What we've done

Assessing the greenhouse gas mitigation potential of organic systems in the Southeastern U.S.

Year: 2013-2016

Gas sampling in the fieldThis three-year project will assess the impact of organic and conventional management on a number of crop and soil parameters in long term systems located at the Center for Environmental Farming Systems (CEFS) in Goldsboro, North Carolina. The three supporting objectives of this project include to 1) investigate how organic systems affect soil carbon (C) and nitrogen (N) dynamics and greenhouse gas emissions, 2) examine how tillage practices and cover crops can be integrated to enhance C sequestration and reduce N2O emissions, and 3) educate the next generation of organic agriculture researchers and farmers through student training and an active, multi-pronged outreach program. For our lab’s portion of this large interdisciplinary project we will be evaluating the impact of a wide range of carbon and nitrogen additions on N2O emissions, N status, and microbial activity in the CEFS long term-system plots at key points in seasonal cropping cycles. System N inputs undergoing evaluation include legume cover crops, manure, pelleted chicken litter, and conventional UAN synthetic fertilizer.

Funded by NIFA Organic Transitions Program Grant ($699,000). It is a collaboration between many other labs, includingDr. Chris Reberg-Horton and Dr. Michelle Schroeder-Moreno in the Department of Crop Science, Dr. Shuijin Hu in Plant Pathology, and the Sustainable Agriculture Lab at USDA Beltsville.

Evaluating the potential of winter cover crops for carbon sequestration in degraded soils transitioning to organic production

Year: 2011-2014

Vetch biomass harvestGlobal 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:

CEFS workshop(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 Agricultural and Technical University, and the labs of Dr. Shuijin Hu in the Department of Plant Pathology, and Dr. Wei Shi in the Department of Soil Science. Funded by NIFA Organic Transitions Program Grant ($699,000).

Rhizobia Ecology and Food Security in Malawi

Mary in MalawiSoil 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.

Lighting up the black box:

Improving legume performance on organic farms by optimizing microbially-mediated plant and soil nitrogen cycling processes


Grant cycle: 2010-2013

This project sought 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 use 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 investigated how non-chemical legume kill methods (rolling-crimping, flail mowing, or incorporation) impact N availability from decomposing legume residues. Our activities included:

  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 was a SE-SARE funded collaboration with the laboratories of Drs. Wei Shi (Soil Science) and Michelle Schroeder-Moreno (Crop Science) at North Carolina State University ($192,000).

How does organic agriculture impact water quality and sediment losses?

Grant cycle: 2009-2012

FletcherThe goal  this project was 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 evaluated 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 was a collaboration with Dr. Deanna Osmond at North Carolina State University and is funded by a USDA-CSREES Integrated Organic and Water Quality award.

Understanding how the Roller-Crimper implement affects N dynamics in no-till organic systems

Grant cycle: 2008-2011


Generally, soils in organic production have shown dramatic increases in organic matter and microbial biomass, in part due to the addition of organic and carbon rich sources of nutrients such as cover crops. The goal of this project was to quantify nitrogen -fixation and N-mineralization potential of 14 different legumes, including 4 hairy vetch cultivars, 4 crimson clover cultivars, 2 Austrian winter pea cultivars, and others. In non-organic systems, terminating cover crops prior to planting is mainly accomplished by the use of herbicides, however organic standards strictly prohibit the use of synthetic inputs. Along with soil nutrient management, weed control is another challenge for organic growers. Organic grain production relies on cultivation for weed control rather than herbicide use. Over the course of a growing season, organic corn and soybeans are typically cultivated 6 to 10 times, raising questions about the impacts of this practice on soil resource sustainability. The roller-crimper is an implement technology that is showing success in allowing organic farmers in the Southeast to develop no-till grain systems that successfully terminating winter legume cover crops and controlling weeds without the aid of synthetic herbicides or cultivation. The tool works by rolling over the cover crop and crimping the stem with blades when the crop is at full bloom-killing it and forming a thick mat on the soil surface that can suppress weeds as well as contribute fixed N to soil pools as legume biomass is decomposed. The cash crop is then no-till planted into the rolled cover crop.

This project was a collaboration with Dr. Chris Reberg Horton at North Carolina State University and was funded by an NRCS Conservation Innovation Grant and a North Carolina Corn Growers award.

