2017 ASHS Annual Conference

Seeds of native plants are needed for rangeland restoration in the Intermountain West of North America. Many of these plants are rarely cultivated and relatively little is known about the cultural practices required for their seed production. Irrigation trials were conducted for two perennial Eriogonum species over multiple years. The two species grown at the Oregon State University Malheur Experiment Station, Ontario, Ore. received 0, 100, or 200 mm of drip irrigation per year. Seed yield responses to irrigation were evaluated by linear and quadratic regression over irrigation rates. In general, seed yields responded quadratically to irrigation. For E. umbellatum, over 11 years, highest yields averaged 260 kg•ha^–1 and ranged from 207 to 508 kg•ha^–1. For E. heracleoides, averaged over 6 years, highest yields averaged 353 kg•ha^–1 and ranged from 168 to 588 kg•ha^–1. To improve the accuracy of estimated irrigation water needs in any given year, regressions were also run on seed yield responses to irrigation plus precipitation during the previous spring; spring and winter; and spring, winter, and fall. Adding spring precipitation to applied water improved the accuracy of estimated water requirements for maximum seed production of E. umbellatum. Averaged over 11 years, seed yield of E. umbellatum was maximized by 208 mm of spring precipitation plus irrigation. For E. heracleoides, adding precipitation to applied water did not improve the accuracy of estimated water requirements for maximum seed production. Averaged over 6 years, seed yield of E. heracleoides was maximized by 126 mm of applied water.