Cardinal temperatures and thermal time requirements for germination of annual and perennial temperate pasture species

Abstract

Cardinal temperatures (base (Tb), optimum (To) and maximum (Tm)) and thermal time (Tt) requirements for germination of 21 temperate annual and perennial grass, legume and weed species were calculated from incubator experiments. Cardinal temperatures were defined using an iterative broken-stick linear regression model of development rate against temperature. Species specific maximum germination rates were all >80% except for the 60% attained by ‘Pawera’ red clover. The maximums were stable from 5 to 20 °C with the exception of ‘Arrotas’ arrowleaf clover, ‘Advance’ tall fescue and ‘Vision’ cocksfoot which had <20% germination at 5°C. To was approximately 26 °C for ‘Woogenellup’ subterranean, ’Mihi’ Persian, alsike, red and strawberry clovers but ≤ 20 °C for white clover and the other annual clover species tested. A base temperature of 0°C was found for all species except ripgut brome (Tb= 4.0 °C) and Tm was ≥ 35 °C. Therma ltime requirements for germination were generally lower for annual than perennial clovers which may reflect adaptation to avoid out of season germination. Annual weed grasses, showed rapid germination which aids their competitive ability to invade establishing pastures. Vulpia hair grass seed germination was over 95% at 25°C and below; barley grass declined with increasing temperatures from 5 to 35 °C.