Assessing on-Farm Performance of Cover Crop Mixtures in Vegetable Cropping Systems.

Cover crop mixtures that include legumes can supply an efficient source of nitrogen (N) to fields while also providing other ecosystem functions. Understanding the ability of legumes to fix N in mixtures is essential to improve N management while optimizing the multifunctional benefits of mixtures. We evaluated 11 cool season cover crop treatments including bi-cultures, three-species mixtures, and monocultures on 10 working farms in Michigan with different soil types and management histories. In the fall and spring we measured aboveground cover crop biomass in different mixtures, N supply from biological N fixation, N in aboveground biomass, winter survival, and weed suppression compared to a no cover crop control. Across farms, mean fall cover crop biomass for all treatments ranged from 836 to 2058 kg ha^-1, and mean aboveground N retention ranged from 17 to 50 kg N ha^-1 with the greatest mean fall biomass and N scavenging in a yellow mustard (Sinapis alba) mixture. However, there was wide variability across the farms. For example, maximum fall biomass of a chickling vetch (Lathyrus sativus)/cereal rye (Secale cereale) mixture was 4460 kg ha^-1. Both high and low chickling vetch seeding rates resulted in similar levels of weed suppression and total N inputs from biological N fixation, but a greater proportion of vetch aboveground N was derived from the atmosphere at the lower vetch seeding density. We compared these results to baseline soil samples from farm fields, and explored how environmental conditions drive cover crop mixture performance. On-farm experimentation allowed us to test cover crops of interest to farmers within realistic socioeconomic contexts.