Temperature responses and calculated heat units for germination of several range grasses and shrubs

Abstract

Quantitative effects of temperature on germination were determined for 17 cool-season grasses, 19 warm-season grasses, and 18 miscellaneous forbs and shrubs associated with semiarid rangelands. These effects, expressed as the reciprocal of days to 50% germination, were used in linear regression analyses to predict the temperature at which the germination rate approaches zero from which heat units to 50% germination and germination indexes were derived. The regression relationships appeared to be linear if data were restricted to the lower range of germination temperatures. The germination rate approached zero at temperatures ranging from 3.7 to 6.3 degrees C for cool-season and from 7.8 to 13.7 degrees C for warm-season grasses. No particular trend was evident among the forbs and shrubs. The reciprocal of the slope of the regression equation was a constant expressing heat units to 50% germination. It was characteristic of each accession. The product of heat units and the zero rate temperature was used to calculate a germination index. This index compared well with selected germination responses observed in the field.