Metal silos are constructed from sheet metal, often by local artisans. They are designed as grain stores but are sometimes used as water tanks. They range in capacity from 90kg to 3000kg. They should be located inside a house or under a shelter and placed on wooden pallets to prevent contact with ground moisture corroding the metal.
When fully sealed metal silos are gas-tight (hermetic) so that when filled with grain and tightly closed, a modified atmosphere is created that will kill insect pests.
Capacity: 90kg - 3t
Lifespan: 15 year - 20 year
Initial cost: US$ 197 - 550
Cost per tonne per year: US$ 11 - 31
CEREALS - Maize (Kenya, Malawi, Tanzania, Uganda); Millet (Kenya); Paddy rice (SE Asia); Sorghum (Kenya, Uganda)
PULSES - Common beans (Kenya, Uganda), Cowpea (Uganda)
Materials:- galvanised metal sheet (0.5mm thick or 26 gauge), and solder (50:50 lead:tin)
Manufactured locally by artisans trained by metal silo projects. Also Kenya has a company (Ekima) that is manufacturing them. Where possible the structures are constructed close to where they will be used to avoid the transport of large awkward structures.
With good maintenance, metal silos typically remain usable for 15 to 20 years. Variations in lifespan depend on conformity to installation and management recommendations, such as provision of shade, positioning on a pallet to avoid contact with moisture. Common malpractices include placing heavy objects on the silo, poor installation (placing the silo on an uneven platform, on the floor and exposure to water and sunshine). Extension messages advocating proper installation can be accessed using a Airtel mobile phone SMS facility called 321.
Marketing and promotions:
Metal silos have been the focus of numerous promotional campaigns across Africa in recent years (see below), and Central America since 1990s. Kenya - 2012-2014; Malawi - A number of campaigns including the launch by the President in April 2007. Metal silos mounted on floats during Independence Celebrations (2008 - 2011), displayed during the National Agricultural Fairs (2007- 2014), displayed in Agricultural Shows at national, Agricultural Development division and district levels (2007- 2014), Farmer field days and open days (2007- 2014); Tanzania- (years not specified); Uganda - Mar 2014-May 2015 (through WFP); Zambia: - 2007 to date; Zimbabwe - 2010 to date.
Success and nature of marketing:
Metal silos have been the focus of numerous promotional campaigns across Africa in recent years, and Central America since 1990s. Kenya - 2012-2014; Malawi - A number of campaigns including the launch by the President in April 2007. Metal silos mounted on floats during Independence Celebrations (2008 - 2011), displayed during the National Agricultural Fairs (2007- 2014), displayed in Agricultural Shows at national, Agricultural Development division and district levels (2007- 2014), Farmer field days and open days (2007- 2014); Tanzania- (years not specified); Uganda - Mar 2014-May 2015 (through WFP); Zambia: - 2007 to date; Zimbabwe - 2010 to date.
Training as part of the campaign:
Training has featured in the promotion campaigns, including: Demonstration of proper use of metal silos (~30 mins). Training local artisans in the fabrication of metal silos (typically a 5 day training during which they each construct a full-size metal silo from scratch and learn about postharvest losses). A training manual for local artisans has been developed (Kenya, Zimbabwe, Malawi). In Malawi some reported that too much emphasis was put on local fabrication and distribution of metal silos and not on training of extension services in the proper utilisation of the technology. More recently CIMMYT has trained front line staff, agro-dealers, and lead farmers and as a result adoption has increased in Mchinji and Lilongwe. Extension training in Zimbabwe took 3-5 days, involving a field visit to a site where the silo was being used, demonstrating the silo model and visiting the workshops at IAE. In Uganda WFP organised a 1 day training on improved postharvest management techniques and practical applications of new handling and storage equipment. This was followed up with on-farm refresher training and correct positioning of new storage technologies.
Degree of adoption:
Despite the significant amount of promotion of metal silos, it appears that no comprehensive adoption study has yet been done. Respondents suggest the following extent of adoption: Kenya - very limited, mainly in Western and Eastern; Malawi - not widely adopted due to high initial costs but wealthy peri-urban farmers adopt them. 500 silos have been made by artisans; Rwanda - only adopted in project target districts; Tanzania - adoption is still very low as it is new; Zimbabwe - adoption is very limited; Uganda - 3,652 metal silos distributed by WFP at 70% subsidised rate in Tororo, Soroti, Gulu and Mbarara; Myanmar - seen but often not used anymore.