Nutrient management in Pasture Raised Pork operations in North Carolina

Grant cycle: 2008-2011

PigIn recent years, consumer demand for pork products from outdoor-raised (marketed as “pasture-raised) hogs has increased substantially. Current outdoor-raised hog production systems in North Carolina differ considerably from confinement operations in that sows and piglets are raised outdoors and allowed to engage in innate behaviors of rooting, wallowing, and eating in their natural habitat. Production practices typically include a range of managerial activities that assure animal comfort and well-being, such as open space that allows for natural animal behavior and the avoidance of concrete flooring. Regardless of the merits associated with animal welfare and profitability, there are significant concerns about management of the soil resource. Many small-scale farms are overstocked and lack documented guidance on how to manage the animals in an integrated cropping/grazing system to prevent soil degradation. Growing pigs have a feed conversion rate of three to one, thus approximately two-thirds of the feed they consume ends up as waste. The concentration of manure and urine over the landscape combined with volatilization and movement through the soil profile and overland present challenges to outdoor hog managers. Our project seeks to understand the movement of soil nutrients in outdoor pig production systems in North Carolina. We will look at the effect of rotation of pigs within the paddock to more evenly distribute nutrients (N03– and NH4+) as well as reduce damage to forage vegetation. 

This project was a collaboration with the Center for Environmental Farming Systems and was funded by a North Carolina Agricultural Foundation award and an NRCS Conservation Innovation Grant.

The Role of Soil Organisms in Carbon Cycling in Anthropic Soils of the Brazilian Amazon

Terra PretaIn this project we, in close collaboration with Brazilian scientists at the Centro de Energia na Agricultura, looked at how the soil microbial community influences a fascinating tropical soil system known as “Terra Preta” (Anthropogenic Dark Earth). Terra Preta (TP) soils found in the Brazilian Amazon are known for their unusually high soil C contents. It is now widely accepted that these soils were created between 500 and 2,500 years before present by indigenous pre-Colombian Indians for their own agricultural use. Since the existence of Terra Preta soils is a strong piece of evidence supporting the hypothesis of high population densities in the Amazon prior to Spanish conquest, fertility characteristics of TP soils are of great interest to scientists and local farmers as well. However, their biological properties remain a mystery. Because the carbon cycling in TP has been shown to be very different from other soils, we think that soil microbial life in TP soils will also be distinct, and characterized this diversity through our research. We used both traditional and novel molecular techniques to assess microbial abundance and diversity, including Polymerase Chain Reaction (PCR) to amplify target sequences of organism DNA, and Denaturing Gradient Gel Electrophoresis (DGGE).

Nitrogen Fixation in Organic Coffee Agroecosystems in Chiapas, Mexico

InterviewCoffee throughout Latin America is cultivated under both shaded (a traditional practice for small landholders) and unshaded (full sun and high external inputs of agrochemicals, especially nitrogen fertilizer) conditions.In the early 1970’s a steady increase in coffee prices in Latin America stimulated a transformation from diverse shaded coffee agroecosystems, where many productive tree species were intercropped with the coffee plants, into homogenous coffee systems containing no trees and coffee that needed to be fed with technological packages of agrochemicals such as N fertilizers. Many of the best-preserved traditionally shaded coffee farms are found in Chiapas, Mexico. This project looked at alternatives to fertilization with synthetic N-fertilizers in Chiapas, with particular emphasis on biological nitrogen nitrogen fixation. Coffee ecosystems are agricultural systems and therefore export most of the nutrients in the harvestable products such as berries and firewood. To sustain annual yields, these lost nutrients need to be subsidized either with inorganic purchased fertilizers, or bio-fertilizers such as leguminous tree leaf litter or compost. Full sun systems require the use of chemical inputs to make up for the loss of the shade tree leaf litter that they once had. Inputs often need to be purchased from large corporations, offsetting profits of increasing yields. Many small-scale poor farmers just cannot afford the fertilizers and thus their coffee goes without the N that would possibly increase their coffee yields. Interest in the use of leguminous species for N addition in shaded systems has increased in recent years. Leguminous tree species, ‘fix’ N through a symbiotic association with soil bacteria and can therefore serve as a biological N addition to the system without needing purchased inputs. This is an important mechanism of bio-fertilization for farmers who are either certified organic, or are in the processing of becoming certified. Organic coffee producers are restricted from using agrochemicals, thus rely in part on nitrogen fixation to provide N to their crop. This research addressed numerous facets of N-fixation on organic coffee farms. These include farmer understanding of soil fertility enhancement processes that they use as a basis for decision-making and experimentation, diversity of N-fixing organisms that are in symbiosis with the shade tree Inga, and the effectiveness of the Inga-rhizobia symbiosis as a source of N for organic coffee.