Feb/March 1998
Proper Sampling Ensures More Consistent Grain Test Results
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Prairie Grains is the
official publication of
the Minnesota
Association of
Wheat Growers,
North Dakota Grain
Growers Association,
South Dakota Wheat,
Inc., and the
Minnesota Barley
Growers Association.
One question asked of Michael D. Peel, NDSU Extension Small Grains Specialist this winter: "will vomitoxin levels increase in the bin?" Under normal storage conditions the answer is no, but let's examine this just a bit.
Vomitoxin is produced by the fungi Fusarium graminearum, and under conditions favorable for growth it could be active in stored grain resulting in increased vomitoxin levels. Favorable conditions include moisture levels of 22% or higher and temperatures in the 50 - 85o F range. Grain stored in these conditions will certainly have problems including storage mold growth resulting in heating and caking. In the absence of these conditions, vomitoxin certainly will not increase.
It is easy to understand why there are questions about vomitoxin in stored grain. It is not uncommon to have a grain sample tested for vomitoxin only to find when the same grain is delivered to the elevator, a second test indicates higher vomitoxin levels. It sounds conniving, but there are also instances when that second test has indicated lower vomitoxin levels.
The most likely explanation for discrepancies between tests for vomitoxin is sampling technique. Obviously, a load of grain in a truck is not a homogeneous mixture of infected and non-infected kernels. When vomitoxin levels are tested on individual kernels, 10 to 100 kernels may be tested before one is found that has detectable levels, and then the range may be from 1 to 600 parts per million (ppm). Imagine how two samples, each from the same truck load, will test if one sample has one kernel per thousand with 100 ppm vomitoxin and the other has two kernels per thousand each with vomitoxin levels above 100 ppm. The results will be dramatically different.
The key to accurate determination of vomitoxin levels is to ensure the sample tested represents the entire seed lot. Imagine a field that had scab in it last year: Was the level of scab across the field uniform? Probably not, and this non-uniformity was undoubtedly transferred from the combine to the truck to the grain bin and so on.
To ensure a representative final sample, the number, location and size of the sample is critical. When sampling a truck or bin both the center and edges should be sampled with a probe, and the probe should ensure the integrity of the sample. A minimum of seven probes should be made, avoiding the extreme edges, that represent the various regions of the container sampled. Each sample should represent the entire depth of the grain, not just the top one or two feet.
The most consistent results will be achieved by having the testing lab grind the whole sample thoroughly, and mixing the ground sample before taking a sub sample for final testing. Since this is probably not feasible, the grain from each probe should be combined and thoroughly mixed and a sub sample of this be tested.
Keep in mind the variability between test levels of vomitioxin of the same seed lot are representative of sampling technique; how your grain is sampled can make all the difference in the world.
Determining kernel counts, viability
Now onto planting preparations for the upcoming growing season. To ensure optimum plant densities, the weight and viability of the seed to be used must be known. Kernels per pound vary with variety and seed lot; obtaining this information and seed viability is essential to achieve a specific plant density when planting.
When planting certified seed, percent germination and kernels per pound are included on the certification label. In North Dakota, certified seed can be sold in bulk but a certificate must be provided with the seed containing the same information as bagged seed.
When using bin run seed, the same information is equally important and can be obtained quite easily. Having bin run seed conditioned will pay dividends and should be done before kernel weight and percent germination are determined.
Whether sampling to determine vomitoxin levels, percent germination, or kernel weight on a seed lot the technique is the same. To determine germination simply lay 200 (or more if you feel inclined) randomly selected seeds from your sample on heavy duty paper towels, role the towels up and secure the role with paper clips, wet the towel and place it in a bread bag. Then place it in a location that remains about 50o to 60o F. After two days count the germinated seed and divide by the total tested, and you have percent germination.
Determining seed weight is even more simple. From the same sample count out 1,000 kernels and weigh them using a scale that's accurate to a tenth of a gram or a hundredth of an ounce; bathroom scales won't cut it here.
Most sensitive scales weigh in grams. This is easily converted to pounds by dividing into 453.6 (there are 453.6 grams per pound). If your 1,000 kernels weigh 32.4 grams then (453.6 ÷ 32.4) x 1000 = 14,000 kernels per pound. Or if your 1,000 kernels weighed 1.14 oz, then (16 ÷ 1.14) x 1000 = 14,035 kernels per pound. Now if you want to plant 1.25 million live seeds per acre, calibrate your drill for {1,250,000 ÷ 14,000 ÷ 0.90 (percent germination) = 99 pounds per acre.
This should give you something to help meet the itch of the next growing season.
USDA official: coffee can sampling worthless
Roger Friedrick, with USDA's Grain Inspectors, Packers, and Stockyards Administration (GIPSA) said that vomitoxin, as a mycotoxin, is unevenly distributed (unlike protein and moisture). So "using the coffee can in the truck is pretty much a waste of the money you spend on testing," he told growers, at the Red River Valley Barley Day last month in Grand Forks.
Even in high-tech laboratories, studies have shown that in a 1 part per million sample, deviation can be up to 50% within the same lab, and even more between different labs testing the same sample.
One part per million (ppm) is equal to 0.0001%. There are approximately 10,000 kernels of barley in a pound. So, 1 ppm is equal to one kernel in a 100 lb. sample.
Friedrich outlined some things that grain handlers can do to make sample consistency more likely:
Get a 2 to 5 lb sample by probing inbound lots in several locations (use a diverter-type mechanical sampler to sample outbound lots).
Use a Boerner divider to get a 100 to 500 gram representative subsample.
Grind the ENTIRE subsample and mix thoroughly with a clean spatula for 30 seconds. (Friedrick noted that this is where most fail: Either they don't grind all of it or they don't mix it thoroughly. This makes the entire process worthless, he emphasized).
Measure out at least a 50-gram portion for analysis.n