Our research is designed to improve our understanding of how plant-soil interactions influence nutrient cycling and availability in organic and limited-resource cropping systems.
Evaluating the potential of winter cover crops for carbon sequestration in degraded soils transitioning to organic production
Global concerns about rapidly rising atmospheric CO2 , coupled with the promise of future payments for 'captured' carbon, have prompted a renewed interest in soil C sequestration, especially in organic systems where application of complex organic materials is a common management practice. This project will strengthen organic production by providing information about how to best manage cover crop residue in Southern climates during the transition process in order to retain and protect recently added carbon. The primary long term goals of this project are:
(1) Evaluate common and novel legume cover crops for their potential to contribute to soil organic matter development in the short-term by investigating direct C contribution from legume cover crops and associated microbial processes.
(2) develop models for educating agricultural stakeholders, students, and low-income urban populations about the benefits and challenges of cover crop use, including public workshops and a unique extension training program for graduate students.
This project is a collaboration between North Carolina Agriculture and Technical University, and the labs of Dr. Shuijin Hu (Plant Pathology), and Dr. Wei Shi (Soil Science). Funded by NIFA Organic Transitions Program Grant ($699,000).
Lighting up the black box: Improving legume performance on organic farms by optimizing microbially-mediated plant and soil nitrogen cycling processes.
This project seeks to improve legume cover crop management on organic farms by examining key soil microbial processes that regulate nitrogen (N) cycling in cover crop legumes. Organic growers in NC are using a diversity of legume cover corps and are experimenting with a wide range of termination techniques, including mowing, incorporation by disking the residue into the soil, and no-till techniques such as rolling and crimping cover crops with a water-filled drum. We will investigate how non-chemical legume kill methods (rolling-crimping, flail mowing, or incorporation) impact N availability from decomposing legume residues. Our activities include:
(1) surveying organic growers to determine current rhizobia inoculant handling procedures and legume perceptions;
(2) establishing legume inoculant demonstration plots and using them to determine how inoculation practices impact legume productivity;
(3) determining how non-chemical winter annual legume cover crop kill methods impact indicators of microbial activity and N supply to crop plants;
(4) disseminating results and jointly educating North Carolina organic growers and students about soil microbial N-cycling processes in sustainable agriculture.
This project is a SE-SARE funded collaboration with the laboratories of Drs. Wei Shi (Soil Science) and Michelle Schroeder-Moreno (Crop Science) at NCSU ($192,000).
Understanding rhizobia ecology in legume cover crops:
Biological nitrogen fixation (BNF) is the major source of new nitrogen in organic agriculture, yet there has been almost no research devoted to understanding how organic management practices impact this process. Furthermore, few widely used, temperate green manures have been characterized in terms of their nitrogen fixing traits and the ecology of the bacteria responsible for legume BNF, called rhizobia. The goal of this project is to improve understanding of biological nitrogen fixation and rhizobia ecology within organic cropping systems so that this process can be most effectively managed. We are using molecular techniques to 'fingerprint' and genetically characterize rhizobia strains that have been both extracted from nodules of legume cover crops and 'trapped' from NC farm soils. We are interested in how history of organic management affects the efficiency of rhizobia inoculants, commonly used when farmers plant legume cover crops. We hope that our research will show us how specific management practices are impacting the ecology of rhizobia found in symbiosis with commonly grown legumes in organic systems.
Rhizobia Ecology and Food Security in Malawi
Soil nitrogen limitations are endemic to the smallholder sector of Malawi due to limited access to fertilizers and a cropping system that depends heavily on maize (Zea mays) with very little integration of legumes. This has led to low yields, famine, and chronic malnutrition among large sectors of Malawian society. Local NGO's and researchers have promoted legume integration for both soil fertility and family nutrition in the Ekwendeni region since the mid 1990's. Farmer interest in new legumes has been countered by difficulty achieving adequate yields of these new crops. Farmers show keen interest in soybean (Glycine max) for its nutritional value, however yields are consistently low for both local "promiscuous" and improved varieties. Smallholder farmers, due to limited knowledge and access to resources, rarely practice inoculation, and poor nodulation is hypothesized to cause yield reductions. Soils in Malawi are also limited in available phosphorous, a necessary nutrient in the nodulation process. In this project, we are investigating how soil nutrient status affects microbial diversity and rhizobia ecology and how this in turn will affect the ability of soybean to nodulate, both with native rhizobia as well as inoculants. We will also be monitoring the fate of inoculants in the soil, and how these introduced rhizobia compete with native strains.
This work is being conducted in collaboration with the Legume Best Bets project, funded by the McKnight foundation.
How does organic agriculture impact water quality and sediment losses?
The goal of this 3-year project (2009-2012) is to measure and model nonpoint source pollution (nitrogen (N), phosphorus (P) and sediment) associated with long-term organic and conventional vegetable farming systems under different tillage practices in the Appalachian Mountains of North Carolina. Water quality and runoff has been shown to be impacted by cropping system, however there is no water quality research that compares the same crop rotations within organic to conventional farming systems under two tillage regimes. In our research we will evaluate soil organic matter, cover crop biomass, and soil nitrogen in order to relate changes in soil properties to nutrient and sediment runoff and water quality.
This project is a collaboration with Dr. Deanna Osmond and is funded by a USDA-CSREES Integrated Organic and Water Quality award (2009-2012).