BEST MANAGEMENT PRACTICES
FOR
AGRICULTURAL NONPOINT SOURCE CONTROL
II. COMMERCIAL FERTILIZER
North Carolina Agricultural Extension Service
Biological and Agricultural Engineering Department
North Carolina State University
Raleigh, North Carolina
In Cooperation With:
•
Agricultural Stabilization and Conservation Service, USDA
Economic Research Service, USDA
Extension Service, USDA
Soil Conservation Service, USDA
Environmental Protection Agency
North Carolina Agricultural Research Service
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STATE-OF-THE-ART REVIEW OF
BEST MANAGEMENT PRACTICES FOR AGRICULTURAL
NONPOINT SOURCE CONTROL
E. COMMERCIAL FERTILIZER
for the project
RURAL NONPOINT SOURCE CONTROL WATER QUALITY
EVALUATION AND TECHNICAL ASSISTANCE
USDA Cooperative Agreement - 12-05-300-472
EPA Interagency Agreement - AD-12-F-0-037-0
PROJECT PERSONNEL
DeAnne D. Johnson Project Assistant
Jonathan M. Kreglow Extension Specialist
Steven A. Dressing Extension Specialist
Richard F. Maas Extension Specialist
Fred A. Koehler Principal Investigator
Frank J. Humenik Project Director
Biological & Agricultural Engineering Dept.
North Carolina State University
Raleigh, North Carolina 27650
William K. Snyder USDA-SCS-Participant
Lee Christensen USDA-ERS Participant
EPA PROJECT OFFICER USDA PROJECT OFFICER
James W. Meek Fred N. Swader
Implementation Branch Extension Service
Water Planning Division Natural Resources
Washington, D.C. Washington, D.C.
AUGUST 1982
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EXECUTIVE SUMMARY
Accelerated eutrophication is one of the chief water quality problems
caused by excessive nitrogen (N) and phosphorus (P) loadings to rural water-
sheds. Fish kills, nuisance algal blooms, heavy aquatic weed growth, poor
taste and foul odors are some of the consequences of eutrophication. Nitrogen
contamination of drinking water supplies can increase the rate of "blue baby"
incidence in consumer populations. Agriculture is one of the major rural
nonpoint sources of nitrogen and phosphorus pollution. Accelerated use of
commercial fertilizer over the past few decades has created a great potential
for N and P contamination of waterways via cropland surface runoff and ground-
water infiltration. It is the intention of this document to identify and
discuss the state-of-the-art in best management practices (BMPs) for control-
ling the pollution of natural waters from agricultural use of commercial
nitrogen and phosphorus fertilizers.
Presently, several Rural Clean Water Program (RCWP), Model Implementation
Program (MIP) and Agricultural Conservation Program-Special Water Quality
(ACP) projects across the United States are designed to demonstrate the
effectiveness of various control mechanisms for abatement of agricultural
nonpoint source water quality problems. In many cases, programs have been
hindered in efforts to achieve water quality goals by a lack of information
on the cause-effect relationships between BMPs and water quality. Data from
these research efforts may expand current assessments of the applicability
of individual BMPs and BMP systems as water quality control mechanisms.
The literature strongly supports soil testing as a key element in
proper fertilizer management. Proper utilization of soil test results will
greatly reduce the losses of N and P from cropland as correct fertilization
and liming rates increase fertilizer uptake efficiency. Spring application
of fertilizer for spring and summer crops is recommended over fall application
in the humid regions of the Pacific Northwest and the Eastern half of the
United States. Split application of nitrogen is a BMP for humid regions and
areas of intensive irrigation.
In conjunction with proper fertilization rate and timing, terraces can
greatly reduce surface runoff losses of nitrogen. Terraces will increase
qoundwater levels of nitrate nitrogen in humid regions and heavily irrigated
areas if N supply exceeds crop demand. Other soil conservation practices
can, in general, reduce nitrogen losses, but data show considerable variability
in their effectiveness. Slow-release nitrogen fertilizers and irrigation
management can help to reduce losses of N to both surface and ground waters.
11
-------
Ammonium and urea may be superior to nitrate fertilizers in efforts to reduce
nitrate nitrogen leaching.
Terraces can effectively reduce total P losses in all regions of the
United States. Crop rotation, rotation grazing and residue management are soil
conservation practices that double as P control mechanisms. Though conservation
tillage reduces total P losses as compared with conventional tillage, it can
cause increased soluble phosphorus losses. Sedimentation basins and flow
control measures can help decrease P losses from intensively irrigated crop-
land.
In regions other than the Corn Belt, little is reported concerning
the effectiveness of control mechanisms for nonpoint source fertilizer pol-
lution. The greatest overall need is a series of watershed studies with a
holistic approach: surface and subsurface water quality, food supply con-
cerns, economics, agronomic concerns and institutional matters. Data from
some of the RCWP, MIP and ACP projects will allow a more refined evaluation
of the cost-effectiveness of selected BMPs and BMP systems for water quality
control. Reports from smaller scale research are necessary to better assess
the merits of various fertilization timing and method schemes. Also neces-
sary is documentation of the relative cost-effectiveness of erosion control
versus other management practices for controlling phosphorus losses. The
combined use of slow-release nitrogen fertilizers with sediment control
practices should be explored for potential of protecting both surface and
ground waters.
Conclusions and recommendations regarding best management practices
for controlling the inputs from commercial fertilizers to surface and ground
waters include:
1. Soil testing is the most important BMP component for all regions
of the United States. Soil test results should be used to help
determine proper fertilization and liming rates.
2. Proper fertilization rates can reduce potential nitrogen losses
by 35-94 percent as compared to excessive rates.
3. Spring nitrogen fertilizer application for spring and summer
crops is superior to fall application in regions with wet soils,
humid climates and high infiltration. Spring application is highly
recommended where practical in the Pacific Northwest and the
Eastern half of the nation.
4. Split application of nitrogen can reduce potential nitrogen
losses by up to thirty percent as compared to single application.
Split application is recommended where practical in the Pacific
Northwest, the Eastern half of the nation, and areas of intensive
irrigation in other regions.
5. Level terraces can reduce total nitrogen surface losses by as much
as 85 percent, but can more than double groundwater nitrate loading
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5. (continued)
as compared to contour farming. Terraces are recommended as
nitrogen controls where no potential groundwater problem exists,
but contour farming should preferentially be used in the humid
Eastern and Pacific Northwest states with groundwater nitrate
problems.
6. Drainage control can help reduce nitrate losses by 50-98 percent
in wet areas and irrigation tracts. More judicial irrigation
management is a BMP for Coastal and Western States under inten-
sive irrigation.
7. Slow-release nitrogen fertilizers can reduce N losses by as much
as 95% versus conventional forms, and are recommended for use
in all regions of the nation.
8. The use of crop rotations, no-till and conservation tillage
may reduce surface N losses by 40 to 85 percent as compared
to conventional practices.
9. Broadcast fertilizer should be incorporated whenever possible.
10. Level terraces can reduce total phosphorus losses by as much
as 67 percent as compared to contour farming. Terrace systems
are a phosphorus control BMP across the nation.
11. Use of rotation grazing, crop rotations, cover crops and conser-
vation tillage can reduce P losses by forty to seventy percent
as compared to constant grazing, continuous cropping and con-
ventional tillage practices. These soil conservation practices
are nationally recommended as phosphorus control BMPs.
12. Sedimentation basins and flow control can be used to decrease
phosphorus losses from irrigation.
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CONTENTS
Executi ve Summary i i
Fi gures vi 1
Tables viii
Preface x
1. Introduction 1
2. Control Mechanisms 10
Increasing Fertilizer Uptake Efficiency 10
Soil testing 10
Liming 12
Rate of application 14
Timing 17
Controls for Ni trogen Loss 23
Control s for Phosphorus Loss 32
Summary 39
3. Research Needs 43
4. Current Research 44
References 46
vi
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FIGURES
Number Page
1 Range of nitrogen concentrations from nonpoint sources 4
2 Range of total phosphorus concentrations from nonpoint sources.... 5
3 Land Resource Regions 11
4 Regions with literature references indicating soil testing
as a BMP 13
5 Regions with literature references indicating liming as a BMP 15
6 Regions with literature indicating proper fertilization
rate as a BMP 19
7 Regions with literature references and projections
indicating elimination of fall application as a BMP 21
8 Regions with literature references and projections
indicating split application as a BMP 22
9 Regions with literature references and projections indicating
increased NOg-N leaching coinciding with sediment control 30
10 Regions with literature references and projections indicating
irrigation management can reduce N03-N leaching to groundwater.... 31
11 Regions with literature references and projections indicating
slow-release fertilizer can reduce N losses 34
12 Regions in which significant phosphorus control research
is available 38
13 Regions with literature references and projections indicating
terraces as a P control BMP 40
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TABLES
Number Page
1 Pollutant Contributions to Surface Waters from Nonpoint Sources... 2
2 Comparative Magnitude of Nonpoint Sources 3
3 Regional Consumption of Nitrogen Fertilizer 7
4 Regional Consumption of Phosphorus Fertilizer 8
5 Pollution Potential Versus Fertilization Rate 18
6 Split Application Versus Single Application 24
7 Terrace Versus Contouring as Nitrogen Controls 29
8 Effective Nitrogen Control Mechanisms 33
9 Conservation Practices as Nitrogen Controls 35
10 Terrace Versus Contouring as Phosphorus Controls 41
11 Conservation Practices as Phosphorus Controls 42
VTM
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PREFACE
There are currently many programs and projects across the country for
reducing nonpoint source pollution from agricultural activities. Public
and private monies are being spent to implement agricultural Best Manage-
ment Practices (BMP's) for improving water quality. To assess these many
efforts on a nationwide basis, a joint USDA-EPA project, "Rural Nonpoint
Source Control Water Quality Evaluation and Technical Assistance," has
been established. This undertaking, commonly known as the National Water
Quality Evaluation Project, will assess the water quality and socio-
economic effects of BMP use in the rural sector.
This document identifies and discusses the state-of-the-art in Best
Management Practices for controlling nonpoint source pollution from agri-
cultural use of commercial nitrogen and phosphorus fertilizers. Any
proposals for major changes in commercial fertilizer management must be
coordinated with economic realities, production concerns and institutional
limitations. Conclusions and recommendations in this document are not
intended to reflect economic, production or institutional factors. There-
fore, any inferences drawn from these statements should contain appropriate
caveats.
The scope of the literature reviewed for this document was restricted
to published documents with supporting data. Two computer-based files,
the Southern Water Resources Scientific Information Center (SWRSIC) and
AGRICultural Online Access system (AGRICOLA), were used for a large
portion of the literature retrieval. Much additional information was
obtained through citations follow-up, and interpretive insight was
solicited from NCSU professionals.
