Germination was investigated in 1-yr and 8-yr-old seed lots of barnyardgrass. Each seed lot was divided into a portion stored dry at 25 C (afterripening) and a portion buried in the field (stratification) in central Europe (latitude 50°N, longitude 14°E). The afterripened seed lost dormancy within 2 yr after dispersal, whereas buried seed passed through annual dormancy/nondormancy cycles. The seed was germinated at five constant temperatures between 17 and 35 C with an 18/6-h light/dark photoperiod. Germination was affected by both seed age and storage conditions. Germination percentage and rate in 8-yr-old afterripened and each of the stratified seed lots varied with temperature. Optimum temperatures for germination were between 27 and 31 C, and the range of adequate temperatures increased with seed age. A common base temperature for germination was 11.7 C. In 1-yr-old afterripened material, the proportion of germinating seed (< 5%) and germination rate were similar at all temperatures. Barnyardgrass thus revealed a plastic strategy of germination. Stratification during the first winter removed dormancy and allowed germination at a narrow range of temperatures. This constraint on optimum germination temperature decreased with increased seed age. Seedling emergence, thus, may vary according to whether seed population originates from the previous year or from old soil seed banks.
Nomenclature: Barnyardgrass, Echinochloa crus-galli (L.) Beauv. ECHCG.