University or Other Affiliation

California State University, Chico


In recent years walnut orchards implemented cover crops in between rows to improve soil’s quality, lessen soil’s erosion, increase organic matter, manage nutrient movement and availability, enhance water retention, and expand microbe, insect, and flora diversity. Commonly selected cover crops in California are from families Poaceae, Brassicaceae, and Fabaceae. Considerations should be made when choosing a particular cover crop mixture to enhance multiple benefits and improve sustainable practices in orchard settings. An experiment was conducted in a walnut orchard to compare functionality and benefits of three systems multi-crop, monocrop, and no vegetation cover crop system. The following components were evaluated: cover crop and weed biomass, cover crop species field distribution, and ability to provide better coverage and weed suppression properties. Brassica mixture, clover and grasses showed highest presence in field conditions and excellent weed competition attributes, while peas and faba beans had low presence and did not compete well growing in a mixture with other cover crops. Multi-crop treatment demonstrated the highest dry and wet biomass as well as the greatest weed suppression. Recommendations are to carefully consider current practices in walnut orchards, to seasonally include vegetation cover rather than bare soil, and to choose multi-crop cover rather than monocrop. Implementation of multi-crop species as a sustainable practice would increase soil’s quality, improve biological management through rise of natural beneficial predators and enhance integrated pest management methods.