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SECTION 1
INTRODUCTION
The Federal Water Pollution Control Act Amendments of 1972, P.L. 92-500
set the tone for future water quality management on a national level by call-
ing for the restoration and maintenance of the "integrity of the nation's
waters." Nonpoint source pollution control is one of the concerns addressed
under areawide waste treatment management in Section 208. Agriculture was
isolated as one of the potential nonpoint sources requiring control mechanisms
for pollution abatement. As indicated in Table 1, cropland, ranges and pas-
tures contribute most of the nonpoint source nitrogen and phosphorus entering
surface waters (4).
Agricultural fertilizer is a major component of nutrient runoff from
cropland. As compared with precipitation and native forest it is clear that
fertilized land can have minimal or large impact on watershed nutrient levels
depending upon management (Table 2). Runoff from agricultural land can carry
nitrate concentrations in excess of the drinking water standard (Figure 1) or
phosphorus concentrations sufficient to stimulate algal blooms (Figure 2).
The National Eutrophication Survey, 1972-1975, set the basis for eval-
uating progress in attaining water quality goals (63). Of 574 classified lakes:
78% were determined to be eutrophic and 18% were considered mesotrophic. It
was concluded that streams draining agricultural watersheds had, on the aver-
age, considerably higher nutrient concentrations than those draining forested
watersheds. Mean concentrations of both total phosphorus and total nitrogen
were nearly nine times higher in agricultural drainage areas than in forested
basins. Furthermore, Corn Belt watersheds had the highest total and inorganic
nitrogen concentrations of any agricultural areas.
Several watersheds across the nation suffer from excessively high nutri-
ent concentrations in either surface water or groundwater. The Chowan River
has had repeated algal blooms in recent years near its mouth at the Albemarle
Sound, North Carolina (99). Cropland runoff accounts for 25 and 20 percent,
respectively, of the nitrogen and phosphorus loadings, while animal waste con-
tributes 23 percent of the nitrogen and 12 percent of the phosphorus. Much of
the remaining nitrogen (34.6%) and phosphorus (46.8%) comes from forests and
wetlands. Mean total P concentrations in agricultural subwatersheds (.08-.66
mg/1) exceed those in a forested subwatershed (.06 mg/1) of the Chowan River,
suggesting agriculture as a potential major pollutant source in selected areas
(71). Intensive cropping practices are the suspected causes of nutrient en-
richment in Saginaw Bay, Michigan (87). Water quality data have shown P con-
centrations of 5-6 yg/1 in Lake Huron, 25-45 yg/1 in Western Lake Erie and
50-71 yg/1 in Saginaw Bay (87), thus indicating agriculture in Saginaw Bay
1
-------
to be a possible source for Lake Erie nutrient loading.
TABLE 1. ESTIMATED POLLUTANT CONTRIBUTIONS TO SURFACE WATERS FROM
SELECTED NONPOINT SOURCES IN THE CONTIGUOUS 48 STATESt
Nonpoint Source Sediment BOD Nitrogen Phosphorus Acids§ Salinity*
Category average load (million tons/yr)
Cropland
Pasture and Range
Forest
Construction
Mining
Urban Runoff
Rural Roadways**
Small Feedlots
Landfills
1870
1220
256
197
59
20
2
2
--
9
5
0.8
--
--
0.5
0.004
0.05
0.3
4.3
2.5
0.39
--
--
0.15
0.0005
0.17
0.026
1.56
1.08
0.089
--
--
0.019
0.001
0.032
--
57.3
--
__
__
3.1
--
—
—
__
Subtotal 3626 15.8 7.4 2.8 3.1 57.3
"Natural
Background"
Total
1260
4886
5.0
20.8
2.5
10.0
1.1
3.8
__
3.1 57.3
t83.8 million ha (207 million ac) in public lands (14% of contiguous U.S.),
mostly in Rocky Mountain Region, were excluded due to inadequacy of information
§As CaCo~.
*From irrigation return flow.
**Deposition from traffic-related sources.
Adopted from Bailey, G.W. and T.E. Waddell, "Best Management Practices for
Agriculture and Silviculture: An Integrated Review," In: Best Management
Practices for Agriculture and Silviculture, Ann Arbor Science, Ann Arbor,
Michigan, p.37, 1979.
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TABLE 2. COMPARATIVE MAGNITUDE OF NONPOINT SOURCES
Source
*Precipitation- U.S.
Lower Limit for Algal Blooms
Maximum Level -Domestic Water Supply
* Precipitation-Ohio
*Forest-Ohio
*Farmland-Ohio
*Precipitation-Coastal Delaware
*Ag. Watersheds-Coastal Delaware
* Precipitation-Minnesota
*Forest-Minnesota
*Upland Native Prairie-Minnesota
*Grassland (112 kg N/ha)-NC
*Grassland (44 kg N/ha)-NC
*Grassland (rotate graze)-OK
*Grassland (cont. graze)-OK
*Corn (204 kg N/ha)-Coastal GA
**Corn (204 kg N/ha)-Coastal GA
*Silvicul tural Piedmont-VA
*Agricul tural Piedmont-VA
*Poorly-Drained Coastal Plain-VA
*Well -Drained Coastal Plain-VA
To-^al
mg/
.73-1.27
"
10
2.0-2.8
.54-. 89
.90-3.11
-
-
-
-
-
-
-
1.52-1.64
2.58-3.25
.17-. 43§
7. 07-10. 31!
1.1-1.8
1.1-3.2
1.7-2.3
1.5-4.1
N
kg/ha/yrf
5.6-10
-
-
12.8
2.1
5.1
44.6-45.4
14.4-15.7
-
-
1.0
2.3
8.4
1.5
6.8
.l-.2§
' 12. 4-25. 8§
2.7
4.4
1.6
4.9
Total
mg/1
-
.025
-
-
.011-. 020
.020-. 023
-
-
.011-. 042
.04-1.2
-
-
-
.56-. 83
1.29-1.32
-
.12-. 19
.10-. 60
.19-. 31
.41-. 65
P
kg/ha/yrf
.05-. 10
-
-
-
.04
.06
1.45-1.48
.39-. 46
.10
.08
.13
-
-
.89
3.24
-
.28
.54
.21
.88
Reference
52
73
73
92
92
92
75
75
86
86
97
40
40
60
60
38
38
10
10
10
10
'"Normalized to precipitation of 76 cm/yr.
*Surface Runoff.
§N03-N.
**Subsurface Flow .
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1 1 1 1 1 1 1 1 1 1
Y//X u-s PRECIPITATION
Refs.: 6, 52, 92.
Y7J( FOREST SURFACE
Refs.: 10, 52, 92.
Y/ / / / / /X GRAS
Ref
i i i i n i i i r'
-DRINKING WATER STANDARD
NITRATE- NITROGEN
Ref.: 73.
(TOTAL NITROGEN)
RUNOFF (TOTAL NITROGEN)
SLAND SURFACE RUNOFF
(TOTAL NITROGEN)
.: 6, 40, 59, 60.
1
SURFACE RUNOFF FROM FERTILIZED CROPLAND (NO,
Refs.: 6, 10, 38, 42, 5^, 60, 92.
1
Y//////V// /AJ///\
DRAIN DISCHARGE FROM FERTILIZED CROPLAND (N(
Refs.: 6, 38, 52, 53. j
i
1 1 1 1 1 1 1 1 1 ! 1 1 1 1 l,| | | | ,
9091 9293
NITROGEN CONCENTRATION (mg/l)
Figure 1. Observed range of nitrogen concentrations from
nonpoint sources.
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i 1 1 1 r~
BLOWER LIMIT FOR ALGAL BLOOMS (.025 mg P/l)
I Ref.: 73.
I
^PRECIPITATION
Refs.: 6, 52, 86.
FOREST SURFACE RUNOFF
Refs.: 10, 52, 86, 92.
GRASSLAND SURFACE RUNOFF
Refs.: 6, 40, 59, 60.
CROPLAND SURFACE RUNOFF
Refs.: 6, 10, 42, 52, 60, 83, 92.
CROPLAND DRAIN DISCHARGE
Refs.: 6, 52, 53.
1
1 1 1 1 1 1
0.25 0.5 0.75 1.0 1.25 1.5 1.75
PHOSPHORUS CONCENTRATION (mg/l)
Figure 2. Observed range of total phosphorus concentrations from
nonpoint sources.
2.0
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Groundwater contamination is a problem at Oakwood Lakes and Lake Poinsett,
South Dakota where NO^-N concentrations exceeded 10 mg/1 in 25% of well samples
taken (3). Irrigated cropland in Long Pine, Nebraska is partially responsible
for NO,-N concentration increases from 1.8 mg/1 in 1950 to 8.1 mg/1 in 1970 at
similar well sites (54). Of 23 domestic wells sampled in 1977-1978, 17.4% had
NOq-N concentrations greater than 10 mg/1. Also in Hall County, Nebraska, 65
of 82 wells sampled in 1979 had NO,-N concentrations exceeding 10 mg/1 (29).
Heavy commercial fertilizer applications are held responsible for the average
N03-N concentrations of 13.6 mg/1 for 139 wells sampled in 1980.
Surface water quality data from the Missouri River Basin (57) showed mean
concentrations in 1969 of 2.67 mg/1 nitrate-nitrogen (NO,-N) and 1.17 mg/1 to-
tal phosphorus (PT). Upper reaches of the basin had as Tow as .31 mg/1 NOo-N,
but downstream near the confluence with the Mississippi River concentrations
reached 4.05 mg/1 NOo-N. Missouri River tributaries flowing through Nebraska
corn regions had levels as high as 5.42 mg/1 N03-N.
Trends show that United States farmers have doubled their fertilizer use
since 1960 (68). In 1976, U.S. farmers used 49 million tons of fertilizer.
Regional data indicate that the Corn Belt and Northern Plains producers have ap-
plied the greatest proportions of nitrogen fertilizer (Table 3). The Corn Belt
and Pacific regions used more phosphorus fertilizer than other areas in the
United States (Table 4) (98). As increased fertilizer use contributes to aquatic
nutrient contamination it also creates greater demands for raw materials. Higher
energy and capital costs for commercial fertilizer production can place a larger
financial burden on the farmer.
Progressing toward a more comprehensive approach to water quality manage-
ment, the Environmental Protection Agency has proposed a groundwater strategy
emphasizing the relationships between groundwater and surface water and those
between water quantity and quality (72). Agricultural irrigation accounted for
70% of nationwide groundwater withdrawals in 1975. Fertilizers and animal waste
are two possible agricultural sources for contamination of aquifers. As indi-
cated by the above, future agricultural policy can greatly affect both ground-
water quantity and quality.
