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

Location: Sustainable Agricultural Systems Laboratory

2014 Annual Report

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.

Progress Report
Under Objective 1, the 18th 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, soybean nitrogen fixation, glyphosate, and roundup-ready soybeans were established, sampled, and harvested. A new project was established at FSP to assess soil carbon with depth and to link that to soil microbial community structure. Preliminary carbon, nitrogen, phosphorus, and potassium balances were developed for the FSP. For Objective 2, germplasm assessments of hairy vetch and crimson clover were continued. The first trials of weed seed indicators of time-temperature target thresholds for pathogen kill in composting manures have been completed. A second trial is on-going. At the Cover Crop Mixture Injection Trial, research continued on cover crop biomass, corn yield and nitrogen uptake, soil nitrogen availability around subsurface bands of poultry litter, greenhouse gas emissions, and litter bag studies. Grazing winter rye cover crop increases economic returns in a cotton no-till system. Farmers are hesitant to use cover crops due to establishment costs even though cover crops provide a number of ecosystem services. ARS researchers in Watkinsville, GA and Beltsville, MD conducted a 4-year study evaluating cotton productivity following a winter rye cover crop grazed in the spring by cattle or killed with a roller-crimper before planting. Cotton yields tended to be better in the non-grazed treatment but were significantly different only in 2009. Four-year average lint yield was 107 lb per acre greater for the non-grazed treatment. Differences between grazed and non-grazed returns ranged from $–10 to $143 per acre annually and averaged $33 per acre when based on market year prices. Although negative effects of soil compaction were observed when spring rains caused poor grazing conditions, returns from grazing had the potential to offset establishment costs of a rye cover crop and increase profits. ARS researchers in Beltsville, MD, in collaboration with scientists from North Carolina State University, found that genetically similar hairy vetch genotypes harbored more similar rhizobium biotypes than more distantly related hairy vetch genotypes. Distinct groups of vetch genotypes and rhizobium biotypes acquired more nitrogen from the symbiotic relationship than others. These findings are important because they are the first step in determining the genetic underpinnings of efficient associations between plants and beneficial root-associated rhizobia. Ammonia emissions from poultry litter trapped using a membrane system in bench-scale chamber tests. A membrane configured in a gutter system captures ammonia into a recirculating acid solution from poultry manure/litter. ARS researchers from the Coastal Plains Research Center and Beltsville, MD designed and constructed a gutter membrane configuration and a tubular configuration system that was then installed in a research poultry unit at the University of Maryland Eastern Shore. Data on ammonia emissions are on-going and design/installation of a tubular ammonia capture membrane system is in progress for an in-vessel composting system at the Beltsville Agricultural Research Center.

1. Novel slow-release fertilizers reduce soil nitrous oxide (N2O) emissions by more than 50%. Soil management practices such as fertilizer and manure applications account for 92% of total US agricultural emissions of nitrous oxide (N2O), a greenhouse gas and catalyst of stratospheric ozone depletion. Slow-release nitrogen fertilizers may provide a means of reducing soil N2O emissions by better synchronizing the release of mineral nitrogen, a precursor of N2O, with plant uptake compared to traditional nitrogen fertilizers. In collaboration with Brazilian scientists, ARS researchers in Beltsville, MD evaluated the impact of novel slow release nanocomposite nitrogen fertilizers developed in Brazil on soil N2O emissions in a winter wheat field. Results show that seasonal N2O emissions following application of nanocomposite fertilizers were reduced by at least 50% compared to emissions following application of conventional urea fertilizer. Emissions following application of some of the nanocomposite fertilizers were no different than emissions from plots to which no fertilizer had been added. Results suggest that these novel slow-release fertilizers may help reduce soil emissions of N2O, which will be of interest to farmers, policymakers, and others interested in reducing the environmental footprint of agriculture.

2. Leguminous cover crops suppress Fusarium wilt of watermelon when used as green manure. Triploid watermelon cultivars are grown on more than 5,000 acres in Maryland and Delaware. Triploid watermelons have little host resistance to Fusarium wilt of watermelon. In field trials by ARS Researchers in Beltsville, MD and collaborators at the University of Maryland, the cover crops hairy vetch and crimson clover suppressed Fusarium wilt of watermelon by as much as 21% compared to no cover crop. Watermelon grown following crimson clover yielded 129% more fruit per acre than the no cover crop treatment in one of three field trials. While hairy vetch has previously been shown to suppress Fusarium wilt of watermelon, this is the first report of a reduction in Fusarium wilt following a crimson clover cover crop incorporated as a green manure. This information will be of use to watermelon growers and agricultural professionals who support them.

Review Publications
Del Grosso, S.J., Cavigelli, M.A. 2012. Climate stabilization wedges revisited: can agricultural production and greenhouse gas reduction goals be accomplished? Frontiers in Ecology and the Environment. 10:571-578.
Schomberg, H.H., Fisher, D.S., Reeves, D.W., Endale, D.M., Raper, R.L., Jayaratne, K., Gamble, G.R., Jenkins, M. 2014. Grazing winter rye cover crop in a cotton no-till system: yield and economics. Agronomy Journal. 106:1041-1050. DOI:10.2134/agronj13.0434.
Maul, J.E., Himmelstein, J., Everts, K.L. 2014. Impact of five cover crop green manures and Actinovate on Fusarium Wilt of watermelon. Plant Disease. 98(7):965-972.