Strength of Adherence of Bark on Cotton Plants

J Weldon Laird, Alan D. Brashears, and Gary L. Barker


 
ABSTRACT

Reduction in cotton lint quality due to bark inclusion is a serious problem for U.S. cotton. Many causes for bark to be peeled off stems and limbs of cotton plants and contaminate lint have been suggested with some conflicts between the suggested causes. It seems certain that interactions of weather and cultural practices affect the loose bark condition. The exact cause-effect relationships are not yet known. This project was undertaken in an effort to develop a method to make repeatable measurements of the strength of adhesion of bark on cotton plants. An instrument and method for measuring bark attachment force was developed and preliminary findings obtained with the device. The method consists of a device that cuts uniform specimens from pieces of cotton stem and a load cell and instrumentation system to peel the bark off the specimen at a controlled rate and record the resulting force-time information. The data extracted from this are peak force, average force, and work to peel the bark off the specimen. The method was used in preliminary studies on several cotton plots in the 1986 crop year and additional work is underway on the 1987 crop. Force to peel bark off is rather variable and follows several different patterns. Bark is apparently attached tighter at spots along the stem and not so tightly in other areas. The force of adhesion for individual specimens within a given sample was highly variable. Peak force while pulling bark off the calibrated specimens ranges from zero to about 350 grams. Average force ranges up to about 150 grams. Work to peel the bark off a 0.2 mm by 3 an specimen ranges up to about 40 milliJoules. An occasional sample is found where the bark falls off in the preparation process before measurable force is applied to it. Standard deviations were 7.5, 48.4, and 1.9 for average force, peak force, and work respectively in 1986 crop plot data. A significant difference between dryland and irrigated cotton was found in both crop years. Work to remove bark was the beat predictor of the percentage of bales reduced in grade because of bark in samples from several large blocks of cotton sampled at a local gin in 1986. Stick content of the harvested seedcotton and the average force level to pull the bark off also related to percentage of bales reduced for bark. However, force necessary to peel bark off was not simply correlated with the tendency for lint to be barky and a reliable prediction relationship has not yet been found. The method is proving to be a useful tool in studying the reasons for loose bark and finding ways to combat the problem. Much developmental work on the method remains to be done. Rate of pulling the bark significantly affected measured results in 1987 tests. Moisture content and/or drying of specimens also affected results.



Reprinted from 1988 Proceedings: Beltwide Cotton Production Research Conferences pg. 161
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998