Crop Advisor’s Casebook: Paling wheat plants a puzzle

A Crop Advisor's Solution from the November 11, 2014 issue of Grainews

Early one morning back in mid-June, Rodney came by my office to share his concerns about his wheat crop at his 4,500-acre mixed grain farm near Carrot River, Sask. His wheat fields had all displayed a lush green colour just a day or two earlier, but now the crop had taken a decided turn for the worse.

Andre Laforge is a Sales Agronomist with Richardson Pioneer Ltd. at Carrot River, Sask.

Andre Laforge is a Sales Agronomist with Richardson Pioneer Ltd. at Carrot River, Sask.
photo: Supplied

The weather had me wondering if moisture could be an issue. The previous fall, Carrot River had been blessed with great harvest conditions, with very little precipitation until late October. This was followed less than normal precipitation in the winter and early spring, although it was enough to insure good germination. Late May and early June had been a completely different story however, with up to eight inches of rain in the area over a three-week period.

When I drove out to Rodney’s place to have a look, I could plainly see that many wheat plants on his sandy loam farm had turned pale green; however, the colouration wasn’t consistent throughout the fields and a regular pattern was evident.

When I asked Rodney about his fertilization program, he told he had applied 80 pounds of anhydrous ammonia or NH3 just prior to seeding at a slight angle to the seeding. What was obvious is that where the seed row intersected the NH3 application, the wheat was a strong green colour, and that the crop colour weakened between these intersections.

Rodney also showed me some of his neighbours’ fields, which shared the sandy loam soil. The wheat in one nearby field was same pale green colour over the entire field, and I was told this grower has used NH3 applied mid-row as his nitrogen source. Another grower, whose wheat still maintained a strong green colour throughout the crop, had dribble banded liquid nitrogen over the seed row.

What could be causing the paling of Rodney’s wheat plants? And why are his and his neighbours’ fields showing such differing results, when similar soil types and similar moisture patterns were in play?

This photo shows a slightly more extreme example of the problem faced by Rodney.

This photo shows a slightly more extreme example of the problem faced by Rodney.
photo: Supplied

Crop Advisor’s Solution: Nitrogen application

When I inquired into Rodney’s fertilization program and what the weather had been like lately, I began to understand what was causing the paling pattern within the wheat field. Rodney had applied 80 pounds of anhydrous ammonia or NH3 just prior to seeding at a slight angle to the seeding — where the seed row intersected the NH3 application, the wheat was a strong green colour and it was pale green in colour between these intersections. There had been a lot of rainfall in the area in the previous three weeks, which led me to believe that the nitrogen had leached below the root zone in the pale green areas of Rodney’s wheat field.

But more perplexing was how to account for disparity between Rodney’s crop and those in his neighbours’ fields. One nearby wheat field had pale green plants throughout, while the crop in another field was consistently strong green in colour. The two fields shared similar soil types and had experienced the same moisture patterns as Rodney’s farm, so why the differences?

The answer lay in placement of the nitrogen. In the case of the mid-row banded application, the nitrogen had been placed about five inches away from the seed row and this had resulted in a pale green crop. In the other neighbour’s field where nitrogen had been placed directly over the seed, there was no evidence of paling. While heavy rainfall had caused nitrogen to leach both instances, it was obvious that the roots still had access to the nitrogen where it was in close proximity to the seed.

But what to do about the problem? Fortunately for Rodney, he was able to acquire some 34-0-0 ammonium nitrate and apply 25 pounds of nitrogen on his worst-looking wheat field. The plants had quickly began to recover and the crop returned to its rich green colour within a week to 10 days.

Andre Laforge is a sales agronomist with Richardson Pioneer Ltd. at Carrot River, Sask.

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