Our marketing system for cotton is based on fiber properties of strength, length, micronaire and color. In addition, cleanliness, moisture and contamination levels are measured. Cotton breeders have done an amazing job in improving the fiber quality parameters of today’s cotton, and, for the most part, 98 percent of the bales’ fiber length (or staple ) and 97 percent of the bales’ strength meet the base or premium specifications.
Micronaire (mic) is an indirect measure of fiber maturity and is related to the amount of cellulose deposited during boll development. The mic is primarily a function of variety, culture and weather, and gins have little effect on mic. Producers receive premiums for the most desirable mic (3.8-4.2), with varying discounts for departures above or below the premium range. About 20 percent of the bales classed received mic discounts, with the majority as high mic.
The primary quality factors ginners can affect are color, length uniformity index (UI), cleanliness and prep.
Fiber color is measured by instrumentation that combines brightness, Rd and yellowness, +b, of the sample into a color grade. A 41 color is considered base, white color grades 11- 31 receive premiums, and 51+ receive discounts. The color of cotton when harvested depends on weather and the presence of stains from green or other material such as soil or deteriorating seed. Storage with high moisture content (more than 12 percent) will also reduce color grade.
Ginners can process cotton with additional lint cleaners to improve color slightly, but lint cleaners cannot obscure full-spotted, tinged or yellow-stained color grades to any degree. It is important to educate producers about the color problems caused in the field and by storing cotton damp.
Leaf grade 4 is considered base. There are small premiums for better grades, but discounts for worse leaf grades. Cotton should be cleaned to a leaf grade the same as the color grade. Example: 31 color and 3 leaf. Providing extra cleaning generally does not compensate for the loss of marketable weight (gin turnout) in the form of lint-cleaner waste or motes and usually results in loss of profit to the producer. When normal leaf grades are being exceeded, one or more of the second-stage lint cleaners should be bypassed due to the loss of some marketable fiber.
Unneeded cleaning has other disadvantages as well; it can reduce staple length and length uniformity index. The UI ranges from 80-82 as a base with discounts below 80. Each lint cleaner reduces staple by up to 1/32 of an inch and is worsened if excessive drying has weakened the fiber. As a general rule, do only the cleaning and drying necessary to achieve the desired leaf grade.
– Thomas D. Valco, PhD, USDA Cotton Technology Transfer, Stoneville, Miss. Contact him via email at Thomas.firstname.lastname@example.org or call (662) 686-5255. Each month Valco offers timely ginning updates in Cotton Farming magazine. His reports also can be found at www.cottonfarming.com. For additional information, go to http://msa.ars.usda.gov/gintech.
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