As he stood in a field near Carman, Man., recently, John Heard was surrounded by plants that were green and yellow.“We have wheat here that has yellow stripes, so what we have is technicoloured crops right now,” said Heard, a crop nutrition specialist with Manitoba Agriculture.Crops in the Carman area have yellowed this spring because of pooled water and saturated soils. But for Heard and hundreds of growers in Western Canada, the million dollar question is what is causing the yellowing.“A lot of plants in low spots are yellowing and that may be because of almost anaerobic conditions,” said Vikram Bisht, a plant pathologist with Manitoba Agriculture. When the plant is under stress from excess moisture, the root systems are impaired and the plant can’t take up nutrients.The other possibility is that nutrients have leached out of the soil, starving the crops of nitrogen, sulfur or both, Bisht said.Heard said determining the exact cause is not easy, which is why he recommends producers hire a consultant before spending money on a rescue fertilizer treatment.“The hardest part for the growers is to decide if they’re throwing good money after bad,” he said.A soil test is a good start, but he said analyzing the results isn’t a simple task.“The nitrogen soil test is very misleading this time of year, because it’s designed for late fall or early spring,” he said. “At this time of year, it’s picking up the nitrogen that’s mineralized and from organic matter.”Heard said a consultant could help assess whether a yellow crop is lacking nitrogen or sulfur.“We’re taking some soil samples (near Carman) just to see how deep the nitrogen has leached and to see if it’s nitrogen or sulfur deficiency that we’re dealing with.”Further complicating matters, Heard said the plant’s roots can grow down to access nutrients located deep in the soil profile.“Often we see early season sulfur deficiency in canola,” he said. “Last year at our (crop diagnostic) school, the plant was deficient early. But by early July, it rooted into it and it was OK. But you don’t know that’s going happen…. You really don’t count on (it).”If sulfur is the culprit, then growers should consider ammonium sulfate because it supplies nitrogen and sulfur, the Alberta Canola Producers Commission recommended in its latest canola report.The report added that a small amount of nitrogen can benefit the crop, but too much and the crop matures later, increasing the risk of frost damage.Heard said there are no hard rules on how much rescue fertilizer to apply.Another factor to remember is that crops like soybeans and flax are susceptible to iron chlorosis, which could explain the yellowing of those oilseeds.Bisht said farmers should consider monitoring how treated seed performs compared to untreated seed under wet conditions.
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