Accuracy of Alternate Oven Drying Procedures

Cotton post-harvest processing research frequently requires moisture content determination for seed cotton, cotton seed, and cotton lint.  Standard procedures documented in 1972 and currently practiced were analyzed to estimate measurement uncertainty.  Understanding the source and magnitude of errors will aid in increasing precision and interpreting results.  Four seed cotton varieties (9.4 to 36.8% foreign matter) and one variety of lint were stored for more than 30 days in a controlled environment (21 C, 65% RH) and thoroughly blended to reach uniform moisture content.  Drying baskets (652 cc) were loaded, in random order, with 25, 35, 50, 71 and 100 grams of material; wet weights were determined in the controlled environment.  Additional samples were placed in plastic zipper bags and sent by air freight or stored on-site.  Replicated sets of seed cotton and lint 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 dry samples outside of the drying oven increased apparent moisture content approximately half of one percent due to buoyancy.  Smaller differences in apparent 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.  Sample location within the drying oven made no difference.