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Research Project: Defining Agroecological Principles and Developing Sustainable Practices in Mid-Atlantic Cropping Systems

Location: Sustainable Agricultural Systems Laboratory

2018 Annual Report


Objectives
The long-term goal is to develop and translate fundamental agroecological knowledge into products and recommendations that help organic farmers meet consumer demand and improve their economic returns. Strategies developed for organic systems will also help increase sustainability of conventional farms. To reach the long-term goals focus will be on the following objectives over the next five years. Objective 1: Identify and elucidate agroecological principles that drive the function of organic and conventional cropping systems and quantify ecosystem services. Sub-objective 1.A. Compare factors controlling crop performance in long-term organic and conventional cropping systems. Sub-objective 1.B. Determine mechanisms controlling soil carbon sequestration and greenhouse gas flux in organic and conventional cropping systems. Sub-objective 1.C. Identify factors controlling soil biological community structure and its relationship to soil functions and the provision of ecosystem services in organic and conventional cropping systems. Sub-objective 1.D. Conduct integrated analyses to assess the impacts of organic and conventional cropping systems on the provision of ecosystem services. Objective 2: Develop technologies and management strategies to improve productivity, enhance soil and water conservation, and improve the efficiency of nutrient cycling on organic and conventional farms. Sub-objective 2.A. Develop new strategies for incorporating legumes (e.g., alfalfa, hairy vetch, clovers) into organic and conventional crop rotations to maximize nitrogen fixation within these systems. Sub-objective 2.B. Develop strategies for beneficial and safe use of animal manures and composts for organic and conventional agriculture. Sub-objective 2.C. Develop optimal agronomic practices for managing nutrients, weeds, and production on organic farms.


Approach
Approaches to identifying and elucidating agroecological principles include investigating the following variables within the Beltsville long-term Farming Systems Project that compares two conventional and three organic rotations, and associated projects: crop performance, soil carbon sequestration and greenhouse gas fluxes, soil microbiological community structure, and integrated analyses that evaluate overall systems performance. Approaches to developing component strategies include: incorporating legumes into organic crop rotations to maximize nitrogen fixation, composting that provides a productive and safe amendment for organic agriculture, integrating cover crop and manure management practices, reducing tillage in organic systems, and evaluating perennial wheat varieties.


