Consider these points before adding supplemental N
By
khardi j mukuyu
Gil Gullickson
Rampant rainfall in areas like south-central Minnesota has farmers concerned about corn nitrogen (N) loss. Since it’s mid-June, University of Minnesota soil scientists say it’s likely that anywhere from one-half to all of applied N — regardless of fertilizer form or application timing, is in the nitrate form. That’s the form — fueled by soil microbial and heat and moisture — most susceptible to environmental loss.
N Loss Mechanics
Nitrate denitrifies when soils are saturated, says Brad Carlson, a U of M Extension educator. Denitrification occurs when nitrate converts into inert nitrogen gas lost to the atmosphere. This microbial process also speeds up in warm soils.
Most recently, the U of M Southern Research and Outreach Center in Waseca reported the 4-inch soil temperature was at 64°F. Research shows saturated soils that stay this temperature for four days will lose approximately 10% of the N present in the nitrate form. The loss approaches 20% if the soil stays saturated for 10 days.
Additionally, nitrate will leach (move downward) as the water drains away. A rule of thumb for this is that nitrate will travel approximately 6 inches for every 1 inch of water that leaves as drainage. It is important to note that these processes will be highly variable across most fields based on local soil and water conditions.
Supplemental N Worksheet
Adding supplemental N can help corn reach its yield potential if a significant amount of N has been lost. The U of M has developed a worksheet to assist farmers with making supplemental N application decisions for corn
Supplemental N Considerations
Here are some considerations to remember before applying supplemental fertilizer.
Soils that have been saturated for a long time will in all likelihood have stunted plants with reduced yield potential. They will require less N.
Where leaching has occurred, it is probable that the N has moved lower in the soil profile. However, it may not be lost, since increased root growth may put the N back in reach of the plant.
Several new technologies focus on making supplemental (and variable-rate) N decisions. While promising, they are new, and the jury is still out with respect to how well they work.
If this was a year that you struggled to get your hay dry or ended up storing it semi-wet, you should be on the lookout for fungal abortions in your herd. Some herds have seen up to 10% of pregnant cattle aborting due to mold, but a more typical number is one or two fungal abortions per herd.
Almost every farm encounters mold in one form or another, but forms like Aspergillus and Mucor in particular can be dangerous for pregnant cattle. These forms are most often found in cattle feed, hay, silage, and wet byproducts, and can lead to fungal abortions when ingested by expecting cattle.
“Many animal feeds naturally have around 10,000 mold organisms per gram of forage,” says Gregg Hanzlicek, director of production animal feed investigations at the Kansas State Veterinary Diagnostic Laboratory. “Once we start to be able to see the mold, there are many times around a million or more organisms per gram.”
Fungal abortions, also known as mycotic abortions, typically occur when a cow is around six to eight months pregnant. Hanzlicek has seen slightly more fungal abortions in 2016 than he has seen in past calving seasons.
Moldy Hay“We think the primary way cattle become infected is by breathing into the respiratory system the mold spores that are in the feed,” Hanzlicek says. Testing hay is important to understand mold levels.
If producers are feeding moldy hay, they can try to dilute the mold in the hay by mixing it with non-moldy hay in a mixer wagon. If that’s not an option, feed the moldy hay out in an open area where the mold may blow away.
To limit mold growth, packing corn silage is known to be effective. Mold inhibitors in feed are really only helpful in programs that use a total mix ration or go through a mixer wagon and into a feed bunk.
Medical SignsUnfortunately, there’s no way to predict whether or not a cow will suffer from a mycotic abortion.
“The heifer or cow that has the mold doesn’t act sick; she just aborts the fetus,” Hanzlicek says. “A small percentage of the aborted fetuses will have either red or white circular lesions on the skin. The white lesions look similar to ringworm.”
Because that’s so uncommon, the easiest way to find out if the abortion was fungal is to send in samples to a lab. Submitting the placenta is the ideal tissue sample for veterinary diagnostic labs to have along with other tissue samples.
“The only way to determine it is to microscopically look at the placenta,” says Hanzlicek. “If we find mold hyphae growing in the placenta, then we know for sure mold was associated with that abortion.”
Even if there was a way of diagnosing these abortions prior to them happening, there are no medical treatment options for prevention.
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