Corn silage nitrate levels could be dangerously high

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COLUMBUS – It’s been a less-than-ideal growing season in much of Pennsylvania and Ohio – particularly northeastern Ohio – and prevailing drought-like conditions threaten to seriously cripple the corn silage crop.

Corn intended for silage is not growing well in many counties. Pollination has been poor and without rain, the ears will not fill out adequately. This all adds up to potentially toxic nitrate levels.

Nitrates absorbed from the soil by plant roots are normally incorporated into plant tissue as amino acids, proteins and other nitrogenous compounds. The concentration of nitrate in the plant is usually low. The primary site for converting nitrates to these products is in growing green leaves.

But under unfavorable growing conditions, like this year, this conversion process is retarded, causing nitrate to accumulate in the stalks and stems, according to Ohio State University corn specialist Peter Thomison.

The highest concentration of nitrates is in the lower part of the stalk or stem. For example, the bulk of the nitrate in drought-stricken corn plants can be found in the bottom third of the stalk.

If moisture conditions improve, Thomison said, the conversion process accelerates and within a few days nitrate levels in the plant returns too normal.

Bad timing. The highest levels of nitrate accumulate when drought occurs during a period of heavy nitrate uptake by the corn plant, Thomison said.

A drought during or immediately after pollination is often associated with the highest accumulations of nitrates.

Extended drought prior to pollination is not necessarily a prelude to high accumulations of nitrate. The resumption of normal plant growth from a heavy rainfall will reduce nitrate accumulation in corn plants, Thomison said.

Harvest should be delayed for at least one to two weeks after the rainfall.

Not all drought conditions cause high nitrate levels in plant, the extension specialist added. If the supply of soil nitrates is in the dry soil surface, plant roots will not absorb nitrates. Some soil moisture is necessary for absorption and accumulation of the nitrates.

When to harvest. If growers want to salvage part of their drought-damaged corn crop as silage, Thomison said it’s best to delay harvesting to maximize grain filling.

Even though leaves may be dying, the stalk and ear have enough extra water for good keep. Kernels will continue to fill and the increases in dry matter will more than compensate for leaf loss unless plants are actually dying or dead.

If nitrate levels are high or questionable, they will decrease as plants get older and nitrates are converted to proteins in the ear.

Watch kernel milk line. The kernel milk line can be used as a guide in determining the best time to cut corn for silage.

When the kernel milk line has moved one-fourth to the distance from the top (or crown) of the kernel to the base, the whole plant generally contains about 60 percent to 70 percent moisture – usually the recommended moisture range for making corn silage.

Test for nitrates. If the corn is to be harvested for silage, it is important to test the nitrate levels at the cutting height of the forage chopper to determine the highest levels of plant nitrate.

If the plant is marginal to high in nitrates, then a lab analysis is recommended before feeding. To get a quantitative nitrate determination, send or deliver a sample of six to 10 plants (cut at the stalk height of the forage chopper) to a plant analysis laboratory. Results of the test can generally be obtained over the phone, fax, or e-mail when tests are completed.

The following feed laboratories will test corn samples for nitrate:

Holmes Laboratory, Millersburg, Ohio, 800-344-1101; Dairy One, Ithaca, N.Y., 800-344-2697;

Cumberland Valley Analytical Services, Hagerstown, Md., 800-282-7522;

Check also with: Litchfield Analytical Services, Litchfield, Mich., 517-542-2915; and Dairyland Laboratories, Arcadia, Wis., 608-323-2123.

Nitrate field test kits are available from: Nitrate Elimination Co., 888-648-7283.

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