EFFECTS OF DAY AND NIGHT TEMPERATURE ON GOATSRUE (GALEGA-OFFICINALIS)AND ALFALFA (MEDICAGO-SATIVA) GROWTH

Goatsrue, a perennial legume, is an exotic noxious weed currently foun d in the United States only in Cache County, Utah. It infests irrigate d pastures, alfalfa fields, and noncropland areas. In order to compare their responses to temperature, goatsrue and alfalfa were grown in ar tificially illuminated controlled-environment chambers in 16 day/night temperature regimes ranging from 1514 to 36/25 C. Growth analysis was used to evaluate effects of temperature on dry matter accumulation, l eaf area production, and biomass allocation. Both species grew best at day/night temperatures of 22/25, 29/18, and 29/25 C. Leaf appearance rates were linearly related to mean daily temperature. Goatsrue produc ed fewer but larger leaves and a greater total leaf area than alfalfa. Biomass partitioning to leaves was greater in goatsrue, whereas parti tioning to stems was greater in alfalfa. Response of vegetative dry ma tter production to temperature closely paralleled response of leaf are a duration in both species. Alfalfa generally had a higher net assimil ation rate, but the greater leaf area duration of goatsrue resulted in greater dry matter accumulation in this species after 50 d of growth. Overall responses to temperature were similar in the two species. Thu s it seems likely that goatsrue could become a much more widely distri buted weed in alfalfa.