Fiber quality — and how to improve it — continues to be one of the hottest topics of conversation among cotton producers throughout the Southeast. A hot and dry growing season followed by cloudy, rainy weather at harvest last year resulted in one of the poorer quality cotton crops in recent memory.
In Georgia, more than a third of the crop was penalized in color grade, about a third was short staple and nearly 50 percent was penalized for high micronaire.
Fiber quality is more important now than ever, as the U.S. crop must be salable in the world market, says Lloyd May, University of Georgia cotton breeder.
“We're beginning to export more than we're using,” says May. “And we're using less and less all the time, as our textile mills move off-shore. Cotton must meet the requirements of yarn manufacturers or they'll look elsewhere for their product. High mike cotton does not meet the requirements of yarn manufacturers.”
Micronaire and staple length are key problems for Georgia growers, he says. “And the question is, what can we do as far as variety selection to avoid these problems? When selecting a variety, you can influence staple length. Variety testing data show that some varieties have longer staple length than others.
“In addition, when we look at variety tests from two locations — Tifton and Plains — we see that the soil at Plains typically produces a longer staple length than at Tifton. So location and environment also can influence staple length,” says May.
But the same is not true for micronaire, he adds. “Variety makes less of a contribution to micronaire than to staple length. Mike is a measure of resistance to air-flow in the micronaire chamber — that's how it's measured on HVI instruments. A micronaire reading reflects fiber maturity and the number of fibers in that sample that are measured for air-flow.”
The solution for the micronaire problem, says May, might be more long-term “We need an integrated approach to micronaire improvement, and the University of Georgia is working on just such an approach. One of the tools we'll use is the new micro-gin currently under construction. It will allow us to implement a ‘dirt to shirt’ approach to fiber improvement, including all disciplines.
“We can look at the influence of genetics and management on cotton in the field, and we'll be able to gin that cotton and substantially replicate a commercial gin. We can measure the fiber and yarn properties and establish programs for keeping Georgia cotton competitive.”
More research needs to be done on the relationship between cotton fertilization and lint quality. “In theory, all of the essential plant nutrients are critical for both yield and quality,” says Glen Harris, Extension soil scientist. “When most people think of the effect of fertilization and plant nutrition on lint quality, the first thing that comes to mind is potassium.”
Potassium, says Harris, is one of the biggest fertilization challenges for Georgia cotton producers. “We've tried increasing the rates, splitting applications and making foliar applications, and we've focused more on yields. But this work also needs to be carried through to lint quality.”
Many potassium problems are due to dry weather conditions, he adds. In some cases, there may be enough potassium in the soil but there's not enough water to get it into the plant.
Most Georgia growers do a good job applying nitrogen on cotton, says Harris. “We rarely can afford to put too much nitrogen on cotton, but excess nitrogen can delay fruiting, which can affect lint quality and micronaire.”
To insure quality lint, growers should continue to focus on a balanced nutrition program with the appropriate micronutrients, while focusing on things such as potassium, boron and nitrogen, he says.
“As we continue to battle potassium deficiencies, we need to be mindful of the fact that a combination of high nitrogen and high potassium can delay maturity and affect lint quality.”
Two insects — aphids and stinkbugs — potentially could affect cotton fiber quality, says Phillip Roberts, Extension entomologist.
“We can build extremely high populations of aphids, and they're basically an additional stress on the cotton plant. Stress, whether from drought or something else, is one of the main factors affecting lint quality,” he says.
A long-term research project looking at aphid management has yet to show any response or difference in lint quality when comparing cotton treated for aphids with untreated cotton, says Roberts.
“Theoretically, aphids could be a problem as an added stress on the plant. But in our trials, looking at eight or nine locations, we haven't seen a difference in any quality parameters resulting from managing aphids,” he says.
Stinkbugs or any boll-feeding bugs also could cause potential quality problems, says Roberts. “We believe stinkbugs prefer to feed on bolls that are 10 to 12 days of age. And there's still a lot of things happening with fiber development when a boll is 10 to 12 days old. If an insect is feeding on a developing boll during this time, it theoretically could have an impact on fiber length and quality,” he says.
Lint, he continues, is nothing more than part of the cotton seed. “If the stinkbug damages the seed, it will impact how the cotton develops. Theoretically, we can see stinkbugs affecting lint quality.”
In a study conducted in 1997-98, researchers looked at the impact stinkbugs were having on quality and yield, says Roberts. Cotton bolls in two counties were tagged as either damaged or not damaged by stinkbugs, judging by external symptoms.
Bolls were hand harvested and examined for differences in yield and quality, he says. Yields from bolls with external spots indicating possible stinkbug damage were 20 percent less than bolls with no signs of damage.
When testing for quality, the bolls were classified as to the extent of damage. Some of the bolls had no damaged locks, while others may have had one or two damaged locks.
“When we ran quality information on these bolls, as the number of damaged locks increased, we obviously saw differences in color. We also saw differences in micronaire. The more damage we had, the lower the micronaire. We did not see a consistent difference in staple length in those studies.”
More studies were initiated in 2000, looking at treated and untreated plots in growers' fields. “We're examining positions on the plants. We know what percentage of the bolls on the plant have internal damage, and we can get fiber information from Cotton Incorporated if we know the level of insect damage versus the level of quality.
“We have seen some differences in length in these studies, but only in cases of severe stinkbug damage. Potentially, stinkbugs could affect staple length, but only where damage is very severe. Our opinion now is that if you're doing a good managing stinkbugs as you should for higher yields, we don't think there will be an impact on quality.”
Georgia cotton has garnered a reputation recently of being low-quality fiber, says Craig Bednarz, University of Georgia cotton physiologist, and the uniformity of the state's crop appears to be lagging behind that of other cotton-producing regions.
A recently completed multi-year study in Georgia showed that as cotton harvest is delayed, fiber strength and length decrease, says Bednarz. “And these are characteristics that textile mills do not want. It would behoove growers to seek means to get their crops out in a timely fashion.”
Cotton and peanuts are a common combination for many producers in south Georgia, he says. Unfortunately, cotton and peanuts both require approximately the same number of days to mature. As a result, cotton harvest generally is initiated following the completion of peanut harvest. This delay, says Bednarz, may cause significant losses in lint yield and quality.
“Research has shown that timely harvest not only will be beneficial from a yield standpoint, but also from a quality and economic standpoint,” he says.
Other research related to cotton quality is focusing on where fruit is set on the plant, says Bednarz. “It's generally accepted that first-position fruit is the highest quality fruit - the biggest fruit with the best quality fiber. But in Georgia, we do things differently from other regions of the Cotton Belt.
“We tend to plant fewer seeds per foot of row. Our population densities are a little lower than other regions. By virtue of that, we've changed where our cotton is produced on the plant. A smaller percentage of our crop is produced in those first positions. So, we're also looking at the effect of population density on fiber quality.”
Georgia cotton producers also tend not to be so concerned about early season insect pressure, notes the physiologist. “We're willing to accept early season square losses. In other regions of the Cotton Belt, growers want their early season retention level to be as high as possible, and they'll take whatever means necessary to keep it as high as possible.”
Georgia growers don't concentrate so much on early season insect pressure because they want to preserve beneficial insects for later in the season, he says.
“If you sustain insect pressure or square losses early in the season, research has shown that the cotton crop will compensate for that by producing main-stem nodes and producing cotton higher on the plant. If you're willing to accept early season losses from insects, you're redistributing where cotton is set on the plant, so that's another thing we're looking at.”
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