Irrigation Requirements for Seed Production of Five Native Lomatium Species

Lomatium species are important components in the rangelands of the Intermountain West.  Relatively little is known about the cultural practices necessary to produce Lomatium seed for use in rangeland restoration. Research at the Oregon State University Malheur Experiment Station in Ontario, Oregon, was initiated in 2006 and 2009 to evaluate the seed yield responses of native Lomatium species to irrigation. The seed yield responses of five Lomatium species to four biweekly subsurface drip irrigations applying either 0, 25 mm, or 50 mm of water (total of 0, 100, or 200 mm/season) were evaluated over multiple years on silt loam in a semi-arid environment. Irrigations were started at flowering initiation, which varied by species from mid-March to mid-April. Precipitation from January through June ranged from 67 to 224 mm. Lomatium grayi and L. triternatum started producing seed in the 2^nd year after fall seeding.  Lomatium nudicaule, L. dissectum, and L. suksdorfii started producing seed in the 3^rd, 4^th, and 5^th years after fall seeding, respectively. Optimum irrigation was determined by regression on seed yield for each species each year. Over six production seasons, Lomatium dissectum seed yield averaged 972 kg/ha and was maximized by 125 mm of applied water per season in cooler, wetter years and by 200 mm of applied water per season in warmer, drier years. Over eight production seasons, Lomatium grayi seed yield averaged 927 kg/ha and was maximized by 0 to 125 mm of applied water per season in cooler, wetter years and by 125 to 200 mm of applied water per season in warmer, drier years. Over 8 production seasons, Lomatium triternatum seed yield averaged 1487 kg/ha and was maximized by 100 to 200 mm of applied water per season in cooler, wetter years and by 200 mm of applied water per season in warmer, drier years. In two years of seed production, Lomatium nudicaule seed yield averaged 605 kg/ha, but was not responsive to irrigation. In the first and only seed production season observed so far, seed yield of Lomatium suksdorfii did not respond to irrigation.