Crop Scene Investigation - 25: The case of the 20-foot header

Monday, April 5, 2010

by BERNARD TOBIN

For Keith Reid, soil fertility specialist for the Ontario Ministry of Agriculture, Food and Rural Affairs, a soil fertility test is as powerful a diagnostic tool as an X-ray. But a fertility test often only confirms a diagnosis that Reid has reached after contemplating every field fact – from damage patterns to field history and even the width of a combine header.

This was the case when Reid arrived at a Bruce County soybean field in mid-July after a grower named Allan called seeking some advice.

"When I visited Allan, he said the weather in his area had been fairly dry. The soybeans were at the early pod fill stage and about knee high," says Reid. "But what was puzzling was the yellowish cast to most of the field and the presence of dark green strips of plants running throughout the field."

In the yellow, stunted areas of the field, Reid noticed that the worst damage was on the lower leaves, which were yellowing from the outside towards the middle. In some cases, the leaves were going brown and were ragged around the edge. But it was the pattern of the green strips across the field that really caught his eye.

"We got out a measuring tape and started pacing off the distance between the green strips that contained perfectly healthy soybeans. There was variation in the width of the strips, but they were evenly spaced across the field. They varied from three to five feet in width and in a few areas would pinch down into nothing. From centre to centre, the strips were consistently 20 feet apart and they went around the field as opposed to being up and down," recalls Reid.

"I asked Allan about his fertilizer program and he told me no fertilizer had been applied to the field. When we dug up some plants in the yellow areas, they appeared to be well nodulated, so nitrogen wasn't a problem.

"We also looked for signs of rhizoctonia or Phytophthora root rot, but we quickly ruled that out. There were no compaction issues in the field and the roots looked healthy, so we also ruled out soybean cyst nematode, even though it's rarely seen in Bruce County.

"Allan's herbicide program didn't set off any alarms either. After a process of elimination, we ruled out herbicide damage, fertilizer application and planting and tillage issues. Quite simply, the traffic patterns didn't match the pattern of the green strips.

"Looking at the field, I made a mental note that the green strip around the field was 10 feet in from the edge and, from there, you could see green strips every 20 feet going further into the field. The solution to this problem had to be connected to this pattern.

Then it suddenly struck me: Allan had a 20-foot header on his combine. That had to be the link.

"Allan told me the field had been in wheat the previous year and he had done some minimum tillage in the spring before planting his soybeans.

I was really curious about what Allan had done with his straw. He told me he typically spread his straw, but last fall he sold the straw off the field.

"The straw was left in a swath behind the combine. Allan had hoped to bale it quickly and get it off the field, but there was plenty of wet weather after harvest, so it sat on the field for six weeks before it was baled.

"I knew then what had happened to the field, but I needed to compare soil tests from both the green and yellow areas of the field to prove it."

Do you know what caused the pattern in Allan's field? 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