Objective 1: Determine how crop management practices (such as cultivar selection) and abiotic factors affect weed ecology in the upper Midwest, especially in vegetable and bioenergy crops. Sub-objective 1a: Identify cover crop residues that favor edamame over the weed. Sub-objective 1b: Quantify the impact of Miscanthus invasion and removal on plant community composition. Sub-objective 1c: Quantify the role of soil environmental parameters (e.g., C, C:N and NO3-:NO2- ratios, pH, diurnal temperature variations, soil moisture) in controlling nitrification along with N-loss (denitrification) vs. N-retention (DNRA), and evaluate the link between measured N-cycle processes to weed seed germination and seedling development. Objective 2: Improve the feasibility of using multi-tactic integrated weed management approaches for regaining control of weeds with resistances to multiple herbicides, and for preventing or slowing the evolution of herbicide resistance in susceptible weed populations. Sub-objective 2a: Evaluate the impact of harvest weed seed control (HWSC) on population dynamics and management of multiple-herbicide-resistant weed genotypes in field crops. Sub-objective 2b: Develop and compare weed management systems in edamame, utilizing cover crops, herbicides, and physical weeding.
Multi-tactic integrated weed management (IWM) offers one potential approach to address the problem of multiple herbicide resistant (MHR) weeds. In IWM systems, suites of multiple complementary tactics are deployed throughout weed life cycles to increase efficacy of weed suppression, prevent survival of weeds that escape earlier management, and reduce weed populations over the long-term. In this project, we evaluate the utility of chemical, cultural, biological, and physical tactics in IWM systems for weed suppression and crop yield protection in fields with MHR weed populations. Edamame (vegetable soybean) cultivars tolerant to cover crop residues will be combined with cover crops, recently registered herbicides, and physical weeding to examine the potential of IWM in legume vegetable production systems. The contribution of improved knowledge of soil N cycling to aid better prediction of weed seedling emergence and community composition also will be evaluated in this production system. In field crops, interactions among weed seed destruction at crop harvest, cover crops, and tank mixtures of herbicides will be quantified for their impact on MHR weeds in corn and soybean. Finally, in a continuation of previous research, the impact of escaped invasive bioenergy crops on weeds of arable areas will be measured.
Substantial progress was made in initiating investigations of weed ecology and management, with special emphasis on understanding and responding to multiple herbicide resistance, in FY 16. A device for mechanical destruction of weed seeds was tested as a stationary device in reducing the seed viability of seven weed species. In spring 2016, we established a field study for quantifying the impact of Harvest Weed Seed Control with the mechanical device on the population dynamics of multiple herbicide resistant weeds in central Illinois, and collected baseline samples of the soil seedbank to measure proportion of resistant plants prior to imposing experimental management treatments. Following a five-year study of the impact of controlled Miscanthus invasions in native plant communities in central Illinois floodplain forests and old fields, we began the process of eradicating Miscanthus in summer of 2015. We have an ongoing monitoring and eradication program in place to detect and control re-sprouting plants. A small number of re-sprouts were found and treated in July 2016, meaning that the monitoring and eradication effort will need to continue for at least one more year. Commercial vegetable production systems continue to benefit from our project’s weed management research, with specific focus on the vegetable versions of corn and soybean. For vegetable soybean, we finalized and published a 3-year study that identified the most effective weed management systems based on herbicides currently registered in the crop. Ongoing research in edamame focuses on improving crop emergence and seedling competitive ability by examining factors such as crop seed size, planting depth, and the use of cover crop mulches. In sweet corn, we finalized and published several important studies, including: 1) a multi-institutional study that identified viable alternatives to atrazine in sweet corn production, 2) a project that showed Goss’s wilt incidence in sweet corn is independent of glyphosate use and transgenic traits, 3) a method to identify hybrids with crowding stress tolerance (CST), 4) quantified relationships among CST traits and crop phenotype, and 5) identified networks of genes involved in CST. Ongoing research involves developing a protocol for the use of CST hybrids on-farm. Nitrogen cycling in soil is primarily mediated by microorganisms, and recent studies now reveal new genes and populations that have high potential for reducing the greenhouse gas nitrous oxide (N2O), a major product generated via microbial processes. High throughput sequencing of bacterial ribosomal genes in soil samples taken over four years at two field sites was completed this year to characterize bacterial taxa within specific soil depths (0-30 cm) that we previously demonstrated to contain distinct populations that harbor nosZ, the gene encoding nitrous oxide reductase. We are currently analyzing this sequence data in correspondence to an existing metagenomic dataset of the most abundant soil nosZ sequences from our field sites (ARS-GA Tech collaboration), to quantify the functional potential of nitrous oxide reducers not yet recognized for their role in soil N-cycling. Ongoing research involves testing dynamical changes of specific identified taxa, including both consumers and producers of N2O (e.g. ammonia oxidizing bacteria) in response to environmental factors such as temperature and N-fertilizer addition to ultimately aid in the predictive strength of greenhouse gas models.
1. A head start on minimizing invasions from bioenergy crops. Perennial plant biomass is an increasingly important part of the U.S. renewable energy portfolio; however, widespread production of exotic perennial vegetation has raised concerns about invasions of bioenergy crops into adjoining natural areas. ARS researchers in Urbana, Illinois found that controlled introductions of Miscanthus x giganteus and Miscanthus sinensis in old-field and floodplain forest habitats did not affect resident plant community composition over a five-year period. Although local Miscanthus invasions in the Midwest and Southeast U.S. show a long term potential for this species to develop problematic populations, these results show that there will likely be a lag of several years or more before new invasions cause damage to native plant communities in natural areas. This should provide enough time for bioenergy producers to implement monitoring and eradication plans that minimize invasions from these bioenergy crops.
