Handling Drought-Stressed Corn
August 21, 2003 10(22):151-153
Joe Lauer, Corn Agronomist
Overall, the 2003 corn crop has experienced good to excellent growing conditions
until about two weeks ago. Yield potential is still good for early-planted corn,
at this point in time, throughout much of the state. However, more and more fields
are experiencing drought conditions. Stressed fields usually have lighter, sandy
soils and were planted late. The general appearance of these fields include: short-statured
plants, plants with leaves which are brown over halfway up the plant, often past
the ear leaf, and kernels beginning to dent prematurely. Leaf death due to drought
usually progresses upwards from the base of the plant.
Drought-stressed corn can be grazed or used for forage, either as green chop or
silage. Because of the potential for nitrate toxicity, grazing or green chopping
should be done only when emergency feed is needed. The decision to chop corn for
silage should be made when:
- You are sure pollination and fertilization of kernels
will not or did not occur and that whole-plant moisture is in the proper
range for the storage structure so that fermentation can occur without seepage or
spoilage losses. If there is no grain now, florets on the ear were either not pollinated
or have not started to grow due to moisture stress, and the plant will continue
to be barren. If the plant is dead, harvest should occur when whole plant moisture
is appropriate for preservation and storage.
- 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 proper range for
the storage structure. These kernels may grow some now, if the plant is not dead
and in those fields receiving rain. If kernels are growing dry matter is accumulating
and yield and quality of the forage is improving.
Green, barren stalks will contain 75-90% water. If weather remains hot and dry,
moisture content drops, but if rain occurs before plants lose green color, plants
can remain green until frost. Drought stressed corn has increased sugar content,
higher crude protein, higher crude fiber and more digestible fiber than normal corn
silage. Drought generally reduces yield and grain content resulting in increased
fiber content, but this is often accompanied by lower lignin production that increases
fiber digestibility. In seasons where the drought comes at the end of the season,
sometimes the grain content is reduced but the stalks are large and well lignified,
so the fiber digestibility is not increased.
A few cautions and suggestions:
- Be sure to test whole-plant moisture of chopped corn to assure yourself that
acceptable fermentation will occur. Use a forced air dryer (i.e. Koster), oven,
microwave, electronic forage tester, NIR, or the rapid "Grab-Test" method
for your determination. With the "Grab-Test" method (as described by Hicks,
Minnesota), a handful of finely cut plant material is squeezed as tightly as possible
for 90 seconds. Release the grip and note the condition of the ball of plant material
in the hand.
- If juice runs freely or shows between the fingers, the crop contains 75 to 85% moisture.
- If the ball holds its shape and the hand is moist, the material contains 70 to 75%
- If the ball expands slowly and no dampness appears on the hand, the material contains
60 to 70% moisture.
- If the ball springs out in the opening hand, the crop contains less than 60% moisture.
- The proper harvest moisture content depends upon the storage structure, but is the
same for drought stressed and normal corn. Harvesting should be done at the moisture
content that ensures good preservation and storage: 65-70% in horizontal silos (trenches
and bunkers), 60-70% in bags, 60-65% in upright stave silos, and 50-60% in upright
oxygen limiting silos.
- Depending upon farm forage needs, raising the cutter-bar on the silage chopper reduces
yield but increases quality. For example, raising cutting height reduced yield by
15%, but improved quality so that Milk per acre of corn silage was only reduced
3-4% (Lauer, Wisconsin). In addition the plant parts with highest nitrate concentrations
remain in the field (Table 1).
Table 1. Nitrate concentration of various corn plant partsts.
Upper 1/3 of stalk
Middle 1/3 of stalk
Lower 1/3 of stalk
derived from Hicks, Minnesota
- If drought-stressed corn is ensiled at the proper moisture content and other steps
are followed to provide good quality silage, nitrate testing should not be necessary.
However, it is prudent to follow precautions regarding dangers of nitrate toxicity
to livestock (especially with grazing and green-chopping) and silo-gasses to humans
when dealing with drought-stressed corn. Nitrates absorbed from the soil by plant
roots are normally incorporated into plant tissue as amino acids, proteins and other
nitrogenous compounds. Thus, the concentration of nitrate in the plant is usually
low. The primary site for converting nitrates to these products is in growing green
leaves. Under unfavorable growing conditions, especially drought, this conversion
process is slowed, causing nitrate to accumulate in the stalks, stems and other
conductive tissue. The highest concentration of nitrates is in the lower part of
the stalk or stem. If moisture conditions improve, the conversion process accelerates
and within a few days nitrate levels in the plant returns to normal. Nitrate concentration
usually decreases during silage fermentation by one-third to one-half, therefore
sampling one or two weeks after filling will be more accurate than sampling during
filling. If the plants contain nitrates, a brown cloud may develop around your silo.
This cloud contains highly toxic gases and people and livestock should stay out
of the area. The resulting energy value of drought-stressed corn silage is usually
lower than good silage but not as low as it appears based on grain content. The
only way to know the actual composition of drought-stressed corn silage is to have
it tested by a good analysis lab.
Marshfield Plant and Soil Analysis Laboratory
8396 Yellowstone Dr.
Marshfield, WI 54449-8401
Phone: (715) 387-2523
A & L Great Lakes Laboratories
3505 Conestoga Drive
Fort Wayne, IN 46808
Phone: (219) 483-4759
- 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 as a guide and taking whole-plant moisture samples to
actually determine harvest date, and beginning to harvest after the dent stage,
when the milkline has moved towards the kernel tip.
- 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. Often questions arise as to the value of drought-stressed
corn. 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).
Below is a summary of this publication.
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."
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).
Other Key References
Utilizing Drought-Damaged Corn (NCH-58)
Weather Stress in the Corn Crop (NCH-18)
Growing Season Characteristics and Requirements in the Corn Belt (NCH-40)