C.O.R.N. Newsletter 2012-31

Dates Covered: 
September 18, 2012 - September 25, 2012
Editor: 
Greg LaBarge

Alfatoxin in the 2013 Corn Crop and the Potential Impact on Its Use for Livestock

Sampling and Testing in Grain: A Recap

Reports of aflatoxin contamination of corn continue to come in from some parts of the state, especially those areas most severely affected by drought conditions. There have also been reports of a few loads of grain being docked at some elevators due to aflatoxin levels above thresholds. Producers in affected areas are encouraged to continue sampling and testing grain for aflatoxin in order to determine whether or not the grain is contaminated and at what level. These are the first and most important steps when making decisions as to what to do with contaminated grain.

In last week’s C.O.R.N newsletter article (http://corn.osu.edu/newsletters/2012/2012-29/#3) we provided guidelines for sampling and testing for aflatoxin, and grain handling to minimize toxin buildup in storage. In this week’s newsletter, we provide a quick recap of testing and sampling protocols, alone with guidelines for feeding contaminated grain to animals.

Remember, toxin contamination is never uniform throughout a grain lot; therefore it is extremely important to pull multiple samples from every part of the lot in order to obtain a representative sample. When sampling from the grain stream, collect samples at regular intervals. Pool and mix the individual samples into one composite sample from which about 5-10 lb. of grain should be sent for testing.

The black-light or UV light test can be use used as an initial screen for aflatoxin, but should not be relayed upon as conclusive evidence of the presence or absence of aflatoxin. Other particles in the sample may also glow under UV light, giving a false positive result.

Commercial quick-test kits are better than the black-light test in that they are specific for aflatoxin. However, several of these tests are only qualitative or semi quantitative, meaning that they tell you whether or not the grain is contaminated or whether the level of contamination is within a certain range, but do not provide precise estimates of the levels of contamination.

By far, the best way to test for aflatoxin is to send samples to an analytical laboratory. Tests from these labs are usually accurate and provide quantitative estimates of the level of contamination. Grain usage and marketing decisions such as dockage and price discounts should be made based on results from analytical lab tests rather than black-light or commercial quick tests.

Animal Use

With the increased risk for alfatoxins in drought-stressed corn, the use of this corn for animal feed needs careful evaluation. The toxicity of the aflatoxin is affected by the amount consumed by the animal and the duration of the consumption, and there are differences among species on the sensitively to aflatoxin toxicity. Aflatoxin accumulates in the liver of the animal, and thus affects the metabolism of this key organ.

The subclinical effect is most often reduced performance (growth or milk yield) and thus reduced feed efficiency. High concentrations for extended periods can result in liver damage and death. In general, the sensitivity of the species is (from highest to lowest sensitive): swine and poultry, horses, and ruminants (sheep and cattle). With contaminated corn, the risk is higher with the species that consume diets highest in grain concentration (e.g., swine and poultry; horses and ruminants consume a lot of forage). Diets for swine, poultry, and horses should not exceed 200 ppb. Diets with as much as 400 ppb fed to feeder cattle can result in tissue residues of aflatoxin.

Besides the health of the animal, aflatoxin consumption by dairy cattle needs to be monitored to prevent aflatoxin concentration in milk from exceeding tolerances set by the Food and Drug Administration (FDA).  The FDA limit is 0.5 ppb for aflatoxin in milk, which has been the limit for many years. Just recently, some milk processing companies have sent out letters to dairy producers about the aflatoxin contamination issue and how the milk will be handled, indicating that if the producer’s milk is found to exceed 0.5 ppb that the milk must be dumped and the producer incur the loss. There is about a 1% transfer of aflatoxin in the diet to the milk.

As mentioned earlier, dairy cattle consume a large portion of their diets as forage. So if the grain had 20 ppb and it is fed in a diet for dairy cattle that’s 50% forage/50% concentrate and the contaminated corn made up 80% of the grain, then there would be about 8 ppb aflatoxin in the TMR. Then with a 1% transfer, there is the potential for 0.08 ppb aflatoxin in milk – 6.25 times below the threshold level.

The primary approaches to prevent problems with aflatoxins on animals or their products is to:

  1. avoid feeding contaminated grain if possible,
  2. if contaminated grain is feed, it should be diluted with un-contaminated grain and/or with forage to lower the dietary contamination to a low risk level,
  3. or add a mycotoxin binder to the diet to reduce the absorption of the aflatoxin. Several of these binders are available commercially and should be used according to the label.

Adjusting Fertility Programs for Lower than Expected Yields

Yield expectations across Ohio are variable based on summer rainfall patterns, so nutrient management strategies will vary greatly. Several good articles from states across the Midwest have highlighted some considerations for adjusting 2013 fertility programs based on lower than expected yields in 2012 (see references below).  Below are some highlights from these articles and past Ohio experiences to consider.

Phosphorous and potassium management:

Phosphorous and potassium are fairly immobile in soil and predictable in crop utilization. Even with newer hybrids and varieties, removal rates are similar enough that book values can be used to estimate nutrient removal from the harvested portions of crops. Phosphorus and potassium removal rates based on Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa bulletin E-2567 are shown in Table 1. To estimate phosphorus and potassium removal, yield is multiplied by nutrients removed per unit of yield.  The table below shows nutrients removed per unit area plus spaces to enter crop yield and removal based on actual yield. Unused fertility can be credited to next year’s crop if annual fertilizer applications are made. If two-year fertilizer applications were made, soil test prior to the 2014 crop.

Table 1. Estimating Nutrients Removed in Harvested Portions of Agronomic Crops.

