Effect of wheel traffic and green manure treatments on forage yield and crown rot in alfalfa (Medicago sativa)

Harvesting alfalfa damages crowns and increases the opportunity for entry of pathogens. Incorporation of green manures into soil increases population density of streptomycetes with broad pathogen antagonist activity. This study aimed to measure the impact of wheel traffic on forage yield and plant health and the effect of green manures to reduce disease. Buckwheat and sorghum-sundangrass were incorporated into soil 3 weeks before seeding alfalfa. Total bacteria, streptomycete, and pathogen antagonist densities were measured prior to planting green manures and alfalfa. Wheel traffic was applied 2 days after each forage harvest. Wheel traffic reduced forage yield 12 % to 17 % depending on year and location, significantly reduced plant counts, and increased crown rot compared to the no traffic control. Cultivar had a significant effect on yield, plant counts, and crown rot. Streptomycete density and pathogen antagonists increased when fall-sown green manure crops were incorporated in spring. Forage yields were significantly higher in plots with greater antagonist density when traffic was applied. Green manure treatments did not affect plant counts or crown rot. Mechanical wheel traffic reduces forage yield and increases disease. Green manure crops may provide benefits in alfalfa production systems by increasing pathogen antagonists.