PARENT SESSION
Oral Session #60: Agroecology- Sustainable Agriculture.
Presiding: R. Bohanan
Wednesday, August 7. 8:00 AM to 11:30 AM. Mesquite Room, Radisson.
Comparing perennial and annual cover crops: Root architecture and soil inorganic nitrogen.
Los Huertos, Marc*,1, Shennan, Carol1, 1 University of California-Santa Cruz, Santa Cruz, CA
ABSTRACT- In organic agroecosystems, nutrient availability is managed using a combination of green manures, cover crops, compost additions, and other organic sources with the assumption an optimum balance between mobilization and immobilization processes will be appropriately timed with plant uptake while minimizing nutrient losses, for example, nitrate leaching. We designed a cover crop experiment comparing a winter cover crop (grass-legume mix) and a perennial cover crop (rye and oversown with crimson clover) to test how they influence nutrient availability in an organic vegetable agroecosystem. We measured root density, biomass, soil ammonium and nitrate concentrations. Prior to incorporation, we used a mini-rhizotron to image root architecture and found that the perennial treatment had a higher density of roots especially at lower depths of the soil (>50 cm). Root biomass was higher in the perennial grass cover crop compared to the annual cover crop. Above ground biomass was higher in the winter cover crops with a higher N content. During the winter rainy season, soil nitrogen and ammonium concentrations were low, less than 1 ppm soil in both treatments. However, in the spring soil nitrate-N was higher in the annual cover crops often greater than 5 ppm soil while the perennial grasses were less than 1 ppm soil. We believe a combination of root architecture and biomass reduce the leaching potential in the perennial grass cover crop treatment.
KEY WORDS: agroecology, nitrate, leaching, roots