Maize Storage in Termite Mound Clay, Concrete, and Steel Silos in the Humid Tropics: Comparison and Effect on Bacterial and Fungal Counts

Authors: OMOBOWALE, M - University Of Ibadan; Armstrong, Paul; MIJINYAWA, Y - University Of Ibadan; IGBEKA, J - Niger-Delta University; Maghirang, Elizabeth

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/18/2015
Publication Date: 6/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63269
Citation: Omobowale, M.O., Armstrong, P.R., Mijinyawa, Y., Igbeka, J.C., Maghirang, E.B. 2016. Maize Storage in Termite Mound Clay, Concrete, and Steel Silos in the Humid Tropics: Comparison and Effect on Bacterial and Fungal Counts. Transactions of the ASABE. 59(3):1039-1048. doi: 10.1303/trans.59.11437.

Interpretive Summary: In developing countries substantial postharvest losses due to spoilage, insect, and pest infestation occur frequently. In Nigeria grain losses have been reported to be as high as 40% and are partly attributed to inadequacy in storage facilities. Farmers in developing countries suffer from lack of funds for modern storage facilities. This study evaluated the use of termite mound clay (TMC) as a construction material for grain storage and was compared to reinforced concrete (RC) and galvanized steel (GS) silos for maize storage in the humid tropics. Results indicated that relative humidity showed greater effects on maize quality compared to temperature. During storage the bacterial and fungal counts of the maize increased to unsafe levels, as set by the Nigerian Industrial Standards (NIS), most rapidly in the TMC silo. For the entire eight months of storage, maize in the GS silo had fungal counts that were below the NIS threshold level. Dry matter loss of 0.5% to 1.0% indicates significant quality changes. Results indicate that maize can be stored safely for up to 4 months in the TMC silo, 4.75 months in the RC silo and up to about 6 to 7 months in the GS silo and only considers fungal and bacterial effects. Greater quality degradation in the TMC and RC silos was attributed to moisture permeation through the semi-porous walls which are areas that need improved design.

Technical Abstract: This study investigated the functional suitability of using the readily-available termite mound clay (TMC) for grain silo construction in comparison to conventional reinforced concrete (RC) and galvanized steel (GS) silos for maize storage in the humid tropics. The extent to which temperature and relative humidity affected the quality of grain during an 8-month un-aerated storage period, covering both dry and rainy seasons, was evaluated using bacterial count, fungal count, and dry matter loss as performance parameters. Average ambient and grain temperature remained was fairly steady over the storage period while average ambient humidity and moisture content of the maize increased. The bacterial counts increased dramatically in the TMC silo compared to the RC and GS silos (120000, 11000 and 8800 cfus/g respectively). Fungal activity was observed in TMC silo on the fourth month of storage which coincided with the start of the rainy season. Fungal count exceeded the acceptable threshold of 1000 cfus/g (Nigerian Industrial Standards) in the TMC (1300 cfu/g) and RC silos (5500 cfu/g) after four and six months respectively. The GS silo remained at a safe level (350 cfu/g). Dry matter content, initially at 88.7%, was reduced to 84.0%, 84.9%, and 87.3 % in the TMC, RC and GS silos respectively. Based on dry matter loss reaching ~0.5% to 1.0%, the allowable storage time for TMC and RC silos was 4 to 4.75 months and for the GS silo was 6 to 7 months. Relative humidity was found to be of great significance compared to temperature in affecting all maize quality parameters considered. The TMC was found suitable for constructing silos for short-term grain storage (four months) under un-aerated condition. Modifications to the current TMC silo design need to address permeability issues to improve its performance for longer-term maize storage.