Corn School: What you need to know about tissue testing


Corn growers often turn to tissue testing to diagnose a problem. When plants in a field are yellowing or pale, grabbing a sample and sending it to the lab can seem an obvious way to confirm a nutrient deficiency.

But there’s more to the tissue testing story than simply identifying a problem and finding a fix. On this episode of the RealAgriculture Corn School, SGS Canada agronomist Jack Legg shares how growers can actively manage their crop and optimize yield by utilizing tissue testing throughout the growing season.

Legg notes that perennial U.S. corn and soybean yield contest winners like Randy Dowdy and David Hula employ tissue testing in an aggressive manner, testing weekly or bi-weekly to actively manage the crop to produce winning yields. In general, however, growers can employ a less vigorous approach to tissue testing and produce a better bottom line for their crop.

For starters, Legg recommends sampling and testing the crop at several stages during the growing season. Growers often rely on a pre side-dress nitrogen test (PSNT) to determine the nitrogen needs for the crop as it prepares to accelerate through rapid growth stages and ear fill.

Legg says pairing a PSNT test with a tissue test gives growers a much better understanding of the nitrogen equation. “Nitrogen is a tricky one. The PSNT is a good tool but because nitrogen can change forms so readily, or be lost to the environment so easily, it really is just a snapshot of how much available N there is at sampling.”

Legg says growers can estimate how much nitrogen is going to mineralize throughout the growing season and use that as a basis to top up the nutrient. However, when “you combine your PSNT test with a plant tissue test you can make sure that the nitrogen concentrations are adequate within the corn plant.” (Story continues after the video.)

About 200 grams of fresh plant material is required for a tissue sample. Legg encourages growers to test throughout the growing season, starting as early as the two-leaf stage and continuing through tasselling and silking. Testing plant leaves at this stage helps identify nutrient deficiencies as the plant enters the grain fill period. With the advent of high clearance sprayers and other new technology, Legg notes that growers now have the capability to address late-season nutrient needs and optimize yield.

In the video, Legg shares tips on how to properly collect a representative field sample, and shares strategies on how contrasting plants — good and bad — can be tested to identify agronomic issues that can be affecting a field.

Legg also comments on the return on investment growers can expect from their tissue testing investment. He notes that most labs charge around $35 to test a plant tissue sample. He recommends one sample be tested per 25-acre field. That’s a little more than $1 per acre.

“If you can identify a problem you can correct in a field and save five, ten or 15 bushels at current crop prices, there’s obvious payback there,” says Legg.

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