By Amanda Huber
A combination of factors go into making fiber reach its maximum length and, then, other factors contribute to degrading and breaking that fiber into shorter lengths. The starting point is knowing how the boll develops.
The Critical Three Weeks
Craig Bednarz, crop physiologist at Texas Tech and Texas A&M, says boll development is divided into three phases. It is during the first phase and in the first three weeks that fibers elongate, beginning with pollination.
“Elongation occurs because of hydrostatic pressure,” he says. “If the crop is in water stress, the turgor pressure is less and the fibers do not elongate.”
Steve Brown, former University of Georgia cotton agronomist and now a cotton development specialist with Dow AgroSciences, agrees.
“Fiber length is set in the first two and a half weeks or so,” he says. “If you have harsh conditions – heat and drought – you can hinder fiber elongation, which increases short fibers.”
Bednarz says fiber length also depends on where the fiber is on the boll and where the boll is on the plant.
“Fibers from the boll apex position are typically shorter, and bolls produced in the outer regions of the plant will tend to be more immature, and immature bolls produce more short fibers,” he says.
“When it comes to the plants’ carbohydrate balance, the exterior bolls do not receive the same amount of carbohydrates as do bolls on the interior positions, and it is likely that interior bolls also receive the first water.”
Genetics Play A Role
Experts agree that genetic makeup of a variety has a definite impact on fiber length. Bednarz says some varieties make more bolls per plant, but the bolls are smaller. This goes back to having more boll apex positions and more bolls in outer positions on the plant – all of which increases the possibility of short fibers.
Glen Harris, UGA agronomist, says some producers choose varieties with a very long growing season because of growing conditions. However, it is those same conditions that can lead to short fibers.
“If you look at the length of time when those fibers are developing, they are probably developing under a number of different environmental conditions and that probably leads to our problem of having more short fibers mixed in there,” he says.
“One of the reasons producers like DP 555 is because it can withstand a drought. It will sit there for a long time, then kick off again when it gets moisture and grow as long as we don’t have an early frost, but that lends itself to having more short fibers.”
However, Brown points out
that there is much variation that naturally goes into fiber production.
Fibers originating from the same boll vary in length, and fibers originating on the same plant vary in length.
“There are varieties that have a tendency to produce shorter-length fibers, but conditions during early boll development also contribute,” he adds.
For example, Brown says, “Now, as hot as it is, the plant can’t cool itself, and that may contribute to short fiber.”
Density And Irrigation
Bednarz says another source of short fibers may be over-irrigation, which can affect the crop as much as drought.
“By over-irrigating, the crop is not cutting out the way it should, and the result is that it is producing fruit later and later in the season,” he says.
Bednarz says previous research attempted to look at the interaction of drought and plant density.
“The prevailing thought was that density should be matched to irrigation water availability, and research does support that to an extent,” he says.
He also says plant density affects fiber length.
“The competition results in smaller bolls and smaller seed, which are a good source of immature fibers.”
As for fertilization, there currently is no recommendation that will necessarily improve fiber quality parameters.
Harris says, “In regard to nutrients, potassium affects strength, and nitrogen affects micronaire, or volume, but as far as uniformity – the measure affected by short fibers – a lot of it has to do with environmental conditions.”
Brown says fertilizer recommendations point more to yield than quality.
“What the farmer wants to do is avoid the penalty range; if you fertilize adequately for yield, you have done what you can for fiber quality.”
Harvest And Ginning
Glen Ritchie, UGA crop physiologist, says producers should try to do what they can to keep the fruiting cycle as compact as possible and to make sure it is as mature as possible before defoliating. He says Bednarz, in research conducted at UGA, found that the best fiber quality was achieved when the crop was defoliated at 60 to 70 percent open boll.
“A better yield may be had at 80 to 90 percent open boll,” he says. “But producers have to be careful not to equate plant maturity with boll maturity. A plant may have real mature bolls, but immatures also.”
Brown says yet another factor is what they do at the gin. The goal is to do as little damage as possible.
“For several years, farmers have been concerned about fiber quality in their region,” he says. “This has given ginners an opportunity to work towards preserving quality. A positive is that although we haven’t made light-year improvements in the market place, we haven’t gone backwards.”
The Southeast cotton industry can be positive about the fact that much has been learned about short fibers – how it is produced and what can be done to reduce it. For producers, it helps to think about it this way: the maximum potential fiber length is achieved during the period of fiber elongation and boll maturity. Once the maximum is reached, every practice and input contributed from that point is meant to preserve that fiber length.
Harvesting beyond optimum quality and letting modules sit in the field, particularly under adverse conditions, reduces that quality potential.
Contact Amanda Huber at (352) 486-7006 or email@example.com.
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