As crop input suppliers and farmers walked corn and soybeans fields this season they may have noticed some telltale signs of nutrient deficiency.
Mosaic senior agronomist Curt Woolfolk says such scouting activities can sometimes allow time for rescue applications, but more importantly deliver vital information for coming crop years.
Scouting is no substitute for annual soil testing, however, which Woolfolk calls the foundation of any well-balanced crop nutrition program.
“It’s like the food pyramid for human nutrition, with its categories of meat, dairy, fruits and vegetables, and grains; crops need balanced nutrition the same way people do,” Woolfolk says. “Plants have 17 essential nutrients to grow and complete their life cycle.”
When scouting, what are the main visible patterns that help identify the different nutrient deficiencies that can affect a crop?
“With nitrogen deficiencies in corn, yellowing is first noticed at the tip of the leaf and extends towards the center of the leaf (midrib),” explains Woolfolk. Imagine taking a diamond shape, grabbing 2 opposing corners and stretching the shape. Patterns like this that are pale yellow in the lower older leaves are good indicators of nitrogen deficiency.
Woolfolk warns that sulfur and nitrogen deficiencies are often confused for one another.
“Sulfur deficiencies will show up yellowing similar to nitrogen, but is found in the younger upper leaves due to the immobility of this nutrient within the plant,” he says. “We typically see sulfur deficiencies on sandy, low-organic-matter soil or cold dry soils in the spring.
“After identifying a visual problem spot, one of the diagnostic tools we have is tissue sampling,” Woolfolk says. “Pull leaf tissue samples from a bad area and samples from a good area; send the samples off your lab for an analysis, and that will support your visual observation of a particular nutrient deficiency and quantify it. Your eyes can deceive you. The tissue sample helps to solidify and back up what you think it might be.”
Woolfolk warns retailers, crop consultants and farm operators about overlooking the obvious.
“Whenever a grower or retailer gets a soil test result, the number one thing that drives everything in soil chemistry and crop nutrition is pH,” Woolfolk says. “It is absolutely crucial that they address pH concerns for a given crop. Anytime you have a soil pH that is too low or too high, you affect all the interactions and the nutrient uptake patterns.”
Woolfolk believes scouting can help fine-tune fertilizer rates for a well-balanced crop nutrition plan. When a sound soil testing plan and accompanying fertilizer recommendations still reveal some visual trouble spots within a field, it is important to mark the location with GPS and follow-up the next year with area-specific soil sampling. This is where visual nutrient deficiency information becomes part of the farmer’s long-term record keeping for balanced crop nutrition.