In concurrence with P.L. 92-500, EPA presented water quality criteria
for various pollutants (73). No standard was set for phosphate - phosphorus
(PO.-P), but it was concluded that concentrations greater than 100 yg/1 may
interfere with coagulation at wafpr treatment plants. Furthermore, averaae
concentrations of more than 25 yg/1 P04-P in lakes and reservoirs at spring
turnover may stimulate nuisance algae or aquatic plant growth. Due to the
many variables associated with eutrophication, it is at best difficult to set
rigid guidelines for phosphate control.
As a safeguard against biological nuisances it has been suggested that
P04-P concentrations should neither exceed 50 yg/1 in any stream at the point
where it enters a lake nor exceed 25 yg/1 in the lake (55). For streams dis-
charging indirectly to lakes, levels below 100 yg/1 PO.-P should protect the
lakes from algal nuisances. Relatively uncontaminated lakes have total phos-
phorus surface water concentrations of 10-30 yg/1 (37).
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TABLE 3. REGIONAL CONSUMPTION OF NITROGEN FERTILIZER, 7/1/79 to 6/30/80
Region^
Northeast
Lake States
Corn Belt
Northern Plains
Appalachian
Southeast
Delta States
Southern Plains
Mountain
Pacific
Percentage of U.S.
Anhydrous
Ammonia
0.6
11.4
36.9
27.4
1.5
0.9
1.4
10.0
4.6
5.2
Ammonium
Nitrate
1.5
4.6
9.5
13.9
12.1
16.0
12.2
13.9
9.7
6.6
. Consumpti
Ammonium
Sulfate
1.6
2.7
5.7
3.2
0.6
1.6
2.6
16.9
23.5
41.3
*
on
Nitrogen
Solutions
3.4
7.0
33.3
13.4
9.2
10.8
1.6
5.4
4.6
10.8
Urea
3.4
16.8
29.0
12.1
3.7
0.4
12.9
5.5
5.7
9.7
Total
N
(mt)§
127,285
772,518
2,418,998
1,571,978
350,747
358,552
297,839
687,746
431,854
601,698
Total (mt)
4,979,800 2,396,505 760,743 6,003,080 1,880,029 7,639,323
t Northeast = CT, DE, DC, ME, MD, MA, NH, NJ, NY, PA, RI, VT, WV; Lake States =
MI, MN, WI; Corn Belt = IL, IN, IA, MO, OH; Northern Plains = KS, NE, ND, SD;
Appalachian = KY, NC, TN, VA; Southeast - AL, FL, GA, SC; Delta States - AR,
LA, MS; Southern Plains = OK, TX; Mountain = AZ, CO, ID, MT, NV, NM, UT, WY;
Pacific = CA, OR, WA.
* Includes Alaska, Hawaii and Puerto Rico.
§ Determined from average weight percentage of N in fertilizers.
Source: 98.
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TABLE 4. REGIONAL CONSUMPTION OF PHOSPHORUS FERTILIZER, 7/1/79 to 6/30/80
Region
Percentage
Phosphate
Northeast
Lake States
Corn Belt
Northern Plains
Appalachian
Southeast
Delta States
Southern Plains
Mountain
Pacific
Rock
6.1
18.1
23.6
1.2
4.1
4.0
0
0.3
17.1
19.3
*
of U.S. Consumption
Superphosphates
-22%
1.2
22.4
3.0
6.0
4.8
17.3
0.9
0.6
2.3
41.5
>22%
2.8
12.3
52.0
8.5
8.4
1.9
1.4
3.3
5.3
3.8
Ammonium
Phosphates
2.2
0.7
0.3
3.1
0
5.8
0.2
25.1
16.8
45.8
Other
Phosphates
4.4
7.6
4.8
0.9
0.8
18.3
8.4
10.2
3.5
39.2
Total
P
(mt)§
7,286
28,137
108,558
20,114
17,913
9,117
3,115
22,196
21,503
39,737
Total (mt)
21,729 111,089 1,557,832 540,762
320,029
Northeast = CT, DE, DC, ME, MD, MA, NH, NJ, NY, PA, RI, VT, WV; Lake States = MI,
MN, WI; Corn Belt = IL, IN, IA, MO, OH; Northern Plains = KS, NE, ND, SD;
Appalachian = KY, NC, TN, VA; Southeast = AL, FL, GA, SC; Delta States = AR,
LA, MS; Southern Plains = OK, TX; Mountain = AZ, CO, ID, MT, NV, NM, UT, WY;
Pacific = CA, OR, WA.
*
Includes Alaska, Hawaii and Puerto Rico.
§ Determined from average weight percentage of P in fertilizer. "Other Phosphates"
not included.
Source: 98.
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The maximum permissible NOo-N concentration in domestic water supply is
10 mg/1 (73). Nitrate itself is not toxic at this concentration, but its re-
duction product nitrite, N0~, can react with hemoglobin in the bloodstream to
impair oxygen transport in warmblooded animals. This condition of methemoglob-
inemia can be hazardous to infants less than three months old. Waters with ni-
trite-nitrogen (NO?-N) concentrations of more than 1 mg/1 can cause methemoglob-
inemia in infants.
Warm water fish can tolerate N03-N levels up to 90 mg/1 (43) and N02-N
concentrations to 5 mg/1 (56) before exhibiting adverse effects. The more sen-
sitive salmonid fishes require N09-N concentrations below .06 mg/1 for success-
ful habitation (78,79). L
Nitrogen forms can also contribute to accelerated eutrophication in streams
and lakes. Plants can assimilate both nitrate and ammonium-nitrogen (NH.-N) for
conversion to protein (73). As with phosphorus, it is difficult to set a rigid
standard for the nitrogen level that will cause accelerated eutrophication. How-
ever, total nitrogen (NT) concentrations as low as 1-2 mg/1 can support algal
blooms when other requirements are met.
The above discussion clearly demonstrates the potential for and some con-
sequences of nutrient enrichment of watersheds impacted by fertilized agricultural
land. However, agricultural nonpoint source pollution can be minimized through
implementation of sound agricultural management practices. It is the intention
of this document to identify and discuss the state-of-the-art in best management
practices (BMP's) for controlling the pollution of natural waters from agri-
cultural use of commercial nitrogen and phosphorus fertilizers.
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SECTION 2
CONTROL MECHANISMS
Nutrients, primarily nitrogen and phosphorus, are of concern from a
water quality perspective due to their potential to accelerate eutrophication
of streams, lakes, bays, and estuaries. All land, regardless of use, con-
tributes N and P to drainage water (77). The issue facing the agricultural
community is the extent to which fertilization increases nutrient loading to
receiving waters.
As agricultural land becomes more heavily fertilized the potential for
contributing nutrients to surface and ground waters increases. All forms of
N and P found in commercial fertilizers are ultimately made available to
aquatic organisms. An equitable comprehensive fertilizer management strategy
is one which will minimize the potential for nutrient loading to receiving
waters while production is maintained at optimal levels for agronomic, economic
and food supply concerns.
There are two basic alternatives for minimization of the potential for
nutrient enrichment of agricultural watersheds. One can properly apply the
correct amount of fertilizer for anticipated yields or keep any excess fertil-
izer from entering the receiving waters. Proposed Best Management Practices
(BMPs) for nutrient control encompass both basic control alternatives. Due to
geoclimatic differences, BMPs in one region may not be BMPs in another. For
the purposes of this discussion BMPs will be described in terms of their
regional and/or national applicability. Regions will be identified by their
Soil Conservation Service Land Resource Region letter (Figure 3).
INCREASING FERTILIZER UPTAKE EFFICIENCY
Fertilizer uptake efficiency is expressed as the percentage of applied
fertilizer utilized by the crop. Generally, this will range between 50-70%,
but it may be greater than 80% under favorable conditions or less than 50%
under poor management (67). In most cases, excess nutrients are not as obvious
or detrimental to crops as are deficiencies, but the farmer invariably suffers
higher fertilizer costs. Eliminating excess fertilizer use is the first step
in nutrient control. The following are practices recommended as methods for
increasing fertilization efficiencies.
Soil Testing
Regular soil testing is a very important component of soil fertility
management. Soil tests are used to estimate the quantity of available plant
nutrients and to make recommendations about fertilizer and lime requirements
(19). Effective implementation of this fertilizer management BMP component
10
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LEGEND
A
B
C
D
E
F
G
H
I
J
K
L
M
N
0
P
R
S
T
U
Northwestern Forest, Forage and Specialty Crop Region
Northwestern Wheat and Range Region
California Subtropical Fruit, Truck and Specialty Crop Region
Western Range and Irrigated Region
Rocky Mountain Range and Forest Region
Northern Great Plains Spring Wheat Region
Western Great Plains Range and Irrigated Region
Central Great Plains Winter Wheat and Range Region
Southwest Plateaus and Plains Range and Cotton Region
Southwestern Prairies Cotton and Forage Region
Northern Lake States Forest and Forage Region
Lake States Fruit, Truck and Dairy Region
Central Feed Grains and Livestock Region
East and Central Farming and Forest Region
Mississippi Delta Cotton and Feed Grains Region
South Atlantic and Gulf Slope Cash Crops, Forest and Livestock Region
Northeastern Forage and Forest Region
Northern Atlantic Slope Diversified Farming Region
Atlantic and Gulf Coast Lowland Forest and Crop Region
Florida Subtropical Fruit, Truck Crop and Range Region
Figure 3. Land Resource Regions (48).
11
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ica-
of
matter.
will minimize the error between optimum and actual rates of fertilizer appli
tion (102). Typical soil tests provide information on soil acidity; levels
available phosphorus, potassium and minor nutrients; and soil organic matter
Expensive nitrogen analyses are performed only under special circumstances.
In California sugarbeet production it was found that a combination of
soil analysis and crop history to estimate initial N application rates fol-
lowed by plant analysis to monitor and fine-tune the recommendation led to
efficient use of fertilizer (34). Soil sampling to 0.9 meters (3 feet) just
after seedling emergence gave the best results. A sampling depth of 0-7.5cm
(0-3in) is recommended for soil testing the pastures and meadows of Missouri
(46). Nitrogen needs of irrigated grain sorghum in the Central Great Plains
can be estimated by utilizing N03-N measurements of surface soil samples (64).
Grain yield was more strongly correlated with residual plus fertilizer N than
with fertilizer N alone. Nitrogen availability indexes were correlated with
corn yield in Pennsylvania field testing (22). Soil testing for liming pur-
poses is advised for farmers in many states (1,5,19). For no-till corn in
Maryland regular soil testing is necessary to monitor pH in liming programs
for acidity control (7).
