Nitrogen and
Groundwater
Kevin Masarik
Center for Watershed Science and Education
The Issue:
Nitrate is the most widespread groundwater contaminant in
Wisconsin’s groundwater and agricultural sources are the
largest source. Impacts from agriculture on groundwater and
surface waters have been largely buffered by the lag time
between current land-use and water quality. As more data
becomes available the unintended consequences are more
noticeable (increasing concentrations in rivers and streams
and municipal wells, widespread nitrate contamination in
groundwater).
Tangible costs associated with it:
•
•
•
Cost of water treatment to remove agricultural
chemicals that cause health effects.
•
Municipal Water Supplies
•
Private wells
Costs associated with treating health problems
associated with drinking water.
Costs of disposing of locally produced nitrogen
sources (manure, bio-solids, industrial sludge)
while sending money out of the state and the
United States to import industrially produced
nitrogen from out of state using fossil fuels.
WI Well Water Viewer
•
•
•
Select county, township or
section to view water quality
summaries at different
scales.
Select from 14 water
quality parameters.
Use the groundwater quality
summary statistics tool to
see statistics of well water
data for user defined areas
(number of samples, median,
maximum, percent unsafe).
http://www.uwsp.edu/cnr-ap/watershed/Pages/wellwaterviewer.aspx
Factors affecting nitrogen loss to
groundwater
• Amount of nitrogen applied
Within our
control
– As a function of crop type
– Nitrogen application rate relative to
economic optimum
• Nitrogen use efficiency
• Percent of land base in production
Out of our
control
• Geology
• Soil Type
• Precipitation / Climate
Nitrate Concentration
Generalized Nitrate Leaching Potential
0
Economic Optimal Nitrogen Rates
Forest/
Prairie/
CRP
Alfalfa
Soybean
Corn Potato
CornSoybean
Masarik, UW-Extension
Nitrate Concentration
Generalized Nitrate Leaching Potential
0
Economic Optimal Nitrogen Rates
Forest/
Prairie/
CRP
Alfalfa
Soybean
Corn Potato
CornSoybean
Masarik, UW-Extension
Water quality as a function of crop N recommendations
Medium Inputs
No Inputs
Amount of nitrogen applied
Water Quality/
Nitrate
Concentration
Good
Poor
High Inputs
What UWEX Nutrient Guidelines
Do and Don’t Do:
– Do save farmers money by ensuring nitrogen is
not over applied.
– Do allow farms to maximize profitability while
holding everyone accountable to some standard
– Do prevent fields from being treated as dumping
grounds for manure and other bio-solids
– Do help prevent excessively high concentrations
of nitrate in groundwater
– Don’t prevent nitrate from leaching into
groundwater
– Don’t ensure groundwater quality meets
drinking water standards
– Don’t ensure that groundwater quality in areas
that already apply at economic optimum rates
will get better over time
Masarik, UW-Extension
Nitrate Concentration
GW NO3-N = f(Crop N Requirements, Excess N, Soils, Geology)
0
Economic Optimal Nitrogen Rates
Forest/
Prairie/
CRP
Alfalfa
Soybean
Corn Potato
CornSoybean
Masarik, UW-Extension
Comparing Land-use Impacts
Corn1
(per acre)
Prairie1
(per acre)
Septic 2
System
Total Nitrogen Inputs (lb)
169
9
20-25
Nitrogen Leaching Loss (lb)
36
0.04
16-20
Amount N lost to leaching (%)
20
0.4
80-90
1 Data from Masarik, Economic Optimum Rate on a silt-loam soil, 2003
2 Data from Tri-State Water Quality Council, 2005 and EPA 625/R-00/008
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
20 lbs
20 acres
20 acres
Comparing Land-use Impacts
20 lbs/septic system x 1 septic systems = 20 lbs
1/36th the impact on water quality
0.44 mg/L
Assuming 10 inches of recharge -
36 lbs/ac x 20 acres = 720 lbs
16 mg/L
Masarik, UW-Extension
Water table
Stream
Water table
Stream
36 lbs/ac x 20 acres = 720 lbs
20 lbs/septic system
Masarik, UW-Extension
Comparing Land-use Impacts
20 acres
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs
36 lbs/ac x 20 acres = 720 lbs
20 acres
36 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs
20 lbs/septic system x 36 septic systems = 720 lbs
Using these numbers: 36 septic systems on 20 acres (0.55 acre lots) needed to achieve
same impact to water quality as 20 acres of corn
Masarik, UW-Extension
Water quality as a function of watershed area in
production of a high input N crop
50%
Percent of land base in production
0%
Water Quality Nitrate
Concentration
Low
High
100%
Water quality as a function of Nitrogen Use Efficiency
Studies show efficiency typically about 30-50% (Cassman et. al. 2002)
Less nitrogen than
economic optimal results
but with same or greater
yield.
