Development of oven and Karl Fischer techniques for moisture testing of grass seeds

The Association of Official Seed Analysts' Rules for Testing Seeds do not contain methods for moisture testing. The oven methods in use by seed testing laboratories in the U.S. are diverse and may produce erroneous results when compared to the Karl Fischer method. The International Seed Testing Association Rules for Seed Testing contain oven testing methods for 95 kinds of seeds, but many of the methods are empirical in nature and lacking in accuracy. This research was initiated to develop more accurate oven methods for testing moisture content of seeds of temperate-climate grass species. The test variables investigated were oven temperature, time of drying, seed grinding, and original moisture level of the seed. The species included were perennial ryegrass (Lolium perenne L.), orchardgrass (Dactylis glomerata L.), colonial bentgrass (Agrostis tenuis L.), Kentucky bluegrass (Poa pratensis Huds.), tall fescue (Festuca arundinacea Schreb.), and red fescue (Festuca rubra L.). Drying to constant weight at temperatures of 90, 100, 105°C gave moisture percentages lower than the Karl Fischer value. Drying periods of 6 h or less at 130°C gave moisture percentages in agreement with Karl Fischer results. Ground and whole seed gave similar moisture percentages after drying to constant weight, but moisture was removed more rapidly from ground seeds. The required drying time for greatest accuracy depended on the original moisture content of the seed. Moisture was removed most rapidly from the highest moisture seed; thus, it is not possible to select one drying period that will provide the same degree of accuracy on seed with different moisture levels. Seed moisture tests on these six temperate-climate grass species should be conducted on whole seed at 130°C. The best compromise for drying periods are 3 h for perennial ryegrass, Kentucky bluegrass, tall fescue and red fescue; 1.5 h for orchardgrass; and 1 h for colonial bentgrass.