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Crop Advisor’s Casebook: Crop trouble follows a pattern

A Crop Advisor's Solution from the April 28, 2015 issue of Grainews

In affected spots in the wheat field, the plants had white heads and dried-up flag leaves. Something was causing the wheat to turn white, but what?
Rachelle Farrell. photo: Supplied

It was back at harvest time the previous year when I received my first SOS about a particular field problem from Joe, who grows canola, wheat and barley on his farm at Morinville, Alta. The performance of his barley crop just wasn’t up to snuff — yield was way down as a result of numerous irregular spots in the field where the heads of the barley had failed to fill.

I went to Joe’s farm to have a look, but I wasn’t able to analyze any plants as there was only straw left in the field at that point. We sent a number of soil samples in for testing but that didn’t reveal anything of much use, either. That was likely because the areas in the field where the samples were taken from were at best rough estimates.

All this meant Joe and I would need to keep a very close eye on the next crop to go in that field, to see if the problem reappeared.

Wheat was planted in the field the following growing season, and by summer there were no apparent issues. I’d gone out to the farm in early July and the crop looked great all around. To be on the safe side, we had a few tissue tests performed but there was nothing out of ordinary that foretold trouble in Joe’s wheat field.

But within a matter of a week or so, that changed.

A clearly frustrated Joe called in mid-July to inform me the problem was back, and that his wheat was starting to turn white. As was the case with the barley crop, the affected wheat was appearing in an irregular pattern, and the patches in the field were even more pronounced than they had been the year before.

When I arrived at Joe’s farm to see for myself, the affected spots in the wheat field were clearly evident. A closer look at the plants revealed white heads and dried-up flag leaves.

Something was causing the wheat to turn white, but what? Joe had been following a fertilizer plan we’d laid out earlier in the season, so the nutrients were there for the crop. There were no signs of insect damage, and while there had been a little bit of rain recently, it wasn’t enough to have affected the crop this way. Something wasn’t adding up.

Crop Advisor’s Solution: Solonetzic soils behind white wheat patches

I suspected there was something else going on in the soil that was causing the problem. Soil tests had been performed the previous fall following the barley harvest, but it’d been difficult to precisely target the affected areas within the field and as a result the test results had been inconclusive.

We decided to test the soil again. This time we were able to clearly see the affected and unaffected areas, and the testing this time around provided our answer. The necessary nutrients were there in all the samples but one quality in the affected areas stood out — a high sodium concentration that indicated a Solonetzic soil.

We determined that while there was a high sodium concentration over the whole field, it is higher in certain spots and these spots corresponded with areas where the topsoil was shallower and had less tolerance to moisture stress. It was these areas that contained the affected plants.

If there had been a severe moisture shortage, the entire field likely would have been affected. This season, there had been just enough rain so that the areas with more topsoil could support the crop, while those with less topsoil didn’t have enough capacity to provide plant roots with enough moisture. The roots were unable to grow through the hardpan that was high in sodium in search of additional subsoil moisture.

Unfortunately for Joe, there wasn’t anything that could be done to salvage his wheat crop at this point. At harvest, the yield was drastically reduced in the affected areas, and was generally low overall for the field.

There would be no quick fix going forward either. Mixing calcium in lime or gypsum form in the hardpan layer through deep, subsoil plowing would help displace the sodium and improve the soil, but this represents a labour intensive and quite costly solution.

Anyone faced with a similar dilemma should keep in mind that Solonetzic soils may only constitute a small part of a field. Soils can be extremely variable within a single field, let alone fields that are close to one another, so it’s important to consider what the return on time and monetary investment will be when considering whether or not to deep plow and apply calcium.

Rachelle Farrell is a crop inputs manager with Richardson Pioneer Ltd. at Morinville, Alta.

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