How detrimental is sowing corn after canola?
Sowing corn after canola can result in corn being impacted by phosphorus deficiency, or what is commonly called “corn after canola syndrome”. Phosphorus enters the corn plant through root hairs, root tips, and the outermost layers of root cells. Beneficial fungi, called mycorrhizae, enhance P uptake in corn early in the season because the mycorrhizae strands increase the effective rooting volume of plants. This is extremely important for uptake of immobile nutrients, such as P.
In corn, up to 80% of early season P uptake is by mycorrhizae since the strand network may extend 8-12 inches from root. Crucifer plants, such as canola, sugarbeets, and mustard, are not hosts for mycorrhizae so the mycorrhizae must regrow from spores. This is why early in the growing season you’ll see corn suffering from P deficiency.
Although the mycorrhizae eventually regrow and colonize the roots, the damage done by lack of P early in the growing season will have already occurred. Yield may be impacted by the early season P deficiency, maturity of the crop may be delayed and grain moisture content at harvest may be higher (leading to higher drying costs).
The initial phosphorus uptake can be an issue but is this practice manageable?
To avoid ‘corn after canola syndrome’, producers should grow a crop less dependent on mycorrhizae for P uptake after canola (corn & flax are two of the most dependent crops).
If rotation requires corn after canola, a “Plan B” is to supply high starter P levels to try and overcome any P deficiency problems that might occur.
Variable results are seen with in-crop treatments to remedy phosphorous deficiency. If products are tried, it is recommended to leave a check strip to determine effectiveness on crop recovery and yield.