 

Nutrients Removed per unit of Yield (lb/unit of yield)

Removal based on Actual Yield (lb/A)

Crop

Unit of Yield

Actual Yield (Unit of Yield/A)

P2O5

K2O

P2O5

K2O

Corn

 

 

 

 

 

 

Grain

Bushel

 

0.37

0.27

 

 

Silage

Ton

 

3.30

8.00

 

 

Soybeans

Bushel

 

0.80

1.40

 

 

Alfalfa

Ton

 

13

50

 

 

Nitrogen management:

Nitrogen is an expensive nutrient, and drought-affected areas with lower than anticipated yields may have excess nitrogen in the form of nitrate. Nitrate is subject to los via leaching (when soils have more incoming water than the soil can hold) and denitrification (when soils are waterlogged). Leaching and dentrification are both less likely to occur under drought conditions.  In a normal growing season, we would not expect nitrate levels to be adequate for the next year’s crop because of loss due to crop removal as well as by denitrification and/or leaching. A fall crop (winter wheat) or cover crop may recover the residual soil nitrogen. However, it is difficult to predict nitrogen uptake of crops and subsequent nitrogen release.

A presidedress soil nitrate test (PSNT)  measures soil nitrate-nitrogen and can be used to predict the likelihood of corn grain yield response to sidedress nitrogen application.  The PSNT is primarily used on soils that had cover crops planted or manure applications. To attain a representative soil sample, collect 15, 1-ft deep random cores from a field and mix them thoroughly. Submit a grab sample from the composite to a reputable lab. If the nitrate-nitrogen level in the soil is between 25-30 ppm then additional nitrogen is probably not warranted. Nitrate-nitrogen levels lower than 25 ppm have an increased likelihood of yield response, but the rates should not be greater than 70 lbs N/A (assuming N was applied prior to or at planting). Work out of Illinois reveals that application of only 50 lbs N/A results in maximum yield over a wide variety of growing conditions.

Soil Testing

If you use soil test results to track trends on your farm, which is a good practice to monitor fertility programs, you may note some soil test results this fall that do not follow trend. Dry soils can affect soil chemistry, soil structure, short-term nutrient cycling and ultimately soil test results. Wait until more normal soil moisture conditions before taking a soil sample. Make sure the soil probe can get into the ground to your standard soil sampling depth of 6-8 inches. Factors which may be affected by dry soil are:

pH- Water pH maybe 0.1-0.3 units more acidic but differences in buffer pH used to calculate lime recommendations are not large or consistent so lime recommendations will not be different under dry conditions.

P&K- Soil K levels are influenced by dry soil. Soils with low K may show an increase in soil test K while soils with high K may show a decrease in soil test K. Soil P test results probably will be affected little by dry soil conditions.       

References:

Phosphorus, Potassium and pH Management Issues Following Drought-damaged Crops. Mallarino, A.  and Sawyer, J. http://www.extension.iastate.edu/CropNews/2012/0823mallarinosawyer.htm [verified 13 September 2012.]

Cover Crops Following the Summer 2012 Drought. Kladivko, E. https://ag.purdue.edu/agry/extension/Documents/CoverCropsFollowingDrought.pdf [verified 13 September 2012]

The presidedress soil nitrate test for improving N management in corn. Sylvie M. Brouder and D.B. Mengel https://www.agry.purdue.edu/ext/pubs/AY-314-W.pdf  [verified 13 September 2012]

Nutrient Management Related to Dry Soil Conditions and Poor Crop Yields.  Jim Camberato and Brad Joern.  http://www.agry.purdue.edu/ext/soilfertility/droughtnutrients.pdf [verified 17 September 2012]

How Reliable Will This Year's Test Plot Data Be?

Ohio's corn and soybean crops experienced a host of problems in 2012, including record high temperature and severe drought in addition to localized violent thunderstorms associated with strong winds and hail. Agronomists often question the value of test plot data in years like 2012 when adverse growing conditions severely limit yield potential. Severe stresses can undermine the value of test plot performance data.

The validity of test plot results depends primarily on whether effects of the varied stress conditions are uniform across test plots. If not, test plot data may be questionable.  To be certain that effects of stress were fairly uniform, it would be necessary to monitor test plots on a regular basis to determine crop response to the various stresses as they occurred; however, such monitoring was probably unlikely in many test plot fields.

Another problem with test plot results is that the various yield limiting factors may accentuate the natural "variability" already existing in the field, and may thereby further "mask" the true treatment effects that are being compared. Stress conditions coupled with slight differences in soil organic matter, drainage, weed control, etc. across a field may magnify differences in crop performance.  Many fields (planted with the same maturity group) are showing differences in soybean maturation due to soil variability.

If one assumes that the varied stress conditions affected test plots uniformly within a field, then interpretation of test plot data becomes an issue. This issue can be especially relevant when evaluating results of a hybrid and cultivar performance trials severely affected by drought. Did a hybrid yield well under drought stress because it genuinely possesses some drought resistance or because it "escaped" the impact of high temperatures and drought by flowering before or after the worst of the stress? If it was the latter, then the hybrid's superior performance may be of limited value under different drought conditions in the future. In past years, we have sometimes observed that if a drought occurs late in the season then early maturing hybrids will have an advantage over later maturity hybrids; if the drought occurs earlier, but is broken by rains later in the season, then the full season hybrids may have the advantage.  Similarly, early maturing soybeans near physiological maturity may not have benefited as much from late-season rainfall as late maturing soybeans with seeds that were still filling.

Test plot information this year can still be very useful but take precautions. Results from single on-farm strip tests should not be used to make a decision on adoption of a treatment or variety. Even replicated data from a single test site should be avoided, especially if the site was characterized by abnormal growing conditions. Use test plot data from multiple sites (and preferably from at least 2 years of testing) and inquire about the weather patterns and conditions associated with the results. Look for consistency in a product or variety's performance across a range of environmental conditions.

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Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.