With the low market values of cotton lint that are currently being experienced, growers are finding that fiber quality is an increasingly important factor to consider in the production process. For example, high micronaire (mike) values have been a problem on many farms in recent years, resulting in discounts on fiber value. As we approach the later stages of the season, a review of fiber properties and the impact of management on these properties may be appropriate.
Fiber properties such as length, strength, micronaire, and grade are all important to consider in terms of crop management. There are many crop management factors that have been associated with fiber quality. Some of these factors include:
The cotton variety planted is probably the most important factor determining the potential for fiber quality. In several studies addressing cotton fiber properties (Meredith 1986 and 1990) genetics has been shown to have a very strong influence on fiber strength and length, accounting for over 80% of the variability associated with these two properties. The Acala varieties that are grown in the San Joaquin Valley of California offer an example of this varietal influence. The length and strength properties commonly associated with the Acala fibers are derived primarily from the varieties (genetics) grown not the environment per se. Variety can also have a strong influence on grade. For example, hairy leaf varieties are commonly associated with higher trash contents.
The following three sections provide a brief summary of the primary fiber properties and the management factors that can have a strong impact on them.
Length Besides variety, water management and maintaining good plant-water relations during fiber development is probably the most important factor affecting fiber length. This is one of the reasons good water management throughout the growing season is stressed. In-season irrigations should be scheduled so that no more than 50% of the plant-available soil-water is depleted between irrigations. Water stress can reduce crop vigor, fruit retention, and yield; as well as fiber length. There is also evidence that fiber length can be reduced by severe weathering (prolonged exposure to the elements) in the field. This might occur if severe or prolonged rainy periods are experienced following boll opening. If harvesting is seriously delayed and open bolls are exposed in the field for a long time (months) fiber length could be affected.
Strength Most varieties that have high yield potentials also have good fiber strength characteristics. Any factor that can cause physical or microbial damage to the fiber can reduce strength. Therefore, similar to affects on fiber length, severe weathering can negatively impact strength as well. Strength can also be reduced in cotton lint from over-ginning.
Micronaire Fiber fineness is also determined primarily by genetics. However, the maturity of cotton fibers can be affected substantially by environment and management. Unfortunately, a single fiber measurement cannot fully distinguish between fineness and maturity. Therefore, major deviations in mike readings for a given variety are most likely due to problems in managing crop maturity. In general, bolls set on the plant early in the season tend to develop high micronaire levels by the end of the season and bolls set on the plant later in the season tend to have lower micronaire, or be less mature. The blending of the fiber from bolls set throughout the season can often result in overall mike values that are acceptable. Whenever the crop experiences a notable drop in boll retention, micronaire can be affected. In Arizona we have commonly seen high mike values for fields that have experienced substantial losses in fruit retention late in the season, commonly associated with the monsoon season. We currently have a significant number of fields in Arizona that have gaps and irregular fruit retention patterns. High mike values in situations like this can be exacerbated by prolonging the crop late in the season without realizing a major gain in boll retention to compensate for bolls lost under the adverse conditions. Without gaining a significant boll load late in the season, plant carbohydrates are directed into existing bolls, creating fibers with higher micronaire. Management factors that lead to crop earliness and uniform fruit retention patterns are very important in terms of fiber micronaire. Therefore; planting date, water, fertility, plant growth regulator, insect, weed, disease, defoliation, and harvest management each can contribute significantly to the overall micronaire and general fiber quality of a crop. In particular, decisions concerning the timing of the final irrigation and applications of defoliants will be important this season.
Each of these factors can affect, independently and collectively, the yield and quality of a cotton crop, and therefore, overall profitability.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director Cooperative Extension, College of Agriculture and Life Sciences, The University of Arizona.
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Information provided by Jeffrey C. Silvertooth, firstname.lastname@example.org
Extension Agronomist - Cotton, College of Agriculture, The University of Arizona.
Material written 7 August 1999.