1a. Objectives (from AD-416)
The long-term research objective of this project is to develop and translate fundamental agroecological knowledge into recommendations and products to improve the economic position of organic farmers and to improve their ability to meet consumer demand for organic products. Objective 1 is to develop component technologies and management strategies that lead to improved productivity, enhanced soil and water conservation, and efficient nutrient cycling on organic farms. Objective 2 is to understand agroecological principles that drive the function of organic cropping systems and quantify ecosystem services.
1b. Approach (from AD-416)
Approaches to developing component strategies include A) incorporating legumes into organic crop rotations to maximize nitrogen fixation, B) composting that provides a productive and safe amendment for organic agriculture, and C) optimal agronomic practices for managing nutrients and production on organic farms. Approaches to determining agroecological principles include investigating the following variables within the Beltsville long-term Farming Systems Project that compares two conventional and three organic rotations, A) crop performance, B) soil nitrogen dynamics in relation to nitrogen inputs, C) soil carbon sequestration and greenhouse gas flux, D) soil biological community structure in relation to soil quality and production performance, and E) soil erosion and nutrient loss potential.
3. Progress Report
Field experiments to evaluate animal manures and OMRI-approved fertilizers as sources of K and P in organic forage production are in their second year at BARC and fourth year on-farm. Seed increases of Purple Bounty and/or Purple Prosperity hairy vetch varieties facilitated the first field scale trial using these varieties in an organic no-till corn production system. Field trials of eight representative hairy vetch gentotypes from around the world have been initiated on station and on farms. The capacity of biofiltration using wood chips to capture ammonia and odors from force-aerated piles, in-vessel composting, and poultry litter drying process was tested. Biofiltration effectively reduced odorous emissions and significantly increased nitrogen content of the wood chip media in the biofilters from 0.3 to 1.7 percent. Analysis of two years of field data indicate that sidedress, compared to pre-plant, application of organic N fertility sources (i.e., feathermeal, poultry litter, or blended materials) can substantially increase N use efficiency. The fourth year of a field trial evaluating the agronomic performance of organic field corn following a hairy vetch cover crop in tilled vs. no-tilled systems is complete. Results suggest delaying hairy vetch termination to optimize N availability can directly impact growing season duration, weed suppressive potential of surface mulches, and subsequent crop performance. Data are being collected for a second year in permanent weed-free and weedy check plots in organic and conventional systems in the FSP. We are monitoring weed population and community dynamics and weed-crop competition. A germinable assay is being conducted to determine long-term persistence of weed seedbanks. A University of Maryland Master’s student found that the DayCent model was better able to predict annual emissions of N2O, an important greenhouse gas, from the two conventional FSP systems than from an organic system, suggesting that the manure and cover crop modules in DayCent need to be improved to better predict N2O emissions from organic and other systems relying on organic sources of nitrogen. Another University of Maryland Master’s student is compiling 16 years of data collected at FSP to compare nutrient budgets (P, K, N, C) among cropping systems and evaluate nutrient management and soil carbon sequestration. A visiting scientist from Brazil (EMBRAPA) is comparing output from the DNDC model with five years of soil N2O emissions data from FSP and is helping collect a sixth year of N2O and supporting ancillary data. An undergraduate student is helping to conduct research on soil N2O emissions at FSP, supported by the FAR-B Summer Internship Program. A visiting PhD student from Brazil is measuring occluded and free particulate organic matter fractions in FSP soils, as part of our effort to evaluate mechanisms of soil carbon sequestration. We have developed and optimized qPCR and tRFLP methods for FSP soils and are using these methods to quantify and characterize denitrification genes. These data are being compared to measured soil N2O fluxes and other measures of soil microbial community structure.
1. Hairy vetch cultivars from around the world are characterized for important agricultural traits. Hairy vetch is an important nitrogen-fixing cover crop used in organic and other sustainable agriculture production systems. Developing varieties with improved winter survival, earlier blooming, and enhanced nitrogen fixation will increase farmer options for integrating this important species in their crop rotations. Breeders need additional information about the genetic potential and variability that exists among hairy vetch accessions globally. Scientists at ARS in Beltsville, Maryland evaluated sixty-four hairy vetch accessions from around the world for flowering date, biomass production, and nitrogen fixation in the field. Genomic marker analysis (AFLP) shows great diversity among accessions and biogeographical linkages among accessions from the same country of origin. This information will be essential for breeders developing improved hairy vetch varieties, and for producers in identifying optimum varieties for implementing use of this important nitrogen-fixing cover crop.
2. Plant available nitrogen provided by soils increases with increasing crop rotation length in organic systems and is greater in organic than conventional systems. Increasing the proportion of a crop’s nitrogen needs met by mineralization of soil organic N reduces dependence on external N inputs required for crop production. Nitrogen fertilizer production, transport and application represent about 30% of energy use in agriculture. Scientists at ARS in Beltsville, Maryland characterized soil organic N fractions from five long-term cropping systems. They found that total soil organic N was similar among three organic systems and a conventional no-till system, and was significantly greater than in a conventional chisel-till system. Particulate organic matter–N, a fraction of soil organic N that is readily mineralized, and mineralizable organic soil N were both greatest in the organic systems and least in conventional systems. Among the organic systems, particulate organic matter–N increased with increasing crop rotation length and mineralizable N was greater in three and six year crop rotations than in a two year crop rotation. These results provide important strategies to reduce N inputs in agricultural systems that will be useful to all farmers, extension educators, nutrient management plan writers, and others interested in sustainable soil fertility management.
3. Feather meal and feather meal-poultry litter blends show potential as side-dress fertilizers to improve nitrogen use efficiency in organic systems. Improving nitrogen use efficiency in corn production will provide economic benefits to farmers and environmental benefits to society. Researchers at ARS in Beltsville, Maryland showed that the N release characteristics of locally available sources of OMRI-approved N (raw poultry litter, pelletized poultry litter, feather meal, and a pelletized blend of feather meal and poultry litter) could serve as viable sources of supplemental N for organic and other grain production. The rate of N release of each material was relatively fast, suggesting that applying them to corn at the V5 growth stage (sidedress) could result in significant improvements in N use efficiency compared to pre-plant applications (the industry standard). Results showed that the feather meal and the feather meal-poultry litter blend were more nutrient dense than the raw and pelleted poultry litter and therefore less costly to transport per unit of available N. This information will benefit producers, extension educators, nutrient management plan writers, and others interested in improved soil fertility and nutrient management in organic and other grain cropping systems.
Spargo, J.T., Cavigelli, M.A., Mirsky, S.B., Maul, J.E., Meisinger, J.J. 2011. Mineralizable soil nitrogen and labile soil organic matter in diverse long-term cropping systems. Nutrient Cycling in Agroecosystems. 90:253-266.