A Berlese-Tullgren funnel system that is used for studying soil invertebrates. This laboratory technique causes soil invertebrates to move away from the soil surface as it is being warmed and dried by the lights above. The invertebrates are caught in jars of ethanol below the funnels, counted, and identified under a microscope.
The Effect of Pre-Emergent Herbicides on Soil in The Sagebrush Steppe
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By Forest and Rangeland Ecosystem Science Center
September 1, 2023
We are studying how herbicides sprayed onto soil to prevent the establishment of exotic annual grasses such as cheatgrass may impact the health, growth resources and microbiota of soils in sagebrush-steppe, where herbicide use is an important and common tool. Our findings will help make herbicide applications more successful.
Background
Sources/Usage: Public Domain. View Media Details
Land managers use herbicides in the sagebrush steppe to try to control populations of invasive annual grasses such as cheatgrass and medusahead. These invasive grasses complete their life cycle and dry out within a relatively short time in early spring, leaving behind a layer of highly flammable plant litter that causes more frequent and larger wildfires. These grasses are also quick to invade after fires, making those areas more likely to reburn before native perennials can recover. Herbicides are used to disrupt this annual grass-fire cycle. The effects of herbicides on vegetation are widely documented, but the effects of herbicides on soil are less known.
The Fire, Invasives, and Ecology in Sagebrush Steppe team (FIREss) is studying the effects of several pre-emergent herbicides on soil. Pre-emergent herbicides prevent weeds from growing by inhibiting the germination of the weeds’ seeds. These differ from post-emergent herbicides which are designed to directly target and control existing weeds that are already established. We are working with partners from many other agencies to study the impact of the herbicides indaziflam, imazapic and rimsulfuron on soil resources, soil processes and soil communities.
Soil resources include readily available mineral forms of nitrogen, such as ammonium and nitrate, and organic forms of nitrogen and carbon. During soil processes, organic forms of nitrogen are converted into mineral forms, and organic carbon is converted into CO2. These soil processes are facilitated by micro-organisms like fungi and bacteria. The soil community consists of a diverse and interconnected group of organisms that inhabit and interact within the soil ecosystem. This community includes a wide range of life, from microorganisms like bacteria and fungi to larger organisms like invertebrates and small mammals. The soil community is essential for maintaining soil health, nutrient cycling, decomposition of organic matter, and overall ecosystem functioning. Invasive plants can alter soil resources, processes, and communities, and using herbicides to control invasive plants can cause further alterations that are not well understood.
Objectives
Our objectives are to use controlled and replicated field experiments to determine:
1) The influence of invasive grasses on soil microorganisms
2) The responses of soil resources, processes, and communities to herbicide treatments
3) The potential for innovative management strategies to minimize negative effects of herbicides on soils
4) The effects of all these factors on restoration outcomes
Methods
We collected over 500 soil samples from hundreds of plots in sites treated with herbicides in southwest Idaho. Soil resources are analyzed at the new FIREss Plant and Soil Laboratory. We are also collaborating with Boise State University and other agencies to extract and sequence DNA from soil samples to characterize soil microbial communities. This work will generate valuable information land managers can use to improve, predict, and set expectations for restoration treatment success.
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Results
In fall 2016, we fenced in three study sites in southwest Idaho to exclude livestock and collected data on pre-treatment vegetation cover and density. After pre-treatment surveys were completed, professional fire crews burned the sites in a controlled manner to simulate post-wildfire conditions encountered by land managers. Each burned site was sprayed with treatments that included:
- Control – No herbicide
- The bio-herbicide D7 (a strain of the naturally occurring soil bacterium Pseudomonas fluorescens, that has been isolated and applied to soils for the control of exotic annual grasses, albeit with mixed results in field studies)
- The chemical herbicide imazapic
-
The chemical herbicide rimsulfuron
A paper published in 2022 describes the effects of a larger set of spray treatments on plant communities. The exotic annual grasses at all sites were strongly reduced for one year by rimsulfuron and for multiple years by imazapic. D7 did not have any effect on plant communities. More information on the effects on target and non-target plants is available in the journal article on the Applied Vegetation Science website.
