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 fourth year of this project plan. Five of six milestones for the third 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 18 papers over the past year (fifteen 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, allelochemical activity in the soil, and cover crop breeding. There was a heavy emphasis on understanding the behavior of grass/legume cover crops in mixture and monoculture and subsequent weed suppression. Under Sub-objective 1A, the fourth year of a long-term multi-tactic weed management cropping systems experiment was continued; all samples were collected and analyzed. Stationary testing of the Harrington Seed Destructor was completed, data analyzed, and a manuscript will be submitted shortly. Weed seedbanks and the overall population dynamics of weeds in two long-term cropping system experiments were completed. 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. Cereal rye roots, not shoots, were found to be the primary contributor of phenolic acids to soil. Further, soil phenolic acid concentrations were little affected by tillage or soil depth. Overall, the allelochemicals decreased immediately after termination. The primary contribution of cover crops to allelopathy is when living. Building this body of knowledge is critical to incorporate allelopathy as part of a multi-tactic weed management system. Work on an ARS Area-Wide herbicide-resistant weed management project that develops multi-tactic weed management strategies was continued. The fourth 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 third year of a cover crop/herbicide interaction study on weed population dynamics. We have made significant advancements in technology transfer in the form of a mature website with extensive static content, social media, and videos. We are developing a web-based app used to guide farmers in herbicide programs that prevent herbicide-resistant weed development. Another round of funding for the Area-Wide project is expected for FY2020 and agreements will be put in place to fund research at cooperating sites next year upon receipt of this funding.
1. Cover crops reduce nitrate leaching. Nitrogen left in the soil after crop harvest is susceptible to leaching loss, which can result in decreased ground- and surface-water quality. ARS scientists in Beltsville, Maryland, performed a global meta-analysis of the available literature to understand how well cover crops reduce nitrate leaching from agroecosystems. Compared to no cover crop controls, cover crops reduced nitrate leaching by fifty-six percent, on average. Soil type, planting and termination dates, shoot biomass, and climate each influenced the extent to which cover crops reduced nitrate leaching. These findings indicate that cover crops are an effective way to reduce nitrate leaching and should be integrated into existing cropping systems for water quality benefits. This work will help farmers to make cover crop management decisions, and inform policy-makers to minimize agriculture’s impact on water quality.
2. Cover crop mixtures outperform cover crop monocultures. While cover crop mixtures are increasingly employed to simultaneously support multiple objectives on a farm (i.e., weed suppression and nitrogen fertility), reported impacts of cover crop mixtures in the literature are inconsistent. ARS scientists in Beltsville, Maryland, conducted a meta-analysis using results from 20 studies and found that hairy vetch/cereal rye mixtures produced sixty percent and 25 percent more biomass compared to hairy vetch and cereal rye monocultures, respectively. When hairy vetch exceeded forty-eight percent of the mixture biomass, the mixtures accumulated equivalent or more nitrogen than the legume monoculture. Results show that farmers can use cover crop mixtures to optimize biomass for weed suppression while also maximizing nitrogen content for subsequent cash crop fertility needs. This information will be of use for farmers and other agriculture professionals.
Thapa, R., Mirsky, S.B., Tully, K. 2018. Cover crops reduce nitrate leaching in agroecosystems: A global meta-analysis. Journal of Environmental Quality. 47:1400-1411.
Evans, J.A., Williams, A., Hager, A.G., Mirsky, S.B., Tranel, P.J., Davis, A.S. 2018. Confronting herbicide resistance with cooperative management. Pest Management Science. 74:2424-2431. https://doi.org/10.1002/ps.5105.
Youngerman, C.Z., Ditommaso, A., Curran, W.S., Mirsky, S.B., Ryan, M.R. 2018. Crop density effect on interseeded cover crops, weeds, and grain yield. Agronomy Journal. 110:2478-2487.
Allred, B.J., Wishart, D., Martinez, L.R., Schomberg, H.H., Mirsky, S.B., Meyers, G.E., Elliott, J., Charyton, C. 2018. Delineation of agricultural drainage pipe patterns using ground penetrating radar integrated with a real-time kinematic global navigation satellite system. Agriculture. 8(11):167. https://doi.org/10.3390/agriculture8110167.
Williams, A., Wells, M.S., Dickey, D.A., Hu, S., Maul, J.E., Raskin, D.T., Reberg-Horton, S.C., Mirsky, S.B. 2019. Establishing the relationship of soil nitrogen immobilization to cereal rye residues in a mulched system. Plant and Soil. 426:95-107.
Vann, R., Reberg-Horton, C., Castillo, M., Mirsky, S.B., Mcgee, R.J. 2019. Winter pea, crimson clover, and hairy vetch planted in mixture with small grains in the Southeast USA. Agronomy Journal. 111:805-815.