Food Technology Information Center

Seed Storage in the Tropics under Gastight Sealed Conditions

Shlomo Navarro, Ezra Donahaye, Miriam Rindner, Avi Azrieli and Refaei Dias

Department of Stored Products, Agr~cultural Research Organ~zation, The Volcanl Center, Bet Dagan 50250, Israel

Abstract: The viabtltty of seeds stored In gastight sealed structures in the open, under modified atmospheres, in troplcal and subtroplcal cllmates was investigated. The essential advantage of sealed storage lies in the generation of an oxygen-depleted and carbon dioxide enriched intergranular atmosphere of the storage ecosystem to arrest insect development. In addition, the sealed storage prevents ingress of moisture into the already dry seeds when the ambient humrdity of the surrounding environment rises. Tne two types of structures lnvestigated were a) frameless flexlble envelopes for bagged grain (Volcanl Cubes) of 5 to 150 tonnes; and b) a granary (GratnSafe) to hold 540 kg of cereal grain.

Under troplcal conditlons, when grain iS stored in the open with no shade, ambient diurnal temperature fluctuations can create temperature gradients withln the stack that cause convection currents to carry molsture to the upper layers of grain. In the granary a protectwe roof dlminishes the effect of temperature gradients. However, to overcome thls effect in the flexible envelopes, the use of a shade screen placed above the structure was lnvestigated. This materlal described as a knitted thermal screen is formed from alumlnum coated high-density polyethylene threads. Trials in Israel and the Philippines showed that the shade screens had a strong attenuating influence on temperature gradients. For dry paddy seeds, it was shown that after five months storage under a shade screen, no perceptible increase in moisture content was found at the top of the stack and the seeds remalned in good condition. Under troplcal climates this solutlon enables safe storage of malze and paddy seeds. Trials conducted with these two types of structures in troplcal and subtropical climates showed that seeds are protected under sealed storage by maintaining the number of live insects below the threshold of economlc damage wlthout the need for pesticides.

Key words: seed storage, sealed structures, germinatlon, insect pest, paddy, maize

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