Progress Report
This is the final report of Project 8042-21660-004-00D, which will end August 14, 2018. The new NP216 project, entitled “Enhancing Sustainability of Mid-Atlantic Agricultural Systems using Agroecological Principles and Practices” is being reviewed via OSQR. Substantial progress was made on the expiring project over the past five years. Under Objective 1, which is focused on the long-term Farming Systems Project (FSP), we showed that there are multiple tradeoffs in sustainability indicators among five cropping systems representative of the mid-Atlantic area. While corn and soybean yields were greater in two conventional than three organic systems—largely due to weed management challenges in the organic systems—economic returns were greater in the three organic than the two conventional systems due to organic price premiums. Among organic systems, increasing crop rotation diversity improved agronomic, economic and environmental performance. Corn yield was greater in a six-year corn-soybean-wheat-alfalfa rotation than in a three-year corn-soybean-wheat rotation, which in turn was greater than in a two-year corn-soybean rotation due to better weed control in complex rotations. The six-year rotation also had lower energy use and greenhouse gas emissions than the other four systems when expressed per unit crop production or per unit area. Greenhouse gas emissions were greater in the shorter organic rotations than in all other systems. Soil organic carbon, total nitrogen, and nitrogen release were greater in the organic than the conventional systems. Among organic systems there were differences in various soil carbon and nitrogen fractions that reflect differences in carbon and nitrogen inputs. In surface soils (top 2 inches), however, soil organic carbon, total nitrogen and aggregate stability were greatest in the conventional no-till system, which resulted in the lowest predicted soil erosion rates. Differences among FSP systems in soil nematode communities, carabid beetles, isopods, diplopods, earthworms, and insect-eating fungi seemed to reflect these differences in soil carbon and nitrogen as well as differences in tillage. These findings provide insights that may eventually be used to manage soil biological communities to foster increased crop production and/or resilience. Analyses of 18 years of FSP crop yield and weed abundance data also provided unique insights into the impact of climate and weather variability on agricultural sustainability. Rainfall during a 5 to 7-week period during late vegetative growth and early grain filling plus at crop establishment explained the bulk of grain yield variability, which ranged from about 16 to 190 bu a-1 for conventional corn, 16 to 128 bu a-1 for organic corn, 15 to 60 bu a-1 for conventional soybean, and 15 to 45 bu a-1 for organic soybean. The efficiency of grain yield per unit precipitation was therefore greater in the conventional than the organic systems. This was partially due to weed competition in the organic systems. Further analysis of weed competition in organic systems showed that corn and soybean production, as influenced by weather patterns, had more impact on weeds than any individual management practice. Extreme weather events are predicted to increase as part of climate change, which will require improved water management including irrigation and water conservation practices in conventional and organic systems. An analysis of soil carbon changes over 40 years in the two FSP conventional systems—using existing data and the CQESTR model—showed that climate change alone would result in a slower increase in soil carbon in the no-till system and would result in decreased soil carbon in the tilled system. These results suggest that system resilience will decrease because of climate change. These declines could be reversed if crop yields increase 10-30%, but the impact of climate change on crop yield has high uncertainty. These results highlight some of the challenges inherent in meeting Grand Challenge goals. Results from FSP also illustrate challenges of managing nitrogen and phosphorus when relying on organic sources of these plant nutrients. ARS scientists used FSP results to develop several projects under Objective 2 to address these challenges. This research showed that most of the nitrogen needs of corn can be provided by legume cover crops in research fields and on farms that have a history of organic inputs. Supplemental animal manure can then be applied at phosphorus removal rates, which reduces the need for animal manures and the subsequent potential of building up soil phosphorus, which is susceptible to loss via erosion and runoff. The FSP also hosted the Plant Health Project, an assessment of the impacts of glyphosate and Roundup-Ready crops on soil microbial communities. Two manuscripts from this project are in preparation. The dataset developed through this project (not yet publicly available) is one of the most extensive assessments of fungal and bacterial rRNA to date within replicated field plots. Under Objective 2, cover crop germplasm screening and selection in collaboration with universities, NRCS Plant Material Centers and others showed that hairy vetch, crimson clover, and winter pea can make rapid improvements in germplasm. Advanced lines are already outperforming commercially available cultivars in early growth and vigor. Current efforts have been expanded to include screening and selection of cereal cover crops and screening of brassicas. Also under Objective 2, an extensive and intensive assessment of cover crop mixtures (grass-legume mixtures of rye and hairy vetch) and poultry litter application methods resulted in the development of multiple novel strategies to manage organic nutrient sources (cover crop residues and poultry litter) for conventional and organic no-till systems. While cereal rye provided the best weed-suppressive mulches when roller-crimped onto the soil surface, hairy vetch provided the most nitrogen release. Cereal rye, however, reduced soil nitrogen availability while rapid decomposition of vetch residue on the soil surface provided poor weed control. By combining these two cover crops in mixtures of 50% rye and 50% vetch by weight, weed control and nitrogen release were optimized. By combining the cover crop mixture with a novel subsurface banding method of applying pelletized poultry litter, corn nitrogen and phosphorus needs were met while maintaining the soil conservation benefits of a no-till system and minimizing the potential for phosphorus loss common when poultry litter was surface applied. This project also included a focus on reducing nitrous oxide (N2O) emissions from agricultural soils, which are the primary source of this greenhouse gas and catalyst of stratospheric ozone degradation. We showed that two different slow release urea-based fertilizers developed by collaborators in Brazil could reduce N2O emissions by 50% or more in Maryland soils while maintaining wheat and corn grain yields. We also showed that combining cereal rye and hairy vetch cover crops could reduce N2O emissions compared to pure hairy vetch stands and that conservation tillage practices in organic vegetable production can also reduce N2O emissions without compromising yield. We developed a new method of interpolating N2O measurements from targeted measurements. Additional assessments showed that quantitative DNA analyses of the soil bacteria responsible for N2O production and consumption could not be used to predict N2O emissions patterns due to the complexity of the processes leading to N2O emissions. Finally, results of a pilot-study supported the concept and technical feasibility of using gas-permeable membrane systems to capture NH3 from poultry houses. The membrane systems resulted in a 35% reduction in ammonia emissions. The potential benefits of this technology include: improved bird productivity and health (4% less mortality), reduced ammonia emissions and energy requirements for heating, cleaner air and emissions, and production of a concentrated ammonium salt as a valuable plant nutrient product. Additional modifications of the membrane configurations to improve performance are underway. Most of the research conducted in this project is part of the Lower Chesapeake Bay (LCB) Long-Term Agroecological Research (LTAR) site (one of 19 LTAR sites in the LTAR Network). Beltsville, Maryland researchers helped develop the LTAR Common Experiment and provided local and national leadership in the LCB LTAR and the national LTAR network. One project researcher also served as Co-Lead of the USDA Northeast Climate Hub, providing expertise on greenhouse gas mitigation strategies and cover crop management to improve agricultural system resilience. Another project researcher coordinated activities of the Northeast Cover Crop Council, which is a clearinghouse for information about cover crops in the 12 northeastern states. Another researcher on this project was co-Principal Investigator on a NSF-funded research coordination network that is facilitating the founding and establishment of the International Agricultural Microbiome Network, whose goal is to bring together researchers from around the world who conduct microbial research within agricultural systems and identify tools and challenges to better serve stakeholders.


