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.
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.
Under objective 1, the 20th year of research at the long-term Farming Systems Project (FSP) was completed with crop yield, crop and cover crop biomass, soil quality and other data collected. Microplots to study the impacts of crop varieties, weed competition, and soybean nitrogen fixation were established, sampled and harvested. The second year of a project was conducted at FSP to assess impacts of management and crop varieties on corn metabolomics and gene expression. For objective 2, germplasm assessments of hairy vetch and crimson clover were continued. Hairy vetch and crimson clover seed were obtained from colleagues in the United States, France, Serbia and Turkey then grown for seed increases at BARC in 2015-16. On-going assessment of nitrogen metabolism of cold-hardy legume cover crops was conducted in 2015 on replicated plots of 45 accessions of field grown crimson clover. Roots, nodules were quantified and collections of Rhizobia populations inhabiting the nodules of each genotype were archived in long-term storage for future Rhizobia inoculum development. Metagenomic sequencing of populations of nodule inhabiting microbes was conducted using Illumina sequencing. Results of a pilot-study support 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.
1. Crop production varies considerably due to variability in meteorological patterns. Scientists in Beltsville, Maryland, analyzed data from a long-term agroecological research project and found that annual fluctuations in corn and soybean yields varied on a periodic basis with periods lasting about 4½ years. Precipitation and air temperature during critical periods in the early and late growing seasons explained much of the yield variability, with precipitation during the late vegetative and early reproductive phases of crop growth accounting for the majority of variability in yield for both crops and five different management systems. Meteorological conditions at the site were partially explained by El Niño Southern Oscillation patterns, such that the lowest critical period precipitation and yield anomalies always occurred during years with extreme La Niña and El Niño sea surface temperature (SST) anomalies, and the highest critical period precipitation and yield anomalies always occurred during years with neutral SST anomalies. The efficiency of grain yield per unit precipitation was higher in conventional than organic systems, highlighting the importance of crop management for optimizing production in response to meteorological variability. Results will be of interest to farmers, government agencies and policy makers involved with policies related to agricultural production.
2. Legume cover crop performance is critical to determining poultry litter application rates to balance nitrogen and phosphorus inputs and outputs. Applying animal byproducts to meet crop nitrogen needs often results in soil phosphorus buildup that poses environmental challenges. Legume cover crops, such as hairy vetch, used in combination with animal byproducts can help balance nitrogen and phosphorus inputs but information is lacking on appropriate application rates. ARS scientists in Beltsville, Maryland, found in a two-year study that when hairy vetch produced a lot of biomass, neither organic amendments or mineral fertilizers increased corn yield further, indicating that vetch alone could meet all of corn’s nitrogen needs. In a year with poor vetch performance vetch provided no benefit to corn and organic amendments increased corn grain yield without raising concerns of soil P buildup at applied rates. While benefits of the four organic amendments were very similar, costs differed substantially such that economic returns to using poultry litter were substantially greater than for the other three materials (pelletized poultry litter, feather meal, and a pelletized poultry litter-feather meal blend). Results will be of interest to organic and conventional farmers who use a hairy vetch cover crop, and to policy makers and government agencies concerned about balancing production and environmental aspects of agriculture.
3. Nitrous oxide emissions from agricultural soils are reduced exponentially by reducing total nitrogen applied in the form of cover crop and poultry litter. Nitrous oxide is a greenhouse gas and the most important catalyst of stratospheric ozone decline whose atmospheric concentration is increasing. Agricultural soils are the dominant source of nitrous oxide but mitigating emissions is challenging due to the dynamic nature of nitrogen in soils. While policymaking guidelines for nitrous oxide emissions accounting assume a linear relationship with increasing nitrogen application rate, field experiments in corn have shown an exponential increase in nitrous oxide emissions with increasing nitrogen fertilizer application rates. Similar data for organic nitrogen inputs are very limited. Three years of field research conducted by ARS scientists in Beltsville, Maryland, along with University of Maryland collaborators found that nitrous oxide emissions were lower when 1) a grass rather than a legume cover crop was used, 2) a grass:legume cover crop mixture rather than a legume monoculture was used, and 3) poultry litter rather than urea fertilizer was subsurface banded following a cover crop mixture. In combination, results show that grass:legume cover crop mixtures with subsurface banded poultry litter can lower nitrous oxide emissions compared to a legume monoculture while maintaining comparable nitrogen inputs. These results will be of interest to policy makers and government agencies concerned about balancing production and environmental aspects of agriculture.
