Role of Mycorrhiza in a Wheat-Flax versus Canola-Flax Rotation: A Case Study

Early-season growth of flax (Linum usitatissimum L.) was reduced in the field following canola (Brassica napus L.) compared to rotation with wheat (Triticum aestivum L.). This effect was associated with reduced formation of arbuscular mycorrhizae in flax caused by rotation with canola. Greater uptake of copper (Cu), phosphorus (P), and zinc (Zn) was seen for flax after wheat. Mycorrhizal stimulation of uptake of these elements likely relates to their immobility in soil. The ratio of biomass of flax after wheat to flax after canola was 1.6. Corresponding ratios of nutrient uptake were 1.5 to 1.8 for Cu, P, and Zn but were between 1.2 and 1.4 for macronutrients other than P. These data illustrate the importance of consideration of a range of nutrients for concentration, uptake, and ratios of uptake among treatments to evaluate the impact of arbuscular mycorrhizae. Rotation of flax after canola should be avoided.