From the literature it is evident that most regions across the con-
tinental United States lend themselves to successful implementation of soil
testing as a Best Management Practice component (Figure 4). For the entire
U.S. it is recommended that an average of one soil sample be taken for every
30 to 45 acres of harvested crop (102). However, in 1977 an average of only
one sample per 104 acres was obtained. As a minimum, it is advised that soil
tests be taken once per three-year rotation for field crops (1,19) and once
every five years for pastures (19). Due to the preponderance of data support-
ing the use of soil testing, it is concluded that this practice is a BMP com-
ponent for all regions in the United States.
Liming
Soils with high levels of exchangeable aluminum, high organic content,
or both can be too acidic for efficient farming. Heavy use of ammonium fertil-
izers also reduces the soil pH. Proper liming to raise pH to optimum levels
has numerous benefits including: supplying Ca and Mg, improving the plant
efficiency of phosphate use, increasing the ability of legumes to fix atmos-
pheric nitrogen, reducing aluminum toxicity and reducing potash leaching and
micro-nutrient deficiencies (5).
North Carolina farmers are advised to soil test and lime routinely to
avoid the possibility of a poor harvest due to aluminum toxicity (44). Liming
deep-till citrus groves in Florida caused lower percentage tile drainage losses
of applied P04-P and K, but higher NO.-N losses than deep-till with no-lime (16).
Liming for pH control of no-till corn is essential in both Maryland and Kentucky
(7,9). Surface soil tends to acidify under no-till, so liming and perhaps in-
corporation are necessary for pH balance. Liming is encouraged in Ohio and New
York to help obtain top yields from new varieties (1,19).
12
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Figure 4. Land Resource Regions with literature references (///) indicating soil testing
as a BMP component.
-------
In general, fields not properly limed can contribute greater amounts of
nutrients to streams for two reasons: decreased fertilizer use efficiency and
decreased crop yields removing less nutrients at harvest and providing less
residue to help control soil and nutrient loss in surface runoff. Literature
citing liming as a BMP was not found for all regions (Figure 5), but wherever
soil test results indicate a need for lime the recommendation should be fol-
lowed. In Florida citrus groves liming may help phosphorus control, but could
cause nitrate problems in ground and surface waters (16). This example points
out the need for local tailoring of this nationally recommended BMP.
Rate of Application
Neither nitrogen nor phosphorus should be applied at rates higher than
those recommended from soil tests or legitimate estimates. Commercial fertil-
izer should be used only to provide those nutrients not present in adequate
amounts for optimum production (95). Growers can neither afford to apply excess
fertilizer to mask poor management nor to apply inadequate amounts to hold down
production costs.
In the San Joaquin Valley of California, fertilizer N was not prevalent
in drainage waters unless fields received excessive irrigation and fertilization
(66). Studies with sugarbeets showed that the N uptake efficiency declined as
the N application rate increased beyond that providing maximum sucrose yield
(33). Furthermore, the N pollution potential was lower at the rate which pro-
duced the maximum yield. In other sugarbeet testing only one of twenty-one
cases showed sugarbeet yield response to fertilizer N when the starter NO--N
level was 252 kg/ha (225 Ibs/acre) or more (34). It was concluded that fertil-
izer N should not be added to these fields unless later plant analyses show an
N deficit. High citrus production is necessary to keep drainage water N levels
below 20 mg/1 NCL-N in California (70). With lower yields much more NO.-N will
be leached to grOundwaters unless the N fertilization rate (112-168 kg N/Ha)
is reduced.
Irrigated grain sorghum yields in the Central Great Plains were best
correlated with residual N plus fertilizer N additions, indicating that proper
fertilization rates are dependent upon cropping patterns and soils (64). In
southern Texas, N application rates for grain sorghum, oats and sudan grass
should not normally exceed the plant uptake in the first 2-3 week period (91).
For irrigated corn in Kansas the grain removed about 25 percent of N applied
at either 50 or 100 kg/ha/yr (61). There was no significant difference between
yields from rates of 50 and 100 kg N/ha/yr for either 1976 or 1977. However,
soil N content was proportional to the fertilization rate. Fields cropped to
a rotation of grain sorghum, cotton and oats in the Texas Blackland Prairie
yielded average surface runoff NO--N concentrations of only 2.3-2.9 mg/1 when
proper fertilization rates were followed for the five-year study period (41).
New York farmers are advised to follow soil test results when selecting
fertilization rates (19). These soil test recommendations are based upon yield
response to added fertilizer. Field studies have shown that N and P losses in
surface runoff are correlated with fertilization rates (103). Subsurface N
concentration was also strongly related to application rate. In other research
14
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Figure 5. Land Resource Regions with literature references (///) indicating liming as a BMP,
-------
NhL-N and soluble P concentrations in tile drains were not significantly in-
fluenced by fertilization rate (104). However, N03-N concentration increased
with rate for a given time of application. In another study soluble NH.-N
loading to surface runoff was not correlated with fertilization rate, but
soluble inorganic P and NO?-N loadings were (42). In summary for Land Resource
Regions L and R, NCL-N losses in both surface and subsurface waters were cor-
related with N fertilization rate, and P losses were correlated with application
rate for surface runoff but not for subsurface runoff.
Corn Belt research on the effects of fertilization rate on water quality
and corn yield has been very conclusive. The average weighted NO^-N concen-
trations in subsurface discharge were 5.8 mg/1 and 21.0 mg/1, respectively,
for continuous corn watersheds fertilized at 168 kg N/ha/yr and 448 kg N/ha/yr
(14). In supporting research, data clearly indicate that NO.,-N leaching below
the root zone can result from excessive fertilization (82). This NO.,-N can
then enter the groundwater or contribute to subsurface flow. Furthermore,
nitrogen applications greater than 168-196 kg/ha increased N runoff losses,
but did not significantly improve yields (101).
Other research in watersheds cropped to corn has shown that both N and P
loadings are potentially greater from fields under excessive fertilization (12).
Phosphorus applications tested were the recommended rate for corn (40 kg P/ha)
and an excessive rate of 66 kg P/ha (59 Ibs/acre). Runoff studies of fallow
plots in Indiana revealed that the average soluble ortho-phosphate concen-
tration in runoff and the extractable P content of sediment were proportional
to the rate of fertilizer application (76). In summary, Corn Belt research
overwhelmingly leads to the conclusion that excessive fertilization, while
having little or no effect on yield, will cause higher levels of nutrient
runoff into surface and ground waters.
In northern Alabama, growers are encouraged to not exceed fertilization
rates recommended on the basis of soil test results (11). Despite the fact
that tobacco is a large cash crop in North Carolina, excess fertilization is
not a safe practice for ensuring high yields (31). Excess N can ruin the
quality of tobacco by browning the leaves, increasing the nicotine level and
by delaying maturity to the point where chance of leaf disease is increased.
Higher N levels will also reduce yields, while excess P will cause P buildup
in the soils (18).
In Georgia, total Kjeldahl nitrogen (TKN) concentrations in surface
runoff from watersheds cropped to corn were related to N application rate
(49). Fields fertilized at the recommended rate did not contribute large
quantities of N to runoff. Alabama corn studies (80) showed that corn utilized
95% of fertilizer N applied at 168 kg/ha, but only removed 50-65% of N
applied at 336 kg/ha. Of course, plant density will affect the nutrient uptake
efficiency at a given fertilization rate. In Maryland, N fertilization rates
are similar for both conventional and no-till corn, but more N can be added to
no-till corn if expected yields are higher (7).
In every research effort cited, data led to the conclusion that excessive
application of N fertilizer will rarely increase crop yield or quality, but
will always increase the likelihood that N will be leached into surface and
16
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ground waters. Research further supports the conclusion that excessive P
application will cause greater surface runoff losses of P and P buildup in
the soil. In short, extra amounts of fertilizer will not ensure better crop
yields, but will increase both the cost to the grower and the potential con-
tamination of surface and ground waters (Table 5). Therefore, proper fertili-
zation rate is a BMP both for those regions which have generated literature
on the topic (Figure 6) and for the rest of the United States.
Timing
Timing of fertilizer application may be the most critical factor in
determining nutrient utilization efficiency and crop yield (50). Each plant
has a unique pattern of nutrient absorption (102), and it is possible to max-
imize plant utilization of nutrients by applying fertilizer near the time of
maximum growth (89). Variables such as crop and soil type, date of planting
and climate affect the optimum timing of nutrient application (102), so it is
crucial that individual farmers manage their fertilization schedules to best
match application with the peak demands of their specific crops in their unique
situations.
For California sugarbeets researchers recommend the use of petiole samples
taken two and four weeks before midseason to determine supplemental N needs (34).
In essence, starter N applications are based upon soil tests and fine-tuned be-
fore midseason based upon petiole analyses. Earlier work determined that the
N uptake efficiency for sugarbeets did not vary significantly among treatments
when 135 kg N/ha (120 Ibs/acre) was applied in single dose at planting or thin-
ning, split equally between thinning and layby, or split equally among plant-
ing, thinning and layby (33). This research, however, did not demonstrate the
optimal fertilization rate for each of the timing options examined. Therefore,
the advantages of adjusting timing remain a question in California, but the use
of pre-midseason petiole analyses suggests that split application is a BMP for
beet production.
Texas growers are urged to apply nutrients at or near the time of crop
need (94). Fall application of N is discouraged for areas of high rainfall and
infiltration. Fertilization schedules should be planned in advance and fol-
lowed closely when possible. Nitrogen applications for grain sorghum, oats and
sudan grass in Texas should be as near to planting as possible (91). No applica-
tions are advised before rainy periods or during the period between October and
February.
Minnesota field experiments on irrigated corn showed that split applica-
tion of N (179 kg N/ha and 269 kg N/ha) caused minimal changes in the aquifer
NOn-N concentration while single applications increased the N03-N concentration
by 7 (179 kg N/ha) and 10 (269 kg N/ha) mg/1 (24). The single N application
also caused a much higher concentration of NO-,-N below the root zone. It is
possible that long term studies would show even more significant differences
between single and split applications because recovery of fertilizer N was 52.1%
for split application and only 30.4% for single application.
