Silage







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
Advantages:
 * 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

Disadvantages:
 * 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, 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

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 (duh!) - 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 also needed to make silage bales or silage tubes
 * compressed earth bricks to build a permanent vertical silo
 * there is often a nitrogen-rich, often highly acidic liquid that drains from larger silos (effluent). It can be used as liquid fertilizer (example here), for growing duckweed, or in hydroponics (although it may have to be buffered first).
 * effluent can be used to clean up soils which are contaminated with heavy metals
 * effluent may be suitable for "charging" biochar with nutrients (untested idea, but high likelihood of working)
 * filter any vented air through a charcoal filter (char later becomes biochar), to reduce smell
 * large scale carbon sequestration: carbon in silage is stable for a long time, does not go back to atmosphere until exposed to oxygen
 * biofuel: ethanol from silage. See article "Silage produces biofuel for local consumption"
 * (speculative, unproven:) is it possible to grow maggots on silage ? (use for aquaculture and as chicken/duck food)