Prevent nutrient deficiencies in crops before they're visible

HURON, S.D. -- Crops look strong about halfway through the growing season across the Dakotas and Minnesota, but some companies promote tissue testing and in-season nutrition to get them to the finish line in the fall.

"You never want to let a crop get to the point where you can visually see a deficiency," says Kyle Gustafson, an agronomist with Winfield Solutions, one of the main players selling fertilizer and micronutrients. "If you can see a deficiency, you're already losing potential yield."

Gustafson serves his company's clients across the northern swath of South Dakota.

He thinks the 2015 crop could be a good one, and he's not alone. The National Agricultural Statistics Service weekly crop condition reports released July 6 indicate things are looking good.

South Dakota's crops in the good to excellent conditions were: corn, 74 percent; soybeans, 74 percent; spring wheat, 60 percent; and alfalfa, 61 percent.

Minnesota crops in good to excellent condition include: corn, 84 percent; soybeans, 78 percent; spring wheat, 82 percent; and hay, 76 percent.

North Dakota crops in the good to excellent range include: corn, 75 percent; soybeans, 78 percent; spring wheat, 80 percent; and alfalfa, 64 percent.

Optimal testing

Gustafson says while the overall picture is positive, farmers have received ample or excessive rains and some nitrogen and sulfur deficiencies have been reported.

"We're also seeing some potassium deficiency," he says.

Micronutrient deficiencies are more widespread than macronutrient deficiencies, and aren't as weather-dependent.

Deficiencies of zinc and boron are showing up "as they do every year," he says.

Winfield Solutions recommends farmers determine their nitrogen needs by using both tissue and soil tests before side-dressing.

The tissue testing "does not replace soil sampling," Gustafson emphasizes. "You have to have a good analysis of your total fertility program to make it work. If you've got a good wrap on that, the tissue testing can help you make adjustments into that system."

North Dakota State University Extension soils specialist Dave Franzen agrees tissue sampling has a place in micronutrient diagnosis, but only if done correctly. Some advisers incorrectly go into fields, collect leaves from multiple plants and lump them as a general sample to compare with charts. This chart-based analysis can falsely indicate lower-than-desired

micronutrient levels, Franzen says.

The correct way of using tissue sampling, he says, is to go into a field and collect samples from two specific areas -- an area that looks the best and an area that looks the worst. Finding those areas could become one of a few key uses for unmanned aerial vehicles in farming.

Samples from the two extremes should be analyzed to find the difference. If the difference in crop health is not indicated by a nutrient difference, there might be a drainage or pest issue, Franzen says. If a nutrient or nutrients turn out to be the problem, that area of the field might need treatment, but the whole field does not.

Soil tests weren't the best indicator of sulfur problems this year, but the tissue analysis would  have been effective, Franzen says.

Dan Kaiser, a University of Minnesota Extension Service nutrient management specialist in St. Paul, agrees taking two extreme samples is the best way to get an accurate analysis.

Kaiser says he sees differences in tissue tests among varieties in a crop and among growth stages. He even sees significant differences when samples are taken within the same plants at various times of the day, or from various parts of a plant.

"There are a lot of errors that can be made," he says.

Kaiser even questions whether it's cost-effective to apply foliar in-season nutrients in annual crops at all because other environmental factors can be limiting.

Sulfur deficiencies

Still, Franzen said sulfur deficiencies were as "widespread as I've ever seen it" in mid-June, and says some farmers are planning to apply supplemental sulfur.

Franzen directed 20 pounds of sulfur per acre as gypsum in a preplant treatment for all of his corn research plots in southeast North Dakota this year.

"Several (plots), particularly in loams and sandy loams, looked like green islands in a yellow sea of corn," he says.

In the southeast part of the state, where rains had soaked clay loam soils, he directed crews to apply ammonium sulfate to his potassium rate trials to make sure they didn't fail because of a lack of sulfur.

He says the sulfur deficiency has worsened through the years, in part because of the improvement in environmental controls over coal-fired electrical plants. This has reduced the incidence of what is often called acid rain, which brought 5 to 6 pounds of sulfur to fields per year several years ago, and 3 to 4 pounds in more recent years.

A dry period from July 2014 to May 2015 didn't release much naturally occurring soil through the mineralization of organic residues. Later, the sulfur was leached to below the root zone because of heavy rains starting in May. Adding to the issue is the fact that many farmers are not used to applying as much sulfur as the crop probably needs because yields of major crops have increased across the years.

Nick Pieske, a certified crop adviser for Centrol Inc., based in Hadley, Minn., subscribes to soil-based results rather than a foliar approach, with no in-season application of micronutrients.

Pieske, who sells only advice and not fertilizers, advises his clients to put some sulfur on their crops, depending on the organic matter in a field. He says he saw no shortages in Murray County this year and any of his clients' side dressed nitrogen applications were planned events with most putting on 40 to 50 pounds on in-season. He says farmers have seen average heat and ample moisture, which breaks down organic matter and releases adequate supplies of nitrogen, phosphorus and potassium.

"We've had some small localized areas where we've seen fields ponded with water a couple of times, but not any nitrogen loss (from leaching) to any great extent. Things look good."

Mikkel Pates is a staff writer for Agweek. To subscribe to the weekly agriculture magazine, call (800) 811-2580 or email subscriptions@agweek.com .