Drought Damaged Corn Silage

Inadequate moisture during silking and pollination can result in poor ear fill or even corn plants without any ear or grain. In extended dry weather situations, farmers can also face the immediate problem of ensuring adequate forage inventories to feed their livestock. Growers attempting to salvage drought damaged corn fields by harvesting them as forage should be aware of some of the harvesting and nutrition implications.

Energy Levels

Tremendous variation can occur in drought stressed corn fields. Some fields may have short plant height with more normal ears. Yields will be reduced, but forage quality will be close to normal. Other fields will be more normal in height but have very small ears or no ears.

Energy levels of corn silage without grain content are low. Quality can be inadequate for high producing dairy cows or feedlot animals. In areas with low forage yields and a need for emergency feed, quality may be adequate for livestock with low to moderate energy requirements. Crude protein may be slightly higher, and there is a higher level of soluble sugars. Fibre levels will also be higher and the lignin content can also be increased. Because 45 per cent of the energy in normal corn silage comes from the starch fraction, the relative energy value of corn with no ears may be as low as 65 to 85 per cent of well-eared corn silage. In the rumen, the residual sugars will be more rapidly available than starch. A rapidly available protein source (soybean or canola meal, high quality alfalfa haylage) should be fed so that the rumen bacteria can utilize the protein and sugars simultaneously.

Feeds should be sampled and analyzed, rations should be balanced and a nutritionist consulted. Starch per cent, NDF and NDF digestibility will give better estimates of energy than ADF and NDF alone.

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Evaluate Yield Potential

Inspect fields to evaluate yield potential. If pollination has occurred, there will be small, white blisters visible a week to 10 days after pollination. Contact Agricorp at 1-888-247-4999 before harvest to determine how using this corn as silage will impact a Crop Insurance claim. Check herbicide labels to ensure adequate days to harvest.

Harvest at Correct Moisture

Ensiling at the correct whole plant moisture is critical. Harvesting at moistures that are too low will result in poor packing, inadequate air exclusion, poor fermentation and greater spoilage. Harvesting at moisture levels above 70 per cent will result in seepage and very undesirable clostridia fermentation. This silage will have high levels of foul smelling butyric acid, with poor feed quality and palatability.

Recommended moisture contents for corn silage are as follows:

• Horizontal bunker silos .................. 65 - 70%
• Bag silos ..................................... 60 - 70%
• Upright concrete stave silos ........... 62 - 67%

It is very difficult to accurately estimate the moisture of earless corn silage without measuring it. There are no milk-lines to use as guides. The whole-plant moisture is often higher than it appears. Leaves may look dry, but the stalk will contain more moisture. Measuring the per cent moisture is recommended. Chop a sample using a harvester or yard chipper. Sample at least 10 plants from the field, avoiding the headlands. Watch for moisture variability within fields.

Use a Koster Tester, microwave or laboratory to determine per cent dry matter. Be aware that samples have residual moisture that is not removed when dried with a Koster Tester or microwave, but will be removed in laboratory ovens or NIR procedures. Miner Institute has estimated that Koster Testers and microwaves under estimate moisture by about 3 per cent. A 68 per cent moisture sample reading is actually about 71 per cent. If using a Koster or microwave, taking the time to carefully dry the sample is important. The finer that the sample is chopped, the easier is will be to dry and the more accurate the result.

A "grab test" can be used to roughly estimate moistures if more accurate measures are not available. This may not be very accurate for something that will impact your animal performance for the whole year, but possibly better than nothing. Tightly squeeze a handful of finely cut material in your hand for 90 seconds. Release the grip and note the condition of the ball:

• Juice runs freely or shows between the fingers — 75 to 85% moisture
• Ball holds its shape and the hand is moist — 70 to 75%
• Ball expands slowly and no dampness appears on the hand — 60 to 70%
• Ball springs out in the opening hand — less than 60%
  

