Convection Oven Technique

Heating times listed in standard S352 were chosen so as to give the best agreement with the Karl Fischer method of moisture determination. For shelled corn, soybeans, and edible beans, 103°C and 72 hours are specified. A temperature of 130°C is used for wheat, oats, rye, sorghum and sunflower. The heating times are, respectively, 19 hours, 22 hours, 16 hours, 18 hours, and 3 hours. For many of the grass and forage seeds, such as alfalfa, bluegrass, clover, and timothy, the specified temperature is 130°C and the heating times are 2.5 hours or less. Note that larger seeds require longer heating times.

Although the standard does not specify the number of replicate samples which are to be tested, at least 2 and preferably 3 replicates should be used. The moistures for each replicate should agree to within 0.2%. If three replicates are tested and two of the three agree to within 0.2%, the third should be discarded. Use of three samples is particularly important when the original sample will no longer be available for testing, as often happens for tests on corn and soybeans where three days of oven drying are required. If none of the replicates agree within 0.2%, then the results should be discarded and the test repeated.