SALEM, Ohio – Farmers who harvest silage know that when it’s time chop, everything else takes a back seat.
But this year’s growing season was dry in many areas of Ohio and Pennsylvania and growers should be wary before they hit the fields.
Dry conditions can do more than just put yield limits on corn. Drought-stressed corn can accumulate nitrates, which are toxic to livestock feeding on a fresh crop or one harvested for silage, reminds Maurice Eastridge, an Ohio State University Extension ruminant nutrition specialist.
Potentially toxic. Nitrates are major constituents of fertilizers and, when processed properly by the plant, are converted to harmless proteins. Corn and some forages, like sorghum and sudangrass, are prone to nitrate toxicity.
“The problem arises when the plant takes up nitrates from the soil, but doesn’t convert that into proteins,” said Eastridge.
Drought-stressed plants have not had enough moisture to convert nitrates, he added.
Don’t rush. Peter Thomison, an OSU Extension agronomist, said that the best recommendation growers can follow to minimize nitrate toxicity is to delay harvest, especially if drought-stressed corn is suddenly subjected to rainfall.
“You don’t want to harvest right after a rainfall,” said Thomison.
If they can, growers should try to wait two or three weeks after rainfall before harvesting, to allow that nitrogen to be metabolized into amino acids and proteins.
“In general, forages high in nitrates should not be grazed or fed as green chop or hay. Animals who feed on a fresh crop are most at risk for nitrate toxicity,” said Eastridge.
The lower the area on the plant closest to the soil, the higher the nitrate concentration, he added.
The lower one-third of a corn stalk can have a nitrate concentration of as much as 5,000 parts per million. By comparison, the leaves accumulate less than 20 parts per million in nitrates.
Eastridge noted that corn, or other forages, stored after harvest cause less nitrate toxicity problems because the fermentation process reduces those toxic levels rapidly – anywhere from 35 percent to 80 percent over a 30-day period.
Thomison recommended that silage be tested for nitrate levels just to be on the safe side.
Dry matter content. Virginia Ishler, Penn State Dairy Alliance, urges producers check whole plant dry matters right now.
The dry matter content of droughty silage should range from 28 percent to 37 percent, she said.
If the corn did not set ears and is green, or if the ears are all brown and the stalk is green, the moisture content may be too high.
If corn is ensiled too wet or too dry and poor fermentation occurs, Ishler said there is little nutritionists can do to overcome this obstacle.
Because rainfall has been so spotty, she added, farms may have fields that have not been affected by the drought as severely as other fields. This can add another layer of variability in feeding this year’s corn silage.
She recommends monitoring dry matters weekly out of storage.
Feed value. Drought-stricken corn, if ensiled at the proper moisture content for the particular storage structure, can make nutritious silage, Ishler said. Absence of ears does not imply that corn silage lacks fermentable energy.
Forage portions can contain reasonably high levels of soluble sugars. It is preferable to allow corn to develop as fully as possible, even if ears and grain are lacking.
The protein content of drought corn is typically higher compared to normal corn silage. The crude protein content can range from 9.5 percent to 12.5 percent, depending on its stage of maturity.
Sample, and test again. If possible, a composite fresh corn silage sample should be taken as the forage is being harvested. A standard forage analysis, including nitrate testing, is recommended.
Another corn silage sample should be analyzed again when feeding out of the storage structure. Nitrate testing is recommended again.
Although nitrate levels should be reduced by half after the ensiling process, it may be beneficial to know what the nitrate levels were prior to ensiling compared to feed out.
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