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Base Temperature and Growing-Degree-Hour Requirements for the Emergence of Canola

Vigil, Merle F., Anderson, R. L., Beard, W. E.
Crop science 1997 v.37 no.3 pp. 844-849
Brassica napus, Brassica rapa subsp. campestris, soil temperature, heat sums, cultivars, planting date, seed germination
Spring canola (L. and L.) is sometimes planted when soil temperatures are below the optimum, causing farmers to have stand losses because of seed rotting in cold soil. Knowledge of the growing-degree hours (GDH) required for emergence of canola from different planting depths could help producers decide when and how deep to plant this crop. Our objectives were to quantify the base temperature (the minimum temperature required) for emergence, the number of GDH required for initial emergence of five cultivars of spring and winter canola, and to evaluate temperature × planting depth Interactions of spring canola. ‘Alto’, ‘Global’, ‘Tobin’, ‘Crystal’, and ‘Glacier’ cultivars were planted 1 cm deep into pots of Weld silt loam (fine, montmorillonitic, mesic aridic Paleustolls). Pots were incubated at 0, 2, 4, and 16°C. Seedlings emerged were counted daily for all temperatures and twice daily during rapid emergence at 16°C. Simple-linear and segmented-nonlinear-regression were used to determine base temperatures and GDH requirements for initial emergence. Calculated base temperatures were between 0.4 and 1.2°C. Regardless of the constant temperature regime, emergence began between 1560 and 1940 GDH for the spring canola. Winter canola emerged at 1600 to 2800 GDH. Two cultivars (Tobin and Global) were also planted at 1-, 2-, 2.5-, 3-, and 4-cm depths and incubated at 4, 8, 12, and 16°C to investigate planting depth × temperature interactions. A reduction in emergence, as a function of an interaction between temperature and planting depth, was found for Global but not Tobin at the temperatures and planting depths used in this study. A match between the accumulated heat units in early spring for a location and the GDH required for initial emergence of the spring cultivars tested can be used to determine early spring canola planting dates. This analysis indicates that severe reductions in stand are possible when canola is planted at soil temperatures that are sustained much below 8°C. The heat unit approach used allows for the transfer of the relationships developed in this study to other locations.