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Nitrate Poisoning

Be aware of the potential for nitrate poisoning. Nitrates accumulate in the corn plants when there is a large amount of soil nitrates, and a lack of moisture that interferes with normal plant growth. Nitrate accumulation may be greater with delayed nitrogen fertilizer application and with fertilizers containing nitrate as opposed to urea. The bottom third of the stalk contains a much higher level of nitrates. If nitrates are a concern, the cutter bar could be raised to leave more of the stalk in the field, but this will also further reduce yields. Nitrate accumulation is often greatest following a rain that ends a dry period. Following rainfall, the conversion of nitrates to plant protein resumes and nitrate levels return to more normal levels in a few days. Wait at least 5 to 7 days following a rainfall before harvesting. Weeds such as lambsquarters and pigweed can also be high nitrate accumulators. Long, sustained dry periods are less likely than brief, intense dry periods to accumulate high nitrate levels.

Fermentation Reduces Nitrates

Nitrates can be reduced 25 - 65 per cent during a proper silage fermentation. Typical reductions are in the 40 per cent range. Allow at least 3 weeks of fermentation before feeding. Corn silage that is harvested too wet or too dry will not ferment properly and dissipate the nitrates. The addition of Non Protein Nitrogen (NPN), such as urea or anhydrous ammonia, to drought damaged corn silage is not recommended.

Don't Graze or Green Chop

Green chopping or grazing drought stressed corn silage should be avoided due to the potential of high nitrate levels and poisoning. Green chop that is not fed immediately undergoes respiration that converts nitrate to nitrite, so the risk is increased.

Toxicity Symptoms

In the rumen, nitrates are normally converted to nitrites, which are converted to ammonia and then amino acids. High levels of nitrites are absorbed in the blood and tie up haemoglobin so that it cannot transport oxygen. Symptoms of nitrate toxicity include a rapid pulse, difficult breathing, muscle tremors and weakness. A blue mucous membrane may develop. Animals typically go down and die suddenly, within 3 hours of the initial symptoms. If you suspect nitrate poisoning, keep the animals quiet and comfortable and call your veterinarian immediately. Subacute or chronic poisoning can cause reproductive problems, including abortion.

Nitrate Analysis

Testing at harvest will provide a general idea of the relative nitrate levels, but not the concentration of nitrates being fed. The best time to test for nitrate concentration is after fermentation is complete. Obtain a representative sample. Keep the samples refrigerated and send to the lab as quickly as possible. If high levels are reported, water and other feeds should also be tested.

Feeding Management

As a general rule, nitrate ion (NO₃) levels should be less than 0.44 per cent, or 1,000 ppm nitrate-nitrogen to be without risk. Levels greater than 1.76 per cent NO3, or 4,000 ppm nitrate-nitrogen should not be fed. Feeding forages with nitrate content between these levels is associated with risks relative to the amount fed and the type of livestock. Careful management is required. Young, nursing and pregnant animals are higher risk. Introduce higher nitrate feeds slowly. Adequate energy in the rumen assists the nitrate to ammonia conversion, which reduces the potential for poisoning. Adequate levels of nonstructural carbohydrates (NSC) should also be fed.

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Silo Gas

The increased nitrate potential increases the risk of silo gas. Nitrogen dioxide, NO₂, is a dangerous chemical asphyxiant and is produced almost immediately after plant material is placed into a silo. Even short-term human exposure can result in severely injured lung tissue and sudden death. It has a characteristic bleach-like odour and may be visible as a reddish-brown haze. It is heavier than air, therefore it will tend to be located just above the silage surface. It may also flow down silo chutes and into feed rooms. Use the silo gas precautions and procedures outlined in "Hazardous Gases" (Factsheet #04-087) on the OMAFRA Forage Website.

Corn damaged by dry weather conditions can be used as corn silage to supplement forage needs, but extra care is required in harvesting at the correct moisture, ration balancing, and managing the nitrate and silo gas risks.

Related Links

• Hazardous Gases (Order No. 04-087)

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