Published online by Cambridge University Press: 01 June 1999
A field experiment was carried out on soyabean (Glycine max (L.) Merr.) to measure the effect of planting date (soil temperature) on seedling emergence. Seeds were sown at weekly intervals on seven planting dates from April until the end of May in SE England in 1997. Planting date had no significant effect on final percentage emergence but had a highly significant effect on time to emergence. The coefficients of variation (c.v.) for the number of days to emergence (calendar days) were high (43–45%), and therefore not a reliable method for predicting emergence. Three accumulated heat unit (AHU) methods based on air and soil temperatures were compared with the calendar day method to determine the most reliable system for predicting seedling emergence. Accumulated soil temperatures above a base of 9·0 °C had the lowest c.v.s (8–15%) and were shown to be the most reliable predictor of emergence.