The effects of herbicide weed control and perennial grass establishment on soil nitrate (NO3-) in arid Great Basin habitats

Authors: Phillips, Jacob; Harmon, Daniel; Clements, Darin; Allen, Fay

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2023
Publication Date: 1/30/2024
Citation: Phillips, J.D., Harmon, D.N., Clements, D.D., Allen, F.L. 2024. The effects of herbicide weed control and perennial grass establishment on soil nitrate (NO3-) in arid Great Basin habitats. Society for Range Management Meeting Abstracts. 77:25.

Interpretive Summary:

Technical Abstract: Weed control in arid Great Basin habitats is essential to promoting a healthy ecosystem. Excess weeds, such as cheatgrass (Bromus tectorum), cause an increase in fire cycles, cause competition for available soil resources like nitrate (NO3-), and result in costly efforts to restore the habit. An increase in annual grass weeds limits the availability of soil resources that would allow shrubs, forbs, and perennial grasses to establish. This causes a repeat cycle of undesirable annual grasses to continue to germinate and outcompete more desirable plants that would be beneficial for wildlife and livestock. Herbicides are known to be a useful tool for weed control. The role of herbicides is to reduce the competition for soil resources by reducing the number of weeds in arid habitats. Imazapic and indaziflam are two commercially available preemergent herbicides that inhibit weed growth. We hypothesized that the reduction in weeds on a site allows more available nitrate for desired plants to establish through seeding efforts. Soil samples were collected from herbicide plots (imazapic and indaziflam - one year after application) and control plots (with heavy weeds present) at three field locations across the Great Basin in Nevada. The data reflects a large effect on the available soil nitrate in an imazapic herbicide plot sampled in June 2022 at one field site (TS Ranch, 48.63ppm NO3-) compared to controls (6.14ppm). Additionally, two sites sampled in June 2022 showed a smaller effect on nitrate in imazapic plots (Bedell and Izzenhood, 11.18ppm and 13.91ppm), but still significant compared to control plots (3.06ppm and 6.40ppm respectively). Similar results were seen for indaziflam for that month. The overall reduction of weeds using herbicides results in more soil nitrate which is available to establish favorable plants such as perennial grasses, forbs, and shrubs through seeding efforts.