HYGROSCOPIC EQUILIBRIUM AND VIABILITY OF NATURALLY AND ARTIFICIALLY DRIED BLUE LUPINE SEEDS

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Abstract
Detns. of hygroscopic ally held percentages of water in naturally and artificially cured seeds of blue lupine (Lupinus angustifolius) in equilibrium with various relative humidities of air within the range of 0 to 100% were made by means of saturated solns. of selected salts, H2SO4 solns., and an electric hygrometer (American Instrument Co., Silver Spring, Md.). Data obtained by the 3 methods did not differ significantly if sufficient time was allowed for attaining true equilibria. Seeds required 7-8 wks. to reach equilibrium with atmospheric moisture in confined air at relative humidities approaching zero and 100%. Comparable data of equilibrium moistures produced in confined air by seeds of different moisture contents were obtainable with the electric hygrometer in 24-72 hrs. The equation representing equilibria between blue lupine seed moisture % (Y) and R.H. of air (X) was found to be of the 3d degree (Y = a + bX - cX2 + dX3) rather than the parabolic form usually reported or inferred for other seeds and grain. Seed viability decreased during storage at low as well as at high humidities, declining from peaks at about 25% R.H. for seeds initially 46% germinable and at about 65% R.H. for several lots of seeds of high initial viability. Loss in germina-bility at high storage humidities was attributed to microbial activity. Viability losses at low storage humidities were unexplained, but usually the seeds were subsequently able to absorb normal amts. of water, and reduction in germinability was therefore ascribed to chemical rather than to osmotic or permeability changes in seeds. Artificially cured seeds retained germinability under high humidity storage better than did naturally cured seeds. The relation of hygroscopic equilibrium of blue lupine seeds to safe storage conditions and to artificial curing practice is discussed.

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