Fertility-research
based economic
optimal nitrogen
application
Economic optimal nitrogen
application results in
greater yield.
Increased nitrogen
application results in
increase in yield without
an increase in efficiency.
More
Less
Water Quality Nitrate
Concentration
Increased nitrogen
application results in
increase in yield but
nitrogen use
efficiency decreases.
Amount of N loss
Less
More
How much nitrogen does it take to raise groundwater nitrate 1 ppm?
The actual amount will vary based on the amount of recharge. For Wisconsin this is likely
somewhere between 6 and 10 inches depending on where you live. For Spring Green we will
assume that nitrogen not taken up by the plant will mineralize and nitrify.
8 in.
1 kg 2.2 lbs
18.1 lbs N
1 ft. 28.32 liters 1 g
= per acre
12 in. 1 ft3
1000 mg 1000 g 1 kg
10 mg NO3-N 43,560 ft2
1 acre
liters
Nitrate-Nitrogen Concentration (mg/L)
1
2
3
4
Inches of
Recharge
N
1
2
3
4
5
6
7
8
9
10
5
10
15
20
30
40
3.4
6.8
10.2
13.6
17.0
20.4
23.7
27.1
30.5
33.9
4.5
9.0
13.6
18.1
22.6
27.1
31.7
36.2
40.7
45.2
6.8
13.6
20.4
27.1
33.9
40.7
47.5
54.3
61.1
67.8
9.0
18.1
27.1
36.2
45.2
54.3
63.3
72.4
81.4
90.5
lbs of Nitrogen per acre
0.2
0.5
0.7
0.9
1.1
1.4
1.6
1.8
2.0
2.3
0.5
0.9
1.4
1.8
2.3
2.7
3.2
3.6
4.1
4.5
0.7
1.4
2.0
2.7
3.4
4.1
4.7
5.4
6.1
6.8
0.9
1.8
2.7
3.6
4.5
5.4
6.3
7.2
8.1
9.0
1.1
2.3
3.4
4.5
5.7
6.8
7.9
9.0
10.2
11.3
2.3
4.5
6.8
9.0
11.3
13.6
15.8
18.1
20.4
22.6
Least
Willingness to implement
Most
Most
Potential to
improve water
quality
Least
Water Quality/
Nitrate
Concentration
Good/Low
Poor/High
Masarik, UW-Extension
Price ($ per lb of nitrogen)
1.2
1
Nitrogen Fertilizer Costs (1960-2012)
Anhydrous ammonia
Nitrogen solutions (30%)
0.8
0.6
Urea 44-46% nitrogen
Ammonium nitrate
Sulfate of ammonium
0.4
0.2
0
1950
1960
1970
1980
1990
2000
2010
2020
Nitrogen Fertilizer Pricing
Form
Cost per ton
Cost per lb of nitrogen
Anhydrous Ammonia (82% N)
$783
$0.48
Nitrogen Solutions (30% N)
$373
$0.62
Urea (44-46% N)
$554
$0.62
Ammonium Nitrate (35% N)
$506
$0.73
Sulfate of Ammonium (21% N)
$451
$1.07
Source: Agricultural Prices for March 2012, National Agricultural Statistics Service, USDA.