The bumper corn crop in the U.S. this year will exceed on-farm grain storage capacity and thus cause farmers to seek alternative storage systems. Since steel (metal) bins or other permanent structures like silos cannot be erected on short notice, the silo bag, also referred to as a grain bag or a harvest grain bag, will be one of the alternatives that farmers will most likely consider. While silo bags have been used for decades for storing silage in the Midwest, and commonly used since the early 90’s in Argentina and since the early 2000’s in Australia for storing commodities such as corn, wheat, soybeans and sunflower seeds, they have only been used in the U.S for storing commodity grain during the last few years. Also note that for high moisture grain stored for feed (> 25%), the grain becomes ensiled, which renders it not marketable as commodity grain.

In this article, I will discuss the use of silo bags for storing commodity grain, the pros and cons of using the bags, and stored grain management when using silo bags for corn and soybeans in Indiana. The term “silo bag” is used in this article rather than other terms that are found in the literature such as grain bag or harvest grain bag.

What are silo bags?

Silo bags are made of a triple layer of thick laminated extruded plastic (polyethylene) about 800 microns thick; the two outer layers are white with UV protective coating while the inner layer in contact with the grain is black. When fully loaded with grain, they are a long sausage-like tubular shape of about 8 to 12 ft in diameter and up to 200 ft in length and can hold 8,000 to 12,000 bushels of grain. They have been used for storing commodities for human on farms in Argentina, Australia, Canada and the U.S. Commodities stored include corn, soybeans, wheat, barley and sunflower. A limited number of trials have been conducted on the use of silo bags for storing dry grain meant to be delivered to the market. These studies evaluated moisture level thresholds, storage period limits and stored product quality. Most were conducted in Argentina, which currently stores as much as one third of its cereal grain and oilseed production in silo bags (Bartosik et al., 2008). Only a few limited studies have been reported in Australia (Darby and Caddick, 2007) and the United States (Channaiah and Campabadal, 2011; Ward, 2012). This is one reason why there are no extension publications on the use of silo bags for commodity grains in the Midwest nor have extensive data on the performance of the silo bags in Midwest conditions been collected. Note that the flexible liners, also termed silo bags, that are used for silage are not the same as those used for commodity grain, even though they look quite similar and have similar structural and loading features. Therefore, when a silo bag is purchased, the buyer should tell the dealer exactly how it will be used.

Factors to consider in locating and using silo bags for commodity grain

Silo bags need to be located on firm, level and well-drained ground, free of cover or harborage for vermin (rodents, wildlife, etc.) that destroy the stored grain or sharp objects that could puncture the bag. Vermin puncture bags causing grain to spill and be damaged by water ingress into the grain by means of the puncture. Therefore it is advisable to locate bags in such as way as to prevent incursions by these creatures. Avoiding spills during loading and the cleanup of spilled grain prevent rodents and wildlife from poking at the bag. Also, the bag should be set in place in such a way as to remove folds (bags stretch up to 10%) at the base that make it easy for rodents to chew the plastic. The base is said to be one spot where vermin punctures typically are seen.

It is also best to set silo bags in an area where the loading and unloading equipment can be maneuvered to enable easy loading and unloading of the bag. Special equipment is needed for loading and unloading, in addition to a tractor to power the equipment. Dealers have quoted unloading and loading equipment costs as just over $50,000. Usually 2 or 3 people are needed to load a bag. Therefore, the cost of labor needs to be taken into account. For farmers who are considering using silo bags for stored grain commodities for the first time, it is advisable that they seek help from the dealership and other producers who have used them before, rather than trying to work alone. Because bags have been used for silage in the Midwest for many years, it would be helpful to speak to farmers who have used bags for that purpose. A final point about using silo bags is that the user should contact their crop insurer to inform them of the decision to use silo bags and ask them whether the crop will be covered by their policy. The insurer will need to know the quality of the grain and quantities going into the bag and removed from the bag at the end of storage. It is also important to note that grain stored in silo bags is not covered under Indiana Grain Buyers and Warehouse Licensing and Bonding Administrative Code. It is strongly recommended that those who use the bags and who are interested in warehouse receipts contact the Indiana Grain Buyers & Warehouse Licensing Agency (IGBWLA) (http://www.in.gov/isda/files/IGBWLA_2013.pdf) and read through the code (824 lAC 2-4-11 Temporary and emergency storage Authority: IC 26-3-7-; Affected: IC 26-3-7-7; IC 26-3-7-10)

Monitoring and Management of Grain stored in Silo Bags 

Some people have referred to silo bags as a hermetic storage system because the flexible plastic liner limits ingress of air, thus causing the build-up of carbon-dioxide levels within the bag, which tends to limit, or at very high levels stop, the growth of fungi and insect pests. However, tests conducted in Australia by CSIRO (Darby and Caddick, 2007) and in the U.S. by Kansas State University (Channaiah and Campabadal, 2011) showed that true hermetic conditions of very high CO2 levels that kill insect pests and stop fungal growth are not reached in the bags used in the field, especially with dry commodity grain. This is because CO2 levels increase very slowly in low moisture grain and at the same time air can ingress due to punctures of the bag by vermin. This means that managing silo bags as thought they provided hermetic storage is not a safe practice.

