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The high yields achieved in crop production in the United
States require that large amounts of nutrients be applied
to the soil to replace those withdrawn in the production
cycle. While animal manure and other organic materials
contribute to nutrient replacement, commercial fertilizers
are the major source of applied plant nutrients. The application
of commercial fertilizers is economically beneficial for
most farmers. However, when manure and/or commercial fertilizer
quantities or application timing are not consistent with
crop requirements and growing cycle conditions, excess
nutrients can harm the environment, polluting ground water
and/or surface water, lakes, streams, and rivers.
Excessive nitrogen or phosphorus in surface water can
cause algae to grow at an accelerated rate and cloud water,
which prevents aquatic plants from receiving sunlight
for photosynthesis. When the algae die and are decomposed
by bacteria, they deplete the oxygen dissolved in the
water and threaten aquatic life. This process, eutrophication,
can result in clogged pipelines, fish kills, and reduced
recreational opportunities. According to EPA, nutrient
pollution is the leading cause of water quality impairment
in lakes and estuaries and the third leading cause in
rivers. At high concentrations in the ground water, nitrates
make drinking water unsafe.
Some farming operations combine livestock, grain and
forage production. These rely upon nutrient sources produced
on the farm, such as manure and legumes, as well as commercial
nutrients purchased from off the farm. However, the management
of nutrients produced on-farm can be more complex than
of those purchased because of the greater uncertainties
in product form, nutrient quality, and environmental impacts.
The choice to use such a farming system or to rely primarily
upon grain crops and commercial nutrients depends upon
the assessment of economic and environmental costs and
benefits and the long-run sustainability of the farm.
Contents
Importance of Nutrient Management
The high yields achieved in crop production in the United
States require that large amounts of nutrients be applied
to the soil to replace those withdrawn in the production
cycle. While animal manure and other organic materials
contribute to nutrient replacement, commercial fertilizers
are the major source of applied plant nutrients. The application
of commercial fertilizers is economically beneficial for
most farmers. However, when manure and/or commercial fertilizer
quantities or application timing are not consistent with
crop requirements and growing cycle conditions, excess
nutrients can harm the environment, polluting ground water
and/or surface water, lakes, streams, and rivers.
Excessive nitrogen or phosphorus in surface water can
cause algae to grow at an accelerated rate and cloud water,
which prevents aquatic plants from receiving sunlight
for photosynthesis. When the algae die and are decomposed
by bacteria, they deplete the oxygen dissolved in the
water and threaten aquatic life. This process, eutrophication,
can result in clogged pipelines, fish kills, and reduced
recreational opportunities. According to EPA, nutrient
pollution is the leading cause of water quality impairment
in lakes and estuaries and the third leading cause in
rivers. At high concentrations in the ground water, nitrates
make drinking water unsafe.
Some farming operations combine livestock, grain and
forage production. These rely upon nutrient sources produced
on the farm, such as manure and legumes, as well as commercial
nutrients purchased from off the farm. However, the management
of nutrients produced on-farm can be more complex than
of those purchased because of the greater uncertainties
in product form, nutrient quality, and environmental impacts.
The choice to use such a farming system or to rely primarily
upon grain crops and commercial nutrients depends upon
the assessment of economic and environmental costs and
benefits and the long-run sustainability of the farm.
For more details on nutrient management, refer to chapter
4.4 of the Agricultural
Resources and Environmental Indicators.
Common Commercial Fertilizers
Used in the United States
Nitrogen (N), phosphate (P2O5), and potash (K2O) use
for all purposes rose from 7.5 million nutrient tons in
1960 to a record 23.7 million tons in 1981 and then declined
to 18.1 million tons in 1984 due to fewer planted acres.
Total nutrient use then resumed an upward trend, totaling
20.6 million tons in 2001.
