Toxicity in Drought-Stressed Corn Silage and Other Annual Forages
Sid Bosworth, Extension Associate Professor,
Department of Plant and Soil Science, University of Vermont email@example.com
major concern with drought stricken corn is the potential for nitrate accumulation
and toxicity. Drought stricken fields of corn, sorghum and sudangrass
are the most likely crops to accumulate nitrate, particularly those fields
that are heavily fertilized with manure or nitrogen. As crop growth
slows down or ceases during periods of dry weather and drought, nitrates
will often buildup in the soil. When rain finally occurs and crop
growth resumes, there can be a sudden uptake of the accumulated nitrate
and for a while, plant nitrate levels will be higher than normal and pose
a risk of toxicity to animals consuming the crop. Below are a few
suggestions for managing nitrate risk:
Do not feed green chopped corn silage. Let it
completely ferment before feeding. The ensiling process itself will
usually convert more than half the nitrate into ammonia, which can be utilized
by rumen bacteria.
Don't chop immediately after the relief of drought stress.
After an extended dry spell, nitrates will rapidly accumulate in plants
as soon as they resume taking up water. Only as the plants resume
photosynthesis and growth will the excess nitrates be converted into plant
proteins. This may take a few to several days depending on the severity
of the drought.
Chop high. This is a difficult recommendation
since corn will be low in yield during a dry year, but nitrate tends to
accumulate most in the lower stalk.
Test for nitrates - If you suspect a problem, have the
forage tested for nitrate levels - but wait until the forage is in the
state that you intend to feed it (i.e., ensiled). For forage nitrate
(NO3) levels fed to dairy cattle, below 0.44% of dry matter is considered
safe and above this should be carefully diluted to a total ration of 0.40%.
Above 1.5% is considered extremely toxic and should be avoided.
Chop Drought-Stressed Corn
Another question is "when do I chop?" The answer
depends on the condition of the corn. If there was no pollination
and fertilization of kernels, then the corn should be chopped as soon as
whole plant moisture reaches 55% to 70% (depending on type of silo).
Be sure to test whole-plant moisture of chopped corn using either a microwave
or a Koster moisture tester.
If pollination and fertilization of kernels did occur,
then be sure the plants have a chance to reach the optimum maturity to
maximize yield and quality. Observe the kernels for maturity and
monitor whole-plant moisture for 55% to 70% range.
This site is maintained by Sid.Bosworth@uvm.edu,
Plant & Soil Science Department, University of Vermont.
Issued in furtherance of Cooperative
Extension work, Acts of May 8 and June 30, 1914, in cooperation with the
United States Department of Agriculture. University of Vermont Extension,
Burlington, Vermont.University of Vermont Extension and U.S. Department
of Agriculture, cooperating, offer education and employment to everyone
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