Source: Ontario Ministry of Agriculture, Food and Rural Affairs
Introduction
Dry weather during corn silking and pollination can significantly reduce grain yield expectations. Inadequate moisture 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 providing adequate forage inventories to feed their livestock. Damaged corn crops with low grain yield potential may be available for salvaging as corn silage for livestock producers that are short of forage. Silage piles and silage bags provide flexible storage. Farmers attempting to salvage corn fields damaged by dry weather by harvesting them as forage should be aware of some of the harvesting and nutrition implications.
Evaluate Yield Potential
Tremendous variation can occur in corn fields stressed by lack of rain. Development of the ears is critical to grain and silage yield, and also silage quality. Some fields may have short plant height with fairly 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. Grain yields will be dramatically reduced, but there may still be some potential to provide some forage for livestock.
Inspect corn fields to evaluate yield potential. If pollination has occurred, there will be small, white blisters visible a week to 10 days after pollination. Detecting successful pollination without waiting for the kernel blisters to appear can be done by carefully removing the husks, turning the ear upside down and gently tapping it. The majority of silks should fall off indicating successful pollination. Silks that remain attached indicate kernels that have not been pollinated.
Contact Agricorp at 1-888-247-4999 to determine how using this corn as silage will impact a crop insurance claim. Check herbicide labels to ensure adequate days to harvest.
Digestible Energy Levels
Digestible energy levels of corn silage without any grain content are reduced. Quality will likely 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.
Starch content will be reduced, but there is likely a higher level of soluble sugars. Crude protein may be slightly higher. Fibre levels will be higher, and the lignin content can also be increased. Because 45 percent 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 percent of well-eared corn silage. In the rumen, the residual sugars will be more rapidly available than starch.
Feeds should be sampled and analyzed, rations should be balanced and a nutritionist consulted. Energy predictions of Total Digestible Nutrients (TDN) using Acid Detergent Fibre (ADF) and Neutral Detergent Fibre (NDF) will not be very accurate. Analyzing for starch, NDF and NDF digestibility will give much better estimates of digestible energy than fibre alone. Wet chemistry analysis rather than near infrared spectroscopy (NIRS) should be used.
Harvest at Correct Moisture
Ensiling at the correct whole plant moisture is critical. Without a normal cob, it can be difficult to correctly estimate whole plant moisture from visual clues. Corn silage damaged by dry weather conditions tends to look drier than it actually is. 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 percent will result in seepage and a 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 – 68 %
Upright concrete stave silos: 62 – 67 %
See OMAFRA Factsheet Harvesting Corn Silage at the Right Moisture, Order No. 13-051.
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. Leaves may look dry, but the stalk will contain more moisture. A common problem is harvesting corn silage from these damaged fields too soon, resulting in run-off and a poor fermentation. If you are in doubt about the whole-plant moisture, chop a sample using a harvester or yard chipper. Use a Koster Tester, microwave or laboratory to determine percent dry matter. Sample at least 10 plants from the field, avoiding the headlands. Watch for moisture variability within fields.
Be aware that samples have residual moisture that is not removed when dried with a Koster Tester or microwave without burning it. Dry matter determined by oven drying at a laboratory is the most accurate. (This can be done by using an overnight courier service.) Koster Testers and microwaves typically underestimate moisture by about 3%. A 68% moisture sample reading is actually about 71% (too wet). If using a Koster or microwave, it is important to take the time to carefully dry the sample. The finer that the sample is chopped, the easier is will be to dry, and the more accurate the result.
Nitrate Poisoning
Be aware of the potential for nitrate poisoning, as well as silo gas. 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 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.
The bottom third of the stalk contains a much higher level of nitrates. If nitrates are a potential concern, the cutter bar could be raised to leave more of the stalk in the field, but this will also further reduce yields in a year when feed is needed. Analyzing fermented silage samples for nitrates and managing dietary levels is recommended. A few other considerations to manage high nitrate potential include:
- Fermentation Reduces Nitrates
Nitrates can be reduced 25 – 65 percent during a proper silage fermentation. Typical reductions are in the 40 percent range. Allow at least 3 – 5 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 this corn silage is not recommended. - Graze or Green Chop with Caution
Green chopping or grazing corn stressed by dry weather can be an option for some producers facing feed shortages, but considerable caution should be used. Nitrate levels can fluctuate daily within the plant, with concentrations higher in the bottom of the plant compared to those found near the top. Corn plants typically contain significantly higher levels of nitrate immediately after a rainfall event that follows a prolonged period of dry weather. The risk of nitrate poisoning while green chopping or grazing this corn is much higher for the 5 – 7 day period after a rainfall than during the actual period of dry weather. Green chopped corn that is not fed immediately undergoes respiration that converts nitrate to nitrite, so the risk is increased. Field sampling and laboratory analysis for nitrates can be useful, but keep in mind that nitrate levels in these plants fluctuate. - Nitrate 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 hemoglobin 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 in the silage 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
There is some confusion over how laboratory nitrate levels are reported and used, so be sure you are interpreting the right method. The nitrate (NO3) level is 4.4 times the nitrate-nitrogen (NO3-N) level. Concentrations can also be reported as “ppm” or as a percentage. As a general rule, NO3-N levels should be less than 1,000 ppm (NO3 levels <0.44%) to be without risk. Levels greater than 4,000 ppm NO3-N (>1.76 % NO3) 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. - 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 OMAFRA Factsheet Hazardous Gases on Agricultural Operations, Order No. 14-017. Refer to the Ontario Farm Safety Association Factsheet Silo Gas Dangers.
Corn damaged by dry weather conditions can be used as corn silage to supplement forage needs, but extra care is required in ration balancing, harvesting at the correct moisture, and managing the nitrate and silo gas risks. Information on harvest and storage of corn silage, including “Pricing Corn Silage”, “Silage Fermentation Problems”, and “Grazing Corn Stover” is available on the Forage index pageOMAFRA Crop Website.
