Sorghum Germination and Development as Influenced by Soil Temperature and Water Content

Abstract In Hungary, the seed‐bed temperature at the customary planting time for sorghum [ Sorghum bicolor (L.) Moench] is typically close to the base temperature, 10°C (the temperature at which there is zero development). At low soil temperatures, soil water may also be critical. This 30‐d phytotron study examined the combined effect of low soil temperature at two soil water levels on sorghum emergence and early development. Ten initial soil temperatures (7–16°C) and two soil water treatments (high and low: −0.04 and −0.2 MPa water pressure, respectively) were used. Since, after 19 d (5–24 June), there was no emergence at soil temperatures below 9°C, soil temperature in all pots was increased to 20°C and was maintained at this level until the end of experiment on 5 July. Percent emergence increased with increasing initial soil temperatures. The slope of this curve was four times steeper with −0.04 than −0.2 MPa water pressure. The improved microclimatic conditions caused by higher initial soil temperatures led to faster emergence, which may have produced better sorghum seedling establishment. Although seeds sown in soil with alternating low (below base temperature) and high seed‐bed temperatures can emerge, quick emergence and adequate plant density is less likely. In Hungary, where both air and seed‐bed soil temperatures vary a great deal around sorghum planting time, it is better to wait until the upper soil temperature stabilizes above 10°C, the base temperature for sorghum.