Squash harvest

Guiding research questions in our laboratory include:

  • How do alternative management practices used on organic and low-input farms impact nutrient cycling in soils?
  • How do legume cover crop species and varieties vary in terms of their nitrogen fixation traits and their relationship to rhizobial symbionts?
  • How do both past and current use of rhizobia inoculants affect the efficiency of nitrogen fixation on organic farms?
  • How does the nitrogen fixing efficiency of indigenous rhizobia in organic farm soils compare to those supplied in an inoculant? When both are present, what factors determine who ‘wins the right’ to occupy a nodule?
  • How does cover crop management on no-till organic farms impact the amount of mineralized N contributed to the system?


Techniques we use to answer our questions include:

  • Quantification of labile organic matter fractions, often increased via the use of legume cover crops
  • Evaluation of Trapping and culturing of rhizobia from soils
  • Molecular techniques such as:
    • PCR based fingerprinting techniques using RFLP and rep-PCR using BOX primers
    • Restriction digest PCR of the 16s rRNA and nifH regions of rhizobia
    • Quantitative PCR to evaluate microbial population sizes in soils
  • Stable isotope 15N analysis of nitrogen fixation in the field
  • Plant tissue and soil analyses for total N, NO3-N and NH4-N
  • Ion resin strips to estimate nitrogen mineralization of decomposing mulch