336 Organic waste recycling: technology and management
Figure 7.9 Comparison of the percentage crude protein of young alfalfa hay with the
crude protein content of eight aquatic weeds (Boyd 1974; © UNESCO 1974; reproduced
by permission of UNESCO)
To make silage, the aquatic weeds is chopped into small pieces and firmly
packed into a silo to produce oxygen-free conditions. Putrefaction is avoided
since material is preserved by organic acids such as lactic and acetic acids,
which are produced during anaerobic fermentation. The process takes about 20
days, after which the pH falls to about 4. Aquatic plants are often low in
fermentable carbohydrates so it is necessary to add sugar cane, molasses, rice
bran, wheat middlings, peanut hulls, cracked corn, dried citrus pulp, etc. to
avoid putrefaction. Silage made from water hyacinth alone is not acceptable to
livestock, but the quantity consumed by cattle increases as the level of added
carbohydrate is increased, although the addition of sugar cane molasses alone
does not improve acceptability. The most acceptable water hyacinth silages to