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Flat silo - The lactic fermentation process is already finished after about 2 weeks. The lactobacilli produce so much lactic acid that the pH drops considerably, ending up somewhere near 4. That's too low even for the lactobacilli, so that they die too. Nothing will grow and the whole thing is well-preserved, possibly for years.
The first phase should be as brief as possible to maintain the quality of the silage. Excessive aerobic fermentation reduces the energy content of the silage and may cause heat damage to proteins.
The second or anaerobic phase begins when available oxygen is used up by respiration and aerobic bacteria cease to function. Anaerobic bacteria (bacteria that grow in the absence of oxygen) then begin to multiply rapidly and the fermentation process begins.
The best silage is produced when the most rapidly growing microorganisms are predominately of the lactobacilli species, as they produce lactic acid from the fermented plant material. Lactic acid lowers the pH of the silage. Fermentation completely ceases after three to four weeks when the pH becomes so low that all microbial growth is inhibited.
(Source: Nutritional Ecology of the Ruminant, P. Van Soest, Cornell University Press, 1994, p. 217.)

Silage in factory farm

Silage is the preservation of green fodder in a silo by means of lacto-fermentation. It relies largely on lactobacilli, especially Lactobacillus plantarum, and is thus similar to the way in which Sauerkraut and Kimchi are preserved.

Advantages and Disadvantages


  • weather at harvest time is largely irrelevant (make hay while the sun shines)
  • often has better nutrient preservation than hay (=> healthier, happier cows)
  • wide range of crops can be used (see below, "feedstocks")
  • weedy harvest can be used - get rid of weed seeds in the process
  • large quantities can be stored, preserved for years
  • no need for further processing
  • even horses can be fed with silage, although the process is tricky and somewhat different from that for regular silage


  • harvest is heavier than hay, i.e. somewhat higher initial energy input is required
  • high weight and water content means that silage cannot be transported very far, therefore has low commercial value
  • equipment may be more expensive than that used for hay
  • infrastructure for storage may have to be built (silo)
  • when plastic sheets are used, there will be plastic waste that creates waste issues / has to be recycled.
  • effluent from silage is very acidic and rich in nitrogen (nitrates) - a potential serious pollutant
  • silage odor !

Suitable feedstocks

grass crops, corn (maize), sorghum, cereals (wheat, oats), hemp, duckweed, azolla, beans, clover, sunflowers, ...

Managing Leachate

Silage leachate is surplus water from silage, which carries soluble sugars, proteins and nutrients with it as it seeps out of the stack. Silage leachate is one of the most potentially contaminating wastes generated on the farm. It is considered to be 200 times stronger than raw domestic sewage, 40 times stronger than dairy shed waste and 8 times stronger than flushed piggery wastes. It is also extremely corrosive and can damage concrete and steel. Silage leachate concentrate is very toxic to stream health so we need to carefully locate and manage the silage pit to avoid any potential leachate entering surface and ground water.

  • locate silo as far away as possible from water resources
  • diversion trenches, roovs, covers over silo.
  • when mixed with manure, leachate produces hydrogen sulfide and other hazardous gases that can kill animals and humans
  • leachate can potentially be used in diluted form to fertilize duckweed and azolla but due to its low (acidic) pH, it may have to be buffered with something alkaline, such as ash
  • duckweed depends on external nitrogen inputs (provided at high levels by the leachate) while azolla makes its own. So perhaps duckweed is the better choice

Applications and Product Ecology

  • the traditional use: as livestock fodder for ruminants (cattle, goats, sheep)
  • feedstock for anaerobic digester to make biogas (popular: corn silage)
  • silage contains abundant lactic acid - a major platform chemical for organic chemistry
  • lactic acid is the basic feedstock for many biodegradable bioplastics such as PLA. In a process described here, silage is pressed and the liquid harvested for its amino acids and lactic acid. The remaining fibrous cake can still be used as fodder for livestock or as biomass for other uses (combustion, pyrolysis, biochar, perhaps as mulch ...).
  • bioplastics are needed to make silage bales or silage tubes
  • compressed earth bricks to build a permanent vertical silo
  • a nitrogen-rich, often highly acidic liquid often drains from larger silos (effluent). It can be used as liquid fertilizer (example here), for growing duckweed and possibly azolla, or in hydroponics (although it may have to be buffered with lime or ash first).
  • effluent can be used to clean up soils which are contaminated with heavy metals; see [1]
  • effluent may be suitable for "charging" biochar with nutrients
  • to reduce odors, ventilation through a biofilter or soil biofilter should be considered
  • large scale carbon sequestration: carbon in silage is can be stable for a long time
  • biofuel: ethanol from silage. See article "Silage produces biofuel for local consumption". Still low yield but may improve in the future with special strains.

See Also

Bioplastics for silage bales
Brick silo, but made of fired bricks, not CEBs