Environmental Engineering Reference
In-Depth Information
Animal production
Animal production has several indirect and direct environmental impacts. Among the indirects,
activities related to feed production are the most important; these include the use of land for feed
crops and production and application of fertilizers and pesticides.
Direct environmental impacts include:
1.
Use of land.
2.
Physical and chemical impacts to the soil.
3.
Direct emission of greenhouse gases and ammonia.
4.
Particulate emissions of dust and microorganisms.
5.
Pollutants release to water streams.
The indirect and direct impact of land use for livestock production is enormous. According
to the FAO report
Livestock's Long Shadow—Environmental Issues and Options
, livestock
grazing uses 26 percent of the planet's surface plus 33 percent of arable land to produce feed
(FAO, 2006).
Soil compaction is the most visible physical effect of heavy livestock (cattle) on the
ground. Compaction leads to destruction of soil structure, which eradicates vegetation and
prevents its regeneration even years after the livestock are removed, and ultimately promotes
erosion. Similarly, pigs raised in outdoor systems destroy the soil structure by digging and
eliminating vegetation that later leads to soil compaction with similar results as those for cattle
(Whitmore, 2000).
Chemical impacts are the outcome of the direct release of manure and urine from the animal
to the soil or due to fertilization with manure. The primary effect is vegetation destruction
because excess of nutrients are toxic to plant root systems. A secondary effect is the contami-
nation of air by ammonia and greenhouse gases and contamination of both surface and ground-
water with nitrates, phosphorus, bacteria, and veterinary drugs. A recent study has shown that
corn, lettuce, and potatoes grown in a controlled environment and fertilized with manure
absorb and accumulate sulfamethazine, a popular antibiotic used in veterinary medicine. This
raises the concern that drugs used to treat farm animals may enter the food supply chain and
promote antibiotic resistance in humans (Dolliver et al., 2007).
Once metabolized, nitrogen from the diet is excreted mostly via urine in the form of urea for
most animals; the exception is poultry that eliminates nitrogen as uric acid. The uric acid is then
converted to urea in a relatively slow reaction catalyzed by microorganisms that may take days:
C H N O
→
NH CONH
[3.11]
5443
2
2
Urea is then converted into ammonia by action of enzymes during a period of hours:
NH CONH
+
H O
→+
NH
CO
[3.12]
2
2
2
3
2
Ammonia gas released to the atmosphere has the propensity to combine with water to form
ammonium ions:
NH
+
H O
→ +
NH
+
OH
−
[3.13]
3
2
4
These ammonium ions are brought back to the land as precipitation and once in the ground
converted to nitrate (NO
3
−
) by nitrifying bacteria, causing acidification of soils and unwanted
fertilization with nitrogen of certain lands.
