The Effect of Tillage System and Proceeding Crop on Phosphorus Response of Flax

Flax is a major oilseed crop grown on the western Canadian prairies, with the majority of the production exported into the industrial oil market. Phosphorus fertilization is a challenge as the crop is very sensitive to seed-placed starter P. Banding fertilizer P, either below or below and to the side of the seed row, is the preferred method of application. In the absence of specialized seeding equipment, some farmers have resorted to increasing the P application in preceding crops as an attempt to supply residual P to the subsequent flax crop in rotation. Flax has been shown to have good association with VAM fungi, allowing it to expand its root absorptive surface area and potential P uptake. Growing flax after a mycorrhizal crop and using no-till seeding systems may help the flax rapidly establish an association with VAM and improve its ability to access residual soil P. The objective of this research is to evaluate the role of preceding crop, tillage system, and P fertilization of the preceding crop in optimizing flax yield and quality.

In 1999, seed yield of wheat and canola was similar under conventional till (CT) and no-till (NT). Where differences existed, seed yield was higher under NT. In contrast, in 2000, seed yield was consistently higher under CT than NT due to delayed seeding in 1999 and cold, wet conditions throughout 2000. There was no P by tillage interaction in either year, indicating that P response of wheat and canola was similar under the two tillage systems. Flax yield in 2000 was generally similar under NT and CT management. Where differences existed, yield was higher under NT, as the flax site was on a well-drained upper slope position, which may have enhanced aeration. Seed yield of flax was higher when grown after wheat than after canola at both locations under both tillage systems. This may reflect increased mycorrhizal infection on the wheat stubble (samples being analyzed). When P fertilizer was side banded at seeding, the flax showed either no yield response or a minor yield decline relative to the unfertilized check. Phosphorus fertilization of the preceding crop led to higher flax seed yield the following year at one of the two locations, with the effect being greater when wheat was the preceding crop as compared to canola. It may be a useful strategy for producers to increase P application in preceding crops, rather than fertilizing the flax crop directly, in order to increase P availability while eliminating the risk of seedling damage. MB-11