BASE TEMPERATURE AND GROWING-DEGREE-HOUR REQUIREMENTS FOR THE EMERGENCE OF CANOLA

Spring canola (Brassica napus L. and B. rapa 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 gr owing-degree hours (GDH) required for emergence of canola from differe nt planting depths could help producers decide when and how deep to pl ant this crop. Our objectives were to quantify the base temperature (t he minimum temperature required) for emergence, the number of GDH requ ired for initial emergence of five cultivars of spring and winter cano la, and to evaluate temperature x planting depth interactions of sprin g canola. 'Alto', 'Global', 'Tobin', 'Crystal', and 'Glacier' cultivar s were planted 1 cm deep into pots of Weld silt loam (fine, montmorill onitic, mesic aridrc Paleustolls). Pots were incubated at 0, 2, 4, and 16 degrees C. Seedlings emerged were counted daily for all temperatur es and twice daily during rapid emergence at 16 degrees C. Simple-line ar and segmented-nonlinear-regression were used to determine base temp eratures and GDH requirements for initial emergence. Calculated base t emperatures were between 0.4 and 1.2 degrees C. Regardless of the cons tant temperature regime, emergence began between 1560 and 1940 GDH for the spring canola. Winter canola emerged at 1600 to 2800 GDH. Two cul tivars (Tobin and Global) were also planted at 1-, 2-, 2.5-, 3-, and 4 -cm depths and incubated at 4, 8, 12, and 16 degrees C to investigate planting depth x temperature interactions. A reduction in emergence, a s a function of an interaction between temperature and planting depth, was found for Global but not Tobin at the temperatures and planting d epths used in this study. A match between the accumulated heat units i n early spring for a location and the GDH required for initial emergen ce of the spring cultivars tested can be used to determine early sprin g canola planting dates. This analysis indicates that severe reduction s in stand are possible when canola is planted at soil temperatures th at are sustained much below 8 degrees C. The heat unit approach used a llows for the transfer of the relationships developed in this study to other locations.