Analysis of soil samples on a subset of the spray treatments revealed that when chemical herbicides reduce the germination of exotic annual grasses, mineral nitrogen in the soil increases. Mineral nitrogen is one component of chemical fertilizers. Exotic annual grasses use a lot of mineral nitrogen for growth, so when they are absent from the landscape there is more nitrogen available to other plants. Ensuring desired native vegetation is present to capture extra mineral nitrogen freed by herbicide treatments could improve restoration success. If desirable plants are not present, those extra nutrients could be used by rapidly growing, nitrogen-loving invaders in the years following herbicide treatment. This paper was published in 2024 and is available on the Restoration Ecology website.
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request.
Funnel system for studying soil invertebrates
A Berlese-Tullgren funnel system that is used for studying soil invertebrates. This laboratory technique causes soil invertebrates to move away from the soil surface as it is being warmed and dried by the lights above. The invertebrates are caught in jars of ethanol below the funnels, counted, and identified under a microscope.
Experimental herbicide treatment plot in Idaho
The Wildcat experimental treatment site in southwest Idaho at the base of the Owyhee Mountains. The brown square was treated with pre-emergent herbicide and is free of cheatgrass, a few native perennial bunchgrasses were able to establish. This image was taken the first Spring after treatment.
The Wildcat experimental treatment site in southwest Idaho at the base of the Owyhee Mountains. The brown square was treated with pre-emergent herbicide and is free of cheatgrass, a few native perennial bunchgrasses were able to establish. This image was taken the first Spring after treatment.
Field technician collecting a soil core
A field technician taking a soil core sample at Wildcat, a field site in southwest Idaho. Scientists are studying the effects of herbicides used to control exotic annual grasses on soil.
A field technician taking a soil core sample at Wildcat, a field site in southwest Idaho. Scientists are studying the effects of herbicides used to control exotic annual grasses on soil.
Cheatgrass invasion of sagebrush habitats after a fire in northwestern Nevada, U.S.A
Cheatgrass (Bromus tectorum) invasion of sagebrush habitats after a fire in northwestern Nevada, U.S.A.
Cheatgrass (Bromus tectorum) invasion of sagebrush habitats after a fire in northwestern Nevada, U.S.A.
Cheatgrass (Bromus tectorum)
Cheatgrass (Bromus tectorum)
Cheatgrass (Bromus tectorum)
We are studying how herbicides sprayed onto soil to prevent the establishment of exotic annual grasses such as cheatgrass may impact the health, growth resources and microbiota of soils in sagebrush-steppe, where herbicide use is an important and common tool. Our findings will help make herbicide applications more successful.
Background
Sources/Usage: Public Domain. View Media Details
Land managers use herbicides in the sagebrush steppe to try to control populations of invasive annual grasses such as cheatgrass and medusahead. These invasive grasses complete their life cycle and dry out within a relatively short time in early spring, leaving behind a layer of highly flammable plant litter that causes more frequent and larger wildfires. These grasses are also quick to invade after fires, making those areas more likely to reburn before native perennials can recover. Herbicides are used to disrupt this annual grass-fire cycle. The effects of herbicides on vegetation are widely documented, but the effects of herbicides on soil are less known.
The Fire, Invasives, and Ecology in Sagebrush Steppe team (FIREss) is studying the effects of several pre-emergent herbicides on soil. Pre-emergent herbicides prevent weeds from growing by inhibiting the germination of the weeds’ seeds. These differ from post-emergent herbicides which are designed to directly target and control existing weeds that are already established. We are working with partners from many other agencies to study the impact of the herbicides indaziflam, imazapic and rimsulfuron on soil resources, soil processes and soil communities.
Soil resources include readily available mineral forms of nitrogen, such as ammonium and nitrate, and organic forms of nitrogen and carbon. During soil processes, organic forms of nitrogen are converted into mineral forms, and organic carbon is converted into CO2. These soil processes are facilitated by micro-organisms like fungi and bacteria. The soil community consists of a diverse and interconnected group of organisms that inhabit and interact within the soil ecosystem. This community includes a wide range of life, from microorganisms like bacteria and fungi to larger organisms like invertebrates and small mammals. The soil community is essential for maintaining soil health, nutrient cycling, decomposition of organic matter, and overall ecosystem functioning. Invasive plants can alter soil resources, processes, and communities, and using herbicides to control invasive plants can cause further alterations that are not well understood.
