Procedures for Moisture Analytical Tests Used in Cotton Ginning Research

Cotton post-harvest processing research requires moisture content determination for seed cotton, cottonseed, and lint. Methods for determining moisture content have changed and are no longer consistent between laboratories. This research compared standard procedures documented in 1972 and those currently practiced for finding moisture content by oven drying. Seed cotton from four modern cultivars (ranging from 9.4 to 36.8% foreign matter), lint, and cottonseed were brought from dry conditions, blended, then stored for more than 30 days in a controlled environment (21 C, 65% RH) to reach uniform moisture content. Additionally, 150 seed cotton samples were placed in plastic zipper bags and sent by air freight to a distant location and back or stored on-site. Drying baskets (652 cc) were loaded, in random order, with 25, 35, 50, 71, and 100 g seed cotton or 10, 14, 20, 28, and 40 g lint. Cottonseed was placed in 45 cc aluminum cups (10 g) or 800 cc aluminum baskets (50 g). Wet weights were determined in the controlled environment. After drying, replicated sets of seed cotton, lint, and cottonseed samples were weighed inside a drying oven, then outside of it while still hot. Some samples were dried for twice the recommended time. Sample location in the ovens was tracked. Weighing hot seed cotton samples outside of the oven after drying increased apparent moisture content approximately half of one percent due to air buoyancy; weighing lint samples outside the oven increased apparent moisture content by one percent. Smaller differences in apparent seed cotton moisture content were found when halving or doubling the amount of material in drying baskets or doubling the drying time. Foreign matter had a minor influence on apparent moisture content. Storage for three days and shipping by airfreight in plastic zipper bags did not measurably change the apparent moisture content of seed cotton. Sample location within the drying oven made no difference. Current practices are satisfactory if dry weight location is taken into consideration. Measurement uncertainty has decreased compared to 50 years ago, but the recommended minimum number of samples per treatment was increased slightly for greater statistical power.