Enhancing U.S. Cotton Classing with Varietal Data

Cotton (G. hirsutum) fiber quality affects the main ring spun yarn properties.  Two well-known predictors of yarn quality measured by the AFIS and Cottonscope are fiber diameter or standard fineness (H_s) and the secondary cell wall area relative to the area of a circle having the same perimeter or Theta. Theta is directly related to maturity ratio (MR = Theta/0.577).  Lower H_s and higher MR tend to produce higher quality yarns.  The micronaire (MIC) measurement is the USDA standard for measuring the these properties.  Indeed, it is well known that micronaire is not a measure of H_s or MR alone, but is a function of both properties combined. This can lead to difficulties in interpreting micronaire, which can translate into price discounts to producers.  For example, varieties with very fine and mature fibers may be discounted while varieties with coarse and somewhat immature fibers may obtain a premium. H_s is largely determined by plant genetics and not by growing conditions, so an established varietal H_s for U.S. cottons could be used to calculate fiber MR using Lord’s Micronaire equation. For this study 1,333 samples were taken from commercial cotton bales at a gin in Texas and tested on the AFIS pro 2 and HVI.  The variety, irrigation, and growing location of all the samples was recorded and used to establish a varietal H_s for all varieties (11 total.)  With this, we calculated fiber MR for all varieties using average varietal H_s and Lord’s micronaire equation and compared to AFIS MR (R² = 0.89).  This suggests that this method could be applied to commercial cotton to provide both H_s and MR from micronaire.  However, variations in H_s under different growing conditions, and the narrow range of  AFIS MR must be fully accounted for to insure the accuracy of this method.