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Stalk nitrate tests confirm N trends

Tom J. Bechman cornstalk cutter
POSTMORTEM TEST: This stalk cutter delivers uniform, 8-inch samples quickly. Stalk samples were removed from 15 stalks in each testing area of the Corn Watch ’21 field and sent for analysis.
Corn Watch: Nitrogen deficiency suspicions are confirmed by stalk nitrate tests.

The Corn Watch ’21 field yielded 207 bushels per acre. The conventional side with one field cultivator pass over bean stubble yielded about 8 bushels per acre better than the no-till side, but also included a lower percentage of harder-to-manage soil types. Weather-wise, it was very cool and wet after planting, wet in parts of June and early to mid-July, and then dry for nearly six weeks, finishing with excessive rain.

That’s not the recipe for top yields, notes Dave Nanda, director of genetics for Seed Genetics Direct, sponsor of Corn Watch ’21. Some lighter soils with drainage issues were waterlogged early, leading to nitrogen shortages.

Related: Cornfield achieves respectable yield in challenging year

“The extended dry period in August didn’t help grain fill,” Nanda says. “Kernel depth was good, but kernels weren’t as plump as they could have been.”

Tissue tests were pulled three times: at V5, V10 and R3. Nitrogen was sufficient on both the conventional and no-till sides at V5, but in every test afterward, it slipped into the deficient range. At the R3 stage, a small area representing 1/1,000 of an acre across 24 rows, used to monitor emergence delays, was tested separately because it was showing visible signs of nitrogen deficiency.

Tissue test results confirmed that nitrogen was lower there than in any other test all year in that field. Ceres Solutions made testing possible, and tests were run at SureTech Labs in Indianapolis.

Stalk nitrate testing  

Stalk nitrate samples were pulled from the conventional portion of the field and from the small emergence plot area about three weeks after black layer and just before harvest. Jim Camberato, Purdue University Extension soil fertility specialist, says the normal sampling period for stalk nitrate tests is about two weeks before to three weeks after black layer.

In this case, 8-inch sections were cut from 15 stalks selected at random in each area to form a sample. Ceres Solutions covered the cost of sampling through SureTech Labs. The sampling device was provided by Greene Crop Consulting Inc., Franklin, Ind.

“Some nitrate could leach out of standing stalks if you sample later in the window,” Camberato says. “On the other hand, if stalk fungi are consuming carbon through stalk rot, the nitrate concentration in dry matter might actually increase.”

What the stalk nitrate test should do is confirm if plants were short or had adequate nitrogen at the end of the season, Camberato says. Results for the conventional area were 383 parts per million of nitrate-nitrogen, vs. 17 ppm in the emergence plots where nitrogen was deficient in tissue testing at R3.

“The numbers fall right in line with what we would expect, with 17 ppm less than optimal for the deficient area and 383 optimal for the higher-yielding area,” Camberato says. Results can run extremely high if too much nitrogen was left over. Anything above 2,000 ppm nitrate-nitrogen is usually considered excessive.

Bower adds a take-home message for the grower. “We can test for soil nitrogen and pull tissue samples during the season that show if nutrition is good or not so good,” she says. “Where N is deficient or there has been crop damage, we can add some extra N during the season, but it likely still won’t overcome the situation completely and yield as well as better areas of the field.”  

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