Abstract
The biophotothermal time scale for barley derived previously and based on daily maximum and minimum temperatures and photoperiod was examined and tested further. The threshold temperature of 4.3°C and the optimum of 19 or 20°C found for the planting to emergence phase, and the optimum temperature values of 18.4°C for minimum and 24.8°C for maximum for heading to soft dough were not inconsistent with the results of other authors. For some of the other cardinal points, no meaningful values were found. Tests of the biophotothermal equations with independent data indicated that they could usefully be applied under the environmental conditions prevailing on most of Canada's present or potential farmland. They gave dubious results when applied to very cool marine climates on some exposed coastal parts of Canada, and were unsatisfactory for the short-day regimes that affected early-season plantings at Buenos Aires. The equations for barley seemed much less universally applicable than those for wheat.
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