs. no-till [NT]), crop rotation (2-yr barley–red clover followed by 4-yr barley–canola–wheat–soybean rotation, compared to a cereal monoculture), and of a prior weed management factor (three intensity levels of herbicide use) on the density, diversity, and community structure of weed seedbanks. Species richness, evenness (Shannon'sE), and diversity (Shannon'sH′) of spring seedbanks varied little across treatments and over time. Total seedbank density generally increased as tillage was reduced, with some variations due to weed management in 1993 and crop rotation in 2006. Crop rotations generally had smaller seedbanks with fewer species than the monoculture. In 1993, seedbanks with minimum weed management were twice as dense as those with intensive or moderate weed management (approximately 6,000 vs. 3,000 seed m−2). By 2006, seed density averaged 6,838 seed m−2across intensive and moderate weed management regardless of tillage, but was nearly twice as large in NT (12,188 seed m−2) compared to MP (4,770 seed m−2) and CP (7,117 seed m−2) with minimum weed management (LSD0.005= 4488). Species with abundant seedbanks responded differently to treatments. Barnyardgrass and green foxtail had larger seedbanks in the monoculture than in the rotation. Common lambsquarters and pigweed species had large seedbanks in tilled treatments in the rotation, whereas yellow foxtail and field pennycress contributed to the large seedbanks observed in NT treatments. The latter two species were also associated with residual effects of weed management treatments (terminated 12 yr earlier) in NT. The differential seedbank response of weed species, attributed in part to contrasting weed emergence patterns and agronomic practice effects on seed rain, explained some of the weak treatment effects observed for total seedbank density and diversity. The large weed seedbanks observed in NT plots after 18 yr confirms the importance of seed rain and seedbank management for the sustainability of NT systems.

Effects of the Tillage Technology and the Forecrop on Weeds in Stands of Winter Wheat

“…methods of tillage and/or crop rotation) determine signifi cantly the composition of weed population and numbers of weeds on fi elds (Ulber et al, 2009). Many authors mentioned a general rule according to which the deeper and more frequent the processing of topsoil, the lower the degree of infestation and also the more limited magnitude of the soil seedbank (Cardina et al, 2002;Moonen & Bárberi, 2004;Légère et al, 2011). In case of reduced (or minimum) soil processing technologies, the weed seedbank is concentrated near the soil surface, above all due to a shallower tillage (Moss, 1988;Cousens & Moss, 1990;Roger-Estrade et al, 2001;Chauhan et al, 2006;Mohler et al, 2006).…”

Impacts of Organic Zero Tillage Systems on Crops, Weeds, and Soil Quality

“…Therefore, shifts in weed community population dynamics frequently occur when any type of conservation tillage is adopted [55,56], including ZT. Understanding tillage effects on weed community dynamics can be challenging because the effects are variable and depend on interactions with other management tactics, environmental conditions, and weed biology [57][58][59]. Most research on ZT effects on weeds has been conducted in conventional systems were synthetic herbicides are used since organic ZT approaches are relatively new [23,40,41].…”

“…Research regarding the effects of ZT on weeds in conventional systems might be used to anticipate consequences of ZT in organic systems for processes such as weed seed distribution within the soil profile. However, other observations from ZT studies that include herbicide applications may need reconsideration when applied to organic systems since herbicide use is such a strong filter on weed community assembly processes [59][60][61]. Likewise, research results from conventional vs. organic tillage studies oftentimes will differ because organic fields tend to have greater weed species density and diversity than fields managed conventionally [6,[62][63][64][65].…”

“…Diverse crop rotations indirectly impact weed population through tillage effects, because tillage timing and frequency varies with crop species [59,61]. Weed species that are phenologically synchronous with a particular crop species tend to survive and proliferate with that crop [72].…”

Stork’s bill (Erodium cicutarium (L.) L’Her. ex Ait) and hemp-nettle (Galeopsis tetrahit L.): a cautionary note for eastern Canada field crops

“…In the case of stork's bill, early and rapid action will be needed to prevent the species from becoming a weed of agricultural importance in eastern Canada. Légère et al 2005Légère et al , 2011.…”