Keith Johnson, Department of Agronomy
Kern Hendrix, Professor Emeritus, Department of Animal Sciences
Hot, dry July and August weather is taking its toll on the corn crop in many areas of Indiana.
Cattle producers may be harvesting drought-stressed corn as silage this year in order to salvage some value and to supplement short pastures and low winter feed supplies.
Following are some factors producers should consider prior to and during harvesting of drought-stressed corn.
Crop Insurance. Contact the company or a representative so that the crop can be appraised prior to harvest.
Farm Service Agency (FSA). Prior to harvest, contact your local FSA office and complete a Form 6033EZ.
Check Pesticide Labels. Before using any stressed corn for feed, be sure to note the harvest restrictions for any herbicides and insecticides. Check the pesticide label or consult your chemical supplier for details. This is especially critical with an early silage harvest.
Harvesting as Whole Plant Silage. Feeding value of drought-stressed corn is influenced by several factors, but in general is higher than expected. Most studies indicate feed value of drought-stressed corn to be 80 to 100% that of normal silage. Purdue studies conducted with stressed corn indicated little or no difference in feedlot gain or in milk production when beef and dairy cattle were fed normal or stressed corn silage. As a rule, drought-stressed corn will have slightly more fiber resulting in less energy, but one to two percentage units more protein than normal silage.
One of the most important factors influencing feeding value, is moisture content at harvest. Ideally, the crop should contain 60-70% moisture at harvest. For up-right silos, to avoid seepage, harvest at 60-65%, whereas for bunker silos, harvesting at 65-70% moisture will result in better packing and storage qualities.
The tendency will be to harvest too soon, resulting in silage with excess moisture, poor fermentation and reduced feed value. Stalks of plants with many or most leaves turning brown will contain considerable moisture. Also, stalks with small ears and little or no grain content will be higher in moisture. Normal harvest indicators such as kernel milk line and black layer may not apply in stressed corn.
A quick way to determine if the plant contains too much moisture is to hand-squeeze a representative sample collected from the forage chopper. If water drips from the squeezed sample, the corn is too wet for ideal fermentation. Moisture content may also be determined using a microwave: http://www.agry.purdue.edu/ext/forages/publications/ID-172.htm.
What About Nitrate Content? Stressed corn can have elevated nitrate levels. However, samples collected from previous drought years indicated nitrates were not a problem in most cases. For example in 1988, based on 70 fresh corn samples, only 18% contained toxic levels of nitrate. In contrast, 71% of the sorghum-sudan grass samples contained toxic levels of nitrate.
Quantitative laboratory analyses for nitrate can be performed at the Purdue University Animal Disease Diagnostic Laboratory (ADDL). Cost is $15.00 per sample plus $7.00 accession fee per individual each time samples are submitted. A one-quart size sample of chopped forage is adequate. Samples should be submitted in paper bags or cardboard boxes, not in sealed glass or plastic containers. Names and addresses of other laboratories to obtain nitrate tests can be found at http://www.ansc.purdue.edu/beef/Hendrix/ForageNitrate.html.
Also, during the fermentation process, 40 to 60 percent of nitrates will be eliminated. Keep in mind, however, that various nitrogen oxide gases produced during the fermentation process are highly toxic to humans and livestock. For the first three to four weeks after ensiling, do not enter a silo without first running the blower for 15 to 30 minutes.
Harvesting for Green Chop. In cases where pasture and stored feed supplies are getting short, producers may wish to consider green-chopping corn for feed. There are two major concerns with this practice. One is the potential for nitrate toxicity and second is the potential to founder animals. To avoid these problems: (1) raise the cutter bar to 12 inches or so the first few days of chopping, (2) gradually introduce animals to green chop, (3) use other feeds that are low in nitrate as part of the ration, (4) feed green chop in small quantities throughout the day rather than large quantities once per day, (5) don't allow green-chop forage to set on a wagon overnight, (6) feed two to three pounds of grain with high nitrate feeds, (7) nitrate levels tend to increase for two to three days following rain, thus take extra precautions during this time period, (8) as plants mature, nitrate levels decline, also animals become acclimated, thus chances for toxicity decrease with time.
Selling or Buying Drought-Damaged Corn. Normally, whole plant corn silage (65%) moisture per ton is valued at 9-10 times the price of a bushel of corn, including harvest and storage costs (i.e. $3.50/bu = $31.50 to $35.00/ton of silage). Standing corn should be discounted $5.00 to $7.00/ton to account for harvesting costs. Discounts due to lower feed value should range from 0 to no more than $4.00 per ton.
Moisture content will greatly influence pricing. For example, let us assume a value of $31.50 per ton of 65% moisture has been established. Each ton at 65% moisture contains (2000 x .35) = 700 lbs of dry matter. Value per cwt of dry matter = $31.50 ÷ 7 = $4.50. If, however, moisture content is 70%, then each ton contains only 600 lbs of dry matter (2000 x .30). To have comparable value, this silage should be priced at $27.00 (6 x $4.50) per ton. On the other hand, if moisture content was 60%, then a comparable price would be (2000 x .40) = 800; 8 x $4.50 = $36.00 per ton.
Yield per acre will vary greatly with moisture content and with grain yield. At 65% moisture, normal yields would be one ton for each seven to eight bushels of grain. However, with stressed corn, and grain yields in the 50 to 75 bushel per acre range, assume one ton of silage for each five bushels of grain. If stalks are mostly barren, an estimate is one ton per foot of stalk, excluding the tassel.
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