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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Research Project #430898

Research Project: Follow-up Shrub Establishment Study

Location: Livestock and Range Research Laboratory

Project Number: 3030-21630-005-02-R
Project Type: Reimbursable Cooperative Agreement

Start Date: Mar 20, 2017
End Date: Jun 30, 2021

In an initial study, we found reducing seed rates of aggressive, cool-season perennial grasses (i.e. western wheatgrass, thickspike wheatgrass, slender wheatgrass, green needlegrass) from typical levels (i.e. 8-12 pounds per acre) to somewhat lower levels (i.e. 4-6 pounds per acre) benefited shrubs without appreciably risking grass stands. While lowering rates of these grasses proved safe, entirely excluding these grasses from seed mixes often led to weak grass stands and infestation by cheatgrass and other annual weeds. Between the extremes of completely excluding the aggressive grasses and seeding them at moderate or high rates there is likely a range of low rates (e.g. 0.1 to 2.0 lb per acre) that is optimal in terms of encouraging both grasses and shrubs. Identifying this optimal rate range will be the goal of this study.

Identifying optimal grass seeding rates will require varying the rates while holding other factors (e.g. rainfall, seeder type, soil type) constant. This will be easily accomplished by having mines apply standard seeding practices and seed rates to entire fields, except for test strips where cool season grass seed rates are reduced to experimental levels. Because weed pressure and weather conditions vary widely from field to field and year to year, it will be critical to implement the test strips in a variety of fields seeded in a number of years. By comparing a range of grass rates under an array of conditions, we will identify a minimum rate range that benefits shrubs without being risky to grass stand establishment. We will seed test strips with experimental grass seed rates in as many fields as possible (at least six fields per year) for three years beginning fall 2016. Coal mines invited to collaborate in the project would include Decker, Spring Creek, Rosebud, and Absaloka. If these mines are not scheduled to seed enough fields, the project will be extended to gravel mines and/or abandoned mine lands. Each test strip will consist of 2 planter passes physically and GPS marked for the duration of the study. Forb, shrub and warm-season grass seed rates will be constant within fields: Both in the test strips and the remainder of the field, these plants will be seeded at permitted rates. Conversely, cool-season perennial grass rates will vary within fields: Each test strip will receive a combined cool-season grass rate of either 0.1, 0.5, 1.0, 2.0, or 4.0 pounds per acre. Therefore, 6 grass seed rates (the standard whole-field rate and 5 experimental test strip rates) will be tested in each field. To ensure drill seeders accurately deliver low grass seed rates, seed will be mixed with dead seed.