In addition, silo bags should not be managed in the same way as grain stored in a steel bins. Because moisture movement within the grain mass stored in a silo bag cannot be controlled using an aeration fan after the grain has been bagged, it is important that the grain placed in the bag be at the correct moisture level. The temperature of the grain in the bags, particularly the portion close to the plastic liner, tends to approach the ambient temperature and the moisture content is fairly stable when the silo bag is well sealed. A greater proportion of the grain stored in the bag (about 18%) is affected by the ambient temperature than would be affected in a conventional steel bin (Darby and Caddick, 2007). Moisture migration can occur within the bags. Moisture tends to move to the surface and moisture can condense on the grain that is in contact with the inner liner due to diurnal temperature fluctuations. This can cause grain spoilage at the surface as has been reported in several published papers on silo bag storage (Darby and Caddick; Channaiah and Campabadal, 2011; Ward, 2012). Aligning the silo bags in the North-South direction allows a more uniform solar load on the surface of the bag and this will help to minimize temperature variations that cause moisture migration and localized heating. Also, sampling of stored grain in the bag requires that the bag be broken and re-sealed. Unfortunately, sampling compromises gas-tightness and the advantages brought by a hermetic system. U.S. studies were conducted in Mississippi by Ward (2012) suggest that commodity corn (at 14%) can be safely stored in silo bags for up to 4 months without marked quality loss, but soybeans stored at 10.4% lost approximately one grade after 4 months of storage in a silo bag. Because the climate and the grain used in the Mississippi study and in the other studies referenced are different from Indiana, below is a listing of some safe storage moisture contents and recommended management procedures including recommendations on safe storage moisture contents:

  • Corn and soybeans stored in silo bags should be at moistures at or below 15% and 13%, respectively.
  • Corn dried using a high temperature dryer should be cooled to within a few degrees of ambient temperature prior to bagging so that heat is not trapped in the bag when it is sealed.
  • Silo bags should not be over loaded; most bags only stretch by about 10% and over filling could result in the bags breaking, especially when they are unloaded.
  • Corn or soybeans should not be stored in the bags beyond spring, and if possible for no more than 4 months. Winter conditions in the Midwest will keep the grain fairly cool and slow down any biological activity. During spring warm up when snow melts water may leak into the bag and as temperatures rise biological activities such as the growth of fungi and insect pests will accelerate in the wet grain.
  • Bags should be inspected frequently for punctures by vermin and any other leaks. Punctures should be patched using specially provided sealants and tapes (not duct tape) available from the silo bag dealer. Note that snow cover can hide punctures and therefore snow should be cleared from the bags in order to effectively assess damage to the flexible liner.
  • Bags should be sampled, using a grain trier when necessary, to determine the extent of water ingress or spoilage that can be detected near the surface. Note that the liner must be punctured to access grain with a trier probe and resealed after sampling.

Benefits of using silo bags

  • They reduce capital investment required when building permanent steel bins (estimated at about $1.50 to $2.00 per bushel of stored grain).
  • They are a cost effective alternative that can act as a buffer providing additional storage, with estimates of 7 cents per bushel of grain stored.
  • They could simplify harvest logistics by providing flexible storage at a suitable location especially when permanent storage is a constraint.
  • They are an easy means for on-farm segregation of commodities thereby providing identity preservation.
  • They maintain grain moisture in storage when a hermetic (air-tight) environment is maintained.

Disadvantages of using silo bags

  • Silo bags need special loading and unloading equipment, which first time users will need to purchase or rent one.
  • Extra time and monitoring is needed to effectively manage grain stored in silo bags.
  • Grain stored in silo bags is more susceptible to negative influences from the environment, especially extreme weather.
  • Grain stored in the bags is vulnerable to damage from vermin (wild life, rodents, insect pests, etc.) and protective measures and monitoring need to be in place.
  • Because silo bags are temporary storage, they cannot be used for warehouse receipt grain. Additionally, silo bags are not covered by the Indiana Grain Buyers and Warehouse Licensing and Bonding Administrative Code and farmers intending to store grain in silo bags should check with their crop insurance agent regarding insurance coverage.
  • When grain is stored in the bags, aeration cannot be used to control moisture distribution, temperature and growth of fungi and insects.
  • Silo bags can only be used once.

In conclusion, silo bags can be used as an effective temporary storage option for grain stored on-farm in the Midwest. Because there is lack of data on safe storage moisture content thresholds and the length of safe the storage under Midwest conditions, farmers are advised to be prudent and conservative when using silo bags. Cereal grain and oilseeds must be dried to safe moisture levels before storage in silo bags (15% maximum for corn and 13% maximum for soybeans) and a new crop harvested in the fall should be stored for no more than 4 months (i.e. no later than February the following year). For more information on other temporary storage options, read Grain Quality Task Force Factshet#38: Temporary Grain Storage Considerations found at https://www.extension.purdue.edu/extmedia/gq/gqtf38/gqtf-38.html.