When should I chop drought-stressed corn?

August 3, 1995 2(20):136-137

Joe Lauer, Corn Agronomist

Overall, the 1995 corn crop has experienced good to excellent growing conditions. Yield potential is high at this point in time throughout much of the state. However, there are isolated badly stressed fields, and some counties in the northeast are experiencing drought conditions.

These fields usually have lighter, sandy soils and were planted late. The general appearance of these fields include: 1) short-statured plants, 2) plants with leaves which are brown over halfway up the plant, often past the ear leaf, and 3) kernels beginning to dent prematurely. Leaf death due to drought usually progresses upwards from the base of the plant. Since severe upper leaf scalding took place in mid-July, all of the leaves on some plants may have turned brown.

Growers questioning when to chop their corn for silage should wait until:

You are sure pollination and fertilization of kernels will not or did not occur and that whole-plant moisture is between 55-70%, so that fermentation can occur without seepage or spoilage losses.

If pollination and fertilization of kernels did occur, do not chop until you are sure that there is no further potential to increase grain dry matter and whole plant moisture is in the 55-70% range.

A few cautions and suggestions:

  1. Be sure to test whole-plant moisture of chopped corn to assure yourself that acceptable fermentation will occur. Use a microwave, an electronic forage tester, or the "grab-test" method for your determination.
  2. Follow precautions regarding dangers of nitrate toxicity to livestock (especially with green-chopping) and silo-gasses to humans when dealing with drought-stressed corn.
  3. Keep in mind that "normal" guidelines for determining when to harvest corn for silage will be useful for many, if not most, corn fields. These include using the kernel milkline, and beginning to harvest after the dent stage, when the milkline has moved towards the kernel tip.
  4. Growers need to carefully monitor, inspect and dissect plants in their own fields as to plant survival potential, kernel stages, and plant moisture contents in determining when to begin silage harvest. Fields and corn hybrids within fields vary greatly in stress condition and maturity.

In order to estimate pre-harvest silage yields, the National Corn Handbook publication "Utilizing Drought-Damaged Corn" describes methods based on either corn grain yields or plant height (if little or no grain yield is expected).

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/acre of 30% dry matter silage (3 tons/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 example, corn yielding 125 bushels of grain per acre, corn silage yields will be 18 to 20 tons per acre at 30% dry matter (5 to 6 tons per acre dry matter yield). See also Table 2 in A1178 "Corn silage for the dairy ration."

Plant height method for estimating silage yield: If little or no grain is expected, a rough estimate of yield can be made assuming that 1 ton of 30% dry matter silage can be obtained for each foot of plant height (excluding the tassel). For example, corn at 3 to 4 feet will produce about 3 to 4 tons per acre of silage at 30% dry matter (about 1 ton per acre of dry matter).

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