Crop Scene Investigation - 51: Why did Ralph's corn look nitrogen-deficient?

Tuesday, March 4, 2014

by BERNARD TOBIN

When Aric Bos first set eyes on Ralph's Huron County cornfield on Sept. 8, he quickly formed an opinion.

"It looked like textbook nitrogen deficiency to me," says the Pioneer agronomist. The plants at the top of the field were pale green, and their lower leaves were fired and turning brown. Down in the low-lying area of the field, however, the plants were deeper green in colour. They had a larger stem diameter and the ears were also much more promising, with more rows around and significantly higher kernel counts.

"It appeared that the plants down in the hollow were thriving because they likely had more available nitrogen," explains Bos. But then the head scratching began.

"When I talked to Ralph, he said nitrogen couldn't be the problem. He had put down 50 pounds per acre at planting in bands using a mounted coulter and later came back and side-dressed 150 pounds at the six-to-eight leaf stage," recalls Bos. "He had a good point. Ralph also questioned why all the corn was the same height. He argued that, surely, if nitrogen was a problem, we would see some stunting in the stressed plants, but there was no evidence of that."

It was time for Bos to get to work and see if he could figure out what was going on.

"I quickly ruled out herbicide interaction as a potential problem," recalls Bos. The field was coming out of glyphosate-tolerant (GT) soybeans and had been planted with GT corn. Ralph had done a preplant burndown with glyphosate and sprayed Marksman + Roundup in-crop. There was also no evidence of dicamba response. From a weed control standpoint, the field was very clean. He had no issues there.

As Bos and Ralph walked through the field, the conversation naturally shifted to the weather. It had been a cool, wet spring across the county and Ralph noted that Mother Nature had "turned on the taps" in mid-May, about 10 days after the corn was planted.

When it came time to side-dress nitrogen, the farmer followed his usual formula, injecting 28 per cent urea ammonium nitrate (UAN). "Ralph noted the field was still awfully wet, but he managed to get over the field without getting stuck. He said he didn't set the coulters very deep and that helped him get through," recalls Bos. "He was just glad to get it done, because over the next couple of days he got four inches of rain."

Ralph had said the field was predominately clay, but things looked a little different from where Bos was standing. "In the hollow where the corn was thriving, you could tell it was a nice, dark, loamy silt loam soil, but as you walked back up the incline, you could see some gravel and that suggests it may have had one of those sub-soils with a little more open bottom, despite the clay-textured topsoil."

The last thing Bos questioned Ralph about was his tillage practices. The farmer told Bos he was a committed no-tiller and had seen tremendous improvements in soil tilth and beneficial insects over the years. But he did note that crop residue and the wet, backward spring had made for some very cool soil temperatures at planting.

With that nugget, Bos had heard enough. He was convinced he knew what had happened to Ralph's cornfield and shared his conclusion.

Do you know what Bos told the farmer? Send your solution to Better Farming at: rirwin@betterfarming.com or by fax to: 613-678-5993.    

Correct answers will be pooled and one winner will be drawn for a chance to win a Wireless Weather Station. The correct answer, along with the reasoning followed to reach it, will appear in the next issue of Better Farming. BF