Bacterial and Archaeal Nitrifier Communities after Seven Years Surface Ground Cover and Nutrient Management in an Orchard Soil.

Understanding how long-term, organic management practices, such as application of surface ground covers and organic fertilizers to perennial systems, affect microbial communities is critical for sustainable soil management. This research aims to investigate ammonia oxidizing bacterial (AOB) and ammonia oxidizing archaeal (AOA) communities based on the ammonia monooxygenase (amoA) gene in the surface top 10 cm of an organically managed experimental apple orchard soil. Plots received seven years of annual, surface applications of poultry litter or commercial fertilizer compared to no fertilizer, combined with compost, wood chips, shredded paper, or mow-and-blow ground cover mulches in a 4 x 3 design. Nitrate concentrations were affected by the interaction of ground cover by fertilizer by year throughout the seven-year experiment, including greater nitrate concentrations in compost in year 3 and the trend of increasing nitrate concentrations in poultry litter compared to commercial and no fertilizer before year 7. Nitrifier richness, diversity, and community composition are being investigated using PCR based techniques. Results of this experiment will improve understanding of how soil nitrifier populations respond to organic ground cover management in low organic matter orchard soil in the mid-southern U.S.