Читать книгу Osmosis: The Molecular Theory - Larry Howlett - Страница 6

Maintaining seed viability during storage is important for commercial seed companies as well as research stations. Treated seed with low germination percentage must be disposed of as waste material and replenished by planting and harvesting. Models for predicting seed viability as a function of storage conditions are important tools for making economic decisions regarding storage methods.

Several researchers have developed models and guidelines to predict seed viability loss in terms of storage conditions (Roberts, 1973, Ellis & Roberts, 1980, Walters, Kameswara, & Xiaorong, 1998, Mead & Gray, 1999) Experimental data for seed viability is correlated against initial seed water content and storage temperature. Seeds are currently stored in controlled temperature and relative humidity environments or in moisture impervious bags at controlled temperature. Experimental measurements of seed viability are correlated to the initial and storage conditions.

Before long-term storage, seeds are dried or humidified to establish specific seed water content. One process used to establish initial values for seed water content is equilibrating seeds in a controlled humidity and temperature environment. Data from these tests has been termed water sorption isotherm curves.

Water sorption isotherm data is reexamined in this paper by introducing a new variable, moisture vapor pressure. At given temperature and relative humidity, moisture vapor pressure is a characteristic of moist air that can be readily calculated from empirical equations. We postulate that at equilibrium conditions, the moisture vapor pressure in the seed is equal to the moisture vapor pressure in the equilibrating moist air environment. Furthermore, we propose that the calculated value of the seed moisture vapor pressure is a characteristic property of the seed at the specified equilibrating moisture content and temperature.