4. Long term applications of fertilizer and animal manure can lead to accumulation of phosphorus (P) in soil. Management can have a significant influence on the forms and availability of soil P. Distribution of various readily available P forms after 18 years of management was studied for three organic and two conventional cropping systems that comprise the Farming Systems Project in Beltsville, Maryland. Stratification of soil labile and total P was observed in the two conventional systems, especially a no-till system. Moldboard plowing in the organic systems created a more uniform distribution of P forms with soil depth, reducing potential transport of the readily available forms, exchangeable inorganic and enzyme-labile organic P. Historical large P loadings in some treatments appeared to contribute to elevated P concentrations 12 or more years later. High (nitrogen based) input levels of poultry litter in the organic systems early in the study along with low output levels (due to yield-limiting droughts) resulted in large pools of readily available soil P. Although poultry litter applications for the past 10 years have been based on soil test P, results suggest P management could be improved for organic systems by accounting for the enzyme-labile organic P pool in soil test recommendations.
Members of this project’s research team were invited to present at the following workshops and conferences that target the organic farming community: Albert Lea Seeds Annual Meeting, Albert Lea, Minnesota, November 15, 2015, Pennsylvania Association for Sustainable Agriculture, State College, Pennsylvania, February 6, 2016, Queen Anne County Organic Production Workshop, Queen Anne Co, Maryland, March 17, 2016, Organic Confluences Summit, Washington, DC, May 23, 2016. Four team members hosted nine student interns from Hispanic Serving Institutions during summer 2016.
Poffenbarger, H.J., Mirsky, S.B., Weil, R.R., Kramer, M.H., Spargo, J.T., Cavigelli, M.A. 2015. Legume proportions, poultry litter, and tillage effects on cover crop decomposition. Agronomy Journal. 107:2083-2096.
White, K.E., Reeves, III, J., Coale, F. 2016. Cell wall compositional changes during incubation of plant roots measured by mid-infrared diffuse reflectance spectroscopy and fiber analysis. Geoderma. 264:205-213.
Poffenbarger, H.J., Mirsky, S.B., Kramer, M.H., Weil, R.R., Meisinger, J.J., Cavigelli, M.A., Spargo, J.T. 2015. Cover crop and poultry litter management influence spatiotemporal availability of topsoil nitrogen. Soil Science Society of America Journal. 79:1660-1673.
Williams, M.M. II, Bradley, C.A., Duke, S.O., Maul, J.E., Reddy, K.N. 2015. Goss’s wilt incidence in sweet corn is independent of transgenic traits and glyphosate. Horticultural Science. 50:1791-1794.
Reynnells, R., Callahan, M.L., Handy, E.T., Roberts, C.L., Felton, G., Ingram, D., Millner, P.D., Sharma, M. 2014. Evaluation of two immunomagnetic separation techniques for the detection and recovery of E. coli O157:H7 from finished composts. Journal of Food Analytical Methods. doi: 10.1007/s12161-014-0068-4.
Patel, J.R., Yossa, I., Macarisin, D., Millner, P.D. 2015. Physical Covering to control Escherichia coli O157:H7 and Salmonella in Static and Windrow Composting Process. Applied and Environmental Microbiology. 81:2063-2074.
Poffenbarger, H.J., Mirsky, S.B., Maul, J.E., Weil, R.R., Kramer, M.H., Spargo, J.T., Cavigelli, M.A. 2015. Biomass and nitrogen accumulation of hairy vetch-cereal rye cover crop mixtures as influenced by species proportions. Agronomy Journal. doi: 10.2134/agronj14.0462.
Wells, M.S., Reberg-Horton, S.C., Mirsky, S.B. 2014. Cultural strategies for managing weeds and soil moisture in cover crop based no-till soybean production. Weed Science. 62:501-511.
Wells, M.S., Reberg-Horton, S.C., Mirsky, S.B. 2016. Planting date impacts on soil water management, plant growth, and weeds in cover-crop-based no-till corn production. Agronomy Journal. 108:162-170.
Martins, B.H., Cavigelli, M.A., Buyer, J.S., Maul, J.E., Reeves, J.B. III and Martin-Neto, L. 2015. Chemical evaluation of soil organic matter structure in diverse cropping systems. In Z. He (ed.). Labile Organic Matter-Chemical Compositions, Function, and Significance in Soil and the Environment. SSSA Special Publication 62:41-65. SSSA, Madison, WI.
Miller, A., Novy, A., Glover, J., Maul, J.E., Raven, P., Jackson, P.W. 2015. Expanding the role of botanical gardens in the future of food. Nature Plants. 1:1-4.