Grain storage on subsistence farms
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Grain storage on a subsistence farm is primarily based on minimizing grain loss. In modern agricultural practices there are methods of managing under 1% grain loss, but small subsistence farms can see 20–100% of grain loss. This can cause starvation and an unstable food supply. Grain loss can be caused by mold growth, bugs, birds, or other contaminants.
One method of preventing loss is hermetic grain storage. Hermetic grain storage strives to eliminate all exchange of gases within the storage system. This mitigates bacterial activity and prevents rodents and bugs from being able to breathe inside the storage systems. The introduction of hermetic grain storage to subsistence farms can create a more stable food supply in the area and reduce the risk of starvation.
Hermetic grain storage systems
[edit]Overview
[edit]Hermetic storage is the process of storing grain or seeds inside sealed compartments, leading to depletion of oxygen and accumulation of carbon dioxide gas. This combination is lethal to insects and molds, making it an alternative to pesticides. This storage method is important to enhancing and elongating grain life while maintaining the grain integrity.[1]
Hermetic storage has been around for a long times and it has been well-received, largely in developing countries, since the inception of the method. The method can exercised using different materials such as sealed clay pots, sealed plastic bags, sealed metals, etc. These materials are effective in their own right, and costs are variable; therefore, caution must be exercised to preclude insects infestation during storage time. Ideally, a successful hermetic storage would mean grains are able to retain all their nutrient quality, and crushable commodities are well-kept for the entire process of storage.
The method is used worldwide in Africa, Asia, and the Americas. The scale of acceptance of this method indicates its quality in preserving small and large scale farmers' crops. The benefits of this storage process are especially useful to developing countries that rely on subsistence farming.
Benefits of using the hermetic storage method include enhancing grain life safely, preventing insect infestation without pesticides; the storage process is defiant and resistant to harsh conditions (with the exception of extremely harsh conditions i.e. temperature 0 to -20 degrees Celsius, being unfavorable for oil palm seeds storage)[2] such as hot and humid climates; precluding mold from developing; and mycotoxins, which have a high likelihood to cause cancer, are annihilated.[3] Prior to hermetic storage, grain had to be properly dried to moisture content range of approximately 12–14% to avoid germination and viability losses. Germination and viability are crucial for crop production; thus, losses lead to a decrease in profits.
History
[edit]Underground grain storage was one of the main methods to preserve cereal early in the nineteenth century throughout southeast European and Asiatic societies, using "airtight" underground silos as an alternative for bottles and jars that were used in the Mediterranean. Writing evidence appeared only in the 16th century. By the 1800s, detailed descriptions of the underground silos were made by knowledgeable agricultural writers of Western Europe. They highlighted airtightness as a major factor to maintain grain quality, although some reports observed that some seeds lost germination power.[4]
Early researches with airtight storage were made from 1819 to 1830, where a French industrialist named Ternaux at Saint-Ouen stored grain in nine series of experiments at a large scale. Ternaux stored the product under unfavorable circumstances; the silos were dug into a wet alluvium and the material was stored without concern for humidity. After several years, only spots of mold were encountered inside the silos, especially in critical areas as the walls, roof, and bottom of the structure. Bread was made with the remaining unspoiled grain, but the taste of it was unsatisfying; thus, the experiment was considered a failure. However, this can be considered one of the first instances of scientific research involving hermetic storage.
Around the world
[edit]The method is heavily used in central and southern parts of Africa, such as Botswana, and South America. Small scale farmers have found the process to be more beneficial in their regions. Botswana is an arid area that can go for long periods of time without rain; therefore, hermetic storage has helped in times of drought. Seeds are well-stored for the next season of plowing, although at times seeds are purchased as a supplementary measure. In Botswana, traditional people usually use hermetic storage using a jute bag to increase efficiency and effectiveness in eradicating living organisms within few days. Also, hermetic storage is crucial in Africa, as most of the seeds are produced and stored in the farm. Experimental results proved that hermetic storage of seeds for twelve months can retain germination and viability characteristics, whilst extremely harsh conditions can render an opposite effect.
Brazilian grain producers have begun to use hermetic bags on site to store grains as an alternative to bins. They claim that the cost is accessible and the quality of the grain remains the same for a period of 18 months. The bags are made of polyethylene that is capable of reflecting sunlight, avoiding heating and degradation by light.[5] Argentina frequently experiences a storage shortage of 20 to 35 million tonnes of grain. This led to quality and quantity loss since the grain has to be transported directly from the farms to elevators, and from elevators to terminal ports. Hermetically sealed plastic bags (silo bags) has gained popularity among producers to overcome this issue. In 2008 harvest season, more than 33 million tonnes of grain were stored using the silo bags in the country for several grains and oilseeds, and this technology is being adopted by other South American countries.[6] Sealed bags have been used to store mostly silage in North America; however, the use of this storage system started to grow in the early 2000s. Still, instead of using hermetic choices, the most common option when dealing with storage shortages is piling the grain on the ground.[7]
Types of hermetic storage
[edit]In the advancement of these hermetic storage benefits, three methods are popular used to safely store grain and seeds under hermetic conditions:[8]
- Organic hermetic storage: This process of storage deprives insects of oxygen, slowing down their metabolic process. In this method, insects are allowed a chance to respire for few days before oxygen depletion takes an effect, leading to death due to suffocation.
