OBSERVATIONS AND MODELING OF INTERACTIONS BETWEEN BARLEY YIELD AND EVAPOTRANSPIRATION IN THE SUB-ARCTIC

Management of cropping systems and conservation of water resources req uires a knowledge of crop evapotranspiration (ET). Yet, ET from field- grown crops and the association among yield, ET, and water stress are virtually unknown in the subarctic region of North America. Irrigated and nonirrigated barley (Hordeum vulgare L.) treatments were establish ed in 1989 at Delta Junction and 1990 at Fairbanks, Alaska, to ascerta in yield-ET relations and to validate a model which simulates relative yield (relative to potential yield) based on the transpiration (T) to potential transpiration (T(p)) ratio. Barley development, soil water content (by neutron attenuation), pan evaporation, precipitation, air temperature, relative humidity, and global radiation were monitored at each location. Regression analysis indicated that grain yield increas ed 26 kg . ha-1 for every mm of water evapotranspired over a range of 180 to 260 mm in seasonal ET. Modeled and measured available water in the soil profile and relative yield were in good agreement. Based on 9 years of measured barley yield and climate data at Fairbanks, modeled ET ranged from 120 to 250 mm and yield decreased as the modeled trans piration deficit (1 - T/T(p)) increased. This study indicated that wat er stress occurs frequently in the subarctic.