Understanding temperature and moisture patterns in selected modified traditional maize storage structures in the Southern highlands of Tanzania.

For three years experiments were conducted to study moisture content and temperature patterns and insect propagation profiles in four types of improved traditional maize storage structures as influenced by ambient temperature and relative humidity. The four types of improved stores were: two cylindrical basket stores made of bamboo and grass respectively and two rectangular stores made from burnt and sun dried bricks respectively. Moisture content was remotely determined using Reethorpe Moisture Monitors and collected using the Marconi Moisture meter. Temperature was measured with thermistors and collected through a programmable data logger. Insect sounds were investigated using an acoustic cassette recorder provided with sensitive microphones. Results indicated that grain moisture content and temperature variations inside the storage structures respectively followed the outside relative humidity and temperature patterns with greatest changes occurring near the floor, top surface and near walls while at the centre changes were appreciably lower. Possible moisture movement mechanisms are discussed. No deterioration of the grain was caused by moisture from the ambient relative humidity. Deterioration of some grain was found in stores which were not totally dry, where moisture content was 17% for more than 10 weeks. Temperatures experienced, till 24°C, had no influence on grain safety. It is of stores can safely store maize in the Southern Highlands of Tanzania, provided basic safety conditions for storage adhered to. Temperature was simulated in a typical improved maize bamboo store. There was high correlation between simulated and observed temperature except near the wall, where the largest difference (for the eastern wall) was not more than 2.5ºC. Model results showed that changes in grain temperature near the wall were influenced by solar radiation, air temperature thermal properties of the wall. Moisture diffusion through walls and grain was studies by deliberate wetting of west walls of the four types of stores. Moisture diffusion was found to be slow but the rates differed depending on store type. In the bamboo store, the rate was higher than in other stores and it was least in the burnt brick store. Main differences between the studied stores appear to be caused by differences in "time constant" that must be caused by differences in shade design, store shape, plaster and wall composition and thickness, that affect exchange coefficients. Soil/cow dung plaster composition ratios were studied. It was found that using less cow dung and more soil gave better plasters than more cow dung and less soil. Recommendations for future research are made. The study also includes weather advisories to the farmers of the Southern Highlands of Tanzania particularly on drying and shading of stores, derived from the results of the experiments.