The overarching goal of our research program is to enhance the efficient management of soil nutrients in low-input and organic farming systems. We do this by conducting basic and applied research that will increase our understanding of how agricultural management affects the cycling of nutrients via soil microbial processes. Organic farmers and those with limited resources are often put in a tricky spot of growing food crops without purchased inputs such as synthetic fertilizers. This increases their reliance on less understood soil microbial processes to provide their crop plants with critical nutrients needed for growth and development. Since nitrogen is an essential nutrient for crop plants, we put particular emphasis on understanding the ecology of the legume-rhizobia symbiosis. In order to develop farming systems that are practical and applicable, our research projects can be found on working organic farms, long-term plots on research station land designed to investigate the long term soil fertility implications of various farming practices, or low input farming systems around the world. To increase our understanding of how soil microbes indirectly and directly affect nutrient cycling and soil fertility in low input systems, we use numerous applied microbiological and field techniques that measure both the specific functioning of microbes that mediate nutrient cycling in soils, and general characteristics of soil health and quality.
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