Plant-soil relationships: long-term monitoring of soil nitrogen and moisture after cheatgrass chemical control

Authors: Harmon, Daniel - Dan; Clements, Darin - Charlie

Submitted to: Society of Range Management
Publication Type: Abstract Only
Publication Acceptance Date: 11/8/2022
Publication Date: 2/7/2023
Citation: Harmon, D.N., Clements, D.D. 2023. Plant-soil relationships: long-term monitoring of soil nitrogen and moisture after cheatgrass chemical control. Society of Range Management. 76:65.

Interpretive Summary: Using Pre-emergent herbicides to mitigate the deleterious effects of weeds and wildfires is an effective means to facilitate sustainable delivery of goods and services from Great Basin Ecosystems. Assessing the multiyear effects of such herbicides as Imazapic and Indaziflam on cheatgrass populations can help land managers and agricultural producers maximize natural resources. Understanding changes in soil properties like moisture and nitrogen in relation to weed control and plant-soil relationships can provide insight to mechanisms that enhance the conservation and restoration of Great Basin Rangelands. We sampled soil at three field locations (TS Ranch, Bedell Flat and Izzenhood) after pre-emergent herbicide weed control treatments, measuring moisture and available nitrogen. Samples were collected monthly for 4 years. Seasonal patterns of soil moisture and nitrogen were determined based on soils data. Mean NO3- for the sampling period found that cheatgrass dominated habitats at TS Ranch had less than 10 ppm (NO3-) compared to 61 ppm the first year after cheatgrass control. Even 4 years after initial herbicide control NO3- averaged 27 ppm, more than 3 times as much as untreated cheatgrass plots. Successful seeding efforts were correlated with higher soil nitrogen and moisture after cheatgrass control. Cheatgrass control also increased initial moisture availability for seedlings of seeded species by nearly 2-fold in many cases. Cheatgrass competition for soil resources results in soil NO3- and moisture limiting perennial seedlings survival which maintains cheatgrass dominance, high fuels and increased wildfire risk. Decreasing cheatgrass densities using pre-emergent herbicides is an effective means to increase soil resources to promote successful rangeland restoration efforts.

Technical Abstract: Using Pre-emergent herbicides to mitigate the deleterious effects of weeds and wildfires is an effective means to facilitate sustainable delivery of goods and services from Great Basin Ecosystems. Assessing the multiyear effects of such herbicides as Imazapic and Indaziflam on cheatgrass populations can help land managers and agricultural producers maximize natural resources. Understanding changes in soil properties like moisture and nitrogen in relation to weed control and plant-soil relationships can provide insight to mechanisms that enhance the conservation and restoration of Great Basin Rangelands. We sampled soil at three field locations (TS Ranch, Bedell Flat and Izzenhood) after pre-emergent herbicide weed control treatments, measuring moisture and available nitrogen. Samples were collected monthly for 4 years. Seasonal patterns of soil moisture and nitrogen were determined based on soils data. Mean NO3- for the sampling period found that cheatgrass dominated habitats at TS Ranch had less than 10 ppm (NO3-) compared to 61 ppm the first year after cheatgrass control. Even 4 years after initial herbicide control NO3- averaged 27 ppm, more than 3 times as much as untreated cheatgrass plots. Successful seeding efforts were correlated with higher soil nitrogen and moisture after cheatgrass control. Cheatgrass control also increased initial moisture availability for seedlings of seeded species by nearly 2-fold in many cases. Cheatgrass competition for soil resources results in soil NO3- and moisture limiting perennial seedlings survival which maintains cheatgrass dominance, high fuels and increased wildfire risk. Decreasing cheatgrass densities using pre-emergent herbicides is an effective means to increase soil resources to promote successful rangeland restoration efforts.