A system for studying the effects of naturally-occurring subzero temperatures on winter barley

Thermostatically-controlled, electrical soil heating cables were used to examine the effects of subzero temperatures on winter barley growing in plots outdoors. Plants in plots without heating cables were exposed to naturally-occurring subzero temperatures (unheated), while those in corresponding plots with the cables (heated) were protected from such temperatures. Measurements of soil, plant and air temperatures in heated and unheated plots showed that the system can, at least with the temperatures encountered during the measurement periods, prevent plant temperature from falling below the temperature set on the thermostat. A field experiment involving different cultivars and sowing dates showed that subzero temperatures experienced did not significantly affect individual plant grain yield or the number of fertile ears produced per plant. However, small, but statistically significant, effects of naturally-occurring subzero temperatures were found in relation to the number of grains per ear, thousand grain weight and harvest index. The nature of these effects varied, and were dependent upon cultivar and/or sowing date. Subzero temperatures were also responsible for reducing the numbers of established plants in late-sown plots through soil heaving. Possible uses of the soil heating cable system for temperature-related studies in the Gramineae are discussed.