University of Vermont

Nitrate Toxicity and Drought Stressed Corn Nitrate Toxicity in Drought-Stressed Corn Silage and Other Annual Forages

Sid Bosworth, Extension Associate Professor, Department of Plant and Soil Science, University of Vermont sid.bosworth@uvm.edu



A 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.


When to 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.

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Last modified May 26 2004 01:29 PM

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