Seeding Rates for Establishing Big Bluestem and Switchgrass with Preemergence Atrazine Applications1

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Abstract
The purpose of this study was to determine seeding rates for establishing switchgrass (Panicum virgatum L.) and debearded big bluestem (Andropogon gerardii Vitman) when atrazine |6‐chloro‐N‐ethyl‐ N'‐(1‐methylethyl)‐1,3,5‐triazine‐2,4‐diamine] is used as a preemergence herbicide. The high seed cost of these grasses makes it uneconomical to use higher seeding rates than necessary. The study was conducted on four eastern Nebraska sites during the period 1981 to 1985. The experimental design was a randomized complete block with six replications. Treatments were grasses (big bluestem and switchgrass) and seeding rates [107, 215, 325, and 430 pure live seeds (PLS) m−2] in a factorial arrangement. Plots were seeded in late spring with a plot seeder with double disk openers on a clean, firm seedbed, and broadcast sprayed with 2.2 or 3.0 kg ha−1 atrazine the day after seeding. Stands and forage yields were measured the first (Year 1) and second year (Year 2) following establishment. The 107 PLS m−2 seeding rate resulted in thinner, but still acceptable, stands (10–20 plants m−2) than the higher seeding rates in Year 1 and at two of the sites in Year 2. The stands from the higher rates, in general, did not differ within a site and were good to excellent ( >20 plants m−2). The lowest seeding rate produced lower forage yields than the other rates in Year 1, but these differences were significant at only one site. There were no differences for Year 1 yield for the other rates or for Year 2 yields for all rates.

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