With the Arkansas Soybean Promotion Board’s financial backing, a multi-year, comprehensive study on soybean seed quality kicked off in 2008. Conducted by a large team of University of Arkansas and Extension researchers, the project aims to bring growers answers to a bevy of questions.
At the recent Arkansas Soybean Research Conference in Brinkley, Ark., Rick Cartwright provided an assessment of the project’s first year (for more see ).
“The issue is this: you pay a lot for soybean seed with a lot of good traits, but sometimes it doesn’t come up,” said the University of Arkansas plant pathologist. “That can mean there’s a lot of expense and work involved in replanting and working things out with the seed companies. This is a complex issue. It isn’t always the seed (that’s the problem) but environmental factors and so forth. We’re conscious of that.”
While many environmental factors are beyond control, “we can do something about understanding the seed quality better so we at least know what’s being planted.”
Pointing to a picture of a patchy field, Cartwright called it a good example of what happens during the “hot, dry period in June and July (Arkansas) often has — or planting soybeans after wheat. The seed is planted down into moisture and one seed lot will come up and another won’t. Or, even within the same seed lots, some seed germinate and push through and others don’t make it.”
All the seeds may even germinate but only a couple of them make it out of the ground. The reason for the successful seeds could be due to better vigor, “a very complex term.”
To test vigor, seed is often subjected to many tests including cold temperatures, accelerated aging under hot, humid conditions, and membrane leakage tests. Seed that does well in the tests has good vigor and better potential to produce a normal seedling in a hostile environment.
On the other hand, the end result of lower seed quality — “and that was the case last summer — are skippy stands, irregular stands or a replant situation.”
To better understand quality of soybean seed, a University of Arkansas lab has been set up “where we can accurately assess germination and vigor to try and determine quality of different seed lots and test quality measurement under Arkansas storage and planting conditions. The University of Arkansas Division of Agriculture provided money for the equipment (to outfit the lab). Then, we hired a seed analyst and entered into an agreement with Ohio State University for the Seed Vigor Indexing System, a computer vision system that looks at germinating seedlings and gives an idea of germination speed and uniformity, both related to vigor. That program is now being used in the Midwest by public and private labs and potentially takes out some of the human element of judging seed quality and speeds things up.”
Setup and findings
At the growing season’s start, researchers also set up a planting seed quality survey. Many Arkansas growers sent in samples. Three labs were used for the sample analysis: Arkansas State Plant Board lab, the Kentucky Seed Testing Laboratory, and the University of Arkansas lab.
“We collected over 440 samples from April through July and asked the cooperators for an estimate of the stand that emerged from the seed the sample was collected from. That led to a big database of many things associated with the fields planted in the seed. We’re still wading through all that information.”
Tests conducted by the labs on 2007-produced seed — “and we knew about this from the seed industry, anyway” — showed there was a vigor problem. After accelerated aging, “the rule of thumb” says good seed is indicated if it has a germ of 65 percent or better. Of the project survey samples tested by the Plant Board and Kentucky labs, 41 to 65 percent had accelerated aging germ readings of less than 65 percent.
About half the fields that samples were pulled from were also visually assessed. Researchers found “good to excellent” stands on 48 percent. Those proved to have an 85 percent germ and 71 percent accelerated aging. “Fair” stands were found on 41 percent of the fields checked with the germ still good at 83 percent while accelerated aging, at 64 percent, “had dropped to marginal.” Eleven percent of the fields were assessed “failure” with a germ of 78 percent and accelerated aging of 58 percent.
“To me, based on these data, the standard germ test is one measurement of quality but didn’t appear to be as important in these samples as the accelerated aging test results, which estimate seed vigor.”
Checking simple germ test, Cartwright graphed the results of the samples tested in the Plant Board’s lab versus the Kentucky lab. “There was a very good relationship between the two labs on germ.” The same was true in comparisons with the University of Arkansas lab.
When looking at the accelerated aging test “the relationship between labs is a bit more variable, but still (solid). I’d certainly take the consistency between labs for accelerated aging if it represented data from much of my other research.”
