Crop advisor casebook: What’s holding back this stunted wheat?

A Crop Advisor's Solution from the March 10, 2020 issue of Grainews

Scott Penner.
photo: Supplied

Randy, a grain farmer near Winnipeg, Man., was surveying one of his wheat fields back in June when he noticed that something was off with the crop. There was a large area running right up the middle of the field that had stunted, pale-looking wheat and he was anxious to find out why.

Randy called me up to see if I could provide an answer. “I guess it could be herbicide spray drift that caused it, but I’m not sure,” he said.

I agreed to come out to the farm to see if I could diagnose what was happening in Randy’s wheat field. When I arrived, I could clearly see the large swath of affected crop running across the field in a wavy pattern. It was visible from one end of the field to the other and was bookended on either side by areas that appeared to be unaffected.

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Randy told me he’d had issues in the past with this section of the field, which he’d purchased 10 years ago as an 80-acre parcel and later added to his two fields on either side of it to create a larger, 320-acre field.

I had a closer look at some of the plants in the problem area. In addition to being pale, they were shorter and had smaller heads than the healthy-looking wheat, indicating maturity was delayed in the affected crop. Randy informed me he had noticed slower plant growth in this part of field throughout the season.

I was able to rule out herbicide spray drift as a possible cause fairly quickly when I learned the same herbicide used by Randy on his wheat crop had been applied in the other wheat fields nearby and none of them exhibited any ill effects. The grower also assured me he is always very thorough in cleaning out the tank when applying different types of herbicides with his sprayer.

I knew that a nutrient deficiency could cause the sort of symptoms exhibited by the affected wheat plants. When I asked Randy about his fertility program, everything appeared to check out. I then looked over the fertilizer application maps generated by Randy’s seeder when he was planting the crop, and I couldn’t see any red flags there either.

At this point, I decided a plant tissue analysis could be used to clarify what was going on. I collected tissue samples from a number of affected plants, which I then sent off to several different labs for testing. I also pulled up an NDVI map of the field from a digital agronomy platform.

Once I had the lab test results and the NDVI map in hand, I had my answer.

Crop Advisor’s Solution: Phosphorus deficiency to blame for Randy’s stunted wheat crop

I learned from Randy that the part of the field with the affected crop was actually land he had purchased 10 years previously. Since then, it had been incorporated into a larger field with farmland Randy already owned.

Between the tissue test results and the background information on the field management history, I thought I had my explanation for the symptoms and their pattern across the field. My prediction was confirmed when I pulled up an NDVI map of the field from a digital agronomy platform, which indicated the vegetation in that area of the field he’d purchased a decade ago was clearly in need of more phosphorus.

Randy ended up with a decent crop at harvest, but the yield in the affected area of the field was still 20 bushels less than the rest of the crop. I recommended for the next growing season that he apply a phosphorus-containing granular fertilizer to the nutrient-deficient area of the field to build up the phosphorus levels in the soil.

The lesson for Randy was when consolidating fields together, it’s important to keep in mind that soil fertility levels may not be consistent throughout. Past management practices can contribute to very different results on fields that look the same on the surface. In this scenario, a composite soil sample from the entire 320-acre field did not reveal a phosphorus deficiency.

In the future, I recommended Randy adjust his methods for assessing soil fertility to get a more accurate picture of the nutrient requirements for every area within the new larger field.

For this reason, Randy plans to collect separate soil samples from the areas that were previously three stand-alone fields and are now being managed as one. This will enable him to utilize variable rate fertilizer technology to ensure nutrient levels are consistent throughout his field, and it is a strategy he can use for the rest of his farm to eliminate surprises that may arise due to in-field variability in the future.

Scott Penner works for Richardson Pioneer Ltd. in Stony Mountain, Man.

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