17
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TABLE 5. POLLUTION POTENTIAL VERSUS FERTILIZATION RATE
oo
Crop
Corn
Corn
Corn
Corn
Wheat/Beans/Corn
Sugarbeets
Comments Annual
Fertilization Rate
contour, conventional 448-N, 66-P
till
174-N, 40-P
448-N, 66-P
174-N, 40-P
approximate contour 447-N
planting 17g_N
plant population 336-N
168-N
irrigated 150-N
50-N
3 yr. rotation 243-N, 32-P
86-N, 12-P
112-N=optimum 280-N
for sugar 224-N
168-N
112-N
Annual Nutrient f Loss (% Reduction for Low Rate vs. High Rate) Reference
Total Surface Subsurface Drains AvailableS
l-n/h-i
50.2 NT 1.1 N03-N 20.7 NO,-N
28.1 NT (44) .6 N03-N (53) 6.7 N03-N (67)
.95 PT
.60 PT (64)
239-278 NT
16-24 NT (90-94)
118-168 NT
8-34 NT (80-93)
97 NT
35 NT (64)
2.75 N03-N*
.46 N03-N* (83)
170 NT
128 N|
92 NT
12
82
80
62
104
33
60 NT (65,53,35)
t NT = total nitrogen, N03-N = nitrate nitrogen, Py = total phosphorus.
§ (Fertilizer applied - Fertilizer uptake by crop).
* Weekly discharge.
-------
Figure 6. Land Resource Regions with literature references (///) indicating proper
fertilization rate as a BMP.
-------
Two studies in New York have shown that N should not be applied between
October and May because crop uptake is low and deep seepage is abundant (42,103).
Nitrate loading in surface runoff was correlated with heavy fall fertilization
before wet periods, but neither NH.-N nor inorganic P surface loadings were
related to time of application (42).
In the Corn Belt, N losses can be reduced significantly by delaying
major N applications until after the root system is developed for rapid N uptake
and after soil water levels decline to allow more storage for rainfall events
(101). By applying 25% of N in bands at planting and 75% in bands at sidedressing,
N losses will be reduced as N use efficiency increases. Furthermore, similar
yields can be obtained under either conventional till or no-till with 25% less N
than presently applied (134-156 kg N/ha).
Corn yields in North Carolina were comparable for fields fertilized with
a split application of 116 kg N/ha (130 Ibs/acre) and fields receiving 160 kg
N/ha (180 Ibs/acre) in a single application (45)- In Georgia, runoff loadings of
plant nutrients from corn fields can be reduced by shifting fertilization dates to
periods of rapid plant canopy development and to periods of less intense rainfall
(49). For tobacco production it is best to add the recommended rate of fertili-
zer during the early stages of development and later replace any leaching losses
with more fertilizer (30,31). Though most of the data for Land Resource Region
P represent production concerns instead of water quality concerns, efficient
fertilizer use will make less fertilizer available for runoff and leaching.
No-till corn in Maryland yields better when N is applied at the time of
peak demand (7). Though more research is needed in this area, peak demand seems
to occur at five to six weeks after planting, or when the corn is 12-18 inches
tall. When N was applied in April, conventional till corn out-yielded no-till
corn, but when N was added in June the trend was reversed. In conclusion, it is
best to split N applications to Maryland corn by adding 27-36 kg N/ha (30-40
Ibs/acre) as a starter and the remainder as sidedress after five to six weeks.
December nitrogen application to sandy corn fields in North Carolina re-
sulted in considerable leaching of N (39). Corn yields were much lower on sandy
fields fertilized in December as compared to those fertilized at planting or at
sidedressing. Pre-plant application was just as effective as sidedressing on
sandy soils. Corn yields on Piedmont soils were affected little when N was ap-
plied in December versus preplant or sidedressing.
As compared with application rate, the data base for drawing conclusions
regarding fertilization timing is small. However,production and water quality data
from three Land Resource Regions support as a BMP the exclusion of fall applica-
tion for spring and summer crops (Figure 7). Common regional characteristics
which most effect the preclusion of fall application are wet soils requiring
drainage and heavy rainfall and infiltration patterns. Therefore, regions
which contain much drainable wet land (84) and humid climates (25) are projected
not to be suitable for fall fertilization (Figure 7).
Split applications of N fertilizer are supported by the literature as a
BMP in several regions (Figure 8), though much research is necessary to draw
20
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Figure 7. Land Resource Regions with literature references (///) and projections (:::)
indicating elimination of fall application as a BMP for spring and summer crops,
-------
ro
ro
Figure 8. Land Resource Regions with literature references (///) and projections (:::)
indicating split application as a BMP.
-------
strict guidelines for application schedules. Available data do indicate that
split application of fertilizer can reduce the amount of Teachable nitrogen
as compared to single application (Table 6). Therefore, split applications
are recommended as a BMP for all humid regions (Figure 8) and areas of intens-
ive irrigation in other regions.
CONTROLS FOR NITROGEN LOSS
Method of fertilizer application and farm management practices can
significantly affect N losses from agricultural lands (102). Irrigation prac-
tices may also impact the percentage of applied fertilizer lost to runoff or
leaching. This section covers those practices which are intended to reduce N
losses regardless of N form. Different regions may experience very different
water quality problems and may require varied control mechanisms.
In California, sugarbeet uptake of N is more rapid when fertilizer is
placed 24 centimeters to each side of the rows as opposed to placement halfway
between rows (33). Several recommendations were made for reducing nitrogen
losses in drainage waters of the irrigated San Joaquin Valley in California (66).
Ammonia and urea are the preferred forms of N fertilizer as both will be leached
less rapidly than nitrate fertilizers. In cases where N is very mobile it is
best to split fertilizer applications and place the nutrients in bands near the
greatest root zone density. Excessive deep percolation can be avoided by ad-
justing irrigation practices to just meet the evapotranspiration requirements
of the crops. Finally, the quantity of N leached to the tile drains may be
reduced if farmers grow high N requirement plants on fine textured soils. Other
methods are designed to remove N from tile drainage before it reaches receiving
waters. Algal stripping, in which aerated shallow ponds remove N through
sedimentation and algal productivity, can reduce drainage water nitrogen con-
centration from 20 mg/1 to 3-5 mg/1 at a 1971 cost of $45 per acre foot (74).
Anaerobic deep ponds with filters decreased drainage water N concentration from
20 mg/1 to 2 mg/1 or less through bacterial denitrification at a cost of $30
per acre foot.
The effects of intensive irrigation of sandy soils in Nebraska further
emphasize the need for better irrigation management as outlined for the San
Joaquin Valley (57, 61). Data indicate that an increase in irrigation was the
greatest cause of steadily increasing NO^-N concentrations in the groundwater.
Research in Texas supports the conclusion that subirrigation with fertilizer
placement above the subirrigation lateral is superior to both furrow and sprinkler
irrigation from the standpoint of minimizing fertilizer NOq-N movement below the
root zone (65). Nitrate passing below the root zone can be removed by either
subsurface runoff or groundwater infiltration. Simultaneous knifed applications
of N and P produced consistently higher winter wheat yields than either broad-
cast or band applications (51). Simultaneous dribble application of liquid N
and P provided good yields, and N-serve™ increased wheat yields in this Kansas
study. Results from plot studies in Texas showed that both N-serveTM and sulfur
coated urea reduced NOo-N leaching by inhibiting the release of NO^-N from ap-
plied fertilizer (91). For any fertilization timing program for grain sorghum,
oats and sudan grass it is suggested that ammonium, urea, N-serve or sulfur
23
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TABLE 6. SPLIT NITROGEN APPLICATION VERSUS SINGLE NITROGEN APPLICATION
no
Crop Comments
Corn Irrigated, 179 kg N/ha/yr
Sugarbeets 135 kg N/ha/yr
Fertilization
Timing
Single
Split
Single-Planting
Single-Thinning
Split-Thinning & Layby
Split-Planting, Thinning
& Layby
Annual t
Leachable NT
(kg N/ha)
124
86
87.2
83
86.3
87.8
%Reduction
of Leachab-le NT
Due to Split
-
31
_
-
none
none
Reference
24
33
t Applied N minus N recovered by plant.
-------
coated urea be used instead of nitrate fertilizers.
In an Oklahoma cropland and rangeland study it was determined that alfalfa
is an economically effective control of sediment and total nutrient loads, but
the resultant increase in soluble NOg-N concentration could present water
quality problems (60). It was also shown that total Kjeldahl nitrogen (TKN)
concentration in runoff from irrigated cotton is positively correlated with
sediment loss, so sediment control measures should decrease TKN losses. From
other Oklahoma research it was concluded that fertilization will initially in-
crease nutrient concentrations in surface runoff from grasslands (59). However,
increased plant cover resulting from fertilization may eventually decrease
nutrient losses by decreasing runoff volume and soil erosion. Broadcast fer-
tilizer on grazing lands will be lost to surface runoff at a rate of up to 5%
of that applied at rates to 75 kg N/ha (67 Ibs/acre). Nitrogen losses from a
rotation of grain sorghum, cotton and oats in the Texas Blackland Prairie
consisted largely of organic nitrogen bound to sediments (41). Under good
fertilization and management practices NO^-N losses to surface runoff were
relatively low. In summary, nitrogen losses from agricultural lands in the
Southwestern prairies can be minimized by controlling sedimentation and fol-
lowing soil test results for proper fertilizer application rates.
In New York it was shown that soil and nutrient losses are greater from
continuous corn fertilized with just mineral fertilizer when compared versus
either corn fertilized with mineral fertilizer, manure and crop residue or
corn in crop rotation (103). A crop rotation of corn, small grain and alfalfa
produced the smallest losses of soil and nutrients in surface runoff. Crop
residue incorporation reduced surface losses, but increased infiltration and
NOo-N leaching. Efficient use of manure both as a source of crop nutrients
and as a soil physical conditioning agent is encouraged (103). Ammonium and
nitrate concentrations in tile drainage from wheat, corn and bean plots were
not affected by residue management or by cover crop establishment (104). Corn,
forage, small grain and soybean growers in New York are advised to band and
sidedress fertilizer to best meet economic and water quality objectives (19).
Data from Ontario, Canada show that heavily fertilized coarse-textured soils
have great potential for NO^-N leaching to receiving waters (29). In summary
for the Lakes States, a trade-off seems to exist between controlling nitrogen
losses to surface waters and to groundwater. Manure and residue incorporation,
crop rotations and cover crops will reduce surface losses of N, but possibly
increase N losses to ground water.
There exists a wealth of published Corn Belt research from which con-
clusions regarding N control can be drawn. Studies addressing surface runoff
losses of N demonstrate conclusively that most of the total N lost in surface
runoff is associated with sediment losses (2, 8, 12, 15, 81, 97). Therefore,
sediment control practices should effectively reduce total N losses in surface
runoff. Compared to conventional tillage corn, no-till corn yields less sedi-
ment, particulate N and total N (101). Level terraces in Iowa watersheds
cropped to corn effectively reduced surface runoff, erosion and particulate
nitrogen loads, whereas contoured watersheds were not as effective in control-
ling N losses (12, 14). Also in Iowa, conservation tillage effectively re-
duced total N loads by controlling erosion (8). Both a level terraced
25
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watershed with corn and a pasture watershed lost much less N to surface runoff
than contoured watersheds as sediment and water losses were reduced significantly
(81).
