Variety selection plays a crucial role in a farmer's ability to produce high yields of top quality fiber, says Norm Hopper, Texas Tech University agronomist. But other information about the seed may provide equally important clues as to how the crop will perform.
Hopper said farmers, many of whom have cut back on seeding rates to reduce costs, should put more emphasis on seed vigor. “Planting high quality seed makes good sense if farmers are planting fewer seeds per acre,” he said.
“Uniform spacing also becomes critical,” Hopper said during a presentation recently at the Southwest Crops Production Conference in Lubbock.
He said farmers should look at more than just germination percentage. Two factors play important roles in a seed's viability — vitality and vigor.
The germination percentage shows that the seed is alive and will germinate. Vigor indicates seed strength and provides at least an idea of how well seeds will germinate and how well seedlings will perform under a variety of growing conditions.
Hopper said vitality ratings come from a warm germination test and show the seed's “ability to germinate and produce normal seedlings under ideal conditions.
“Vigor rates the seed's potential for rapid, uniform emergence and development of normal seedlings under varied conditions.”
He said seed quality peaks at physiological maturity while it's still on the plant. From that point on, it begins to deteriorate. Viability deteriorates slowly, to a point, and then increases. Vigor, Hopper said, deteriorates more rapidly.
Vigor testing takes place at a 64 degree Fahrenheit temperature and that temperature can't vary more than one degree up or down.
“We don't expect cool germination temperatures to equal warm test ratings,” he said. “We may get 60 percent, 70 percent or 80 percent instead of the 80 percent to 85 percent we're accustomed to in warm germ tests.”
He said a cool/warm vigor index is a combination of warm and cool tests. The procedure is: Run the cool germination test and count normal seedlings greater than 1.5 inches long after seven days; Run the warm germination test and count normal seedlings 1.5 inches long after four days; Add the results of the two tests.
A value of 160 to 200 on the warm/cool vigor test earns an excellent score. From 140 to 160 qualifies as good; 120 to 140 would be fair and anything below 120 is poor.
Hopper said the vigor rating could help farmers decide when to plant certain seed lots.
“In early May, temperatures are fairly cool, especially at night but with periods of warm temperatures.” The vigor index provides a gauge for planting under these adverse conditions.
“Growers should use seed with better test results when environmental conditions may be most stressful and plant the weaker seeds when temperatures are more favorable for germination and early growth,” he said.
Hopper said cottonseed need 50 degree-days at 60 degrees (DD 60s) to emerge.
“Cotton germinates best at temperatures above 65 degrees and germinates very little below 60 degrees. Below 50 degrees, expect chill injury; temperatures below 40 degrees can cause death of the seed.”
Hopper said seed are most sensitive when they first begin to absorb water and approximately two days after beginning of imbibition (when seeds begin to swell). He said ideal planting conditions exist when the daytime maximum temperature forecast for the next five days indicates temperatures higher than 85 degrees and nighttime temperatures greater than 50 degrees. “That allows for 5 DD 60s per day,” Hopper said.
He said good stands establish the potential for high yields. “A good stand results, in part, from using high quality seed, fungicide treatments and planting under warm conditions.”
Uniform stands should include uniform spacing and uniform growth of healthy plants, he said.
Hopper said a planting guide for best yield and quality should include:
Select an adapted variety for the area.
Insist on good quality seed.
Provide fungicide protection
Plant in a warm soil with a warm forecast.
Plant into a well-prepared and moist seedbed.
Set the planter correctly, spacing, depth, etc.
Calibrate the planter properly.
Hopper said waiting for ideal conditions might prove a pipedream for some growers who must get over significant acreage in a short period. Starting out with high quality seed, he said, will improve their chances of achieving a uniform stand of healthy cotton plants.