1a. Objectives (from AD-416):
Our overall goal for this project is to develop cover crop-based, reduced-tillage grain production systems that improve farm production sustainability, minimize herbicide resistant weeds, reduce weed-crop competition in organic agriculture, and maximize agro-ecosystem services. Objective 1: Improve the feasibility of using multi-tactic weed management approaches for field cropping systems by developing optimal configurations of cover crops, chemical and cultural weed controls, and soil and crop management. [NP304, Component 2, Problem Statement 2A3] • Sub-objective 1A. Develop cropping systems that integrate multi-tactic weed management practices (physical, chemical, and biological) to address herbicide resistant weeds and weed-crop competition in conventional and organic systems, through optimal combinations of soil management, cover cropping, and at harvest weed seed removal. • Sub-objective 1B. Characterize allelochemicals and nitrogen compounds from living and decomposing cover crops; track their influence on crop: emergence and yield, and weed: emergence, growth rates, and fecundity.
1b. Approach (from AD-416):
Sub-objective 1A. Develop cropping systems that integrate multi-tactic weed management practices (physical, chemical, and biological) to address herbicide resistant weeds and weed-crop competition in organic systems, through optimal combinations of soil management, cover cropping, and at harvest weed seed removal. Experiment 1A.1. Determine individual and combined effects of cover crop mixtures, fertilizer source/rate/placement, and herbicides on weed competitiveness and community assembly in high residue no-till corn production. Experiment 1A.2. Test the impact that harvest weed seed collection (HWSC), herbicides, and cover crops have on weed population dynamics and management of multiple-herbicide resistant weed genotypes in soybean. Sub-objective 1B. Characterize allelochemicals and nitrogen compounds from living decomposing cover crops; track their influence on crop: emergence and yield, and weed: emergence, growth rates, and fecundity. Goal 1B.1. Quantify allelochemical and nitrogenous products released into the soil as a function of cover crop: species, growth stage, and termination method. Experiment 1B.2. Determine the magnitude and duration of weed suppression from cereal rye allelopathic compounds and their interaction with herbicides, and mulch mass on herbicide-resistant weeds.
3. Progress Report:
This is the first year of this project plan. We initiated the long-term cropping systems experiment a year earlier than initially planned, which did not have a milestone in year one. We submitted nine papers (six of which were accepted) on cover crop-based corn and soybean production, cover crop management for optimal weed and nitrogen management, life cycle analysis of cropping system experiments, the role of cover crop mixtures in suppressing weeds, managing nitrogen, and greenhouse gas flux over the past year. We also used empirical trials to validate and calibrate process-based models that determine nitrogen release from cover crops. Field trials and laboratory assays examining the allelopathic effects of cover crops on weeds were initiated and sample analysis is ongoing. The final year of a cover crop mixture experiment looking at cover crops and manure fertility in conventional and organic corn was completed. The final year of weed responses to starter fertilizer experiments were completed and a manuscript submitted. There is an ARS Area-wide project to develop multi-tactic weed management strategies that address herbicide resistant weeds associated with this project. For this Area-wide project a long-term experiment was initiated at three sites (Illinois, Arkansas, and Maryland) to examine the independent and combined effects of cover crops, harvest-time weed seed control, and herbicides on weed control. In addition, all 14 cooperating sites on the Area-wide project initiated a weed seed rain study to examine which weed species are candidates for control using harvest-time weed seed control tactics. Data compiled over the past year was presented at the national weed science conference. At the annual Area-wide collaborator meeting, linkages were made between the socio-economic components of the project and the weed biology components. A post doc was hired to develop bio-economic models that examine the impact of weed management decisions on herbicide resistant weeds when implemented at the farm scale as compared to a community based approach. Another round of funding was received for the project and agreements put in place to fund research at cooperating sites next year. Finally, a multi-tactic weed management study using herbicides and cover crops was designed that will be implemented this fall.
1. Combining grass/legume cover crop mixtures maximize both nitrogen content and biomass. Cover crops are nonmarket crops that are used as multi-functional tools to provide agro-ecosystem services. Combining species into a cover crop mixture is a useful approach to maximize multiple services. Therefore, ARS researchers in Beltsville, Maryland, conducted a study that combined grass and legume cover crop species at two locations for two years and determined total above ground biomass, nitrogen content, and biological nitrogen fixation. Cover crop biomass tended to be higher in mixture or similar to the greatest yielding monoculture. Nitrogen content was maximized in the cover crop when 50% of the cover crop was composed of the legume. This work provides a decision framework for farmers when considering how to combine grass and legume cover crops and how management and initial soil fertility levels can influence cover crop composition.
2. Hairy vetch and cereal rye cover crop mixtures can provide both improved nutrient management and weed suppression as compared to monocultures of each species. Legumes are useful in providing nitrogen to the subsequent cash crop while grasses provide good weed control and scavenge soil nitrogen. To best make recommendations to farmers on how to use cover crop mixtures, we must understand how soil and crop management practices (fertilizer and tillage) influence the cover crop once terminated. Therefore, ARS researchers in Beltsville, Maryland, conducted an experiment at two locations for two years to assess how cover crop sown proportions, tillage, and poultry litter application and method of application (broadcast vs. subsurface banded) influence cover crop decomposition. The findings show that maximum residue persistence can be achieved using a pure cereal rye cover crop and no poultry litter or subsurface banded poultry litter. Pure hairy vetch residue released the most N, particularly when incorporated with poultry litter; however, incorporation also sped up the rate of N release, making it less synchronous with corn demand. Subsurface banding is the recommended poultry litter application method to conserve surface residues. Our work will be used to develop process-based models for estimating cover crop decomposition across broad regions. Such models will then be used to develop web-based decision support tools for growers for optimal adaptive nitrogen management.
5. Significant Activities that Support Special Target Populations:
Two team members hosted seven student interns from Hispanic Serving Institutions during summer 2016.
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.
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.
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.
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.
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.
Bybee-Finley, K., Mirsky, S.B., Ryan, M.R. 2016. Functional diversity in summer annual grass and legume intercrops in the Northeastern United States. Crop Science. 56:2775-2790.