2. Goss’s wilt incidence in sweet corn is independent of the use of the herbicide glyphosate and transgenic traits. Claims have been made in recent years that corn susceptibility to plant diseases, including Goss’s wilt, increases with the use of glyphosate use and transgenic traits. ARS researchers in Urbana, Illinois, Beltsville, Maryland, and University, Mississippi conducted research that showed Goss’s wilt incidence was independent of glyphosate use and transgenic traits in sweet corn. Contrary to a detrimental outcome, crop yield improved with the use of these technologies. This research dispels unsubstantiated negative claims about glyphosate and transgenic traits; technology that adds an additional weapon in the combat to manage herbicide resistant weeds in sweet corn.
3. Potential major source of nitrous oxide from soil. Fungi have been implicated in nitrogen turnover for over 30 years, but of the estimated 1.5 to 5.1 million fungal species comprising ~25% of the global biomass, only ~2-7% have been cultivated, with few tested for denitrification and N2O is the main fungal product. Monitoring tools to measure the presence and abundance of denitrifying fungi were largely lacking. ARS researchers in Urbana and collaborators isolated new fungal denitrifying species using new cultivation approaches, resulting in development of molecular tools to target p450nor, the gene encoding nitric oxide reductase, a key enzyme in the production of N2O by fungi. These tools now open opportunity to detect and measure fungi as N2O sources in soil N-cycles.
Williams, M.M. II 2015. Relationships among phenotypic traits of sweet corn and tolerance to crowding stress. Field Crops Research. 185:45-50.
Williams II, M.M. 2015. Stress test: identifying crowding stress-tolerant hybrids in processing sweet corn. Agronomy Journal. 107:1782-1788.
Williams, A., Davis, A.S., Ewing, P., Forcella, F., Grandy, S., Kane, D., Mortensen, D., Smith, R., Spokas, K.A., Jordan, N.R. 2016. A comparison of soil hydrothermal properties in zonal and uniform tillage systems across the northern U.S. corn belt. Soil and Tillage Research. 273:12-1.
Welch, R., Behnke, G., Davis, A.S., Masiunas, J., Villamil, M.B. 2016. Using cover crops to alleviate compaction in organic grain farms: effects on weeds and yields. Agriculture Ecosystems and Environment. 216:322-332.
Lou, Y., Davis, A.S., Yannarell, A.C. 2016. Interactions between allelochemicals and the microbial community affect weed suppression following cover crop residue incorporation into soil. Plant and Soil. 399:357-371.
Regnier, E.E., Harrison, K., Loux, M.M., Holloman, C., Venkatesh, R., Davis, A.S., Taylor, R. 2016. Crop advisor perceptions of giant ragweed distribution, herbicide-resistance, and management in the Corn Belt. Weed Science. 64:361-377.
Hill, E., Renner, K., Sprague, C., Davis, A.S. 2016. Cover crop impact on weed dynamics in an organic dry bean system. Weed Science. 64:261-275.
Muthukrishnan, R., West, N.M., Davis, A.S., Jordan, N.R., Forester, J. 2015. Evaluating the role of landscape in the spread of invasive species: the case of the biomass crop. Journal of Applied Ecology. 317:6-15.
Williams, A., Kane, D., Ewing, P., Atwood, L., Jilling, A., Li, M., Lou, Y., Davis, A.S., Grandy, A., Koide, R.T., Spokas, K.A., et. al, 2016. Soil functional zone management: a vehicle for enhancing production and soil ecosystem services in row-crop agroecosystems. Frontiers in Plant Science. 7:65.
Choe, E., Drnevich, J., Williams II, M.M. 2016. Identification of crowding stress tolerance co-expression networks involved in sweet corn yield. PLoS One. doi: org/10.1371/journal.pone.0147418.
Higgins, S.A., Welsh, A., Orellana, L.H., Konstantinidis, K.T., Chee-Sanford, J.C., Sanford, R.A., Schadt, C.W., Loeffler, F.E. 2016. Detection and diversity of fungal nitric oxide reductase genes (p450nor) in agricultural soils. Applied and Environmental Microbiology. 82(10):2919-2928.
Barney, J.N., Davis, A.S., Porter, R.D., Simberloff, D. 2016. A life-cycle approach to low-invasion potential bioenergy production. Council for Agricultural Science and Technology Issue Paper. QTA 2016-1.
Williams II, M.M. 2015. Managing weeds in commercial edamame production: current options and their outcomes. Weed Science. 63:954-961.
Boydston, R.A., Williams, M. 2015. Sweet corn hybrid tolerance to weed competition under three weed management levels. Renewable Agriculture and Food Systems. 31:281-287. doi: 10.1017/S1742170515000204.
Williams, M.M. II, Bradley, C.A., Duke, S.O., Maul, J.E., Reddy, K.N. 2015. Goss’s wilt incidence in sweet corn is independent of transgenic traits and glyphosate. Horticultural Science. 50:1791-1794.
Williams, A., Davis, A.S., Ewing, P., Grandy, A., Kane, D., Koide, R.T., Mortensen, D.A., Smith, R.G., Snapp, S., Spokas, K.A. 2016. Precision control of soil N cycling via soil functional zone management. Agriculture Ecosystems and the Environment. 231:291-295.
Williams, A., Hunter, M.C., Jordan, N.R., Kammerer, M., Kane, D.A., Smith, R.G., Snapp, S., Davis, A.S. 2016. Soil water holding capacity mitigates maize production downside risk and volatility across the US Corn Belt: Time to invest in soil organic matter?. PLoS One. 11(8):e0160974.