Denitrifier Community Response to Seven Years of Ground Cover and Nutrient Management Practices in an Organic Apple Orchard Soil.

The goal of organic management is to facilitate efficient internal terrestrial N cycling without promotion of N losses, especially as those can result in atmospheric and aquatic pollution. Biological denitrification is an anaerobic, microbially mediated process that results in gaseous N losses from the soil. The objective of this study was to determine the effects of repeated annual additions of the combinations of four ground covers (compost, wood chips, paper mulch, mow-n-blow) and three organic fertilizers (poultry litter, commercial organic, no fertilizer) treatments on denitrification potential and community composition in an organic apple orchard soil established in 2006. The functional gene nirK encodes the copper containing enzyme nitrite reductase, facilitating a key step in the denitrification pathway. A comparison of the abundance of nirK and diversity of nirK fragments from 2007 to 2013 were used in conjunction with dissolved organic carbon and inorganic nitrogen concentrations to measure community response. Determining how these ground covers and organic nutrients have changed the denitrifier community will provide insight into the fate of N and ultimately the sustainability of these treatments.