Leaf appearance and extension in field-grown winter wheat plants: the importance of soil temperature during vegetative growth

Abstract

SUMMARY: Mainstem leaf appearance and leaf extension were monitored at 7-day intervals throughout the vegetative development of field-grown winter wheat plants, during two growing seasons 1977–9. Using hourly air and soil temperature records, it was found that the rate of leaf appearance was controlled by soil temperature, with the best linear relationships being obtained using accumulated soil temperature above a base temperature of 0 °C at 1 and 5 cm depth. Leaf appearance could be predicted equally well using 09.00 G.M.T. screen air temperatures although deviations from each linear relationship were found during very cold periods when slow leaf extension rates delayed leaf appearance.Leaf extension was also found to be linearly related to temperature, with the best fit being obtained using accumulated soil temperature above 2·5 °C at 5 cm depth, suggesting a threshold of 2·5 °C for leaf extension. The response to temperature (extension per unit of accumulated temperature) was the same for all the leaves of a given plant, or sowing date; however, the fact that the rate of leaf extension increased progressively with sowing date suggests that plant response to temperature may be determined at crop emergence (possibly mediated by rate of change of day length). Leaf extension rates could be predicted satisfactorily using 09.00 G.M.T. soil temperatures (5 or 10 cm) but less so using screen air temperatures.The prediction of plant leaf areas or crop leaf area indices using such relationships between temperature and leaf growth was found to be hampered by rapid and irregular rates of leaf senescence.