Crop Scene Investigation - 29: The curious case of row unit number eight

Monday, December 6, 2010

by BERNARD TOBIN

In late June, when Pioneer Hi-Bred agronomist Scott Fife walked across Bill's 20-acre corn field in Dundas County, one in every 12 rows was significantly stunted. While all the corn had reached the eight-leaf stage, the stunted rows were much shorter and yellow in colour – very different from the dark green, healthy-looking plants in the other rows.

"There were no obvious nutrient deficiencies with the corn – no zinc, manganese, potash or phosphorous issues. It just didn't look good. It had to be a planter problem," thought Fife. He quickly made note that the poor performance was confined to the same row across the field, which was always planted by the eighth row unit on Bill's 12-row planter.

That unit was the key to this mystery and he was keen to take a look.

But first he wanted to cover off a few details with Bill, who noted the field was planted on May 24. That was much later than the rest of the corn crop in thisarea, where most growers had finished planting in late April thanks to near-ideal planting conditions. This field was planted later because Bill took off first-cut forage before no-tilling corn directly into sod.

The first thing that came to Fife's mind was refuge requirements. Did Bill put a different hybrid in the eighth row unit to satisfy a refuge requirement? That notion was ruled out when Bill confirmed that he used the same hybrid across the entire field. 

"Sometimes when you're planting into hay fields, you get more problems with pests or insects chewing on the seed," says Fife. "We thought about grubs and wireworm, but that didn't make sense because the problem was uniform across the field and confined to specific rows." The same seed treatment was used throughout the field and no granular insecticide was applied.

Fife's next move was to dig up some seed, but he couldn't find any obvious problems. "There were no signs of insects and the planting depth of the seed was fine. When you have planter problems, the first thing that comes to mind is planting depth. We assumed the seed was either too deep or too shallow in these rows, but after digging up some plants we realized the planter had done a good job. The seed was consistently set at two inches, just the way we wanted it."

Fife then thought there might be a problem with the seed trench not closing, given that it was a no-till field which had been planted in very dry, less-than-ideal conditions. Maybe the seed trench had not closed properly and emergence was delayed? But, after a closer look, again the planter had done a good job. The seed trench was always closed and emergence was relatively uniform.

For Fife, the planter remained the prime suspect, but it continued to pass every test. "We looked at the seed disc openers. If they're worn out, you're going to have non-uniform seed placement, but Bill had recently replaced them so there was no problem.

"We then looked at the seed tubes. If they're cracked or broken, they can deflect the seed and prevent it from falling into the bottom of the trench. That can affect seed depth, but the planter tubes were also new.

"We also checked the down pressure on the planter. If you have too much down pressure, it can cause sidewall compaction, which makes it harder for the seed roots to get through the seed trench. That can also delay emergence. But, again, these settings were the same across the planter."

Fife was now running out of possible answers. So back to the field he went. Because the field was dry, Fife noted that a lot of the seed-placed fertilizer applied by the planter was still sitting in the fertilizer trench, two inches beside the seed trench. As he rooted at a stunted row, he realized the row had no fertilizer trench. He then proceeded to inspect the other stunted rows and found that none had a fertilizer trench.

He then stepped back from the rows to observe the entire field. It appeared the stunted rows' row spacing was off slightly. He hadn't noticed it before, but a tape measure confirmed that the affected rows were different than the others – row spacing was 27 inches on one side and 33 inches on the other. The healthy rows were 30-inch centres.

Fife then quickly returned to the planter and grabbed hold of row unit number eight. The investigation was complete.

Do you know why Bill's corn field had stunted rows? 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