Using data from other research, it was determined that crop residues are
important both as nutrient sources and as erosion controls (35). Corn residues
contain 62-71 kg N/ha (55-63 Ibs/acre), and soybean residues contain 68-73 kg
N/ha in the Corn Belt. In this region there exists an opportunity to balance
N gains and losses through conservation tillage and residue management. A
balanced nutrient budget on the farm will not necessarily help to improve
water quality unless nutrient losses are minimized. The above research indicates
that conservation tillage can reduce N losses to receiving waters.
In simulated rainfall studies in Minnesota, it was shown that fertiliza-
tion method can be varied to control N losses in surface runoff (96). In this
test of four methods, total nitrogen loadings were lowest from fields with fertil-
izer broadcast onto a plowed surface. When fertilizer was broadcast onto oats
stubble and incorporated by plowing down and disking, N loads were the same as
for the check (plowed and disked, no fertilizer) plot. Nitrogen losses were
not controlled when fertilizer was broadcast and disked on a plowed surface. The
greatest N loads came from plots upon which fertilizer was broadcast on a disked
surface. Seasonal studies have shown that the largest fraction of annual N loss
from corn plots occurs during the period covering planting to crop establish-
ment (April-June) (2, 15). Level terraces effectively reduced N losses in one
study (2), and a corn-oats-hay rotation controlled sediment losses more ef-
fectively than continuous corn in other plot research (15). However, this
rotation is generally not considered economically feasible.
While controlling surface runoff losses of nitrogen, many control mechan-
isms simultaneously increase NCU-N leaching into groundwaters. In Missouri it
was determined that most applied fertilizer is carried downward into the soil
with precipitation instead of being washed away in surface runoff (85). Iowa
research on watersheds cropped to corn revealed that subsurface N03-N losses
account for 84-95% of the average annual soluble N discharged by stream flow
(12, 14). Furthermore, though they reduced particulate N losses in surface run-
off, level terraces yielded greater subsurface discharge of NO^-N than did
contoured watersheds. Tile effluent from corn fields in Ohio carried the
greatest amount of N to receiving waters in June when flow was high amd corn was
not yet established (53).
As for the Lakes States, it appears that individual nitrogen control
mechanisms in the Corn Belt can either reduce surface runoff losses or ground-
water infiltration, but not both. Sediment control measures, especially level
terraces, are very effective in reducing total N losses in surface runoff, but
also promote increased infiltration and the resultant leaching of available
N03-N.
In rain simulator studies of corn plots in Indiana, 170 kg N/Ha (152 Ibs/acre)
was applied before «ach of five tillage systems to test their effects on surface
runoff (77). Both coulter-plant and chisel-plant systems were effective in
controlling sediment loss and particulate nitrogen loading. Till-plant and disk-
coulter-plant practices were less effective in controlling sediment and associated
26
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nutrient loss. Conventional till-plant plots yielded the greatest sediment
and participate N runoff losses, but had the smallest soluble N loadings. In
general, those practices which effectively reduced sediment and particulate N
loadings also caused the greatest losses of soluble N. In northern Alabama
researchers concluded that most N is lost with sediments (11). Subsurface
soluble N03-N concentrations were as much as five times as great as those found
in surface runoff. Sulfur coated urea pellets did not help control N runoff,
possibly because pellets were washed away with other runoff. In cases where
sulfur coated urea is used, it is probably best to incorporate the fertilizer.
In summary for Land Resource Region N, it is very likely that surface losses
of N will be reduced at the expense of increased subsurface leaching of NCL-N
when sediment control practices are installed to control nutrient losses.
Louisiana plots seeded to pearl millet were used to determine the runoff
loads of different blends and types of fertilizer (21). Nitrogen loads from
both the high (33.3-8.7-16.6 as N-P-K) and low (8-3.5-6.6 as N-P-K) blends
were low, but losses were generally greater from the higher analysis source.
Four (1974) to 37 (1973) times less N was lost from plots fertilized with in-
corporated sulfur-coated urea as compared to plots with incorporated uncoated
urea. It appears that incorporation of slow-release N fertilizer is a BMP
in the silt loams of the Mississippi Delta.
For small acreages of North Carolina tobacco the application of fertili-
zer in two bands ten days after transplanting consistently provides the highest
yields and reduces the chances of early leaching (18). For larger acreages
upon which an extra trip over the fields is impractical, two bands of fertili-
zer at planting will guarantee good yields. Broadcast and single band applica-
tions are not recommended for consistent yields. Subsurface leaching of NCu-N
is very possible under high moisture conditions in the Southern Coastal Plain
as water passes readily through sandy surfaces to the relatively impermeable
clay horizon (38, 93). In a Georgia Coastal Plain watershed planted to corn,
subsurface drainage accounted for 80% of the total runoff and 99% of the total
N03-N loading (38). Weighted average NCL-N concentrations in subsurface drain-
age (5.8-12.6 mg/1 NCL-N) were much higher than those in surface runoff (0.11-
3.0 mg/1). In other Georgia research a double-cropped watershed with graded
terraces and a grassed waterway controlled N losses more effectively than a
similar watershed with no conservation practices (49). Both watersheds were
cropped to corn and received split N applications (140 kg N/ha). Ammonium
and TKN loads were 35-40% less from the conservation watershed, but NO^-N
losses did not differ significantly between watersheds. Reduced sediment loss
was largely responsible for the smaller N losses form the conservation water-
shed.
Maryland no-till corn studies have resulted in a few conclusions regard-
ing proper fertilization techniques (7). Since urea is not incorporated in
no-till volatilization losses can be high. Therefore, as regards fertilizer
uptake efficiency, ammonium nitrate appears to be superior to unincorporated
urea. If an applicator is available, urea can be injected several inches be-
low the soil surface to improve fertilizer uptake efficiency. Also, liquid
N fertilizer should not be sprayed over the top of growing plants.
27
-------
Several research efforts support the conclusion that excess fertilizer
on well-drained Atlantic Coast soils will be leached to groundwater over the
winter months (23,26,27,39). Nitrate concentration in North Carolina coastal
ground-water reaches its peak in the winter (26), and drainage control with
flashboard risers can be used to reduce NO,-N entry into surface waters by re-
ducing flow through the tile lines in moderately well-drained soils (27). In
poorly drained coastal soils most NCyN was lost through denitrification (23),
but attempts to increase denitrification by raising the water table failed
(27). Data indicate that NO^-N leaching from Atlantic Coast soils can be con-
trolled by matching fertilizer applications with crop needs and minimizing water
transport through drainage lines, especially during winter months.
In a major effort to determine the effectiveness of soil and water con-
servation practices (SWCPs) for pollution control on non-irrigated field crops
in the Eastern half of the United States (28), the following conclusions were
made regarding N control:
1. Contouring, terraces, sod-based rotations, conservation til-
lage and no-tillage significantly reduce edge-of-field losses
of particulate N because they reduce erosion.
2. Sod-based rotations significantly reduce losses of soluble
N in surface runoff.
3. Contouring, terraces, conservation tillage and no-tillage
moderately reduce soluble N losses in surface runoff by re-
ducing surface runoff. These practices may increase soluble
N losses in subsurface drainage.
4. Management of N fertilizer applications to meet crop needs
can reduce soluble N losses in both runoff and percolation.
5. The effects of SWCPs on N runoff losses show significant yearly
variations.
From the many research efforts conducted across the United States it
is possible to draw both hard and tentative conclusions regarding national BMPs
for nitrogen control. The following are hard conclusions based upon a large
quantity of research:
1. Sediment control mechanisms, especially terraces, will sig-
nificantly reduce total nitrogen loadings to surface waters
(Table 7).
2. Unless fertilizer management is altered to increase plant up-
take efficiency, sediment control mechanisms will cause in-
creases in N03-N leaching to subsurface waters as surface run-
off losses are reduced (Figure 9).
3. Intensive irrigation increases the probability of N(k-N
leaching to groundwaters. By adjusting irrigation practices
deep percolation and NCyN leaching can be reduced (Figure 10)
28
-------
TABLE 7. TERRACE VERSUS CONTOURING AS NITROGEN CONTROLS
Crop Comments
Practice
Annual Nutrient'1' Loss (% Reduction vs. Other Practice) Reference
Total
Surface
kg/ha-
Subsurface
Corn 448 kg N/ha/yr Level Terrace* 16.2 N (59)
3 year study
*
450 kg N/ha/yr Contour 39.9 N
.1 N03-N (89)
.2 NH4-N (75)
1.2 N03-N
.8 NH4-N
13.1 N00-N
.5
5.4 N03-N (58)
.1 NH4-N (74)
12
ro
UD
§
Corn 168 kg N/ha/yr Terrace, pipe
39 kg P/ha/yr outlets & mulch
till
.2 NH -N (18)
7.2 Sediment-NT (15)
1.8 NO -N
9.2 NT
Contour
.3 NH4-N
8.5 Sediment-Nn
.4 N03-N (76)
9.2 N-r
NT = total nitrogen, N03-N = soluble nitrate nitrogen, NhL-N = soluble ammonium nitrogen.
Conventional Till.
Terrace installation partly responsible for heavy nutrient losses in first year of 4-year study.
-------
OJ
o
Figure 9. Land Resource Regions with literature references (///) and projections (:::)
indicating increased NOo-N leaching coinciding with sediment control.
-------
Figure 10. Land Resource Regions with literature references (///) and projections (:::) indicating
irrigation management can reduce NCU-N leaching to groundwater.
-------
3. (continued) - (Table 8).
4. If incorporated, slow-release nitrogen fertilizer can ef-
fectively be used to reduce nitrogen losses to surface and
ground waters (Figure 11) (Table 8).
Other conclusions regarding nitrogen control mechanisms are based upon
less firm data, and are therefore tentative:
1. Crop rotations, no-till and conservation tillage may reduce
surface runoff N losses (Table 9).
2. Banding or other directed placement of fertilizer may in-
crease fertilizer uptake efficiency.
3. Contour practices may moderately reduce surface runoff N
losses.
4. Broadcast fertilizer should be incorporated.
5. Where NO,-N leaching is a problem it may be better to use
ammonium and urea instead of nitrate fertilizers.
CONTROLS FOR PHOSPHORUS LOSS
In order to better evaluate the relative merits of phosphorus control
mechanisms, it is necessary to characterize the water quality impacts
of the various P forms. Soluble ortho-phosphate is completely available
for algal growth, and soluble organic P and polyphosphate are readily con-
verted to ortho-phosphate (89). However, in water with less than .1 mg/1
dissolved inorganic P it has been determined that only about fifty percent
of this P is available to algae (20). Separate reports have indicated that
approximately twenty percent of all particulate P is available to algae
(20, 36). Once a water quality problem is effectively assessed, it is then
possible to determine whether P control mechanisms should be directed toward
the soluble, particulate or total P fraction.
