Grain storage methods and their effects on Sorghum grain quality in Hararghe, Ethiopia

摘要

The majority of peasants in Hararghe, eastern Ethiopia, store sorghum grain in underground pits. These pits usually elevate grain moisture and storage temperature to levels that favour insect pests and fungi, causing grain spoilage. Information on pit environment, microflora association prior to storage, effects of storage methods, and changes in grain chemical components over time is sparse. The objectives of this thesis were to assess: (1) storage pit environment and grain weight loss; (2) mycoflora associated with grain prior to storage; (3) impact of storage methods on storage environment and grain quality; and (4) effects of storage methods, time and agro-ecological zones on grain chemical components. The reports in the thesis are based on field surveys in Hararghe districts, storage experiments and laboratory analyses. Mean storage pit temperature in seven districts ranged from 24.5 to 33.3 oC while the mean grain moisture varied from 15 to 17% after 7 to 9 months. The mean relative humidity in pits of the districts ranged from 58.3 to 86.1%. The grain bulk density decreased by 4% in 7 months. The district mean grain weight loss varied between 2 and 13% for the same storage period. Mean germination in the districts decreased from 83 to 27% in 7 to 9 months. Frequencies of Aspergillus and Penicillium species increased over time on grain stored in soil pits in the districts. Field fungi including Alternaria, Cladosporium, Fusarium, and Phoma species were associated with the grain in Alemaya prior to storage. Trace Aspergillus and Penicillium species were detected in association with the grain in some sampling sites prior to storage. Frequency of Penicillium species increased over time. Granary temperature and grain moisture content were higher in the soil pits than in the above-ground bins, and cement- and dung-lined pits at Alemaya University. The grain bulk density of samples from the soil pits decreased by 9% in 17 months while the changes in the other three store types were not significant. Germination of grain from the soil pits decreased by 6% per storage month while no significant difference was detected among the above-ground bin and non-soil pits. Soluble carbohydrate contents decreased from 2.4 to 1.2% in 7 to 9 months for samples from Hararghe districts and from 2.4 to 1.9% in 7 months and to 0.97% in 17 months for samples from soil pits at Alemaya University. The organic matter content decreased from 97.8 to 91.6%; and the crude protein increased from 10.1 to 11.2% in 17 months in samples from soil pits at Alemaya University. Storage fungi were associated with grain from the soil pits. Use of improved above-ground bins and/or modified underground pits is required to maintain the grain quality and to extend storability.