Abstract
AbstractReplacing tillage with cover crops (CC) for weed management in corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] systems with mechanical weed control has many soil health benefits but in the western Corn Belt, CC establishment after harvest is hampered by cold temperatures, limited labor and few compatible CC species. Spring-planted CC may be an alternative, but information is lacking on suitable CC species. Our objective was to evaluate four spring-planted CC with respect to biomass production and weed suppression, concurrent with CC growth and post-termination. Cover crop species tested were oat (Avena sativa L.), barley (Hordeum vulgare L.), brown mustard [Brassica juncea (L.) Czern.] and yellow mustard (Brassica hirta Moench). They were compared to no-CC treatments that were either tilled pre- and post-planting of soybean (no-CC tilled) or not tilled at all (no-CC weedy). CC were planted in late March to early April, terminated 52–59 days later using an undercutter, and soybean was planted within a week. The experiment had a randomized complete block design with four replications and was repeated for 3 years. Mustards and small grains produced similar amounts of biomass (1.54 Mg ha−1) but mustard biomass production was more consistent (0.85–2.72 Mg ha−1) than that of the small grains (0.35–3.81 Mg ha−1). Relative to the no-CC weedy treatment, mustards suppressed concurrent weed biomass in two out of 3 years, by 31–97%, and small grains suppressed concurrent weed biomass in only 1 year, by 98%.Six weeks after soybean planting, small grains suppressed weed biomass in one out of 3 years, by 79% relative to the no-CC weedy treatment, but mustards did not provide significant weed suppression. The no-CC tilled treatment suppressed weeds each year relative to the no-CC weedy treatment, on average 87%. The ineffective weed control by CC reduced soybean biomass by about 50% six weeks after planting. While spring-planted CC have the potential for pre-plant weed control, they do not provide adequate early season weed suppression for soybean.
Highlights
Weeds are the major cause for yield reductions in organic soybean systems that rely on mechanical weed management (Cavigelli et al, 2008)
Cover crop biomass production was influenced by the cover crops (CC) species by year interaction (Table 2)
Mustards and small grains had the same amount of biomass (1.55 and 1.53 Mg ha−1, respectively, P = 0.906), mustards were more reliable producers, with a narrower range of biomass production (Fig. 1)
Summary
Weeds are the major cause for yield reductions in organic soybean systems that rely on mechanical weed management (Cavigelli et al, 2008). Weed control in these systems includes tillage prior to planting soybean, and during early soybean growth until canopy closure. Cover crops (CC) are often used to improve soil structure and soil organic matter (Blanco-Canqui et al, 2015), but they are increasingly recognized as a tool for sustainable weed management. CC suppress weeds by competition (Sturm et al, 2018) and by creating a physical barrier in the form of their residue (Teasdale, 1996). CC residue modifies the quantity and quality of solar radiation, in particular altering the ratio of red:far-red light that reaches the surface, decreasing weed seed germination (Teasdale and Mohler, 1993)
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