| Summary: | Arizona has experienced a trend toward increasing fiber micronaire values in recent years resulting in substantial discounts on fiber value. There is some evidence to suggest management can influence fiber micronaire. Approximately 560 cases were identified in cotton production areas in Arizona ranging from the lower Colorado River Valley to near 2,000 ft. elevation with grower cooperators in the 2000-2002 seasons. Field records were developed for each field by use of the University of Arizona Cotton Monitoring System (UA-CMS) for information such as variety, planting date, fertility management, irrigation schedules, irrigation termination, defoliation, etc. Routine plant measurements were conducted to monitor crop growth and development and to identify fruiting patterns and retention through the season. As the crop approached cutout and the lower bolls began to open, open boll samples were then collected from the lowest four, first position bolls (theoretically the bolls with the highest micronaire potential on the plant) from 10 plants, ginned, and the fiber was then analyzed for micronaire (low 4). From that point forward, total boll counts per unit area and percent open boll measurements were made on 14-day intervals until the crop was defoliated. Following defoliation, final plant maps were performed. Relationships among low 4 sample micronaire, irrigation termination (IT), defoliation, and final crop micronaire were analyzed. Results indicate strong relationships with final fiber micronaire for factors such as total heat units (HU) accumulated by the crop from planting to IT, variety, region of production (environment), and green boll load at cutout. Results showed that as total HU accumulated from planting to IT exceeded 2945 that micronaire levels increase significantly, especially for some districts (Paloma and Maricopa) and producers.
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