The flotations in the germination of seeds in the field are governed by a group of environmental factors. In the present work it was analysed the effects of the pH, salinity and aluminium on the germination of seeds, and of the sowing depth on the rate of seedling emergency of the pasture weeds Cassia tora and Urena lobata. All studies were carried out in laboratory, excpet those of sowing depht which were accomplished at a greenhouse. The germination and the seedling emergency rate were monitored in period of 15 and 20 days, respectively. The results showed that the pH in the band from 3 to 11 and the concentration of aluminium of 0 to 2,0 meq/100 ml, did not affect seed germination of the two weeds Cassia tora and Urena lobata answered similarly to salinity until the level of 150 mM. However, for the concentration of 300 mM Urena lobata was more tolerant to salinity than the Cassia tora, whose seeds did not germinate in this salt concentration. The relationship between seedling emergency rate and sowing depth was quadratic for both species. Cassia tora, however, showed larger capacity to emerge than the Urena lobata at the depth of 8 cm, this later species presenting a rate of emergency zero when sowed in this depth.
pH; salinity; aluminium; weeds; pastures