Determining Aluminum Tolerance and Critical Soil pH for Winter Canola Production for Acidic Soils in Temperate Regions

A growing interest in winter canola ( Brassica napus L.) across the southern Great Plains has brought about many issues regarding production. One of the issues to be addressed is winter canola's tolerance of Al when grown on acid soils. The objectives of this study were to determine the maximum Al concentration and minimum pH for canola production in a temperate region with a known acid soil problem. To evaluate this, a field experiment was conducted in north‐central Oklahoma comparing eight different commercially available winter canola cultivars over an existing pH gradient (ranging from pH 4.0–6.5). In addition to the field study, a laboratory study was conducted to screen the same eight cultivars in the lab for tolerance to Al. In the field study, winter canola seed yield decreased linearly below a soil pH of 5.8, which corresponded to a KCl‐exchangeable Al concentration of 11 and 15 mg kg −1 for 2007 and 2008, respectively. Laboratory screening results indicated that winter canola root growth was reduced when Al concentrations of 20 mg L −1 were present. Consideration will have to be given to soil pH to optimize winter canola seed yield in the southern Great Plains and other temperate regions.