While phosphate and potash contributed to the dramatic
increase in fertilizer use during 1960 and 1970, nitrogen
use increased more rapidly during the same period. In
1960, nitrogen use was about 37 percent of total commercial
nutrient use. By 1981, nitrogen use represented over 50
percent of total nutrient use. Nitrogen use was 11.5 million
tons in 2001, or 55.6 percent of total commercial nutrient
use. This relative gain stems from increased fertilizer
demand following favorable crop yield responses, to nitrogenous
fertilizers, especially in corn.
Phosphate's share of total commercial nutrient use declined
from 34.5 percent in 1960 to 20.5 percent by 2001. Potash's
share declined from 29.9 percent in 1960 to 23.8 percent
in 2001. Potash use, historically lower than both nitrogen
and phosphate, exceeded phosphate use for the first time
in 1977, a trend that continues.
The forms in which fertilizer products are used have
been changing from mixed fertilizers (containing two or
more nutrients) to direct-application materials (containing
primarily one nutrient). This trend results because of
higher nutrient concentrations and lower production and
application costs. The share of total fertilizer used
as mixed fertilizers declined from 63 percent in 1960
to 35 percent in 1998, and it remains at that level in
2001. This change is due mainly to increases in direct
application of nitrogen.
The use of major direct-application nitrogen materials
increased through the early 1980's. High-analysis products
such as anhydrous ammonia, nitrogen solutions, and urea
benefited from economies in transportation, distribution,
and storage, and from the ease and accuracy of applying
nitrogen solutions.
Directly applied phosphate fertilizer products have declined
since the early 1970's because of the increased use of
diammonium phosphate (DAP). The trend throughout the 1960's
and 1970's was toward increased use of triple superphosphates
(products that contained a higher percentage of phosphate)
relative to normal superphosphates because of transportation,
distribution, and storage economies. Since 1979, consumption
of both normal and triple superphosphate has declined.
The use of DAP, a mixed fertilizer containing 18 percent
nitrogen and 46 percent phosphate, has increased dramatically
since the 1960's, reflecting its low production cost,
high phosphate analysis, high water solubility, and good
handling and storage characteristics. Phosphate use was
4.2 million tons in 2001.
The use of potassium chloride, the major directly applied
potash fertilizer (containing about 60 percent potash),
has also increased greatly since the 1960. Total use of
potash reached a record 6.3 million tons in 1981, up from
2.2 million tons in 1960. Potash use was 4.9 million tons
in 2001.
Fertilizer Use for Major Crops
Corn continues as the dominant user of commercial fertilizers
(N, P2O5, K2O) in 2000, followed by wheat, cotton, and
soybeans, based on the 2000 Agricultural
Resources and Management Survey (ARMS). The ARMS survey
for 2000 crops covers the major producing States, including
11 corn, 13 soybean, 8 upland cotton, 5 spring wheat,
16 winter wheat, and 11 sugar-beet States.
Corn, soybeans, wheat, and cotton were planted on 98
percent of the cropland represented in the 2000 ARMS survey.
Corn is the major cropland user, followed closely by soybeans.
Fertilizer application rates were relatively unchanged
from those of 1999, but fertilized acres declined, resulting
in slightly reduced total fertilizer use in 2000.
Corn was the largest user of nitrogen, phosphate, and
potash fertilizers, followed by wheat, soybeans, and cotton.
- Nitrogen was applied to 98 percent of 61.2 million
planted corn acres in major producing States, fertilized
with an average application rate of 137 pounds per acre.
- Nitrogen application rates for corn in the 1990s
were lower than in the 1980s, but have increased in
2000.
- Phosphate was applied to 85 percent of corn acres
fertilized, with an average application rate of 58 pounds
per acre. Phosphate application rates for corn have
declined slightly since 1980.
- Potash was applied to 69 percent of corn acres fertilized
in 2001, with an average application rate of 83 pounds
per acre. Potash application rates for corn ranged around
80 pounds per acre since 1980.
- Nitrogen, phosphate, and potash application rates
vary substantially among corn producing States.
Highlights of Common Nutrient Management Practices on
Major Field Crops in 2000
The most common time to apply fertilizer to corn and
soybeans continues to be spring, before planting. For
other crops, the most common times for fertilization are:
- At planting for durum and spring wheat
- After planting for upland cotton
- Fall/before planting for winter wheat and sugarbeets.
