Management of Fresh Wheat Residue for Irrigated Winter Canola Production.

Winter canola (Brassica napus L.) is popular with many irrigated growers as it provides excellent disease control and other benefits for potatoes (Solanum tuberosum L.) and other crops grown in rotation. There is a belief among irrigated canola growers that fresh wheat (Triticum aestivum L.) residue must be burned and the soil then heavily tilled before winter canola is planted.  These growers are convinced that fresh (i.e., newly harvested) wheat straw is toxic to winter canola.  We are conducting a field experiment near Odessa, WA, as well as greenhouse and laboratory tests to: (i) determine how five different winter wheat residue management practices affect the plant health and seed yield of winter canola; (ii) find the cause(s) for any decline in winter canola vigor and seed yield as affected by management of fresh winter wheat residue, and (iii) test methods to retain winter wheat residue without adversely affecting winter canola health and seed yield.  Our hypothesis is that fresh wheat stubble is not phytotoxic and that irrigated winter canola can be successfully produced in a direct-seed system after wheat harvest as a viable alternative to field burning plus heavy tillage.  Five winter wheat stubble management treatments are established in late August – early September just prior to planting winter canola. These treatments are: (i)  Stubble burned + disked; (ii) stubble chopped + moldboard plowed; (iii) stubble burned, then direct seeded; (iv) direct seeding into standing and undisturbed stubble; and (v) winter canola broadcast into the standing (i.e., not yet harvested) wheat crop.  Crop year (Sept. 1 - Aug. 31) application of irrigation water totals 380 mm and precipitation averages 250 mm.  To date, no root or foliar diseases have been detected in any of the treatments.  Winter canola seed yields in 2013 ranged from 3014 to 3276 lbs/acre with no statistical differences (P=0.40) among treatments.  Winter canola stands in all five treatments for the 2014 crop year were excellent and no root or foliar diseases were detected in any of the treatments.  We are encouraged by the results of the experiment to date, but additional years of research need to be conducted before conclusive results can be provided.