Factors affecting carbon dioxide concentration in interstitial air of soybean stored in hermetic plastic bags (Silo-bag)

Cardoso L., Bartosik, R., Rodriguez, J., Ochandio, D.

National Institute of Agricultural Technologies (INTA).
Student Agricultural College of Mar del Plata National University.
Ruta 226 km 73,5, Balcarce (7620), prov. Buenos Aires, Argentina

Abstract: In 2007 about 35 million tonnes of grains were stored in hermetic systems (silo-bags) in Argentina, and about 17 million tonnes of that were soybean. The soybean stored in these silo-bags is mostly used for processing in the local industry (oil and soy-meal), but also for seeds to be used during the next planting season. The goal of this research was to conduct a series of field experiments in order to identify the main factors affecting the CO2 concentration as an indicator of biological activity and appropriate soybean storability conditions.
The experiments consisted of monitoring the gas composition of the interstitial air, grain moisture content (MC) and temperature of several silo-bags. Additionally, the overall condition of the silo-bags was checked (broken areas, improper sealing, bottom side perforations, etc). On average, biological activity, measured as CO2 concentration, did not increase substantially when soybean MC increased from 11 to 15.2%. The CO2 concentration for soybean with 14% MC or lower was below 2%. The average CO2 concentrations for silo-bags with soybean at 14 to 15.2% MC remained below 2%, however, in some silo-bags the CO2 concentration increased to 5% at the most. The average temperature of the soybean stored in silo-bags followed the pattern of the average ambient air temperature through the seasons. There was a small increase in the average CO2 concentration as a function of the grain temperature increase (1.5% points of CO2 for about 10°C of temperature increase). When individual silo-bags were analyzed, the CO2 concentration measured during the warm storage season was up to 3 percentage points higher than when measured during the cold storage season.

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