Species‐Specific Contributions to Productivity and Weed Suppression in Cover Crop Mixtures

Abstract

Core Ideas Mustard, oat, sudangrass, and buckwheat were the most productive cover crops. Excluding mustard from spring mixtures sometimes increased weed biomass. Excluding sudangrass from summer mixtures sometimes increased weed biomass. Forage radish was less productive, but suppressed weeds in monoculture and mixture. Cover crops can provide many ecosystem services and on‐farm adoption is increasing. Cover crop mixtures are popular, but little is known about the functional contributions of individual species in mixture. On‐farm field studies were conducted across 3 yr (2014–2016) and two locations (organic farms in central and northern Illinois) to assess the productivity and weed suppressive capacity of 12 cover crop species planted in monoculture and in mixture. Species were split into two equal (six species each) and seasonally appropriate groups (cool vs. warm season), planted in all possible monocultures and five‐way mixtures (divided proportionally to monoculture rates), and compared with a weedy control. Mustard [Brassica juncea (L.) Czern.] and oat (Avena sativa L.) were among the most productive (as much as 4.48 and 3.95 Mg ha−1, respectively) and weed suppressive spring cover crops. In 2 of 5 site‐years, excluding mustard from five‐way mixtures resulted in increased weed biomass. Sudangrass [Sorghum bicolor (L.) ssp. Drummondii] and buckwheat (Fagopyrum sagittatum Moench) were typically the most productive summer cover crops (as much as 8.78 and 7.11 Mg ha−1, respectively) and also reduced weed biomass. In 2 of 6 site‐years, excluding sudangrass from the mixture led to increased weed biomass. Forage radish (Raphanus sativus L.) had less aboveground biomass, but reduced weed biomass by 45 to 100%. Results are among the first to document species‐specific contributions to an ecosystem service in cover crop mixtures, and can be used to inform recipes for mixtures designed for greater productivity and weed suppression.