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Kansas Geological Survey, Public Information Circular (PIC) 14
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Sources of Nitrate

As fig. 1 illustrates, sources of nitrogen to the soil or land surface include fertilizer, legumes that fix nitrogen in the soil, and animal wastes. Losses include crop uptake and removal, conversion of nitrate to nitrogen gases (denitrification), ammonia volatilization, and leaching of nitrate from the soil zone to the ground water. Nitrogen at or near the land surface may move downward toward the water table by leaching with water (precipitation or irrigation water, for example).

It is useful to divide the sources of nitrogen contamination into nonpoint and point sources. Nonpoint sources are diffuse, as opposed to point sources, which are single, identifiable sources of contamination. Nonpoint sources of nitrate include long-term, widespread overuse of chemical or manure fertilizers (on cropland, lawns, or golf courses) and long-term leaks in sewer lines. Point sources include areas of concentrated livestock confinement, leaky septic or sewer systems, and areas of chemical or manure storage or spills. Unplugged abandoned wells and boreholes, improperly constructed wells, and sinkholes are avenues that can allow rapid contamination of ground water from point sources at the surface. Point sources may result in extremely high nitrate concentrations in localized areas.

Nitrate in ground water is frequently associated with agriculture, the largest industry in Kansas. Plants have basic needs: water, nitrogen, and other nutrients. Statistics from the Kansas Department of Agriculture (KDA) show that sales of nitrogen fertilizers increased dramatically from the mid-1940's to the present (fig. 2). In 1997 over 700,000 tons were sold, which gives an approximate idea of the amount actually used. As fig. 2 shows, during the same period, the number of water rights issued also increased (Will Gilliland, KDA, Division of Water Resources, 1998, personal communication). Because more fertilizer is generally applied to irrigated than non-irrigated cropland and because irrigation increases the amount of water available for leaching, the potential for nitrate leaching into ground water from unused fertilizer increases.

Figure 2--Total nitrogen fertilizer sold in Kansas from 1945 to 1997 (Kansas Department of Agriculture, 1998), and the cumulative water rights issued from 1945 to 1997 (Will Gilliland, KDA, Division of Water Resources, 1998, personal communication).

Use of fertilizer rose sharply from 1960s through 1970s; has stayed flat since then.

Animal-waste sources of nitrogen include feedlots, manure applied as fertilizer, and septic systems. Of these, the biggest source of nitrogen is the waste from beef cattle (table 1). Because of the potential volume of nitrogen available from both fertilizer and animal sources, proper management for control of all sources of nitrogen is vital in protecting the state's ground water.

Table 1--Nitrogen from animal wastes in Kansas. Population statistics from 1990 U.S. census as reported by the Environmental Working Grop, 1998; Animal Statistics from Kansas Department of Agriculture, 1997.

Source of
Nitrogen
Amount of
Nitrogen
Approx.
Number of
Animals/Humans
Tons of
Potential Available
Nitrogen per year
Dairy Cattle 10 lb./ton manure 79,000 4,680
Beef Cattle 14 lb./ton manure 2.35 million 180,000
Swine 10 lb./ton manure 1.305 million 9,530
Humans Using
Septic Systems
14.5 lb./person/year 765,000 5,550

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Kansas Geological Survey, Public Outreach
1930 Constant Ave., Lawrence, KS 66047-3726
Phone: (785) 864-3965, Fax: (785) 864-5317
bsawin@kgs.ku.edu
Web version July 1999
http://www.kgs.ku.edu/Publications/pic14/pic14_2.htm