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Title:Do benefits from cover crops vary by species or mixture composition?
Author(s):Holmes, Ashley Ann
Advisor(s):Wortman, Samuel E; Lovell, Sarah T
Department / Program:Crop Sciences
Discipline:Crop Sciences
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):cover crops
cover crop mixtures
Abstract:Cover crops are often used to manage weeds and increase productivity on organic farms, but questions remain about which species or combinations of species have the strongest impacts as living cover and which species and combinations are financially feasible for adoption in organic systems. An on-farm field study was conducted in 2014 and 2015 to assess the impact of 18 cover crop species on biomass production and weed suppression. The 18 species were split into three seasonally appropriate groups (six species per season) and planted in all possible monocultures and five-way mixtures with a weedy and weeded control on two organic farms in central and northern Illinois. Results suggest that cover crop species and mixtures had different capacities for producing biomass and competing with weeds, and they performed differently depending on year and location. Legumes were generally not competitive with weeds, resulting in up to 90% weed biomass in legume monoculture treatments. Cover crop mixtures were more competitive with weeds than legume monocultures and other monoculture treatments, depending on yearly variation in abiotic and biotic stressors. Mustard, sudangrass, tillage radish, and rye planted in mixture generally had higher partial land equivalent ratios than other species and overyielded in mixture compared to monoculture, indicating their relative dominance in mixtures. The most competitive mixtures tended to be those lacking one legume species. These types of mixtures were also the most cost-effective in each season because of the high relative cost of legume seed versus grasses and non-legume broadleaves. We suggest that farmers carefully assess their goals for cover cropping when considering species choice for mixtures, and to adjust seeding rates according to their goals, i.e. increase seeding rates for legumes if nitrogen fixation is a higher priority than weed suppression. The use of cover crops in mixture is becoming increasingly popular in organic farming systems. However, relatively little is known about how diverse species mixtures affect soil nitrogen cycling and soil microbial activity. An on-farm field study was conducted in 2014 and 2015 to assess the impact of 18 cover crop species on soil nitrate levels, tissue nitrogen accumulation, and soil microbial activity. Cover crops were divided into 3 seasonally appropriate groups and planted in monoculture and all possible 5-way mixtures and were compared to a ambient weeds and a weedy control. Although cover crops differed significantly in biomass production, they differed less in their effects on soil microbial activity and tissue nitrogen accumulation. Weeds did not differ significantly from cover crops in terms of nitrogen accumulation or nitrogen scavenging (e.g., ability to reduce available soil nitrogen and possible nitrogen loss). Soil nitrate levels under cover crops and weeds were reduced by up to 75% compared to the weeded control. Soil nitrate levels approximately one month after cover crop incorporation differed little among cover crop treatments and weeds. Because no explicit species differences were observed in this study, we suggest that farmers choose an inexpensive cover crop monoculture or mixture that fits their cover cropping goals, or perhaps consider alternative management strategies using weeds as a cost-free "cover crop."
Issue Date:2016-07-20
Rights Information:Copyright 2016 Ashley Holmes
Date Available in IDEALS:2016-11-10
Date Deposited:2016-08

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