Crop Scene Investigation - 23: Why did Arthur's soybeans get 'the streaks?'
Tuesday, February 16, 2010
by BERNARD TOBIN
In spring, when growers see nice, even emergence across a soybean field, there's an immediate sense of relief. But when random streaks of discoloured plants appear throughout the field, that feeling of satisfaction turns to dread as thoughts of vanishing yield overpower spring optimism.
That's what Pioneer Hi-Bred agronomist Scott Fife encountered when he received a mid-June call from a grower seeking his advice.
"I got a call from Arthur, a dairy farmer, who was wondering if any growers were having problems with the seed variety he had planted. I told him there were no seed issues, but I would be happy to take a look at the field and help him get to the root of the problem," Fife recalls.
"When I arrived at the farm, Arthur took me to the problem field and pointed out these five-foot-wide streaks of lighter green, almost yellow, plants that ran throughout the field. The first thing that came to my mind was nitrogen deficiency, but what really grabbed my attention was the pattern of discolouration.
"Surveying the streaked areas, I noticed that entire plants, including the leaves, were a lighter shade of green. This ruled out both potash and manganese deficiency as potential suspects. With potash deficiency, for example, you tend to see yellowing on the margins of the leaf, but there was no evidence of that here.
"Herbicide damage from spraying overlap was also a consideration, but Arthur had planted Roundup Ready soybeans that were custom sprayed with Roundup.
"The next thing on my checklist was compaction. The light colour of the plants could be the result of restricted root growth, which can be a symptom of compaction. But when I dug up plants in both the yellow and green areas of the field, there was no difference in the soil structure. The field was more of a loamier clay and we tend to see less compaction in these soils as compared to heavier clays. Because it was still early in the season – the plants were at third trifoliate – there was also no evidence of nodulation.
"The one thing that was really puzzling was the pattern of streaking in the field. It didn't appear to follow any of the tillage, planting or herbicide application patterns.
"As I walked around the field, I began to notice that the affected areas appeared to have a much higher concentration of straw on the soil surface. At the same time, the manure pit behind Arthur's barn caught my eye.
"Arthur had told me that the previous crop was corn and he had worked it in with a tillage pass early in the spring. But the manure pit had me curious.
He obviously used lots of straw and his manure was stored on a dirt pad at the back of the barn, which meant that nitrogen was probably being lost through leaching.
"I asked Arthur how he spread his manure. 'I just fill up the spreader whenever it gets full and take it out to the field and spread it. We do it all the time,'" he explained. "He then mentioned that he had spread a couple of loads on the soybean field prior to planting."
Do you know why Arthur's soybean field had "the streaks?" 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