Irrigation Requirements for Seed Production of Two Eriogonum Species in a Semiarid Environment

Seeds of native plants are needed for rangeland restoration in the Intermountain West. 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 over multiple years for two perennial Eriogonum species, Eriogonum umbellatum Torr. and Eriogonum heracleoides Nutt. The two species grown at the Oregon State University Malheur Experiment Station, Ontario, Ore., received 0, 100, or 200 mm·year−1 of drip irrigation. Seed yield responses to irrigation were evaluated by linear and quadratic regression against 1) applied water; 2) applied water plus spring precipitation; 3) applied water plus winter and spring precipitation; and 4) applied water plus fall, winter, and spring precipitation. In general, seed yields responded quadratically to irrigation. For E. umbellatum, over 11 years, highest seed yields averaged 260 kg·ha−1 and ranged from 207 to 508 kg·ha−1. For E. heracleoides, over 6 years, highest yields averaged 353 kg·ha−1 and ranged from 168 to 588 kg·ha−1. Adding spring precipitation to applied water improved the accuracy of estimated water requirements for maximum seed production of E. umbellatum. For E. heracleoides, adding precipitation to applied water did not improve the accuracy of estimated water requirements for maximum seed production. Averaged over 11 years, seed yield of E. umbellatum was maximized by 209 mm·year−1 of spring precipitation plus irrigation. Averaged over 6 years, seed yield of E. heracleoides was maximized by 126 mm·year−1 of applied water. Both species required relatively small amounts of irrigation to help assure seed yield, and the irrigation needed for E. umbellatum could be adjusted by taking spring precipitation into account.