Effects of Summer Weather Modification (Irrigation) in Festuca idahoensis-Agropyron spicatum Grasslands

Abstract

A simulated summer cloud seeding program was conducted for 4 years on a Festuca idahoensis-Agropyron spicatum grassland. Production and phenologic responses were essentially nil when plots were given 1.1, 1.2, 1.4 times natural rainfall on a per storm basis by sprinkler irrigation. Watering at the rate of 5 cm/week extended the flowering period in only one species, Tragopogon dubius; extended the green leaf season in most species; and increased the production of only three species, Festuca idahoensis, Balsamorhiza sagittata, and Tragopogon dubius. The increased production occurred only in the year following irrigation and may have been due to increased plant reserves and vigor. It appears that summer cloud seeding programs will have little or no positive effect on production in this vegetation type.