- Vacuum hermetic fumigation – In this process, air suction takes precedence. Air within the hermetic storage is sucked out, leaving little oxygen for living organisms to survive on. Suction of the air creates a low atmospheric pressure, which is unconducive for life.
- Gas hermetic storage – This method involves filling the hermetic storage facility with carbon dioxide to expedite oxygen depletion.
The main factor that affects the mortality of insects is the low oxygen and high carbon dioxide concentrations. Studies show that the synergetic effect between oxygen depletion and carbon dioxide gas accumulation is necessary to effectively control insects in a hermetic storage.[3] Also, moisture content plays an important role: the lower the water present in the grain mass, the higher the mortality, due to the desiccation effect on insects by low oxygen and high carbon dioxide.[9][10] All methods described previously are equally applicable because all ensure that oxygen which would otherwise by insects is totally depleted to avoid infestation on stored grain. The most prominent method is organic hermetic storage.
Postcosecha silos
[edit]Postcosecha silos are galvanized steel silos. Bulk products such as maize, beans, sorghum, rice, wheat, barley, and seeds can be stored in silos. Products must be dried to or below 14% moisture content before being placed in silos to prevent fungi growth. These silos are usually built locally with simple tools, making them easy to assemble, and are sold by local artisans to the locals. The silos have a small outlet port at the base of the silo so small amounts of grain can be taken out at a time.
Purdue Improved Cowpea Storage (PICS) System
[edit]A team at Purdue University developed the Purdue Improved Cowpea Storage and promoted its use in Western Africa with funds from the Gates Foundation. This method achieves hermetic grain storage using three bags. This method is generally used for storage and transport of cowpeas, hence the name, but the method can be used on other grains. The heavy polyethylene bags with 80 μm thickness come in 50 kg or 100 kg sizes. The first polyethylene bag is filled completely and then tied securely. The first bag is then placed into a second polyethylene bag with same thickness, and that bag is tied securely as well. Finally, these two bags are placed in a third woven nylon or polypropylene bag used for its strength. Farmers and markets can handle this third bag without bursting the inner two.
Recycled plastic containers
[edit]In parts of sub-Saharan Africa, markets sell recycled plastic containers that can be used for hermetic storage. One must make sure the containers can hermetically seal, or the containers will only provide a minimal protection to the grain inside.[citation needed]
Estimated cost
[edit]| Container Type | Maize Capacity (kg) | Cost (US$) | useful life (years) | Storage Cost (US$/Mg/year) |
|---|---|---|---|---|
| Postcosecha silos | 1360 | 145 | 25 to 40 | 4.26 to 2.67 |
| PICS | 100 | 3 | 3 | 10.00 |
| GrainPro bags | 70 | 3.6 | 5 | 10.00 |
| Recycled Containers | 7.74 | 1 | 3 | 43.06 |
Final grain quality
[edit]Seeds stored hermetically have shown to exhibit prolonged quality. Researches in Ghana investigated the effectiveness of storing seeds using three different types of grain storage.[11] The three methods used in the research included the jute, polypropylene and triple layer hermetic storage. Two destructive insects pests, adult Prostephanus truncatus and Sitophilus, were infested in each bag. These two insects pests are common in Africa and are very destructive to maize. Unprotected maize in storage can be totally annihilated by these organisms. Of these three methods, the triple layer hermetic storage offered the best results of seed quality with prolonged germination rate and viability despite insect infestation. Additionally, to ensure that grain maintains its natural quality in storage, it must be stored at optimal moisture contents of approximately 12–14%. The bags have to be sealed for the entire period of storage, and regular check-ups must be done to ensure that the seal remains intact.
Another study investigated the efficacy of controlling bean pests, i.e. Acanthoscelides obtectus, on the quality of beans by employing the hermetic storage system (silo bags and plastic bottles) and non-hermetic glass containers.[12] Beans were stored at high moisture contents of 15%, temperature 25°C and relative humidity 70±5%. In the study the hermetic method showed no alteration in quality.
