Interactions of temperature and dormancy-relieving compounds on weed seed germination.
A study was carried out to investigate the effects of different temperatures and the use of potassium nitrate, thiourea, ethephon, sodium azide and hydrogen peroxide on the seed germination of Chenopodium album, Rumex crispus and Avena fatua. Ethephon and sodium azide slightly stimulated germination of C. album seeds at 20°C while nitrate, thiourea and sodium azide interacted positively with alternating temperatures (5°/25°C, 8 h/16 h). Germination (expressed in normal equivalent deviates) increased linearly with the logarithm of the chemical dose up to an optimal concentration. When sodium azide was pre-applied for 24 h, the optimum concentration was 100 times greater than when it was applied during the test. Fluctuating temperatures broke dormancy of R. crispus seeds and the chemicals only inhibited germination at high doses. Exposure to light, when pre-applying sodium azide and peroxide, increased germination of C. album and R. crispus, but did not affect the actions of the chemicals. The compounds tested had little or no effect on A. fatua at constant or alternating regimes with a mean temperature over 10°C, but dormancy was relieved by sodium azide and potassium nitrate at low temperatures (3-10°C).