Dairy Focus: Poor corn pollination affects quality

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The corn crop in North Dakota and surrounding states is as variable as the recent weather, and the encroaching drought has taken its toll on some fields.

Poor corn pollination can be caused by numerous factors, including drought, hail, frost, corn rootworm silk feeding and foliar diseases. As a result, some corn is poorly pollinated and will yield limited or no grain.

Often, cattle operations can use poorly pollinated corn, although pollination success influences corn forage quality.

Corn has two peaks in forage quality: at pollination and at harvest maturity.

Forage quality, as measured by milk per ton, is high during vegetative phases prior to flowering. As with all forages, corn quality decreases after flowering.

However, unlike other forages, corn silage quality improves beginning around stage R3.

The early peak in forage quality at pollination is high, but the corn is too wet for ensiling. The later peak is more familiar and is the one we typically manage for when producing corn silage because it maximizes biomass yield and quality.

In general, if some kernels are developing, wait to harvest. But if the plant is barren, then harvest at any time.

The first quality peak occurs around flowering and will continue if pollination is unsuccessful. While not useful for corn grain production, drought-stressed corn has good feed implications because it contains increased sugar content, higher crude protein, higher crude fiber and more digestible fiber than normal corn silage. Drought generally reduces yield and grain content, resulting in increased fiber content, and this often is accompanied by lower lignin production that increases fiber digestibility.

Be sure to check with your crop insurance agent before harvesting and follow his or her instructions for collecting adjustments. You cannot graze an insured crop or chop it for forage or silage without first receiving permission from your crop insurance agent or you will forfeit indemnities. Also, make sure no herbicide restrictions affect the forage for livestock feeding.

Remember, you do not have to use the forage yourself; you can sell it to someone else who needs it.

The harvesting challenge is that green, barren stalks will contain 75 to 90 percent water. If the weather remains hot and dry, the corn's moisture content drops, but if rain occurs before plants lose their green color, they can remain green until frost.

The proper harvest moisture content depends upon the structure in which you plan to store the crop, but the moisture content is the same for drought-stressed and normal corn. Harvesting should be done at the moisture content that ensures good preservation and storage: 65 to 70 percent if storing the corn in horizontal silos (trenches, bunkers, bags), 60 to 65 percent if storing in upright stave silos and 55 to 65 percent if storing in upright oxygen-limiting silos.

If you plan to harvest the crop for ensiling, the main consideration will be proper moisture for storage and fermentation. The crop will look drier than it really is, so moisture testing will be critical. Be sure to test whole-plant moisture of chopped corn to ensure that acceptable fermentation will occur. Use a forced-air dryer (Koster), oven, microwave, electronic forage tester, near infrared reflectance spectroscopy or the rapid "grab-test" method for your determination.

In the "grab-test" method, squeeze a handful of finely cut plant material as tightly as possible for 90 seconds. Release your grip and note the condition of the ball of plant material in your hand. Here is how to interpret what you see:

* If juice runs freely or shows between your fingers, the crop contains 75 to 85 percent moisture.

* If the ball holds its shape and your hand is moist, the material contains 70 to 75 percent moisture.

* If the ball expands slowly and no dampness appears on your hand, the material contains 60 to 70 percent moisture.

* If the ball springs out in your open hand, the crop contains less than 60 percent moisture.

Grazing the corn field is an option, but be aware of the potential for nitrate toxicity. This is especially likely to be a problem if growth was reduced to less than 50 percent of normal and/or high levels of nitrogen were applied to the crop.

The risk of nitrate poisoning increases as pollination becomes poorer. Nitrate problems often are related to concentration (the greater the yield, the less chance of high nitrate concentrations in the forage). If pollination is poor, only about half of the dry matter will be produced, compared with normal corn forage.

Under stressful growing conditions, especially drought, this conversion process is slowed, causing nitrate to accumulate in the stalks, stems and other conductive tissue. If moisture conditions improve, the conversion process accelerates, and within a few days, nitrate levels in the plant return to normal.

The only way to know whether your silage contains nitrate is to have it tested by a testing facility such as NDSU's Plant Diagnostic Laboratory. Get samples taken for nitrate tests analyzed immediately or freeze them until they can be tested because nitrate will decline in tissue in three to four hours.

If drought-stressed corn is ensiled at the proper moisture content and other steps are followed to provide good-quality silage, nitrate testing should not be necessary. Nevertheless, feed the silage to a few cull cows before feeding it to your other animals.

Always follow precautions regarding dangers of nitrate toxicity to livestock, especially with grazing and green-chopping, and silo gasses to humans when dealing with drought-stressed corn. If the nitrate is above toxic levels, feed hay or some other forage in the morning and allow your livestock to graze the corn for a couple of hours in the afternoon.

Source: J.W. Schroeder, Dairy Specialist, NDSU Extension Service


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