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 second year of this project plan. Five of six milestones for the second year of this project were met. The sixth milestone was not met due to the retirement of a support scientist assigned to this aspect of the project plan. We submitted 17 papers over the past year (eleven of which were accepted) on cover crop-based corn and soybean production, cover crop management for optimal weed and nitrogen management, integrated cover crop and manure management fertility, weed management with high residue cultivators, effects of chemical weed management programs on cover crop performance, and cover crop effects on greenhouse gas flux. Under Sub-objective 1A, the second year of a long-term multi-tactic weed management cropping systems experiment was continued; all samples collected and analyzed. Stationary testing of the Harrington Seed Destructor was completed. Weed seedbanks and the overall population dynamics of weeds in two long-term cropping system experiments was completed. Manuscripts were prepared on the interactions between cover crop and manure management on weed performance. Under Sub-objective 1B, we used empirical trials to validate and calibrate process-based models that determine nitrogen release from cover crops as well as develop incubation studies to define the decomposition kinetics of cover crops. Field trials and laboratory assays examining the allelopathic effects of cover crops on weeds were completed and manuscripts are in preparation. Work on an ARS Area-Wide project directed at developing multi-tactic weed management strategies that address herbicide resistant weeds was continued. For this, the second year of a long-term experiment was completed 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 completed the second year of a weed seed rain study to examine which weed species are candidates for control using harvest-time weed seed control tactics. Finally, a cover crop/herbicide interaction study on weed population dynamics was initiated; and the first year field trial completed. Data from the Area-Wide project 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. Work from the Area-Wide project was also featured at the Global Herbicide Resistance Management Summit. We have completed manuscript preparation of a bio-economic model and have begun simulations assessing individual and combined effects of numerous weed management tactics (harvest weed seed control, cover crops, tillage, crop rotation, and herbicides). This model examines 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 for the Area-Wide project is expected for FY2018 and agreements will be put in place to fund research at cooperating sites next year upon receipt of this funding.
1. Optimized cover crop management in organic rotational no-till corn and soybean production. The success of cover crop-based organic rotational no-till corn and soybean production is critical to expanding organic grain production; however, cover crops have only been tested in single crop entry component experiments in these no-till systems. Since cover crops run the risk of becoming weeds in the subsequent cash crop in organic no-till systems, a long-term cropping systems experiment was required to determine the risk of cover crops becoming weeds in subsequent crops. This cropping system experiment was conducted at three locations in the Mid-Atlantic to test how timing of cover crop termination affects cover crop biomass production, control, and contamination in subsequent cash crops during the transition to organic production. It was shown that cover crop termination at mid-flowering resulted in successful control of the cover crop and minimized long-term impacts on the subsequent cash crops. This work will aid scientists in integrating cover crops into organic no-till corn and soybean production systems.
2. Determined the optimal timing for high residue cultivation of weeds in organic rotational no-till soybean production. A successful reduced-tillage organic grain production system is needed to reduce labor requirements for existing organic producers and to attract more soil conservation minded conventional producers to organic grain production. Supplemental weed control tools like high residue cultivators are needed to limit weed competition in reduced-tillage organic grain production systems. We performed an experiment to determine the optimal time of cultivation with a high residue cultivator to maximize weed control and minimize crop yield loss. We observed that cultivation with the high residue cultivator 5 to 6 weeks after soybean planting ensured both sufficient weed management and minimal impact on soybean yield. This information is essential for the development of a reduced-tillage organic grain production system.
3. Nitrogen in surface applied crop residues is transferred to soil by fungi. When cover crops with high carbon to nitrogen ratios, such as cereal rye, are incorporated into soil the amount of plant available nitrogen in soil is reduced because soil microorganisms use the nitrogen during decomposition of the plant residues. In a nitrogen fixing cash crop like soybeans, the low nitrogen availability can impact weeds. When cover crop residues are left on the soil surface it is possible that soil fungi, which can grow into the residue from the soil, reduce soil nitrogen by translocating it into the crop residue during decomposition. Therefore, we conducted a field experiment to determine the extent to which nitrogen translocation into cereal rye residue occurs in a cereal rye cover crop-based no-till soybean production field. We observed a 36% increase in cereal rye residue nitrogen that appears to be due to fungal translocation. This work defines the nutritive mechanism in which weeds are suppressed by cover crop mulches and will aid researchers in developing cover cover crop-based weed management systems.
Spargo, J.T., Cavigelli, M.A., Mirsky, S.B., Meisinger, J.J., Ackroyd, V. 2016. Organic supplemental nitrogen sources for field corn production after a hairy vetch cover crop. Agronomy Journal. 108:1992-2002.
Zinati, G., Mirsky, S.B., Seidel, R., Grantham, A., Moyer, J., Ackroyd, V. 2017. High-residue cultivation timing impact on organic no-till soybean weed management. Weed Technology. 31:320-329.
Davis, B.W., Mirsky, S.B., Needelman, B.A., Cavigelli, M.A., Yarwood, S.A., Maul, J.E., Bagley, G.A. 2016. A novel approach to estimating nitrous oxide emissions during wetting events from single-timepoint flux measurements. Journal of Environmental Quality. 46:247-254.
Geene, C., Curran, W.S., Wallace, J., Mirsky, S.B., Ryan, M.R., VanGessel, M., Barbercheck, M. 2017. Cover crop termination timing is critical in organic rotational no-till systems. Agronomy Journal. 109:272-282.
Wells, M.S., Reberg-Horton, S.C., Mirsky, S.B., Maul, J.E., Hu, S. 2017. In situ validation of fungal N translocation to cereal rye mulches under no-till soybean production. Plant and Soil. 410:153-165.