Accomplishments
1. Tillage, climate change and crop yields impact soil organic carbon stocks. Soil organic matter (SOM), often expressed in units of soil organic carbon (SOC), is the foundation of soil quality and contributes to cropping system resilience. The impact of climate change on SOM in agricultural systems, however, is poorly understood. ARS scientists, using data collected from the long-term Farming Systems Project in Beltsville, Maryland, and the CQESTR model, found that predicted climate change alone reduced SOC compared to current climate scenarios over the next 40 years. However, the negative impact of climate change on SOC levels could be mitigated by increases in crop yield. These results will be of interest to those interested in how agricultural management and climate change will impact agricultural sustainability.

2. Meteorological and management factors influence weed abundance in organic crop rotations. Weed management represents one of the largest challenges for organic grain farmers because weeds, which can reduce crop yields substantially, can be difficult to control without herbicides. An analysis of 18 years of weed cover data in three organic crop rotations by ARS scientists at the long-term Farming Systems Project in Beltsville, Maryland, showed that the most important factor impacting weed abundance precipitation during late vegetative and early reproductive crop growth stages. This result, showed that practices that favor corn and soybean competitiveness provide the most effective weed management in organic grain production systems.

3. Adaptive nitrogen management decision support tool updated with cover crop data. Growers need decision support tools that can estimate nitrogen release from cover crops in real-time to make robust fertility management decisions. The concentration of carbon and nitrogen in cover crop shoot and root biomass influences the rate of nitrogen release from decomposing cover crops but these data are not often collected under a wide range of conditions. ARS scientists in Beltsville, Maryland, collected these types of data and used them to calibrate and test the Adapt-N simulation model. Results improved the ability of Adapt-N to predict nitrogen release from terminated cover crop mixtures, which will help improve nitrogen management in U.S. agriculture, thereby saving farmers money and reducing environmental impacts.

4. Seeding rate recommendations help optimize hairy vetch biomass production in the Eastern U.S. ARS researchers from Beltsville, Maryland, and collaborators conducted an experiment at sites in Massachusetts, New York, Pennsylvania, Maryland, and North Carolina to determine minimum acceptable hairy vetch seeding rates at various dates and timings of termination. For every 100 growing degree days, hairy vetch biomass increased by an average of 530 kg ha-1. In Massachusetts, New York, and Pennsylvania hairy vetch reached maximum biomass production at seeding rates of 10-20 kg ha-1. In Maryland and North Carolina, hairy vetch reached maximum biomass when seeded at 5-10 kg ha-1. These results will be of value to extension and ag-industry personnel when making recommendations about hairy vetch planting and management and help farmers maximize benefits accrued from hairy vetch while minimizing production costs.