Researchers are also running the samples through the aforementioned Seed Vigor Indexing System system, which uses a high-resolution scanner with proprietary software. It looks at germinating seeds three days after they’ve been placed in a test and can be used in conjunction with an accelerated aging chamber, a standard germination test or other tests.
“This machine will interpret vigorous growth and provides a number which correlates well with the quality of seed as indicated by standard germ tests or vigor tests, including the accelerated aging test.
“The good thing about this in the preliminary tests is you can run the same sample through several times and, as long as you don’t change things greatly, the same number (results). On the other hand, if you allowed three people to assess the same samples, we get more variability in results. Using this system potentially reduces human error.
“We’ll be working with this quite a bit and see if it can be adapted to use in the South. It’s already been adopted by the Ohio Crop Improvement Association” and its Wisconsin counterpart.
There is a genetic aspect to soybean seed that Mid-South researchers — including the University of Arkansas’ Pengyin Chen, a soybean breeder, and Rusty Smith, a USDA soybean geneticist at the ARS facility in Stoneville, Miss. — have been studying.
“Genetics in some of the soybean lines can lead to improved seed quality. Those genes will continue to be measured.”
Chen is also working on other aspects of soybean seed like size and coat toughness that may have influence on seed quality. “There are also genes for resistance to phomopsis seed decay and, potentially, purple seed stain. (Chen) has a graduate student studying those. They’re crossing with those genes and trying to come up with lines resistant to diseases.”
In this first year of the project, John Rupe, University of Arkansas plant pathologist, planted the “same variety of seed having three levels of quality in two locations: Poinsett County and Keiser. They were planted at different seeding rates, with and without seed treatments, etc. As expected, the stands were greatly affected by seed quality — especially vigor as measured by accelerated aging. Fungicides did a pretty good job of increasing stand, especially on the lower-quality seed samples — a 23 percent increase at the Poinsett County location, 30 percent at Keiser.
Harsh or normal?
“Everyone said, ‘planting conditions were harsh late in June and July.’ But, to me, that’s pretty normal here in Arkansas. That’s something we need to overcome one way or the other. If we’re going to plant soybeans in the summer, we’ve got to have seed, management and planting options that allow us to get a stand in the normal, albeit harsh, conditions of the Mid-South.”
Most of the calls Cartwright and colleagues received on stand failures came in after June 10.
Among the seed samples collected, seed vigor as measured by accelerated aging declined over time across the samples while the standard germ measurement required on seed bags did not.
“Based on what we saw this year, if I were planting in June and July, I wouldn’t think standard germ information alone was enough to make the best decisions. It’s probably okay for optimum conditions since the test is conducted under those conditions to provide the seed the best chance to germinate. But in tougher conditions, like those in Arkansas, you need to know more about the seed you’re paying for. In addition to the germ on the bag, I would have the seed sampled and tested for vigor using the accelerated aging test before planting in June or July. …Testing of seed for vigor should be done as close to planting as possible — and it takes two weeks, or so, to get test results back.”
Other Cartwright suggestions:
• Ask your seed company or dealer if vigor testing was done on the seed you’re buying. If so, what were the results?
“Many companies don’t mind sharing this information. However, you should remember that vigor can decline over time so you may still need to test the seed closer to planting to be sure it’s still vigorous.”
• Keep reference samples in a cool, dry place until needed.
In many cases, “farmers won’t receive the seed they bought until a day, or so, before planting. In these cases, I would keep 1 to 3 pounds of the seed from each lot in a paper bag in an air-conditioned room until the stand emerges, or doesn’t. Then, I’d decide to have the seed tested, or not. Keeping a ‘reference’ sample is a good idea regardless, since in the case of a stand failure, you’d have an example of the seed planted.”
This winter, “we’ll be providing more information on the type of bags, testing labs available, etc., to Arkansas growers.
“Soybean seed is one of the most expensive, but most valuable inputs, for a successful crop. But you should know its quality — after all, you are paying for it.”