Ground broadcast continued to be the principal method
of fertilizer application on the major crops, followed
by banding and injection.
Soil testing for fertilizer needs ranged from 84 percent
of acres for sugarbeets to 25 percent for all soybeans.
Most acres were tested for nitrogen.
Data on fertilizer
use and practices are available for individual
surveyed States by crop.
Review of 1999 Nutrient Use and Practices on Major
Crops
-
Total nutrient use was down about 2 percent in
1999 compared to 1998 with nitrogen use up 1 percent,
phosphate use down 6, and potash use down 5 percent.
-
Acreage planted to corn and wheat, the two crops
using the most fertilizer, was less than in 1998,
while acreage planted to soybeans and cotton was
up. Corn used 40 - 45 percent of all fertilizer.
-
Application rates varied by crop when compared
to 1998. For corn, the annual nitrogen application
rate was up a pound, phosphate the same, and potash
down 2 pounds.
-
On soybeans, application rates were down for all
nutrients.
-
On cotton, rates were up for all nutrients.
-
Only one wheat-producing State was surveyed, so
comparisons to 1998 were not done.
-
Potatoes received the highest annual application
rates per acre for field crops, with nitrogen averaging
222 pounds, phosphate 176 pounds, and potash 167
pounds.
-
Most fertilizer was applied in 1999 at or before
planting on field crops.
Review of 1998 Nutrient Use and Practices on Major
Crops
-
Total nutrient use was less than 1 percent lower
in 1998 than in 1997, with nitrogen and phosphate
use about the same time, and potash use down about
2 percent.
-
The major factor decreasing nutrient use in 1998
was lower fertilized wheat acreage, which used about
14 percent of all fertilizer.
-
Nitrogen and phosphate application rates on wheat
were about the same in 1998 as in 1997, but potash
application rates were less.
-
Corn acreage, which used 40 to 45 percent of all
fertilizer, was about the same in 1998 as in 1997.
Common Nutrient Management Practices
used by U.S. Farmers
A number of nutrient management practices are used to
enhance fertilizer use efficiency and reduce nutrient
losses into the environment. These practices include:
- Assessing nutrient need through annual or regular
soil and plant tissue testing before applying nutrients,
in contrast to limited or no testing before applying
nutrients. Soil testing identifies the amount of nutrients
already available for plant uptake, and is used to identify
the additional amounts of nutrients needed to meet a
realistic yield goal. A plant tissue nitrogen test uses
chlorophyll (or greenness) sensing to detect nitrogen
deficiency during the growing season to assist in assessing
the need for additional commercial fertilizer applications.
Correction of any nitrogen deficiency is then made through
chemigation or other foliar application.
- Timing nutrient application to tailor feeding to plant-growth
needs, for example, split application of nitrogen fertilizer
into at planting and after planting, in contrast to
fall and early spring applications of nitrogen before
planting.
- Applying nutrients close to the root zone so they
are more readily accessible to the plant, through banded
and injected applications and chemigation, in contrast
to ground and air broadcast and application in the furrow.
With side-dressing or banded application, granule or
liquid nitrogen fertilizer is placed to one side of
the plant or placed every other row at planting or during
the growing season.
- Selecting the nutrient product according to the chemical
stability in the soil, in order to minimize nutrient
loss to the environment. For example, use an ammonia-based
fertilizer on fields with high leaching soils, and a
nitrate-based fertilizer on fields where ammonia volatilization
is a problem.
- Rotating nitrogen-using with nitrogen-fixing crops.
Cover crops are planted between crop seasons to tie
up and preserve nutrients, in contrast to continuous
planting of the same nitrogen-using crop and not planting
any cover crops.
- Applying manure and organic waste based on manure
and waste test results and nutrient management plan.
Adequate storage is available for manure so that applications
will mesh with plant nutrient needs and applications
are injected or incorporated into the soil.