Reason for adoption:
- User friendly for women (women who are mainly accountable for HH level food security) like the outlet location
- More durable than other storage facilities. Solid and sturdy. Life span of >15 years
- Kills insects
- Easy use of chemicals during grain storage (e.g. they can use phostoxin once/ year)
- Strong protection of grains (no rats can enter metal silos)
- When hermetic, they eliminate the need to use storage pesticides so no residue on food
- Occupy only a small space
- Can store grain within the house, providing grain security
- May be locked, this reduces theft of grains within the house
- It is often given out for free
- Portable (when empty) and can be set up at a homestead at short notice
- Locally made
- Choice of different grain capacities
- Does not require local natural resources (e.g. wood, thatch) to be harvested each year for construction
- Very limited maintenance required
- Status symbol for farmers
Weaknesses of this store:
- Often difficult to seal the inlet and outlet ports and therefore to create the hermetic conditions and maintain them during the storage period
- Not necessarily hermetic so that farmers may need to fumigate them
- Needs to be handled with care during long-distance transport
- Needs to be located within a house or under a shelter to protect from sun and rain
- Can be difficult to install a metal silo in a house with a small door
- If grain >14%mc is stored then caking and discolouration of the grain may result, unlike storage with PP bags where grain may lose moisture during storage in dry conditions
- Silo quality may be variable as metal silos are handmade
- Loading and off-loading grain can be difficult
Barriers to adoption:
- Costly. Requires large initial capital, so it is difficult for smallholders to afford metal silos
- Often no commercial supplier of metal silos
- Poorly developed supply chain for necessary construction materials
- Some houses are too small to accommodate metal silos, and the farmer may then have to build a shelter outside at further cost
- Are they really cost effective? Are PHL more than the buy back cost of grain from local retail market?
- Understanding the concept of a hermetic store can be tricky for smallholder farmers, and this may lead farmers to be sceptical
- Agricultural extension officers don’t treat crop storage a key activity and so don't prioritise the technology
- Trained artisans do not have initial capital to start the enterprise, especially when demand is not certain, they alos need agri-business training
- Govt or project should subsidize metal silos so they are affordable for poor farmer
- Commercial approach combined with financial products for farmers
- Removal of tax on metal sheets or at least provide government subsidy for metal sheeting intended for silo construction
- Encourage youth to attend training as they may better understand the science behind hermetic conditions
- Redesign outlet to facilitate easy sealing
- Silos should not be promoted as a hermetic only, but also to use in combination with a grain protectant
- Rubber tubing is becoming more scarce as many vehicles use tubeless tyres nowadays, so supply of rubber to seal inlet and outlet ports needs attention
- More training in agri-business/market based approaches, value chain systems, technical postharvest aspects
- Forming farmer groups to ease access to credit or to set-up merry-go-round savings scheme
Use by institutions:
Malawi - Somebody Cares Ministries in Lilongwe (assisting the vulnerable groups-widows, elderly and orphans), Maziko Vocational Centre in Salima, NGOs (World Vision, CADECOM, Rural Livelihoods, Care, Eagles Relief, OXFAM, Blantyre Synod, Stephanos Children’s Home etc), Community Grain Banks (too numerous to mention), St Patrick’s Catholic Church; Zimbabwe - some metal silos have been constructed at prison facilities, boarding schools (6 x 1 mt metal silos in 2 provinces) and at an orphanage. Schools, churches, prisons, village chiefs, cooperatives, hospitals.
Water tanks, scrap metal
What to like:
Very durable and can be produced locally so creating employment. Cost benefit analysis suggests it is cheap compared with other stores. Re-cycling is easier than with plastic. Can be made airtight, so avoids use of insecticides. The metals walls are smooth and hygiene is easy to maintain. It is proof against insect pests, rodents and ambient moisture and temperature (if instructions to keep it under complete shade are adhered to). Deals with rodents and insects (including LGB) effectively without use of pesticides.
What to dislike:
At household level keeping them airtight is not easy and becomes more difficult with the larger silo sizes. The initial costs of silos is high for farmers and as they need to be located in the shade either inside the house or under a special shelter, this adds to the costs. Once a silo is constructed within a house it is very difficult to transfer it to another place through the main door. The grain near the silo bottom is not easy to withdraw, unless someone gets into the silo and quality control is difficult. It is difficulty to source raw materials on a consistent basis. There is a shortage of artisans in farming regions for silo construction.