Granted, no farmers want to be caught short of nitrogen (N) for their corn crop. Yet, farmers may not need as much N on corn as they think.
Fabian Fernandez, University of Minnesota (U of M) Extension soil fertility specialist, points to a 2016 U of M corn fertility test near Wells in south-central Minnesota.
“Like 2016, this was also a year with high spring precipitation,” says Fernandez. “Yield constantly increased until we hit 127 pounds of N applied.
“When we say apply the optimum, we are talking about economic optimum,” says Fernandez. “Those last few bushels of yield you produce typically above that level cost more than they’re worth.”
This leftover N also could denitrify and be lost going into spring. “The soil is not a good savings account for nitrogen,” says Fernandez.
A soggy and delayed 2018 harvest canceled many fall N application plans. If this occurs again this fall, remember that spring N applications remain an option.
U of M tests show spring urea applications spur greater yields with less N loss than fall anhydrous applications teamed with a nitrification inhibitor, says Fernandez. It mattered little if anhydrous ammonia was fall-applied on continuous corn or followed soybeans, he says.
“Under wet conditions, it is hard to get a good seal on the ammonia knife track,” he says. “There can be an open channel for anhydrous ammonia to escape. You will have to go a bit deeper to adjust for those conditions.”
Farmers who fall-apply N should use anhydrous ammonia rather than urea, says Fernandez. U of M tests showed corn fertilized in the fall with urea yielded an average 11 bushels per acre less than those acres fertilized with anhydrous ammonia.
Fall urea nitrifies faster than anhydrous ammonia. Once in nitrate form, this N is subject to loss that hurts farmers economically and also ends up in the environment.
If fall-applying anhydrous ammonia, wait until soil temperatures dip below 50°F. and also add a nitrification inhibitor. Although it will keep N in the ammonia form longer, loss potential still exists, reminds Fernandez.
Planting and weed control should take priority over spring N applications, says Peter Scharf, University of Missouri soil fertility specialist.
“Delayed corn planting can cost a lot of money and could have a domino effect on other time-sensitive operations,” he says.
If a wet spring nixes preplant N applications, remember that corn requires little N early in the growing season.
“If you can sidedress between V4 and V8, you will be OK,” says Fernandez. “Don’t wait any longer than that, unless field (and weather) conditions prevent you from sidedressing.”
Continuous corn is the only exception, he adds. Substantial corn-after-corn residue can immobilize N and slice early-season N availability. Cold growing conditions could exacerbate the situation, as little N mineralization results.
In a worst-case scenario that prevents all fall and spring preplant and early sidedress N applications, postplanting N applications can still work, says Scharf.
Data from five states over the past three decades compiled by Scharf shows the same yields resulted from N applied in a single shot of urea in waist-high corn vs. planting-time applications.
Obviously, this isn’t a preferable situation, says Scharf. Still, if farmers get backed into a corner, N applications as late as waist-high can still salvage a crop.
Waterhemp and marestail often form a rogue’s gallery of weeds that trouble corn and soybeans. This year, though, volunteer corn also entered the mix in areas like southern Minnesota, says Tom Hoverstad, a scientist at the University of Minnesota Southern Research and Outreach Center at Waseca, Minnesota.
“It was a function of what happened in the fall of 2018,” he says. “Things were in good shape until early September, and then we hit stormy, windy, and rainy weather. Farmers had trouble getting to some fields, and corn went down in those fields.”
There’s not much that can be done if herbicide-tolerant corn is planted on the same kind of herbicide-tolerant corn. In corn rotated to soybeans, though, there are some good products (such as Select Max) that can control it, says Hoverstad.
Well, this year’s soggy spring nixed those stands in many fields. Many farmers were backed into a corner, having to plant into soggy soils or risk not planting at all. This raises havoc with stands.
Respectable yields can still result, according to University of Minnesota (U of M) trials. For example, farmers who aim for a stand of 34,000 plants per acre (ppa) or greater and only glean a 28,000-ppa final stand can still get about 95% of full yields, says Jeff Coulter, U of M Extension agronomist. Meanwhile, U of M trials show a 24,000-ppa stand can still glean about 91% of a full stand.
“All plants emerging at about the same time and at the same height eliminates competition against each other,” he says.
A corn plant that’s two leaf stages behind its neighbor will yield just one half of what it would yield if it were the same height, he says.
“September normally has some good drying days, with warm days typically taking .75% to 1% daily off corn moisture in Minnesota,” says Jeff Coulter, a University of Minnesota Extension agronomist.
“Beyond mid-October, grain drying is much slower,” Coulter adds. “You should prepare for wet corn.”
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