- Using nitrogen inhibitors and other products to slow
the release of nitrates from ammonium fertilizers until
later in the growing season, by delaying the conversion
of ammonium nitrogen into nitrate nitrogen, which is
susceptible to leaching. N-inhibitors can also be used
with manure and other forms of organic nitrogen fertilizer.
- Urease inhibitors—Chemical compounds that
can be added to urea to slow the conversion of urea
to ammonium and therefore to slow nitrate leaching.
- Slow-release nitrogen fertilizer—Fertilizer
coated with chemicals that can retard release of
nitrogen from applied fertilizer and prolong the
supply of nitrogen for plant uptake.
- Refraining from broadcasting nitrogen fertilizer,
or if broadcast, incorporating the product into the
soil, which reduces the losses of nitrogen to the atmosphere.
Certain nitrogen products, especially urea, are subject
to extensive volatilization when broadcast. Certain
nitrogen products are injected or knifed-in, usually
12-24 cm below the soil surface. Nitrogen can also be
incorporated into the soil by tillage. High-pressure
liquid nitrogen such as anhydrous ammonia is the most
common form of nitrogen injected into the soil. Nitrogen
solutions in low-pressure liquid form are also injected
into the soil.
- Applying all nitrogen at and/or after planting, when
the demand by the crop is greatest, which reduces the
risk of nitrogen loss through leaching. Conversely,
applying all nitrogen in the fall can increase the risk
of leaching, under certain soil and weather conditions.
Results from the 1996 USDA Agricultural
Resources Management Study survey of corn farmers indicate
a modest utilization of nutrient testing techniques on
corn acreage. Soil tests were the most extensively used
(on 44 percent of the corn acreage). Nitrogen tests, nitrogen
inhibitors, and broadcast applications with incorporation
were used to lesser degrees. Nitrogen management on those
acres receiving the nitrogen test followed recommendations
closely, with 82 percent receiving nitrogen at rates exactly
as recommended or lower. Nitrogen fertilizer was applied
to corn several times during the year, with the largest
acreage receiving it before planting of corn, either in
the fall, spring, or both. The second largest bloc of
acreage had nitrogen applied at or after planting time,
followed by all the nitrogen applied in the fall.
Potential Contribution of Precision
Agricultural Technologies Contribute to Nutrient Management
Precision agriculture is typically characterized as a
suite of information technologies used to monitor and
manage sub-field spatial variability. Variable rate application
of seeds, fertilizers, pesticides, and irrigation water
has the potential to enhance producers' profits and reduce
the risk to the environment from agricultural production
through the tailoring of input use and application more
closely to ideal plant growth and management needs.
Precision agriculture developments reflect innovations
during the last decade in the computer, telecommunications,
and satellite industries which have made more detailed
spatial and temporal management of nutrients and other
inputs within fields technically feasible. The application
of these information technologies, known as precision
farming or site-specific farming, enables producers to
monitor and differentially manage small areas of a field
that have similar soil or plant characteristics. Components
of a comprehensive precision farming system typically
include:
- Intensively testing soils or plant tissues within
a field
- Equipment for locating position within a field
via the Global Positioning System (GPS)
- Ayield monitor
- A computer to store and manipulate spatial data
using some form of Geographic Information System (GIS)
software
- A variable-rate applicator.
More involved systems may also use remote sensing from
satellite, aerial, or near-ground imaging platforms during
the growing season to detect and treat areas of a field
that may be experiencing nutrient stress.
Precision farming has the potential to improve net farm
income by: (1) identifying places in a field where additional
nutrient use will increase yield, and thus farm income,
by more than the added cost; and (2) identifying places
where reduced input use will reduce costs while maintaining
yield. One preliminary estimate of additional fixed and
variable costs of precision farming for corn is about
$7-$8 per acre (Lowenberg-DeBoer and Swinton, 1995). Precision
farming also has the potential to reduce off-site transport
of agricultural chemicals with surface runoff, subsurface
drainage, and leaching (Baker and others, 1997; Watkins,
Lu, and Huang, 1998). Two years of Kansas field data indicate
less total nitrogen fertilizer use with precision farming
than with conventional nitrogen management (Snyder and
others, 1997).
