Influence of pH on germination promoting chemicals in weed seeds.
The effects of pH on dormancy-relieving chemicals (sodium azide (A), potassium nitrate + ethephon (NE), NE + A, NE + A + thiourea + hydrogen peroxide) were investigated in seeds of Chenopodium album, Avena fatua and Rumex crispus. Seeds were placed in soil trays or in paper (in vitro) with buffer solutions. The response to NE was not affected by pH from 3 to 9. Sodium azide had the greatest effect on seed decline, but its effect was pH-dependent. This compound was extremely deleterious for C. album and A. fatua seeds in acid soil (pH 4), while in basic soil the dormancy of A. fatua was relieved. At pH 6.2 the combination of NE + A was detrimental to C. album and A. fatua. Mixing all 5 compounds together reduced the influence of pH on the deleterious effect of sodium azide. This effect was less affected by temperature than its dormancy-relieving action. The solution extracted from both soils did not affect the response to chemical treatments in vitro at different temperatures compared with buffers at similar pH. The influence of soil characteristics on the efficacy of dormancy-relieving or weed killing treatments in the field is discussed.