Ground cover and organic nutrient management practices altering the denitrifier community in an organic apple orchard soil

Project Overview

Project Type: Graduate Student
Funds awarded in 2013: $11,000.00
Projected End Date: 12/31/2015
Grant Recipient: University of Arkansas
Region: Southern
State: Arkansas
Graduate Student:
Major Professor:
Dr. Mary Savin
University of Arkansas

Annual Reports


  • Fruits: apples, general tree fruits


  • Crop Production: nutrient cycling, organic fertilizers
  • Natural Resources/Environment: biodiversity
  • Production Systems: organic agriculture, transitioning to organic
  • Soil Management: nutrient mineralization, organic matter, soil analysis, soil microbiology, soil quality/health

    Proposal abstract:

    Organically managed orchards require sources of nutrition acquired from organic fertilizers or ground covers, the alternative to synthetic, inorganic fertilizers used in conventionally managed systems. Through the addition and subsequent decomposition of organic matter, microbial activity is stimulated. Processes involved in the nitrogen cycle can be altered, depending on the inputs of organic substrates and the resultant changes in microbial community composition. Denitrification is an anaerobic, microbially mediated process that results in gaseous N losses from the soil. Nitrous oxide is a greenhouse gas and a potential product of denitrification. 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. The objective of this study is 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 (composted poultry litter, poultry litter based commercial, no fertilizer) treatments on denitrifcation potential and community composition in an organic apple orchard soil established in 2006. The data obtained from this study will provide greatly needed management information to producers in the mid-south regarding organic ground cover and fertilizer treatments and if these combinations will be beneficial for nitrogen cycling and availability.

    Project objectives from proposal:

    1) Determine changes in the soil microbial community composition in response to seven years of annual ground cover and nutrient amendments to an organically managed apple orchard.
    Alternative hypotheses:
    • Seven years of annual ground cover and nutrient amendments will have resulted in detectable shifts in the soil microbial community composition, size, and activity.
    • Diversity will be greatest in treatments that add the most organic matter and with the greatest decomposition as measured by the highest DOC levels. High abundance of nitrate is expected to preferentially benefit r-strategist organisms and thus reduce diversity.

    2) Determine if different annual ground cover and nutrient amendments result in various lengths of time before treatment effects are detected and differentiated at the 10-30 cm soil depth.
    Alternative hypothesis:
    • Treatment effects in microbial community responses and nutrient availability will be delayed compared to the surface 10 cm and will not be detected in the 10-30 cm depth until production phase. However, changes in denitrifier communities from ground cover and nutrient source management that lead to increased DOC and NO3- at the 10-30 cm depth are expected to increase denitrifier gene abundance and alter community diversity.

    3) Determine if annual ground cover and nutrient amendments to an organically managed apple orchard have altered denitrification potentials.
    Alternative hypothesis:
    • Denitrification potentials (as quantified using qPCR of denitrifier gene fragment abundances) will increase as determined by larger pools of organic N, NH4+, NO3-, DOC, microbial biomass, and higher soil moistures.

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.