Exactly what impact does the age of seed have on yield? That's a question Delta and Pine Land, Co., Mississippi State University and the University of Georgia are trying to figure out in an ongoing study.
The project, which began in 2000, compared Deltapine NuCOTN 33B cotton seed production from 1999, 1998, 1997 and a blended seed lot. The blended lot contained at least 90 percent seed from 1998.
The seed lots were planted in replicated field trials in four states with a total of five locations in Arizona, Georgia, South Carolina and two locations in Mississippi.
The vigor of the four seed lots were measured using the seed vigor index — the sum of the cool germ test and a slightly modified warm germ test. The index, which correlated to the age of the seed, averaged 178, 173, 148 and 155 for 1999, 1998, 1997 and blended, respectively.
According to Tom Kerby, vice president for technical service for Delta and Pine Land Co., the study found that lots with lower vigor seed generally produced fewer plants. But the study also showed that, “once a plant has emerged and put on a few leaves, it's as productive as any other plant.”
He noted that seed age did not affect the node of the first fruiting branch, plant height, number of nodes, the rate and height of node development or the rate at which plants moved toward cutout.
The skippy plots were apparently able to compensate for the lack of plants, too. Overall, there were no statistical differences in yield across the five locations in the study. In fact, in three of the five locations, two-year old seed out-yielded fresh seed.
However, one location, on Willard Jack's farm in Belzoni, did show a yield correlation to seed age. Two-year old seed yielded 817 pounds, compared to 870 pounds for one-year old seed and 915 pounds for fresh seed. Blended seed yielded 916 pounds.
“We haven't been able to determine exactly what happened there, but we had some early season injury from something,” said Kerby. He added that the yields between the various seed ages in the Belzoni plots, “were not statistically different.”
However, Jack noticed problems with older seed, even though the seeds germinated and came up like they were supposed to. “I didn't like the way the (older seed) grew during the season,” he said.
The data comes from one year of research. Planting and emergence conditions were very favorable in all five of the field locations and only one planting date was used.
In 2001, the study will include several planting dates, including one in early April. The study will be hamstrung somewhat this year because no new seed will be available for current year comparisons. “We grew some NuCOTN 33B, but it didn't make quality,” Kerby said.
Kerby says the April-planted plots observed so far this year did not produce good plant stands, especially in some of the 3-4 year-old-seed plots. “Those are probably going to have a lower plant density and a lower yield. But it's not because it's bad seed. It's older seed with a lower vigor and it didn't produce a stand. Kerby says that in on-farm situations, a grower would replant a field that doesn't produce an adequate stand.
A major point, stresses Kerby, is that growers should not place too much emphasis on the age of seed. “If it has good warm germ and cool germ, it's still good seed, even if it is five years old. The only thing is when seed finally does start to break down and lose that rating, it may lose it rather quickly.”
Kerby suggests that if you have any doubts, have your seed tested. “If it had dropped, we would replace the seed or do what we have to do.”
What happens to year-old seed when it's returned to the seed company?
First, it's warm germ and cool germ are re-tested. If either fall below a certain level, the seed is destroyed. Most seed companies decline to divulge that standard.
It's possible for an entire bag of seed that is a year old to be re-offered for sale, but it's not legal to do without a new label and a new analysis.
After old seed is re-tested, it can be blended with new seed. Seed companies typically blend seed, primarily for inventory control. Since Freedom to Farm lifted restrictions on acreage in 1996, the amount of returned seed has increased and inventory control has become much more challenging for seed companies.
But seed companies insist that the actual blending percentage is based on maintaining quality control and reducing costs to growers, not reducing inventory.
“Blending is one of the ways we keep seed from being 20 percent higher,” said Bud Hughes, president of Stoneville Pedigreed Seed, Co.
A simple calculation helps the seed company decide how much blending can take place and still achieve a desired standard.
For example, if a bag contained 90 percent new seed with a warm germ of 90 percent and 10 percent year-old seed with a warm germ of 76 percent, the warm germ of the blended bag of seed would be 88.6 percent.
After the blending takes place, samples are still taken from the bag before sealing. Something can go wrong with the mechanics of blending, for example stop-ups or breakdowns may result in a higher percentage of old seed/new seed being bagged.
Hughes also stresses that growers should not assume that older seed is less vigorous. “If seed is two years old, still has good vigor and germination, then it's fine.
“But there are only so many ways to test seed. The one thing we don't have is one test that tells you that seed is good. There's a dozen tests that tell you it's suspect. We do know that as seeds age, they deteriorate. The question is how fast.”
Hughes noted that the cool germ test, “is the most important test for determining vigor. But the problem is the inconsistency between labs testing for cool germ. If the equipment used to test the cool germ varies more than a degree in any direction, the results are going to be off by as much as 20 percent.”
Seed companies can fax, e-mail or provide cool germ and blending information over the telephone upon request by growers. Hughes suggests that before planting a bag of seed, “know the warm germ, the cool germ and the five-day weather forecast.”
Kerby noted that California cotton producers actually prefer older seed to newer seed. “There is very much a bias in the San Joaquin Valley that farmers want two-year old seed. We've had some tests there where we've had one-year-old seed and two-year-old seed in side by side tests and the two year old seed got out of the ground a lot faster.”