Corn production represents a potentially large market
for precision agriculture technologies as corn producers
are the largest users of cropland and agri-chemicals in
U.S. agriculture. USDA surveys in 1996 and 1997 indicate
that about 10 percent of all corn farms in the United
States are using some aspect of precision farming (Daberkow
and McBride, 1998). Among precision agriculture adopters,
70 percent used some aspect of precision agriculture—grid
soil sampling, variable-rate technology (VRT) for lime
or fertilizer application, or yield monitors.
Results
from 1996 USDA Agricultural Resources Management Study
found precision agriculture adopters more likely than
non-adopters to:
- Operate larger farms with greater assets and sales
- Farm in the central Corn Belt (IL, IN, or IA)
- Have more corn acres and achieve higher yields
- Earn greater cash farm income
- Have completed college
- Use a computerized farm record system
- Be less than 50 years of age
- Rely on crop consultants for information on precision
farming
Additional information is available from precision agriculture
technology web sites.
Extent of Animal Manure Use in
U.S. Corn Production
Animal manure contains nutrients and organic matter
that can contribute to plant growth. However, its availability
and content variability often limits its use in crop production.
In the case of corn, data from the 1996 ARMS survey of
U.S. corn growers in the 16 major corn producing States
show that 8.4 million acres, 12 percent of the corn acres,
received 50 million tons of manure. The average application
rate was 5.9 tons per acre.
Pennsylvania had the largest percent of corn acres treated
with manure, 58 percent, followed by Minnesota and Michigan.
Dairy manure was the most common source of manure, applied
to 42 percent of the corn acres on which manure was applied.
Next in importance were cattle manure, applied to 27 percent
of corn acres receiving manure, and hog manure, applied
to 23 percent of the manure-receiving corn acres. Sixteen
percent of corn acres on which manure was applied were
soil tested for nitrogen.
The method of spreading and incorporating (or not incorporating)
manure on corn acres influences the amount of nitrogen
available for the crop. Typical application methods include
surface broadcast using a manure spreader, irrigation
systems, a tank wagon followed by incorporation by plow
or discing, or injection (knifing) under the soil surface.
For the States surveyed, manure was applied in a solid
form to 72 percent of the corn acreage with the remaining
acreage share receiving it in liquid form. Incorporation
at time of application occurred on 68 percent of the manured
acres, with 32 percent not incorporated.
In general, the closer to planting time that manure is
applied, the greater the availability of nutrients for
plant growth. Early spring application of manure before
planting, thus allowing for the mineralization of organic
nitrogen, is considered the best for corn production.
Fall application of manure, even with incorporation, can
result in large nitrogen losses because of the time between
application and the next growing season. In the surveyed
States, 60 percent of the manured acres received applications
in the spring before planting, and 39 percent received
the manure in the fall. Fifty percent of the manured acres
received one application, and the remainder received two
and three applications.
For more information refer to Chapter 4.4, Agricultural
Resources and Environmental Indicators.
Trends in Precision Agriculture
for Major Crops
Precision agriculture is a suite of information technologies
used to monitor and manage different crop needs within
a field. Variable-rate application of seeds, fertilizers,
pesticides, and irrigation water can raise producer profits
and reduce environmental risk from agricultural production
by tailoring inputs more closely to ideal plant needs.
The 1996-2002 USDA Agricultural Resource Management
Surveys found that adoption of precision agriculture
continues to grow.
Yield monitors are the most common precision agriculture
technology used on major field crops, especially by
corn and soybean producers. The use of monitors more
than doubled on acreage planted to corn and soybeans
between 1996 and 2001/2002.
The most common use of variable-rate technology (VRT)
is for application of fertilizers, followed by pesticide
application and seeding. Corn growers were most likely
to use precision
agricultural technologies while cotton growers were
least likely.
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