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/ QUALITY CONTROL AND STANDARDS

3. The total amount of short fibres present de- yields the best physical and visual properties
creases as the length increases. possible. Cultivars and technology that provide
4. The uniformity index increases as fibre length good quality fibre, together with good growing
increases. practices can consistently produce good, long
staple cotton that can reach the best prices.
The length of the fibre does not affect its
elongation values, trash count, trash area, or Rd References
and +b values. The degree of reflectance (Rd) in- • Gordon, S. & Hsieh, Y.-L. (2007). Cotton:
dicates how bright or dull a sample is, whereas Science and Technology. Cambridge:
the yellowness (+b) indicates the degree of col- Woodhead Publishing Limited.
our pigmentation. • Uster Technologies AG. (2019). Uster
The only value that is negatively affected by Statistics 2018. Uster Technologies AG.
the length increase is the micronaire. It is out-
weighed by the importance of fibre length, which
explains why such a high premium is placed on
longer staple cotton. Longer cotton will retain its
physical properties better, while the visual grad-
ing properties remain independent.
There are also harsh discounts for lower
strength values in the market, which explains
the large price difference between high and low
classes of cotton. Furthermore, the quality of cot-
ton is attributed to the plant’s genetics, which is
why so much is invested in breeding cotton that

mm Continued from page 31
Figure 4: Comparison of fibre uniformity between cultivars per growing region Micronaire values fluc-
for the 2018/19 season, until 16/01/2020 (n = no. of samples). tuate (Figure 3), which seems
to be consistent with it being
dependent on environmental
conditions. This is especially
true during specific critical
development stages of boll
formation and maturation.
Figure 3 is an excellent
example of the micronaire
ran ge around an average
value, between cultivars.
The average uniformity
index of cotton is 81% and
each of the values shown
is within 80% to 82%
(Figure 4). This shows that all
Fibre length values (Figure 2) are mainly the values fall within a small range of variation,
determined by each cultivar’s specific genetics, and that the differences are insignificant. The
without much deviation. Candia is a long-staple fibre properties across all cultivars and growing
cotton, and the DP cultivars are medium- to long- regions for the 2018/2019 season are good
staple cultivars, while Paymaster produces short- and give a good representation of the qualities
staple fibres. of the South African cotton crop.

Volume 22 No 1 February 2020 | 33