Moisture Absorption, Mold Growth, and Decomposition of Rice Straw at Different Relative Humidities1

Abstract

AbstractMoisture and humidity relationships of rice straw are important in relation to the extent of decomposition that may occur during the winter season. Ground rice straw was exposed to constant relative humidities to measure moisture absorption, decomposition, and mold growth. Moisture absorption by rice straw was very rapid during the first few hours and approached equilibrium within 1 to 4 days depending upon the relative humidity. Moisture content at equilibrium at a given relative humidity was always greater at 8 than at 25 C. The relation between moisture absorption and relative humidity above 70% followed a parabolic function of the form M = a + bR + cR2 where M = % moisture, R = relative humidity, and a, b and c are constants. The rate and extent of straw decomposition were found to increase and the lag period of decrease with increasing relative humidity and temperature. The transition between slow and active decomposition of rice straw was at about 90% relative humidity. The threshold moisture content of rice straw for mold growth, defined as the highest moisture content at which it takes infinite time for the initiation of fungal growth, was found to be 7.5%.