Post-harvest losses (grains)
Pre-harvest losses occur before the process of harvesting begins, and may be due to insects, weeds, and rusts.
[1] Important in many developing countries, particularly in Africa, are on-farm losses during storage, when the grain is being stored for auto-consumption or while the farmer awaits a selling opportunity or a rise in prices.
With a high moisture content, grain is susceptible to mould, heating, discoloration and a variety of chemical changes.
Even with grain in perfect condition, correctly set milling and polishing machinery is essential to yield high processing outturns.
Complete separation of edible from less-desired products is always difficult to achieve but, even so, there are significant differences in milling efficiency.
[3] Insects and mites (arthropods) can, of course, make a significant contribution towards the deterioration of grain, through the physical damage and nutrient losses caused by their activity.
The metabolic activity of insects and mites causes an increase in both the moisture content and temperature of infested grain.
The worst case is found in small production in developing countries, where, according to the World Food Programme, 40% is common.
[7] However, despite efforts over the years to develop acceptable techniques for measuring grain losses, this remains an imperfect science.
[8] There are particular difficulties associated with accurately measuring on-farm storage losses over a long period when farmers are continually removing grain from stores to meet their own consumption needs.
"Inordinately high- and low-loss situations must be put into perspective rather than giving them overemphasis as has been the case in some instances.
"[9] The origin and justification of grain-loss estimates has thus never been particularly well- founded and attempts to measure losses suffer from the fact that it is an extremely complex and costly exercise to do well.
A further important feature of APHLIS is that it provides a version of its loss calculator that can be downloaded from the website as an Excel file.
Users can change default values in the spreadsheet and make calculations of losses at any desired geographical scale below the level of ‘province’.
There have been numerous attempts by donors, governments and technical assistance agencies over the years to reduce post-harvest losses in developing countries.
Despite these efforts, losses are generally considered to remain high although, as noted, there are significant measurement difficulties.
[11] There is thus a continual need to balance and blend technically ideal procedures and approaches with social, cultural, and political realities.
In the 1980s, there was considerable enthusiasm for the introduction of ferro-cement and brick bins throughout Africa, but these were often found to be too complicated for farmers to construct, and too costly.
Small Breeze block silos also experienced construction difficulties and were found to be not economically feasible.
More positive achievements have been recorded in the Central African Republic, using a simple 1-tonne capacity structure that was found by farmers to be easy to construct and proved popular even without donor subsidies.
A relatively new development is hermetically sealed bags, which appear to offer good possibilities to store a variety of quantities, although further socio-economic evaluation is still required.
