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

Samac, Deborah A., Lamb, JoAnn F. S., Kinkel, Linda L., Hanson, Lindsey
Plant and soil 2013 v.372 pp. 349
Fagopyrum esculentum, Medicago sativa, Sorghum bicolor subsp. drummondii, Streptomycetaceae, alfalfa, antagonists, biological control agents, biomass, buckwheat, crop damage, crown rot, cultivars, forage, forage yield, green manures, harvesting, mechanical damage, plant pathogens, planting, population density, population growth, soil, soil bacteria, spring, traffic
Harvesting alfalfa (Medicago sativa) results in mechanical wheel traffic on plants, which may damage crowns and increase the opportunity for entry of pathogens causing crown rot. Developing resistance to crown rot is problematic due to the large number of pathogens involved. Incorporation of plant biomass (green manures) into soil has been shown to increase 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 determine the effect of green manures for reducing crown rot. Green manure crops, buckwheat and sorghum-sudangrass, were incorporated into soil 3 weeks before seeding alfalfa. Bacterial density, streptomycete density, and proportion of pathogen antagonists were measured from soil cores prior to planting green manures and alfalfa. Wheel traffic was applied 2 days after each forage harvest over every plant in the traffic treatment. Forage yield was measured over 2 years. Plant health was assessed at the end of the second year from plant counts and crown rot score. 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 the proportion of 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 but fallow-control plots had highest yields in the no traffic control. Green manure treatments did not affect plant counts or crown rot. Mechanical wheel traffic reduces forage yield and increases disease. Selection of plants with increased tolerance to traffic may be possible. Green manure crops provide benefits in alfalfa production systems by increasing pathogen antagonists.