Review Publications
White, K.E., Coale, F.J., Reeves III, J.B. 2018. Degradation changes in plant root cell wall structural molecules during extended decomposition of important agricultural crop and forage species. Organic Geochemistry. 115:233-245.
Cavigelli, M.A., Nash, P.R., Gollany, H.T., Rasmann, C., Polumsky, R.W., Le, A.N., Conklin, A.E. 2017. Simulated soil organic carbon changes in Maryland are affected by tillage, climate change, and crop yield. Journal of Environmental Quality. 47(4):588-595. https://doi.org/10.2134/jeq2017.07.0291.
Treonis, A.M., Unangst, S., Kepler, R.M., Buyer, J.S., Cavigelli, M.A., Mirsky, S.B., Maul, J.E. 2018. Characterization of soil nematode communities in three cropping systems through morphological and DNA metabarcoding approaches. Scientific Reports. 8:2004. https://doi.org/10.1038/s41598-018-20366-5.
Spiegal, S.A., Bestelmeyer, B.T., Archer, D.W., Augustine, D.J., Boughton, E., Boughton, R., Clark, P., Derner, J.D., Duncan, E.W., Cavigelli, M.A., Hapeman, C.J., Harmel, R.D., Heilman, P., Holly, M.A., Huggins, D.R., King, K.W., Kleinman, P.J., Liebig, M.A., Locke, M.A., McCarty, G.W., Millar, N., Mirsky, S.B., Moorman, T.B., Pierson, F.B., Rigby, J.R., Robertson, G., Steiner, J.L., Strickland, T.C., Swain, H., Wienhold, B.J., Wulfhorts, J., Yost, M., Walthall, C.L. 2018. Evaluating strategies for sustainable intensification of U.S. agriculture through the Long-Term Agroecosystem Research network. Environmental Research Letters. 13(3):034031. https://doi.org/10.1088/1748-9326/aaa779.
Hoffman, E., Cavigelli, M.A., Gustavo, C., Matthew, R., Ackroyd, V.J., Richard, T.L., Mirsky, S.B. 2018. Energy use and greenhouse gas emissions in organic and conventional grain crop production: accounting for nutrient inflows. Agriculture Ecosystems and the Environment. 162:89-96.
Teasdale, J.R., Mirsky, S.B., Cavigelli, M.A. 2018. Meteorological and management factors influencing weed abundance during 18 years of organic crop rotations. Weed Science. 1:8. https://doi.org/10.1017/wsc.2018.15.
Wayman, S., Kucek, L.K., Mirsky, S.B., Ackroyd, V., Cordeau, S., Ryan, M.R. 2016. Organic and conventional farmers differ in their perspective on cover crop use and breeding. Renewable Agriculture and Food Systems. 32:376-385.
Melkonian, J., Poffenbarger, H.J., Mirsky, S.B., Ryan, M.R., Moebius-Clune, B.N. 2017. Estimating nitrogen mineralization from cover crop mixtures using the Precision Nitrogen Management model. Agronomy Journal. 109:1944-1959.
Vann, R.A., Reberg-Horton, S., Mirsky, S.B., Poffenbarger, H.J., Zinati, G.M., Moyer, J.B. 2017. Starter fertilizer for managing cover crop-based organic corn. Agronomy Journal. 109:2214-2222.
Mirsky, S.B., Ackroyd, V.J., Cordeau, S., Curran, W.S., Hashemi, M., Reberg-Horton, S., Ryan, M., Spargo, J.T. 2017. Hairy vetch biomass across the eastern United States: Effects of latitude, seeding rate and date, and termination timing. Agronomy Journal. 109:1510-1519.
Curran, W.S., Hoover, R.J., Mirsky, S.B., Roth, G.W., Ryan, M.R., Ackroyd, V.J., Wallace, J.M., Dempsey, M.A., Pelzer, C.J. 2018. Evaluation of cover crops drill interseeded into corn across the mid-Atlantic region. Agronomy Journal. 110:435-443. https://doi.org/10.2134/agronj2017.07.0395.