STRAIGHT FROM THE HORSES MOUTH

Duane A. Lienemann,
 UNL Extension Educator,
Webster County
August 25, 2012 Edition

There will be some years in Nebraska when, even following the recommended management practices, that the rainfall is not sufficient to support profitable grain yields. I don’t think it is a secret that this is one of those years. This is particularly true on our dryland corn fields. Drought, environmental challenges and insect pressure can cause problems such as molds and most critically Aflatoxins. We will discuss that later, let’s first look at what may be more prevalent, the high potential for high nitrate levels in many plants, including those that may be destined for livestock feed.
High Nitrates: When grain crops have been established satisfactorily, and rainfall is insufficient to support grain yields for economic harvesting, alternative uses of the crop should be considered very cautiously. This is especially true with respect to fields which have been fully fertilized with nitrogen for normal yields. Crops which are sufficiently drought-stressed that grain yields will be too low for harvest, and the alternative of harvesting the crop for its forage value is considered, the producer might want to consider collecting stover samples and have them analyzed for excessive nitrates. Plants that are stressed by drought may accumulate nitrate to lethal levels. Nitrates will not decrease in harvested crop plants but can be cut almost in half by making the forage into silage. Therefore it is very important to have the nitrate test run on the plant tissue before it is either grazed or mechanically harvested for livestock consumption.
Of course the best way is to take the samples to a professional lab but there is a quick and easy test that the farmer can do to determine if he should take samples in for quantitative tests. The diphenylamine quick test has been used in the field to determine tissue nitrate levels greater than 1 percent. The reagent is composed of 0.10 gm of diphenylamine salt dissolved in 30 ml of sulfuric acid. When contained in a bottle with an eye dropper, the solution can be dribbled onto the exposed pith of split corn stalks and the reaction observed. Within seconds, a blue or blue-black coloration will develop if high amounts of nitrates are present. Faint tinges of blue that rapidly dissipate are considered safe.
It should be noted that the test is not quantitative, but it may be useful to determine the need for more accurate testing at a commercial laboratory. The plant to be tested should be cut at the soil level and the stalk split lengthwise, with the exposed pith facing upward. Either place it on the ground or hold it at a 45-degree angle away from you. Allow some test solution to fill the dropper and let a drop fall on the pith 2 to 3 inches from the base of the stalk. Let another fall about 8 inches up, and place others further up the stalk. You will generally find that the reagent immediately turns dark blue or black where nitrates are present at levels greater than 1 percent. If you split an ear, a leaf midrib, or a tassel, you would probably find only a mild tinge of blue or no color change at all. It is the bottom 12 to 18 inches of stalk that contains most trapped nitrates. Now if you find that you suspect high nitrates and you need the feed we better sample.
Stover samples should be collected which includes the whole plant as will be harvested. The equivalent of five corn or sorghum plants should be submitted for nitrate analysis. It should be remembered that nitrates in the lower stalks will likely be higher than that in the leaf tissue. Therefore, before harvesting drought-stressed crop plants as forage, the nitrate content of a representative sample of these plants should be determined. Nitrate analyses of samples may be obtained from several agricultural laboratories the closest of which are Servi-Tech in Hastings and Ward Laboratories in Kearney.
Corn and sorghum stubble, or corn and sorghum fields, which are too dry to make a crop, can be utilized by livestock through haying, silage or grazing. If tests indicate that you are relatively safe you may want to consider some options for the drought-effected crop. It should be pointed out that corn, sorghum and even weed plants that contain more than 1 percent nitrates (on a dry matter basis), may result in livestock death when fed or grazed. Even if the animals survive this level of nitrates, other economic losses may occur, such as: abortion, weak or poor viability of recently born young, infertility and difficulty in conception, lameness, and decreased milk production.
Aflatoxin in Corn: Drought and high temperatures promote development of the disease Aspergillus ear rot. The fungi that cause this disease (most commonly, Aspergillus flavus) can produce aflatoxin. Aflatoxin is one of many chemicals in a group known as mycotoxins that are produced by fungi (molds). Mycotoxins, such as aflatoxin, can be toxic to animal and human consumers and, at certain concentrations, can lead to dockage or rejection of grain at elevators. These molds are usually found in fields that sustained substantial drought damage leading to early maturation and plant death. Farmers and crop consultants can scout high risk fields for Aspergillus ear rot as an indicator for aflatoxin, but only lab testing of grain samples can accurately identify the concentrations of aflatoxin in the grain. The highest risk fields include: drought-damaged fields, including rainfed (dryland) fields and non-irrigated pivot corners. Fields or areas with higher incidence of corn ear-feeding insects, such as the corn ear worm and rain damaged before or during harvest or after harvest while in storage. I understand that many terminals and grain elevators are using black lights to check for aflatoxin contamination in loads of grain. The component that produces fluorescence under black light is called kojic acid. Although kojic acid is produced by the same fungus that produces aflatoxin, its presence is not necessarily an indicator of aflatoxin and might lead to false positive results and unnecessary rejection of grain. Just be prepared for testing for this mold on your grain!

The preceding information comes from the research and personal observations of the writer which may or may not reflect the views of UNL or UNL Extension. For more further information on these or other topics contact D. A. Lienemann, UNL Extension Educator for Webster County in Red Cloud, (402) 746-3417 or email to: dlienemann2@unl.edu or go to the website at: www.webster.unl.edu/home