Dr. Sarah T. Lovell
Department of Crop Sciences, University of Illinois at Urbana-Champaign
1201 S Dorner Dr. Urbana, IL 61801
Dr. Sam E. Wortman
Department of Agronomy and Horticulture, University of Nebraska – Lincoln
279 Plant Sciences Hall, Lincoln, NE 68583
Non-technical Executive Summary:
Cover crop mixtures are popular among farmers because of the perception that mixtures will provide a greater quantity and quality of ecosystem services. We know that cover crop biomass is usually greater in diverse mixtures compared to component monoculture plantings, but information about ecosystem services provided by cover crop mixtures is lacking. The objective of this study was to assess the relative contribution of 18 cover crop species to mixture productivity and ecosystem services including, soil microbial activity, soil nitrogen retention, nitrogen fixation, and weed suppression. Six individual cover crop species and all possible five-way mixture combinations of those species were planted in each of three possible rotational phases (spring, summer, and fall) on two organic vegetable farms in central and northern Illinois. Soil microbial activity was sometimes greater in cover-cropped plots compared to bare fallow, but did not vary by species or mixture composition. After eight weeks of growth, cover crops reduced soil nitrate by up to 70% compared to bare fallow, but again, there was no difference among species or mixture composition. Legume root nodule biomass per plant was usually not different between legume monocultures and mixtures; however, legume shoot biomass often decreased in mixture indicating the potential for reduced nitrogen fixation. Mustard, sudangrass, buckwheat, and tillage radish were among the most weed suppressive species when planted in monoculture, and when these species were removed from five-way mixtures, weed biomass increased (suggesting species-specific contributions to weed suppression in mixtures). We did not detect allelopathic weed suppressive benefits of any species or mixture one month after residue incorporation in soil. Results from this study suggest that farmers can choose the least expensive cover crop species or mixture when the primary objective is to retain soil nitrogen or stimulate microbial activity. However, when the primary objective is weed suppression, farmers should carefully design cover crop mixtures to ensure weed suppressive species are included.