Cover Crop Mixtures Build Soil Quality in Organic Hop Orchards

Cover crops are well known for their capacity to improve soil physical, chemical, and biological properties; provide supplemental nutrients; and help suppress weeds in horticultural production systems. Living cover crops planted between crop rows could also provide habitat for beneficial insects. Planting mixtures of cover crop species may provide greater system benefits than individual species, but the ideal combination to provide multiple benefits in organic hop systems has yet to be determined. We evaluated seven different cover crop mixtures alongside a no cover crop control at two on-farm research sites in Washington and Michigan over a period of three years.  Each treatment was replicated with one of four hop varieties to test treatment X genotype interactions.  Cover crop mixtures were sown each spring and terminated each fall following hop harvest. Soil samples were collected each spring, summer and fall, and ammonium and nitrate concentration determined using KCl extractions. Baseline and final year soil samples were analyzed for various soil chemical and biological properties. Results to date indicate that cover crop species mixtures differentially influenced soil properties in each trial, but results varied given location. For example, active soil carbon was greatest with the roadway mix treatment in Washington, while the rye/vetch/buckwheat provided the greatest active soil carbon in Michigan. Hop variety also influenced soil properties, with variety 1 resulting in greater active soil carbon than variety 3 in Michigan. In Washington, there was a significant interaction between hop variety and cover crop treatment with respect to active soil carbon, with variety 1 varying between treatments, while variety 3 was not impacted by cover crop treatment. These results indicate that cover crop mixtures can positively impact soil quality in organic hop orchards, but the ideal mixture will vary given location and hop variety.