Environmental Engineering Reference
In-Depth Information
In fields and farms
Until reaching a food-processing plant, edible parts of fruits, vegetables, and seeds are
subjected to postharvest losses of about 13 percent on the global scale according to estimates
presented in Figure 10.2.
The nonedible part of plant foods (i.e., crop residue) is the vegetative material that remains
after harvest and separation of the edible parts. This is especially important in the case of
oilseeds, such as soybeans and sunflower; grain crops, including corn, wheat, rice, and barley;
and less significantly in the case of fruits and vegetables—although, fruit orchards require
periodical pruning that generates biomass that needs disposal.
Crops residues are used in several ways including incorporation back to the ground to
enhance fertility of the soil; harvesting (either partially or totally) and use as forage for rumi-
nant livestock; harvesting and used as bedding material for livestock; or burning in the fields.
The practice of burning crop residues has the purpose of removing large volumes of biomass
in short-turn-around crops, recycle nutrients, control diseases and pests, reduce weeds, and
decrease fire hazards.
Even when crop residue burning is a common practice, it is discouraged because of its
negative impact on air quality as a result of the production of particle matter in the form of
smoke, the instant release of greenhouse gases (mainly carbon dioxide and methane), the lib-
eration of nitrogen to the atmosphere instead of its incorporation into the soil, the exposure of
the soil surface to wind and water erosion, and the constitution of fire and smoke hazards
(“Crop residue management,” 1999).
During farm animal production, manure (the combination of feces and urine) is the main
solid waste generated, which depends on the species, diet, and age of the animal (EPA, 2004).
Table 10.1 provides some typical amounts of manure generated by different animal species.
The United States produces an estimated amount of manure from farming animals that
exceeds 304 million tonnes (335 million tons) per year in dry basis (US Department of
Agriculture [USDA], 2006). Animals raised in grazing conditions disperse their manure in the
fields, which under good management practices is absorbed by the soil as nutrients. However,
when grazing management is inadequate, manure can contaminate surface water and ground-
water and overenrich the soil with nutrients.
Intensive animal productions systems, such as cattle feedlots, dairies, poultry houses, and
swine farms, produce enormous amounts of manure concentrated in relatively small areas. For
Table 10.1
Manure production per tonne (1,000 kg) of live weight per year of different
animal species.
Animal Species
Manure produced (kg/1000 kg
live weigh/yr)
Typical Handling
System
Swine
29,000
Liquid
Poultry:
Broilers
28,000
Solid
Layers
22,000
Liquid
Turkeys
16,000
Solid
Beef
21,000
Solid
Dairy
30,000
Liquid
Humans
1,223
a
Liquid
a
Based on an average person weight of 68 kg that produces 0.22 kg of fecal matter per day.
Adapted from Environmental Protection Agency (EPA), 2004.