Idaho research on irrigated lands showed that most P in irrigation and
surface drainage waters is associated with sediment (17). Both total unfiltered
P and total ortho-phosphate (ortho-PO.) concentrations were correlated with
sediment concentration, but dissolved ortho-PO. losses were not related to
sediment runoff. Phosphorus runoff from irrigated tracts can be limited by
minimizing the quantity of surface drainage water and by using sediment reten-
tion basins or low slope drains.
As noted for N control, simultaneous knifed applications of N and P
were superior to both broadcast and band applications for winter wheat produc-
tion in Kansas (51). The researchers credit the higher yields from knifed
applications both to the deeper placement of N and P which insured more
moisture for nutrient uptake and to a possible change in P chemistry produced
by high concentrations of NH4-N in the phosphorus retention zone. Higher
32
-------
TABLE 8. EFFECTIVE NITROGEN CONTROL MECHANISMS
Control Mechanism
Comments
Annual Nutrient Loss (% Reduction vs. Other Practice) Reference
Surface Drains
Flashboard Riser
Drain Control
None
Mod. well-drained
soils
Mod. well-drained
soils
1-7 kg N03-N/h.a (72-98)
25-40 kg N03-N/ha
27
Flashboard Riser
Drain Control
None
Poorly drained soils
Poorly drained soils
12-15 kg N03-N/ha (50)
25-30 kg N03-N/ha
27
Sulfur-Coated Urea
Uncoated Urea
Rye grass, 224 kg 1.1-2.1 kg N^ha (57-95)
N/ha/yr, incorporated
4.9-21.9 kg
21
* NOo-N loss calculated from reported 50% reduction vs. drain with no controls.
t NO--N = soluble nitrate nitrogen, NH--N = soluble ammonium nitrogen.
fj NH.-N + N03-N + urea; losses for 48-51 days during late fall and early winter.
-------
GO
.£=.
Figure 11. Land Resource Regions with literature references (///) and projections (:::) indicating
slow-release fertilizer can reduce N losses.
-------
TABLE 9. CONSERVATION PRACTICES AS NITROGEN CONTROLS
Comments Practice Annual Nutrient Surface Loss
(% Reduction vs. Other Practice)
Crop
Reference
Corn
112 kg N/ha/yr &
29 kg P/ha/yr*
56 kg N/ha/yr &
29 kg P/ha/yr*
Continuous
Rotation
1.2 kg N03-N/ha
.7 kg Org-N/ha
.4 kg NH4-N/ha
23.6 kg NT/ha
21.2 kg Sed. Org-N/ha
.4 kg N03-N/ha (64)
.3 kg Org-N/ha (54)
.2 kg NH4-N/ha (51)
14.2 kg NT/ha (40)
13.0 kg Sed. Orq-N/ha (39)
Pasture
No Fertilizer Continuous Grazing
Rotation Grazing
7.4 kg Org-N/ha
9.7 kg NT/ha
1.8 kg N03-N/ha
.4 kg NH4-N/ha
1.3 kg Org-N/ha (82)
2.1 kg NT/ha (78)
.5 kg N03-N/ha (74)
.3 kg NH4-N/ha (38)
15
Corn/Beans/Wheat
3 year rotation No Residue or
Cover Crop
Return Residue &
Cover Crop
6.0 kg N03-N/ha
.5 kg NH4-N/ha
1.2 kg N03-N/ha (80)
.5 kg NH4-N/ha (0)
42
60
* Recommended rate, fall plow, spring broadcast and disk.
t NT=total nitrogen, N0,-N=soluble nitrate nitrogen, NH4-N=soluble ammonium nitrogen, Org-N=soluble
organic nitrogen, Sed. Org-N=sediment associated organic nitrogen.
35
-------
soluble P concentrations were found in surface runoff from fertilized
(75 kg P/ha broadcast) Oklahoma rangeland watersheds than from unfertilized
watersheds (59). Elevated soluble P concentrations from fertilized watersheds
persisted for at least one year, but the total amount of P lost to surface
runoff will probably not exceed five percent at rates to 75 kg P/ha.
Research in Wisconsin showed that the greatest total P loads from plots
occurred with the greatest sediment losses (100). In short, sediment control
practices were determined to have the greatest potential for reducing P
losses from Wisconsin glacial till farmlands.
New York investigations showed that soluble P concentrations in tile drains
were not significantly influenced by residue and crop cover practices (104),
but soluble inorganic P loads in surface runoff were smaller when residue was
returned and cover crops were used as compared to no residue or cover crop (42).
Furthermore, P transport was far greater in surface runoff than in subsurface
flow (103). Most lost P is associated with sediment, and total P losses are
directly correlated with surface runoff volume.
Corn Belt research has provided the most data regarding P control
mechanisms. Several studies have shown that most P lost in surface runoff is
associated with sediments (2, 12, 15, 85, 97). Level terraces were effective
in reducing P discharge from corn fields via surface runoff (12). Soluble P
loads in subsurface discharge represented a very small fraction of the annual
fertilizer application. Total surface P loads were nine times less from Iowa
watersheds with level terraces as compared to contoured watersheds (83). The
larger terraced watershed lost eight times less surface runoff and nineteen
times less sediment than the contoured watershed. Other Iowa research showed
that disking, ridge-plant and coulter tillage practices reduced total P sur-
face runoff loads as compared with conventional tillage, chisel-plow and tin-
plant practices (8). Conservation tillage did not affect soluble P loads, but
soluble P concentrations in surface runoff increased as residue cover in-
creased. Studies in Minnesota (97) and Missouri (85) both showed that
erosion control practices can be used to effectively reduce P losses in surface
runoff.
Seasonal studies in Land Resource Region M showed that most P from corn
fields is lost with sediment during the critical erosion period from planting
to two months later (2, 15). Once again,level terraces were very effective
in reducing P discharges in surface runoff (2).
In a Minnesota plot study of four broadcast fertilizer placement options,
P losses were smallest from plots where fertilizer was broadcast onto a plowed
surface (96). Incorporation by plowing and disking over oats stubble also ef-
fectively controlled P discharges, while both disking broadcast fertilizer and
broadcasting fertilizer onto a disked surface were ineffective.
More than 95% of total P lost from Alabama cotton, corn, millet and
soybean plots was associated with sediment (11). Therefore, growers are en-
couraged to use erosion control practices to reduce P runoff. In an Indiana
study of the effects of tillage practices on P losses from corn plots it was
36
-------
found that coulter-plant and chisel-plant systems controlled soil erosion more
effectively than either till-plant or disk-coulter-plant systems (77). Con-
ventional tillage caused the greatest soil and water runoff. Discharges of
soluble P from the various systems ranked in the order: coulter-plant»till-
plant>chisel-plant>disk-coulter-plant»conventional-plant. Runoff loads
of P associated with sediment decreased by tillage practice in the following
order: conventional>ti11-piant>disk-couHer-plant>coulter-plant>chisel-
plant. For control of total P load in surface runoff the systems ranked in order
of decreasing effectiveness: chisel-plant>disk-coulter-plant>till-plant>
coulter-plant>conventional-plant. In Ohio, 85-100 percent of P lost from
pastured watersheds is soluble (69).
For Louisiana plots seeded to pearl millet, phosphorus losses were
slightly greater from the higher analysis fertilizer source than from the
lower analysis source, but all losses were considered to be small (21).
Mean monthly phosphate concentrations in submerged and open tile drains in
Florida were higher for citrus plots treated with shallow-tillage (.19-.90 mg
PO.-P/l)than for plots under deep-till with and without liming (<.4 mg PO.P/1)
(16). From these sandy Florida plots 14.2 percent of applied P was lost from
shallow-till treatment, whereas lower percentages were lost from deep-till
(3.4 percent) and deep-till with lime (2.0 percent).
For non-irrigated field crops in the Eastern half of the United States,
the following conclusions were drawn regarding the effectiveness of soil and
water conservation practices (SWCPs) for phosphorus pollution control (28):
1. Contouring, terraces, sod-based rotations, conservation tillage
and no-tillage significantly reduce edge-of-field losses of
particulate P because they reduce erosion.
2. Sod-based rotations significantly reduce losses of soluble
P in surface runoff.
3. Practices such as no-tillage and conservation tillage which
involve residue management have an uncertain effect on losses
of soluble P in surface runoff.
4. SWCPs such as contouring and terraces which are not based
on residue management, moderately decrease losses of soluble
P in surface runoff.
A review of the literature regarding phosphorus control mechanisms has
shown that very strong conclusions are based upon very little data (Figure 12).
With the exception of the Corn Belt, the use of erosion control practices to
limit P losses has virtually been assumed because most P is associated with
sediment in surface runoff. Very few studies have addressed P leaching into
groundwater and subsurface flow as related to surface runoff controls. As a
result of the inability to uncover a large quantity of literature regarding P
control mechanisms, few conclusions can be drawn about their effectiveness:
1. Level terraces effectively reduce total P losses by limiting
37
-------
GO
00
Figure 12. Land Resource Regions in which significant phosphorus control research is available (///)
-------
1. (continued)
water and sediment runoff (Figure 13) (Table 10).
2. Soil conservation practices such as residue management,
sod-based rotations and rotation grazing can decrease
total and soluble P losses in surface runoff (Table 11).
3. Conservation tillage practices generally reduce total P
discharge as compared with conventional tillage.
4. Conservation tillage practices can increase soluble P losses
as compared with conventional tillage.
5. Sedimentation basins and flow control can be used to decrease
P losses from irrigation systems.
SUMMARY
A discussion of the various control mechanisms for N and P losses leads
to the conclusion that an integrated system of BMPs is best in most cases.
Soil testing is a must for every BMP system. Nitrogen and phosphorus
application rates should not at any time exceed the assimilative capacity of
the crop. Where possible, timing of nitrogen application should be matched
with maximum plant nutrient demand. Methods of N and P application that best
place these nutrients within reach of a crop will decrease potential losses
to surface and ground waters. Where nutrient application rate, timing and
method best match crop needs little N and P is available to pollute receiving
watersheds. Such a situation minimizes the need for erosion control practices
to control N and P losses.
While it is obvious that the technology exists for reducing agricultural
N and P discharges to receiving waters, any proposals for major changes in
commercial fertilizer management must be assimilated with economic realities,
production concerns and institutional limitations. Conclusions and recommenda-
tions in this document do not adequately reflect economics, production or
institutional concerns. Therefore, any inferences drawn from these statements
should contain appropriate caveats.
