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Corn+Soybean Digest

Tissue Testing: Leveraging Fertilizer Dollars Or A Misused Diagnostic Tool?


Ohio farmer Bill Bayliss thought some of his fields had a manganese deficiency, and did some tissue testing to find out for sure.

Just over 600 miles away, Fredericksburg, IA,

farmer Kyle Wendland has completely reengineered his fertility program based on six years of test results.

University agronomists and fertility experts say both farmers, like hundreds of others, may have the wrong expectations for tissue testing in the first place.

“I would not use tissue testing to make a fertilizer recommendation,” says Ed Lentz, associate professor with Ohio State University Extension’s agronomic crops team. “With commodity prices as high as they are, some farmers aren’t completely evaluating whether they need the additional product, since a 1-bu. increase may easily cover the additional input cost.”

Based on Wendland’s experience, Lentz’s concerns over the motives underlying farmers’ use of tissue testing may be right on the money.

“With the dollars involved in potash (K), MAP and DAP, you really need to micromanage nutrients,” Wendland says. “The days are gone when you can say ‘I removed this much, so I’ll put on this much.’ We need to pay attention to what the plant is saying.”

Wendland farms more than 1,000 acres in northeastern Iowa. He started tissue testing in 2006 to determine if he was using the right nitrogen (N) rates for corn-on-corn production, and if he was assuming the correct amount of N was left over for corn following soybeans.

In the interceding years, the test results revamped his basic fertilizer strategy.

“I went from fall-applied anhydrous ammonia to spring-applied, to this year sidedressing without any anhydrous. Gradually my fall nitrate rates have gone up as I used N more effectively. I’m timing application based on availability to the plant as opposed to timing for my schedule.”

Wendland, like Bayliss, started testing this season for purposes other than gauging N uptake, taking samples from plants in both spring and summer.

Bayliss’ initial concern was a presumed nutrient deficiency in his soybean fields. “This was the first time I’ve done it,” explains the West Mansfield, OH,grower. “I’d read a lot about it, but what got my attention was some yellow spots in our fields, and I thought we might have manganese deficiencies.”

The test results, however, didn’t give a clear answer, just generalities, he says. “We’ll do it a few more years to get a pattern of information. I was trying to pinpoint a problem area, and wasn’t able to do that the first attempt.”

Lentz says the approach of generating patterns of information before making major decisions about a fertility program is good practice. “If we’re seeing the same problems year after year, and a tissue test consistently confirms a deficiency, then we should probably adjust our fertilizer program, which may include corrective action during the season.”

The trend he and his colleagues are finding, however, is for tissue testing to be used to make fertilizer recommendations for secondary and micronutrients on the go, rather than as a basic diagnostic tool. He says research necessary to make specific nutrient recommendations is not yet complete. Insufficient research exists on which to base specific application rates from tissue-test results.

Also, Lentz says sufficiency levels for plant analysis are determined at a specific growth stage when it’s generally too late to make corrective fertilizer applications. For example, he explains, silking is the correct time to tissue test corn.

Purdue University Agronomist Jim Camberato says, “I am not a proponent of tissue testing in the way that it is being promoted by some companies. I don't know of any university folks who are.”

Lentz explains that when every bushel counts, a farmer might think it is in his best interest to test mid-season and take corrective action if a deficiency is identified. That mindset, however, might actually lead to wasted money applying a product either by incorrectly diagnosing a problem, or diagnosing a problem that doesn’t actually exist.

“Let’s say someone gathers samples from a field and shows you’re a little low on a micronutrient, then they can justify putting a foliar product on a field,” he says. “This year we saw products being applied to fields where micronutrient levels were not low enough that research has ever shown a deficiency or a benefit from application.”

Bayliss actually expected an application recommendation for his presumed manganese deficiency, though test results actually indicated a different set of “problems.”

“We found that all of our fields were ‘excessive’ for N,” he says. “After I thought about it, soybeans make N, and we sampled around the time the plants were probably producing the most natural N. My gut instinct is that we just sampled when the plant was generating more N.”

On the other hand, across four fields and nearly 250 acres sampled, every field showed a potassium deficit. Bayliss notes that the levels reported corresponded with his own appraisals of the better or poorer fields, “so that made sense.”

Even so, Bayliss isn’t ready for a full-scale overhaul of his fertility program yet. He says he’ll test for at least a few more years to glean any trends or patterns that might indicate action is warranted.

“We were somewhat aware already from soil testing that we were a little low on K, and the tissue tests confirmed that, so we’re going to adjust accordingly,” he says. “That was a key take-home. Along with my soil test, we confirmed one issue to correct next year.”

Lentz says the use of tissue testing in conjunction with soil testing is a more appropriate approach to the decision-making process.

“If we have a field, for example, exhibiting symptoms of K deficiency, we’d recommend a tissue test and a soil sample and then comparing the two,” he explains. “If your soil test came back fine and your tissue test came back deficient, then you’d know you had a growing-season issue like weather, rather than a fertilizer issue. On the other hand, if the soil test also came back low, then you could apply more K next year.”

Lentz, Camberato and other university experts agree tissue tests are diagnostic, and not designed for making specific nutrient-application recommendations.

With relatively high corn and soybean prices, however, Wendland may speak for many farmers in summing up his feelings about the additional data: “I don’t think enough people are micromanaging their crop the way they should. You can’t just throw a little fertilizer out there spring and fall and expect it to be there for the plant when it needs it.”

TAGS: Soybeans Corn
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