Fibre quality: the strength of our reputation
Despite our relatively small crop, Australian exports still make up over 10 per cent of the medium/high medium grade cotton volume in the export market. The quality of Australian cotton has improved over the last two decades and has earned a very good reputation amongst spinners for its good spinning ability and low contamination. Nearly all of Australia’s cotton lint is exported for high-quality end use in mills in South East Asia. It is used primarily for producing high-quality fine to medium count yarns for use in the woven and knitted apparel sectors.
What do you need to know?
The price received for cotton is dependent on the quality of each bale of cotton. Cotton prices are quoted for ‘base grade’, with the base grade refers to the grade of cotton that is used by cotton merchants as a basis for contracts, premiums and discounts. Currently the base grade in Australia is Colour 31 (Middling) and Leaf 3, length 36 and micronaire G5 and premiums and discounts apply for higher and lower grades respectively.
The key characteristics:
Colour: Currently the colour of a sample is currently measured both visually by a trained cotton classer and by a high volume instrument (HVI).
Leaf: Also known as ‘trash’, is a measure of the amount of leaf material remaining in the cotton sample. The amount of trash present in a bale of cotton is affected by the variety, harvesting methods and conditions and whist the gin removes most of the trash, some remains in the sample which is removed in the spinning process resulting in a reduction in lint yield and increases cost. Hence, cotton with high levels of trash attracts a discount. Leaf grades range from 1 (lowest amount of trash) to 7 (highest amount of trash).
Staple length: Length is measured on a sample of fibres known as a ‘pull’ when hand classing and is measured to the nearest 1/32 inch. HVI determine length in 100ths and in 32nds of an inch or on a ‘beard’ or tuft of lint formed by grasping fibres with a clamp. Australian cotton is all classed using HVI measurements.
Upland length conversation chart:
|24||0.79 & shorter||36||1.11 – 1.13|
|26||0.80 – 0.85||37||1.14 – 1.17|
|28||0.86 – 0.89||38||1.18 – 1.20|
|29||0.90 – 0.92||39||1.21 – 1.23|
|30||0.93 – 0.95||40||1.24 – 1.26|
|31||0.96 – 0.98||41||1.27 – 1.29|
|32||0.99 – 1.01||42||1.30 – 1.32|
|33||1.02 – 1.04||43||1.33 – 1.35|
|34||1.05 – 1.07||44 & +||1.36 & +|
|35||1.08 – 1.10|
Micronaire: Micronaire is measured by placing lint in a chamber, compressing it to a set volume and subjecting it to a set pressure. The micronaire result measured in this way is in fact a function of both fibre maturity and fineness (linear density). As the reading is an approximate guide to fibre thickness the trade use the following micronaire ranges to describe samples:
|5.0 – 5.2||G6|
|3.5 – 4.9||G5|
|3.3 – 3.4||G4|
|3.0 – 3.2||G3|
|2.7 – 2.9||G2|
|2.5 – 2.6||G1|
The premium range is 3.8 to 4.5 and the base range is 3.5 to 4.9 (G5) and discounts apply for cotton with a micronaire outside the base range. Discounts for low micronaire can be substantial.
Strength: Fibre strength is highly dependent on the variety, although environmental conditions can have a small effect. Raingrown cotton strength is usually not adversely affected by growing conditions. Most Australian varieties are of high strength and local plant breeders have agreed to eliminate varieties that do not meet a minimum standard, thus keeping Australian cotton highly competitive in the world market. Fibre strength is measured by clamping a bundle of fibres between a pair of jaws and increasing the separation force until the bundle breaks.
Strength is expressed in terms of grams force per tex with the following classifications:
Strength (grams per tex)
|Weak||23.0 & below|
|Intermediate||24.0 – 25.0|
|Average||26.0 – 28.0|
|Strong||29.0 – 30.0|
|Very strong||31.0 & above|
Contamination: Australian cotton is recognised as one of the least contaminated cottons in the world and receives a premium - so any contaminants lower the value of the product and can potentially damage our reputation. Contaminants can either be natural (like rocks, wood, leaf, bracts, bark, green leaf, burrs, grass and honeydew), or man-made (like as torn cotton tarps and plastic wrap, twine, oil, hydraulic oil, grease, pieces of metal and equipment, food wrappers, drink bottles, mobile phones, and cleaning rags). In Australia the biggest issue is plastic, since most of the crop is harvested with harvesters that produce round modules covered with plastic wrap.
Stickiness: Cotton stickiness, when it occurs, can present a major problem, in terms of textile processing performance and cost and product quality. If a country gains a reputation for stickiness, they have difficulty selling their cotton, and incur large discounts. The most common and problematic causes of stickiness are those due to excess sugars related to insect secretions, notably aphids and whitefly and are generally referred to as honeydew these being responsible for some 80 to 90 percent of stickiness problems. In addition, a black sooty mould can also grow on honeydew, darkening the lint and adversely affecting grade.
So, what should you do on your farm?
Fortunately, the majority of crop management factors which increase/optimise yield will also increase/optimise fibre quality. Below are a few decisions which could affect your fibre quality;
- Select an appropriate variety for your region according to recommendations from CSD.
- Choose the optimal sowing date for your area to maximise yield and fibre quality.
- Effective control of weeds to minimise contamination, staining and reduced harvest efficiency.
- Meeting the nutritional requirements of the crop is as nutritional deficiencies can have a significant effect on fibre quality.
- Implement good IPM strategies to avoid insect damage and avoid unnecessary pesticide applications.
- Avoid aphid and whitefly infestations to avoid sticky cotton.
- Optimise the timing of cut-out to minimise harvest of immature bolls.
- Apply good defoliation (product, rate and time) and a timely harvest.
- Implement good farm hygiene practices to avoid contamination.
- Ensure harvesters (pickers and strippers) are regularly maintained and correctly set up.
- Avoid picking/stripping seed cotton with moisture content ≥ 12 per cent.
- Ensure module wrap/tarpaulins are intact and not damaged.
For more information on fibre quality visit the myBMP fibre quality module.
Where should you go for more information?
René van der Sluijs – Technical Lead Fibre Quality
Ph: 0408 88 5211
- Australian Cotton Production Manual
- Cotton Incorporated's Classification of Cotton classing booklet
- CSIRO's Contamination and its significance to the Australian cotton industry booklet