39
-------
Figure 13. Land Resource Regions with literature references (///) and projections (:::) indicating
terraces as a P control BMP.
-------
TABLE 10. TERRACE VERSUS CONTOURING AS PHOSPHORUS CONTROLS
Crop Comments
Corn 448 kg N/ha/yr
& 82 kg P/ha/yr
450 kg M/ha/yr
& 84 kg P/ha/yr
Corn 168 kg N/ha/yr
39 kg P/ha/yr
Practice
Level Terrace,
Conventional Till
Contour,
Conventional Till
Terrace , pipe
outlets & mulch
till
Contour,
Conventional Till
Annual Nutrientf Loss (% Reduction vs. Other Practice)
Total Surface Subsurface
.37 PT (67) .04 Sol. P (74) .26 Sol. F
1.14 P, .15 Sol. P .05 Sol. P
T (82)
.12 Sol. P
.33P,
.20 Sed. P (2)
.08 Sol . P (38)
.28 PT (13)
.21 Sed. P
Reference
12
2
PT = total phosphorus, Sol. P = soluble phosphorus, Sed. P - sediment associated phosphorus.
§
Terrace installation partly responsible for heavy nutrient losses in first year of 4-year study.
-------
TABLE 11. CONSERVATION PRACTICES AS PHOSPHORUS CONTROLS
Crop
Comments
Practice
Annual Nutrient Surface Loss
(% Reduction vs. Other Practices)
Reference
Corn
-pa
ro
56 kg N/ha/yr &
29 kg P/ha/yr
112 kg N/ha/yr &
*
29 kg P/ha/yr
Rotation
Continuous
.17 kg Sol. P/ha (48)
3.14 kg PT/ha (43)
.33 kg Sol. P/ha
5.55 kg PT/ha
No Residue
or Cover Crop
.25 kg Sol. P/ha
15
Corn/Beans/
Wheat
3
year
rotation
Return
& Cover
Residue
Crop
.13
kg
Sol.
P/ha
(48)
42
Pasture
No Fertilizer
Rotation Grazing
Continuous Grazing
1.27 kg PT/ha (72)
.13 kg Sol. P/ha (variable)
4.60 kg PT/ha
.14 kg Sol. P/ha
60
f P = total phosphorus, Sol. P = soluble phosphorus.
* Recommended rate, fall plow, spring broadcast and disk.
-------
SECTION 3
RESEARCH NEEDS
Much is now known about the types of nutrients washed from agricultural
land, but in regions other than the Corn Belt little is reported concerning
the effectiveness of control mechanisms for nonpoint source fertilizer pol-
lution. The greatest overall need is a series of watershed studies with a
holistic approach: surface and subsurface water quality, food supply con-
cerns, economics, agronomic concerns and institutional matters. If the goal
is to achieve water quality improvement without putting a large burden upon
agriculture, the cost-effectiveness of BMPs for water quality control must be
known. The International Joint Commission has recommended that further
research be done to determine the costs of BMPs for incremental water quality
benefits (90).
To answer the more specific questions regarding the effectiveness of
BMPs it is necessary for other regions to perform systematic studies similar
to the Corn Belt efforts. Long-term comparisons are needed to assess the
water quality benefits of implementing various BMPs and BMP systems. Both
the International Joint Commission (90) and Cornell University (28) suggest
further research to determine if soil and water conservation practices can
simultaneously serve both soil conservation and water quality goals. Cornell
also recommends field and modeling studies to explore the transport of pol-
lutants from field to stream or aquifer and their subsequent fate (28).
Better understanding of the effects of various timing and method schemes
for fertilization can be obtained from systematic research designed to
eliminate as many experimental variables as possible. The use of slow-release
nitrogen fertilizers should accompany sediment control practices to determine
if both surface and ground waters can be protected while allowing farmers
reasonable latitude in fertilization rates.
The end result of systematic research directed toward answering an
array of questions regarding BMPs is a predictive capability for assessing
the total costs and benefits associated with alternative management schemes.
Appropriate planning decisions can become more commonplace as investigations
provide data to more completely piece in the BMP puzzle.
43
-------
SECTION 4
CURRENT RESEARCH
Presently there are several regional projects directed toward evaluating
agricultural nonpoint source control mechanisms. These projects are largely
funded through the U.S.D.A. and U.S.E.P.A., but planning and operational
functions are performed at all levels of government. It is the intention that
these projects exhibit the holistic approach toward water quality management.
The Lake Herman Model Implementation Project in South Dakota is focusing
on abatement of a water quality problem created by sedimentation and associated
nutrient discharge. Several federal, state and local agencies are cooperating
in an effort to monitor water quality changes associated with the implementa-
tion of sediment control structures. Provided that economics, land use and
water quality data are good, this project should provide conclusions regarding
the cost-effectiveness of sediment controls for nutrient control.
A number of Rural Clean Water Programs across the United States are
dealing with nutrients as pollutants. It is estimated that 31% of the P
loading to the Lower Manitowoc watershed in Wisconsin is associated with
cropland erosion. Fertilizer management and several soil conservation
practices are some of the BMPs for this project. Since 52% of the P loading
is from livestock wastes, it may only be possible to see the water quality
effects of commercial fertilizer management within the context of an overall
BMP system approach.
Prairie Rose Lake in Iowa has had algal blooms and has lost some of its
desirable fish-species due to sedimentation and associated nutrient transport.
Best Management Practices for this project include soil and water conservation
practices, animal waste management and fertilizer management. Due to the
animal waste input and the lack of intensive water quality monitoring, the
water quality effects of commercial fertilizer management will not be isolated.
Groundwater has been contaminated with increasing NCL-N levels in the
Long Pine Creek Watershed, Nebraska. Irrigation return flow, croplands,
rangelands and livestock confinements are some of the primary sources of
pollution. Interactions between surface and ground waters will be observed
for this watershed as fertilizer management and erosion control BMPs are imple-
mented. To further evaluate BMP effectiveness, selected fields will be
monitored throughout the project.
Surface waters of Lake Poinsett and Oakwood Lakes in South Dakota are
44
-------
hypereutrophic, while the underlying Big Sioux aquifer has excessively high
NCL-N levels in many areas. Cropland and animal waste management practices
are being implemented to control N, P, and sediment loadings to the lakes and
groundwater. Terraces are being located in areas where it is believed they
will not contribute to the groundwater nitrate problem. It will be interest-
ing to see if any controls other than very strict fertilizer management can
be used to solve both surface and ground water nutrient problems simultaneously.
Intensive cropping in the Saginaw Bay A.C.P. Special Project watershed
is held responsible for the high nutrient loadings to Lake Huron. Nearly
ninety percent of the project area is cropland. Much can be learned about the
relative advantages of different tillage practices from this project as side-
by-side comparisons are set up in different areas.
The Chowan River project in North Carolina offers data regarding small
watershed responses to fertilizer management and soil conservation practices.
Specific BMPs will not be evaluated, but the combined water quality effects
of soil testing, no-till planting, field borders, grassed waterways and fer-
tilizer management may be seen.
Results from Black Creek indicate that it is possible to conserve soil
within the limits adequate for maintaining the soil resource, but still not
meet water quality goals (47). Data also show that nitrate loss is not con-
trolled with sediment controls. In general, results from Black Creek support
the conclusion that the most successful approach for minimizing nutrient losses
in surface runoff from cropland combines soil erosion control with fertilizer
incorporation.
Discussion of the current major research efforts clearly demonstrates
that the holistic approach is now being utilized. As the joint USDA-EPA
efforts in the RCWP progress, data will be available for analyses of water
quality changes versus land use changes, institutional problems and successes,
implementation costs, production changes, and general project acceptance. If
funding persists, the long-term costs and benefits of BMPs can be assessed.
An evaluation of the cost-effectiveness of erosion control systems for im-
proving water quality should result from these large research efforts. Un-
fortunately, it does not appear that the alternative of fertilizer manage-
ment will be evaluated on a cost basis because it does not seem to be the
major focus in any of the projects. When the data from all major projects
are finally analyzed there should be enough information on specific practices
to allow a greater understanding of how the whole agricultural management
system can be altered to effect changes in water quality.
45
-------
REFERENCES
1. "1981-82 Agronomy Guide," Cooperative Extension Service at Ohio State
University, Bulletin 472 (Agdex 100), Columbus, Ohio, 97 pp., 1980.
2. Alberts, E. E., Schuman, G. E., and R. E. Burwell, "Seasonal Runoff Losses
of Nitrogen and Phosphorus from Missouri Valley Loess Watersheds,"
Journal of Environmental Quality, 7(2):203-207, 1978.
3. "Application for Rural Clean Water Program Funds," South Dakota State
Coordinating Committee, 1981.
4. Bailey, G. W. and T. E. Waddell, "Best Management Practices for Agricul-
ture and Silviculture: An Integrated Review," In: Best Management
Practices for Agriculture and Silviculture, Ann Arbor Science, Ann Arbor,
Michigan, pp. 33-56, 1979.
5. Baird, J. V., McCracken, R. J., Kamprath, E. J. and P. H. Reid, "Liming
Acid Soils," Extension Circular No. 495, N. C. Agricultural Extension
Service, Raleigh, N.C., 1974.
6. Baker, J. L., Johnson, H. P., Borcherding, M. A. and W. R. Payne,
"Nutrient and Pesticide Movement from Field to Stream: A Field Study,"
In: Best Management Practices for Agriculture and Silviculture, Ann
Arbor Science, Ann Arbor, Michigan, pp. 213-245, 1979.
7. Bandel, V. A., "Fertilization Techniques for No-Tillage Corn," Agri-
chemical Age, 25(7):14-15, 1981.
8. Barisas, S. G., Baker, J. L., Johnson, H. P. and J. M. Laflen, "Effect
of Tillage Systems on Runoff Losses of Nutrients, A Rainfall Simulation
Study," Transactions of the ASAE, 21:893-897, 1978.
9. Blevins, R* L., Murdock, L. W. and G. W. Thomas, "Effect of Lime Appli-
cation on No-Tillage and Conventionally Tilled Corn," Agronomy Journal,
70:322-326, 1978.
10. Bliven, L. F., Humenik, F. J., Koehler, F. A. and M. R. Overcash,
"Dynamics of Rural Nonpoint Source Water Quality in a Southern Water-
shed," Transactions ASAE, 23(6):1450-1456, 1980.
11. Bradford, R., "Nitrogen and Phosphorus Losses from Agronomy Plots in
North Alabama," Environmental Protection Technology Series. EPA-600/2-
74-033, 1974.
46
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12. Burwell, R. E., Schuman, G. E., Heinemann, H. G. and R. G. Spomer,
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55
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