1a. Objectives (from AD-416):
Objective 1: Measure effects of management, climate, and soil conditions on microbial processes (herbicide degradation, nitrogen cycling, and weed seedbank dynamics) in corn/soybean ecosystems. Objective 2: Evaluate the effects of management and climate change on the biology and ecology of weedy and invasive species, including potential weedy cellulosic bioenergy crops, in Midwestern cropping systems. Objective 3: Identify effective combinations of weed management components through application of both new and existing knowledge that exploit useful plant and environmental interactions in vegetable cropping systems.
1b. Approach (from AD-416):
Each objective of the proposed work seeks to advance knowledge of specific topics that directly or indirectly relate to weed-crop competition for resources, providing a basis to identify tactics of routine management that shift the competitive advantage to the crop. We examine the ecology of microorganisms and plants, and combine these efforts into a synthesis that applies research findings toward practical solutions. Each objective utilizes the whole scientific team, and regardless of scale, experiments include samples from a common group of sites, providing extensive metadata support. Studies under Objective 1 address microbial activities that are influenced by agricultural management, climate, or soil conditions. Primary climatic factors to be addressed are temperature and rainfall. In Objective 2, management and climate change will be evaluated as to effects on the biology and ecology of weedy and invasive species, including potential weedy cellulosic bio-energy crops, in Midwestern cropping systems. A particular focus will be on spatiotemporal variation in demographic parameters and population growth rates at multiple levels of scale. As a means of unifying observations, whole life cycles of weeds will be the unit of study whenever possible. Objective 3 identifies effective combinations of weed management components through application of both new and existing knowledge that exploit useful plant and environmental interactions in vegetable cropping systems.
3. Progress Report:
Investigations of weed management in a changing climate, begun in FY 12, were continued in FY 13. Competition of Palmer amaranth genotypes from the southern U.S. with soybean was measured in southern, central and northern Illinois, following strict protocols to avoid introducing a seed bank for this species. Pure line seed increase of these genotypes was performed to support an additional study year in FY14. We completed a final year of monitoring and measuring the demography and growth of the energy crops Miscanthus giganteus and Miscanthus sinensis in old field and forest environments in central Illinois, again with special procedures to minimize invasion risk. Finally, statistical analysis of management and environmental risk factors associated with the evolution and spread of glyphosate resistant waterhemp in Illinois grain crops was completed. Retooling weed management systems using new and existing knowledge that exploits useful plant and environmental interactions continue to be examined in vegetable cropping systems. Sweet corn - one of the most widely grown vegetable crops (~700,000 acres) - serves as a model crop. We completed field trials quantifying the extent to which climate region (Midwest versus Pacific Northwest), cytochrome P450 genotype in sweet corn, and herbicide tank-mix influenced crop tolerance to HPPD-inhibiting herbicides. The data have been analyzed and a manuscript is in preparation. Extramural funding was secured to develop integrated weed management alternatives to atrazine - the most widely used herbicide in corn production. Field trials throughout the Midwest, and a few locations in the PNW, are being initiated. Finally, several manuscripts on biological factors contributing to weed escapes in sweet corn have been published, including crop disease incidence (maize dwarf mosaic) and crop population density. Molecular probes developed for detection of new bacterial genes associated with the reduction of the greenhouse gas N2O were applied to monitor the spatiotemporal dynamics of populations in two contrasting field sites that differ in characteristics of water drainage and C/N nutrient retention. We completed Year one of a three-year study and are currently in Year two to demonstrate seasonal and diurnal shifts in bacterial populations associated with denitrification and non-denitrifier-mediated N2O reduction (both N-loss mechanisms), and dissimilatory nitrate reduction to ammonia (DNRA, N-retention process) according to soil depth and in response to diurnal temperature cycles. Extramural funding was obtained to extend this work to sequence the metagenomes at both field locations associated with this project, particularly genes associated with N-cycling processes. Additional work was added this year to obtain high throughput sequencing of the nrfA gene associated with DNRA to provide novel data supporting a high diversity of nrfA genes in wide-ranging soil types.
1. Management guidelines for preventing bioenergy crop escapes. Herbaceous perennial grasses grown for bioenergy purposes can provide huge amounts of biomass, but also have the potential to become invasive if natural areas surrounding plantations are not monitored carefully for escapes. Such escapes can influence species composition in non-agricultural areas, potentially reducing wildlife habitat and forest productivity. ARS researchers at Urbana, IL, addressed the need for streamlined monitoring procedures for land managers to detect bioenergy crop escapes by conducting controlled studies of factors influencing the establishment of Miscanthus seedlings. This work demonstrated that light gradients control Miscanthus seedling establishment success, with little seedling recruitment in deep shade areas. For detection of potential escapes in forests and other low-visibility sites, land managers should focus search efforts on large canopy gaps.
2. Atrazine significance and need for alternatives. Despite extensive use of atrazine herbicide, weeds continue to cause crop loss in most sweet corn fields. Regulatory changes are reducing atrazine availability; therefore, information concerning crop loss due to weed pressure without atrazine is needed. Research by ARS scientists (Urbana, IL) documented that greater weed escapes and crop losses are likely when atrazine is removed from current weed management systems. These results stimulated research aimed to identify economically viable alternatives to standard atrazine-based weed management systems. This will reduce the environmental risks from atrazine use while safe-guarding the production of America’s most popular vegetable – sweet corn.
3. Identification of understudied microbial nitrogen (N)-cycling populations in soil. The microbial process of nitrate consumption leading to production of either N2O or N2 gases (denitrification) was traditionally held accountable for the primary losses of N from soils, especially in N-fertilized agricultural soils. Current greenhouse gas (GHG) flux models require input of biological variables that accurately account for production and consumption of N2O, a potent greenhouse gas, yet predictions of N-gas emissions based on a few previously well-studied denitrifying bacteria (denitrifiers) are often inaccurate. Research by ARS scientists (Urbana,IL) demonstrated significant microbial populations common to agricultural soils that include both non-traditional denitrifiers and non-denitrifiers able to reduce N2O to N2. These newly identified populations are as abundantly present as many of the conventional and well-studied denitrifying populations used as the previous focus in N-cycling and in GHG emissions models. The importance of this research is the identification of new microbial populations that have functional significance related to N2O reduction and identifies these as important targets of biological N-cycling to monitor in agricultural soils. This accomplishment has further led to the development of an important and growing database (>150 new gene sequences identified) used by ARS researchers in Urbana along with university collaborators to aid identification of important functional microbial populations using the newest technology to sequence and identify genes present in whole soil metagenomes (i.e. all the genetic material from an environment). Collectively, the end-product of this research will provide more comprehensive identification of the biological factors leading to more efficient N-fertilizer use and more accurate predictive scenarios of GHG emissions.
Matlaga, D.P., Davis, A.S. 2013. Minimizing invasive potential of Miscanthus × giganteus grown for bioenergy: identifying demographic thresholds for population growth and spread. Journal of Applied Ecology. 50:479-487.