Objectives
Our objectives are to use controlled and replicated field experiments to determine:
1) The influence of invasive grasses on soil microorganisms
2) The responses of soil resources, processes, and communities to herbicide treatments
3) The potential for innovative management strategies to minimize negative effects of herbicides on soils
4) The effects of all these factors on restoration outcomes
Methods
We collected over 500 soil samples from hundreds of plots in sites treated with herbicides in southwest Idaho. Soil resources are analyzed at the new FIREss Plant and Soil Laboratory. We are also collaborating with Boise State University and other agencies to extract and sequence DNA from soil samples to characterize soil microbial communities. This work will generate valuable information land managers can use to improve, predict, and set expectations for restoration treatment success.
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Results
In fall 2016, we fenced in three study sites in southwest Idaho to exclude livestock and collected data on pre-treatment vegetation cover and density. After pre-treatment surveys were completed, professional fire crews burned the sites in a controlled manner to simulate post-wildfire conditions encountered by land managers. Each burned site was sprayed with treatments that included:
- Control – No herbicide
- The bio-herbicide D7 (a strain of the naturally occurring soil bacterium Pseudomonas fluorescens, that has been isolated and applied to soils for the control of exotic annual grasses, albeit with mixed results in field studies)
- The chemical herbicide imazapic
-
The chemical herbicide rimsulfuron
A paper published in 2022 describes the effects of a larger set of spray treatments on plant communities. The exotic annual grasses at all sites were strongly reduced for one year by rimsulfuron and for multiple years by imazapic. D7 did not have any effect on plant communities. More information on the effects on target and non-target plants is available in the journal article on the Applied Vegetation Science website.
Analysis of soil samples on a subset of the spray treatments revealed that when chemical herbicides reduce the germination of exotic annual grasses, mineral nitrogen in the soil increases. Mineral nitrogen is one component of chemical fertilizers. Exotic annual grasses use a lot of mineral nitrogen for growth, so when they are absent from the landscape there is more nitrogen available to other plants. Ensuring desired native vegetation is present to capture extra mineral nitrogen freed by herbicide treatments could improve restoration success. If desirable plants are not present, those extra nutrients could be used by rapidly growing, nitrogen-loving invaders in the years following herbicide treatment. This paper was published in 2024 and is available on the Restoration Ecology website.
If you are unable to access or download a product, email fresc_outreach@usgs.gov a request.
Funnel system for studying soil invertebrates
A Berlese-Tullgren funnel system that is used for studying soil invertebrates. This laboratory technique causes soil invertebrates to move away from the soil surface as it is being warmed and dried by the lights above. The invertebrates are caught in jars of ethanol below the funnels, counted, and identified under a microscope.
A Berlese-Tullgren funnel system that is used for studying soil invertebrates. This laboratory technique causes soil invertebrates to move away from the soil surface as it is being warmed and dried by the lights above. The invertebrates are caught in jars of ethanol below the funnels, counted, and identified under a microscope.
Experimental herbicide treatment plot in Idaho
The Wildcat experimental treatment site in southwest Idaho at the base of the Owyhee Mountains. The brown square was treated with pre-emergent herbicide and is free of cheatgrass, a few native perennial bunchgrasses were able to establish. This image was taken the first Spring after treatment.
The Wildcat experimental treatment site in southwest Idaho at the base of the Owyhee Mountains. The brown square was treated with pre-emergent herbicide and is free of cheatgrass, a few native perennial bunchgrasses were able to establish. This image was taken the first Spring after treatment.
Field technician collecting a soil core
A field technician taking a soil core sample at Wildcat, a field site in southwest Idaho. Scientists are studying the effects of herbicides used to control exotic annual grasses on soil.
A field technician taking a soil core sample at Wildcat, a field site in southwest Idaho. Scientists are studying the effects of herbicides used to control exotic annual grasses on soil.
Cheatgrass invasion of sagebrush habitats after a fire in northwestern Nevada, U.S.A
Cheatgrass (Bromus tectorum) invasion of sagebrush habitats after a fire in northwestern Nevada, U.S.A.
Cheatgrass (Bromus tectorum) invasion of sagebrush habitats after a fire in northwestern Nevada, U.S.A.
Cheatgrass (Bromus tectorum)
Cheatgrass (Bromus tectorum)
Cheatgrass (Bromus tectorum)