Agricultural-Based Food Production Geoenvironment Stressors - Sustainable Practices in Geoenvironmental Engineering - page 196

Atmosphere
Runoff leading to
eutrophication, heavy
metal, and bacterial
contamination
Increased soil
organic content
NO - , NO -
Contaminated groundwater
FIGURE 6.8
Illustration of the emissions and leachates due to manure spreading practices.
spread the manure on enough land surface so that nitrogen levels in the drinking water
are maintained within water quality guidelines. About 5% of all cropland is fertilized by
manure according to the USDA Report to Congress (USDA, 2009). Approximately, 50% of
lake water and 27% of river water in the United States are also contaminated with nutrients
(Gleick, 1993). Runoff of the manure during rain events causes high BOD levels in sur-
face waters. Non-point sources pollution of surface waters (rivers, lakes, and oceans) and
groundwater are considered to be the major source of water pollution.
Coarse-textured soils are particularly susceptible to (a) increased movement of nitrate
below the surface and (b) increased salinity levels and groundwater nitrate concentra-
tions as manure application rates increases. More effective means of spreading fertil-
izers by correlating with plant needs are required. Plant uptake capacities should not be
exceeded.
Han et al. (2001) reviewed the accumulation and distribution of heavy metals in soils
amended with animal wastes, sewage sludges, and other wastes (Figure 6.9). For poultry
litter amended soil, copper, and zinc concentrations increased at a rate of 2 mg/kg-year.
Most of the copper was present in the organic (46%) and residual fractions (52%), whereas
most of the zinc was found in the easily oxidizable (48%) and organic (23%) fractions.
Mobility studies indicated that there was slight movement of zinc downward in the soil,
and copper moved to the 40-cm depth. Zinc was particularly mobile. At depths of 60 cm,
iron oxide and residual fractions were twice that of the non-amended soils.