Agriculture Reference
In-Depth Information
8
Water-related Issues in Sustainability:
Nitrogen and Phosphorus Management
K. Knowlton* and P. Ray
Department of Dairy Science, Virginia Polytechnic Institute and
State University, Blacksburg, Virginia, USA
Introduction
imbalance related to animal agriculture in devel-
oping and developed countries, and impacts of
more stringent regulations on water quality.
Water quality in the USA and around the world
is threatened by contamination with nutrients,
primarily nitrogen (N) and phosphorus (P).
Animal manure can be a valuable resource for
farmers, providing nutrients, improving soil struc-
ture and increasing vegetative cover to reduce ero-
sion potential. At the same time, application of
manure nutrients in excess of crop requirements
can result in environmental contamination.
Concentrated animal agriculture has been
identified as a significant source of nutrient con-
tamination of surface water, N contamination of
groundwater and ammonia emission. Areas fac-
ing the dilemma of an economically important
livestock industry concentrated in an environ-
mentally sensitive area have few options. If agri-
cultural practices continue as they have in the
past, despite the significant changes in agricul-
tural intensity and changing environmental con-
ditions, continued damage to water resources
and a loss of fishing and recreational activity are
inevitable. If agricultural productivity is reduced,
however, the maintenance of a stable farm
economy, a viable rural economy and a reliable
domestic food supply are seriously threatened. This
chapter reviews impacts of nutrient pollution
on ground and surface water, issues of nutrient
Water Quality Concerns
When N in manure or commercial fertilizer is
applied to land in excess of crop uptake, contam-
ination of groundwater via nitrate leaching
may occur. Nitrate in drinking water is con-
verted to nitrite in the human digestive tract.
Nitrite can replace oxygen in haemoglobin,
resulting in cyanosis, or oxygen starvation, espe-
cially in infants. The current EPA drinking water
standard for nitrate N is 10 ppm (US EPA, 2002);
all public water systems must comply. While pri-
vate water supplies are not required to comply
with this regulatory standard, a US Geological
Survey report indicates that 7% of private wells
are contaminated with nitrate (Hamilton
et al
.,
2004). Nitrate concentrations exceeded stand-
ards in 20% of shallow wells in agricultural
areas, as compared with 3% of wells in urban
areas. Nitrate concentrations were highest in
shallow groundwater beneath agricultural land
use in areas with well drained soils (Burow
et al
.,
2010). Alarmingly, nitrate concentrations in
groundwater increased by 2 mg l
−1
in the
