Environmental Engineering Reference
In-Depth Information
mushroom cultivation. Wheat straw, often mixed with horse manure and hay, is
used for the cultivation of
Agaricus bisporus
(white button mushroom), while
Volvariella volvacea
(straw mushroom) is grown in wetted rice straw or straw mixed
with cotton waste (de Carvalho, Sales-Campos, and de Andrade 2010).
The availability of crop residues is usually calculated by using residue:crop (that
is, most often, straw:grain, or S:G) multipliers. These values are usually given as
ratios of the fresh weight of the harvested plant parts to the dry matter of the crop's
residual mass, and for modern cereal cultivars they are typically around 1.0, ranging
mostly between 0.7 and 1.5. Residue yields can be also determined as the inverse
value of a crop's harvest index (the ratio of crop yield to the crop's total aboveg-
round phytomass), but in this case the total is somewhat larger than the one
obtained from the S:G ratio because the latter measure does not include stubble.
Harvest indices of major crops have been increasing, which means that S:G ratios
have been declining (for more details, see the next chapter).
Forest Phytomass
When the harvests of forest phytomass are considered from a global perspective,
the key distinction is between wood to be used as a construction material (round-
wood in forestry statistics, which becomes sawn wood, commonly timber or lumber
in everyday parlance) or pulped to make paper and woody biomass collected
and cut for fuel (fuelwood or i rewood), whose oven-dry energy density is about
19 MJ/kg (Francescato et al. 2008). This distinction does not apply in afl uent
countries, where all but a small amount of fuelwood is a part of the roundwood
harvest that is conducted by standard mechanized commercial methods of tree
felling and transportation to processing facilities.
But the distinction is important in all of those low-income countries of Asia,
Africa, and Latin America where wood (or charcoal) is either the dominant or the
single most important source of energy for household cooking (and heating) as well
as for many local artisanal manufactures: in all these cases the term woody phyto-
mass is much more i tting than forest phytomass. Most of it is collected by house-
hold members, usually by women and children, who bring home head loads of up
to 25 kg, some of it bought in local markets; this wood has not been harvested by
mechanized felling, and much of it does not come from forests but from any woody
phytomass, including bushes, tree groves, and commercial plantations (rubber,
coconut), as well as roadside and backyard trees. These sources may account for
more than half of all wood burned by rural households. Surveys by the Regional
