Corn damaged by drought: Use as grain crop or forage?
Farmers, agronomists and others are evaluating cornfields hit by drought and planning when and how to harvest them for greatest economic advantage. This involves assessing condition of the crop in individual fields relative to normal, and to think through several harvest scenarios such as: Will this field have a harvestable grain crop? Are there other concerns? What use or management alternatives do you have?
• Farmers with drought-damaged corn can consider using it for forage alternatives.
• Options are green chop it, or use the corn for silage or as dry corn stover.
• Harvesting drought-damaged corn as silage is not a good option for everyone.
To help answer those questions and more, Iowa State University Extension forage agronomist Steve Barnhart and Extension corn agronomist Roger Elmore provide the following information.
• With enough grain on ears, corn is more valuable harvested for grain. Most of Iowa’s corn crop is intended for use as dry grain. If it has sufficient grain content and quality, a field will be more valuable as harvested grain. If the field or parts of it fall short of economic grain potential, some farmers can harvest the crop as low-yield corn for silage or graze it.
Predicting grain yield during mid-season is difficult. It involves assessing what you have in the field and comparing that with normal crop growth and development. With normal corn development, the number of pollinated kernels should be visible at about 10 to 12 days after silking (blister stage). This represents potential grain set. If weather conditions have adversely affected pollination, it will be evident at blister stage.
For the remainder of the summer, weather conditions influence how many of the pollinated kernels develop and the stage of development. Harvest decisions can then be based on knowledge of seed development gained by monitoring. If the crop doesn’t appear to be developing well, and you’re making early forage harvest decisions, use the following guidelines for estimating silage yield of moisture-stressed corn.
• Grain yield method for estimating silage yield. For moisture-stressed corn, about 1 ton of silage per acre can be obtained for each 5 bushels of grain per acre. For example, if you expect a grain yield of 50 bushels per acre, you will get about 10 tons per acre of 70% moisture silage (3 tons per acre dry matter yield). For corn yielding more than 100 bushels per acre, about 1 ton of silage per acre can be expected for each 6 to 7 bushels of grain per acre. For corn yielding 125 bushels of grain per acre, corn silage yields will be 18 to 20 tons per acre at 70% moisture (5 to 6 tons per acre dry matter yield).
• Plant height method for estimating silage yield. If little or no grain is expected, a rough estimate of yield can be made assuming 1 ton of 70% moisture silage can be obtained for each foot of plant height (excluding tassel). For example, corn at 3 to 4 feet will produce about 3 to 4 tons per acre of silage at 70% moisture (about 1 ton per acre of dry matter).
In addition to yield, consider other factors. Stage of development or condition of growth also influences the feed value of the harvested crop. Compared to normal corn, corn that would yield 20 to 40 bushels per acre would have about the same pound-for-pound feed value. Very poorly pollinated stalks with 0 to 20 bushels per acre yield potential would have about 80% to 90% the feeding value of normal corn. Short, barren stalks have only about 70% to 80% of the feed value of normal corn.
In what form will the corn be harvested and used? The three most practical options for using drought-damaged corn are green chopping, ensiling and storing as dry stover. Each system has advantages and disadvantages. Consider the fungicides, herbicides or insecticides used on the field. Each of these products has a legal preharvest interval. Early harvest or grazing may violate the intervals. Carefully check the label for any restrictions that may affect harvest or harvest timing.
• Green chopping corn. This provides an immediate source of feed for dry lot or supplementing animals on pasture. A disadvantage may be a potentially high level of nitrates in drought-damaged, fresh forage. Have fresh-chopped corn tested for nitrates at a nearby commercial feed testing lab if there is any concern about high levels.
• Chopping corn for silage. This provides a less immediate feed source, but a form that can be stored and fed over a longer period. One of the main management challenges of harvesting drought-damaged corn for silage is cutting the plant at proper moisture content for the type of silo structure where the forage will be stored. Corn should be stored at 65% to 70% moisture in a bunker or trench silo and at 60% to 65% moisture in upright silos.
In plants with at least some grain, the drydown rate of the grain will provide a rough guide for predicting whole-plant moisture. Plants with no grain but with some live green leaf tissue still evident will have surprisingly high moisture content (75% to 80%), too high for direct-cut ensiling.
In some cases even when all visible leaves have turned brown, the whole-plant moisture is still above 70% moisture. Plants that have died will lose moisture very quickly and could drop below 50% moisture in a short time, too low for best nutrient conservation as silage.
This article published in the August, 2012 edition of WALLACES FARMER.