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Prevention of Moisture Migration in Sealed Grain Stacks Stored in the Open in the Tropics Using Reflective Covers

J. Donahaye*, S. Navarro*, F. Caliboso, G. Sabio, G. Malle and J. Dator

Abstract: A sealed structure that provides protection of grain without the use of chemical pesticides and termed a 'Volcani Cube' was used in these experiments. A major advantage of the Volcani Cube is that it can be used to safely store grain outdoors when no suitable storage buildings are available. However, under tropical conditions, when grain is stored in the open with no shade, ambient diurnal temperature fluctuations can create temperature gradients within the stack that cause convection currents to carry moisture to the upper layers of the grain. To overcome this, an upper insulating layer of bags containing straw or husks was employed. Under Filipino conditions this solution enables safe storage of maize and paddy for periods of up to three months, while for more extended periods the top moistened layer of husks should be replaced with dry material. This method, although solving the problem, suffers from the inherent disadvantages of reduction in effective storage capacity, the necessity to procure and transport material to fill the bags, and the added expense of bags not used for storing grain.

In a search to develop an alternative, inexpensive and convenient method of insulating the stack from diurnal temperature fluctuations, the use of a shade screen placed above the cube was investigated. This material, described as a 'knitted thermal screen', is formed from aluminum-coated high-density polyethylene threads. Trials in Israel and the Philippines showed that the reflective covers had a strong attenuating influence on temperature gradients and condensation at the top of the cubes on the condition that a space for the free moyement of air was allowed between the cover and the plastic liner. For dry paddy, it was shown that after five months storage under a reflective cover, no perceptible increase in moisture content was found at the top of the stack and the grain remained in good condition.

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