Deterioration in grain quality arises from several factors: high moisture content at the time of storage, leading to development of molds which renders the grains unusable or unsafe for consumption; failure to keep storage bags air tight from oxygen, accelerating insect infestation and leading to destruction of grain, since hermetic conditions are not met to secure the grain from insects; failure to keep the bags watertight to prevent moisture infiltration; and high temperatures leading to grain discoloration and insect infestation.[13]
Insect mortality
[edit]The longer the exposure of insects to low oxygen and high carbon dioxide, the higher the mortality of these pests in hermetic storage. However, temperature and life stage also have an influence on this factor to determine how long the grain should be stored. The table below shows the time required to kill 90% of insects stored in a low pressure hermetic storage depending on the insect species, life stage, and temperature. It lists the exposure time (h) required to obtain 90% mortality of three development stages of three species of store-product insects under low pressure at four temperatures.[14]
| Insect species | Life Stage | 25 °C | 33 °C | 37 °C | 40 °C |
|---|---|---|---|---|---|
| "T. castaneum" | Egg | 19.76 | 10.65 | 7.17 | 3.13 |
| "T. castaneum" | Larvae | 2.54 | 2.51 | 1.91 | 1.37 |
| "T. castaneum" | Pupae | 10.18 | 8.72 | 6.79 | 2.76 |
| "P. Interpunctella" | Egg | 20.86 | 4.45 | 3.09 | 2.00 |
| "P. Interpunctella" | Larvae | 3.12 | 2.02 | 1.61 | 1.67 |
| "P. Interpunctella" | Pupae | 3.95 | 1.48 | 1.81 | 1.91 |
| "R. dominica" | Egg | 134.68 | 63.00 | 33.75 | 8.61 |
| "R. dominica" | Larvae | 63.66 | 35.31 | 14.17 | 4.78 |
| "R. dominica" | Pupae | 73.09 | 40.54 | 15.68 | 6.49 |
References
[edit]- ^ Bern (January 2013). "Heremetic storage systems for maize stored on subsistence farms".
- ^ Ellis, R. H., T. D. Hong, E. H. Roberts, and U. Soetisna. 1991. Seed storage behaviour in Elaeis guineensis. Seed Science Research 1 (02):99-104.
- ^ a b Kerry, R., Ingram, B.R., Garcia-Cela, E. and Magan, N., 2021. Investigation of the potential to reduce waste through sampling and spatial analysis of grain bulks. Biosystems Engineering, 207, pp.92-105. doi:10.1016/j.biosystemseng.2021.05.001
- ^ Shejbal, J. (1980).Controlled Atmosphere Storage of Grains. Elsevier Scientific Publishing Company. ISBN 044441939X
- ^ "Aumenta a procura em MT por silos bag para estocar grãos no campo". 18 October 2014.
- ^ Bartosik, R (2010). Challenges and characteristic of the South American grain and oilseed postharvest system. 10th International Working Conference on Stored Product Protection. doi:10.5073/jka.2010.425.302
- ^ Maier, E. D., Cook, S. (2014). Increasing Global Food Security and Reducing Post-Harvest Loss with Hermetic Storage of Grains. 1st International Conference of Grain Storage in Silo Bag. Mar del Plata/ Balcarce. Argentina.
- ^ Villers, P, T de Bruin, S Navarro, I Lorini, B Bacaltchuk, H Beckel, D Deckers, E Sundfeld, JP dos Santos, and JD Biagi. 2006. Development and applications of the hermetic storage technology. Paper read at Proceedings of the 9th International Working Conference on Stored-Product Protection, ABRAPOS, Passo Fundo, RS, Brazil, 15–18 October 2006.
- ^ Navarra, S. and Calderon, M. 1973. Carbon dioxide and relative humidity: interrelated factors affecting the loss of water and mortality of Ephestia cautella (Wlk.) (Lepidoptera, Phycitidae). Israel Journal of Entomology, 8, 143 - 152.
- ^ Navarro, S. 1978. The effect of low oxygen tensions on three stored-product insect pests. Phytoparasitica, 6, 51-58.
- ^ Anankware J. P., and Bonu-Ire M., (2013), Seed Viability And Oxygen Depletion Rate Of Hermetically Stored Maize Infested By Major Insect Pests, Sci. Agri., 4 (1), 2013: 13-19
- ^ Freitas R.S., Faroni L.R.A., Sousa A.H., (2016), Hermetic storage for control of common bean weevil, Acanthoscelides obtectus (Say), Journal of Stored Products Research 66 (2016) 1-5
- ^ Hawthorne W., Meldrum A., and Cumming G., (2010), Grain Bags for Pulse Storage – Use Care, Pulse Australia Bulletin
- ^ Mbata, George N.; Phillips, Thomas W. (2001). "Effects of Temperature and Exposure Time on Mortality of Stored-Product Insects Exposed to Low Pressure". Journal of Economic Entomology. 94 (5): 1302–1307. doi:10.1603/0022-0493-94.5.1302. PMID 11681698. S2CID 21314305.