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

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

Summary

An assessment of the effects of seven years annual ground cover and nutrient amendments to an organically managed apple orchard on the soil microbial community is in progress. Analyzing soil nutrient data and examining the microbial community via molecular techniques from 2007 to 2013 will determine possible treatment effects. Extraction of DNA from 0-10 cm and 10-30 cm soil samples followed by PCR, qPCR and DGGE will be implemented to gain insight into the size and diversity of the denitrifying community.

Objectives/Performance Targets

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.

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.

3) Determine if annual ground cover and nutrient amendments to an organically managed apple orchard have altered denitrification potentials. 

Accomplishments/Milestones

DNA extraction was completed for 2007 and 2013. Protocols for PCR, qPCR and DGGE of nirK were established and DGGE was optimized. The DGGE of nirK for both depths and years were completed and data are currently being analyzed. The analysis of the soil nutrient data has been completed and findings are being drafted for publication.

Impacts and Contributions/Outcomes

An experimental organic apple orchard was established in 2006 using SARE funds. The goal was to provide regionally appropriate science to understand sustainable management of an orchard in the Mid-South. A challenge in perennial systems involves determining how orchard soils respond to repeated annual additions of organic nutrient containing materials and decompose and build soil organic matter without promoting N losses. Orchards have been better studied in the northeastern and northwestern U.S., but the soils, climate, and pest pressures are different from those in the south, and producers in the south need regionally appropriate recommendations.

Utilizing seven years of soil nutrient data and supporting molecular analyses will strengthen the understanding of the dynamic changes that happen in a complex system over time. The DGGE analysis provides a picture of how the microbial community differs in terms of composition and diversity of targeted genes and reveals changes that may support or contrast conclusions made measuring soil nutrient concentrations.  Long-term analyses are imperative when striving to make sustainable recommendations for agricultural practices, especially in perennial systems such as orchards.

Preliminary results were presented at the American Society of Agronomy/Crop Science Society of America/ Soil Science Society of America Annual Meeting in Long Beach, CA in November, 2014.

Ford, J. N., M. Savin, and C. R. Rom. 2014. Denitrifier community response to seven years of ground cover and nutrient management practices in an organic apple orchard soil. In 2014 Annual Meeting Program. ASA, CSSA, and SSSA, Madison, WI. Available at https://scisoc.confex.com/scisoc/2014am/webprogram/Session13347.html (accessed 12/19/14).

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