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Pasture and forage

Jerry Volesk, Daren Redfearn
and Brad Schick
Nebraska Extension

Have you noticed any black nightshade in your corn stalks that you are grazing or plan to graze? If these fields have too much black nightshade, be careful, it might be toxic.

Black nightshade is common in many corn fields in the fall, especially those that had hail damage in the summer or any situation where the corn canopy became thin or open. It usually isn’t a problem, but if the density of nightshade is very high, there is the potential that it could poison livestock that graze many of the plants. Almost all livestock, including cattle, sheep, swine, horses and poultry are susceptible.

Black nightshade plants average about 2 feet in height and have simple alternating leaves. In the fall, berries are green and become black as the plant matures. All plant parts contain some of the toxin and the concentration increases as plants mature, except in the berries. Drying as hay or after a freeze will not reduce the toxicity.

It is very difficult to determine exactly how much black nightshade is risky. Guidelines say that a cow would need to consume 3 to 4 pounds of fresh black nightshade to be at risk of being poisoned. These guidelines, though, are considered conservative since there is little data on the actual toxicity of nightshade plants. Also encouraging is that reports of nightshade poisoning have been very scarce in the past.

Fortunately, even though nightshade plants remain green fairly late into the fall, cattle usually don’t appear to seek out nightshade plants to graze. However, green plants of nightshade might become tempting toward the end of a field’s grazing period, when there is less grain, husks, or leaves to select.

So common sense and good observation must be your guide. Scouting fields to estimate the general density of nightshade plants will help you determine any potential risk. Secondly, and particularly near the end of a field’s grazing period, closely observe what the cattle are eating to see if animals might be selecting nightshade plants.

CATTLE COMPACTION IN CROPLAND: FACT OR FICTION?

Are you looking for additional income from your corn acres? Grazing corn residue is a low-cost winter feed source for cattle and a source of additional income for farmers without negative effects on the cropland.

Many crop producers are concerned that trampling from cattle grazing corn residue negatively affects crop yields. But when grazed at proper stocking rates, small but positive effects on crop production after grazing have been observed.

Research conducted at the University of Nebraska has shown that grazing corn residue at the recommended stocking rate does not reduce corn or soybean yields in irrigated fields the following growing season.

In fact, a long-term study in eastern Nebraska at the Eastern Research and Extension Center showed 2 to 3 bushel per acre improvements for soybean production following grazed corn residue in a corn-soybean rotation. This result was the same whether cattle grazed in the fall from November through January or spring from February through April.

A five-year study in western Nebraska measured corn yields from continuous corn after cattle grazing in the fall and found no negative effects on corn yields the following year.

It must be noted that minor surface compaction can result from grazing during wet weather. However, this compaction often disappears through the natural wetting and drying and freezing and thawing processes. And the compaction level for restricting root growth and does not carry over into the following growing season.

Grazing corn residue benefits both cattle and crop producers. Corn residue should be viewed as an economical source of winter roughage for cattle that can provide an extra source of income from corn production that does not affect next year’s crop production.

If you are interested in listing crop residue fields available for winter grazing and connecting with livestock producers, sign up at cropresidueexhange.unl.edu.

FALL FERTILIZATION ON CORN STALKS BEFORE GRAZING

Grid sampling and application of dry fertilizer is common in the fall, but is it safe to graze corn residue fields that have had the fertilizer applied?

The answer comes down to how much risk in animal wellbeing we are willing to take. The risk potential is different for different fertilizer components. Potassium, zinc, nitrogen, and sulfur could all be toxic, but that risk is all about consumption rate and the amount animals can physically consume. To reduce risk, wait to graze until after precipitation whether that be rain or snow melt. Waiting for rain is more important if the application stuck to damp or wet residue.

Calculations can tell if what was applied would pose a risk.

Nitrogen fertilizers can cause toxicity in different ways and differing amounts so any spill available for consumption is a higher risk. There are other fertilizer components in a grid sampled application that may or may not be a problem due to the how much is in the mix. Here are some other components and elemental levels that would be toxic. Potassium would be toxic at 30,000 mg/kg of intake or 3% of the diet which is very unlikely. A very high potassium intake could cause a magnesium deficiency, so making a high magnesium mineral available might be considered. High sulfur intake could cause polio encephalomalacia or PEM, but that is also unlikely. A lot of downed corn could also increase the risk of PEM. Cattle can tolerate 0.5% sulfur in the diet, but corn residue only contains close to 0.1%. Zinc consumption is fine up to 1,000 mg/kg without problems and phosphorus can be tolerated up to 1% of the diet.

Bottom line: The safest approach for grazing corn stalks is too wait until a rain or graze before fertilizer application, but that may not be realistic. Assessing the fertilizer amount will give a good idea of risk level. If the fertilizer can easily be seen on the residue, be more cautious when grazing. ❖


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