Efficient Fertilizer

1. The Efficient Fertilizer
The Efficient Fertilizers
Guide
Soil Defined
FeThe Soil Profile
The soil profile comprises two or more soil layers called horizons, one below the other, each
parallel to the surface of the land. Important characteristics that differentiate the various
horizons are:
 Color, texture, structure, consistency, porosity and soil reaction
 Thicknesses ranging from several feet thick to as thin as a fraction of an inch
 Generally, the horizons merging with one another and which may or may not be showing
sharp boundaries
A Horizon
The uppermost layer in the soil profile or surface soil. It includes the mulch layer and plow layer.
Living organisms are most abundant in this horizon, consisting of plant roots, bacteria, fungi and
small animals. Organic matter is most plentiful, particularly in the mulch layer. When a soil is
tilled improperly, the A Horizon may be eroded away.
B Horizon
Lies immediately beneath the A Horizon and above the C Horizon. It is called the subsoil. The B
Horizon has properties of both A and C. Living organisms are fewer in number than in the A
Horizon, but more abundant than in the C Horizon. Color is transitional between A and C as
well. It is frequently higher in clay than either of the other horizons.

2. C Horizon
The deepest of the three. This is the material from which the mineral part of the soil forms. It is
the parent material of soils. It may have accumulated in place by the breakdown of hard rock, or
it may have been placed there by the action of water, wind or ice.
Fertile Soil
A fertile soil contains an adequate supply of all the nutrients required for plant growth. The full
potential of crops is not realized if a shortage of nutrients occurs at any time during the growth
cycle. This is true even though plants are capable of remarkable recovery from short periods of
starvation.
A fertile soil is not necessarily a productive one. The second major requirement is that the soil
must be adequate for plant growth. This soil is based on environmental factors including texture,
structure, soil water supply, pH, temperature and aeration.
Soil Texture, Structure and Color
Soil Classes and Textures
An important factor in soil productivity is texture, defined as the relative percentage of sand, silt
and clay. Soils are classified on the basis of texture of each of the horizons. The relative
proportions of clay, silt and sand determine the soil textural class.
Clays are the smallest particles in soil; silts are somewhat larger in size, followed by sands that
are coarse enough that the individual particles are visible to the naked eye. The following table
shows the proportion of sand, silt and clay normally found in the various textural classes of soils.
SOIL CLASSES % SAND % SILT % CLAY
Sands 85+ 0-10
Loamy Sands 70-90 0-15

3. SOIL CLASSES % SAND % SILT % CLAY
Sandy Loams 43-85 0-20
Silt 80+ 0-12
Silt Loams 50-88 0-27
Loams 0-52 0-50 7-27
Sandy Clay Loams 45+ 0-28 20-35
Clay Loams 0-45 0-53 27-40
Silty Clay Loams 0-20 40+ 27-40
Sandy Clays 45+ 0-20 35-55
Silty Clays 40+ 40+
Clays 0.45 0-40 40+

4. Soil Structure
The arrangement of soil particles into groups or aggregates determines the "structure." A single
mass or cluster of soil particles held together in a particular way imparts physical characteristics
to the soil, such as a clod, prism, crumb or granule. Soil structure is often more important than
the texture to the farmer. Soil structure can be changed to produce improved soil conditions for
maximum yield and profits. Structure is especially important to water movement and in
preventing root growth restrictions, both of which affect nutrient availability to the crop.
Examples of various types of soil structure are shown at left.
Soil Color
Color in various types of soils is due primarily to the amount of organic matter and the chemical
state of the iron and other compounds in the mineral fraction of the soil. Other minerals such as
quartz, granite and heavy black minerals may also influence soil color. Unweathered parent
materials tend to be gray in color, or else will have the color of the natural minerals from which
they are derived.
The color of subsoils can reveal a great deal about the age and drainage conditions in the soil.
Iron compounds can exist as oxidized forms (red), hydrated oxides (yellow), and as reduced
forms (gray).
The Relationship Between Subsoil Color and Drainage

5. SUBSOIL COLOR DRAINAGE CONDITION
Red Excellent
Reddish Brown or Brown Good
Bright Yellow Moderately Good
Pale Yellow Imperfect to Fair
Gray Poor
Dark (Black) Variable

6. Soil
Organisms
The mineral soil harbors a varied population of living organisms that play an important role in
the dynamic changes occurring within the soil. Many groups of organisms live in the soil, and
range from microscopic to those visible to the naked eye.
Some of the microscopic-sized organisms are the bacteria, fungi, actinomycetes, algae and
protozoa. Most soil organisms depend upon organic matter for food and energy. Consequently,
they are generally found in the top 12 inches of soil. One of the most important functions of soil
microorganisms is the decomposition of crop residue. Some of it is converted into more stable
organic compounds that are stable in the soil over long periods of time. But a large percentage
of the organic material is released to the atmosphere as carbon dioxide. Also, nitrogen and
other essential plant nutrients are released and made available to growing crops.
Rhizobium bacteria form a symbiotic relationship that results in nitrogen fixation in legume
plants. These organisms penetrate plant roots, causing the formation of small nodules on the
roots. They then live in symbiotic relation with the host plant. The beneficial effect of this
process is realized when cultivated legumes, such as alfalfa, clovers, soybeans, etc., are
inoculated at seeding with the proper strain of the rhizobium bacteria.

7. The millions of microorganisms in the soil play critical roles in plant nutrition, although many are
unidentified. The improved understanding of the microbiology of plant nutrition is one of the
important unmet challenges of crop nutrient management.
Harmful Microorganisms
Some soil microorganisms are harmful to soils and growing plants, in the form of diseases,
toxins produced and denitrification. When the supply of air in a soil is limited, certain aerobic soil
organisms can get their supply of oxygen by reducing highly oxidized compounds, such as
nitrates. Further reducing action may result in free nitrogen (N2) being produced and lost to the
atmosphere. This is not an environmental problem, because 78 percent of the atmosphere is
N2 gas, but the result is a net loss of N available for the crop. Other microorganisms contribute
to loss of N as NOx gases, potent greenhouse gases that can be an environmental problem.
Nitrogen Fixation by Crop
CROP LB/ACRE N FIXED
Alfalfa 196
Ladino Clover 178
Sweet Clover 116
Red Clover 112
White Clover 103
Soybeans 98
Cowpeas 89
Lespedeza 85

8. Nitrogen Fixation by Crop
CROP LB/ACRE N FIXED
Vetch 80
Garden Peas 71
Winter Peas 54
Peanuts 42
Adapted from "Fertilizers and Soil Amendments"by Follett, Murphy and Donahue.

9. Cation Exchange Capacity
Each soil colloid contains a net negative electrical charge due to its structural and chemical
makeup. Soil colloids have the ability to attract and hold positively charged elements by
electrical attraction. Most chemical compounds when in solution dissolve into electrically
charged particles called ions. Ions with positive charges are called cations and ions containing
negative charges are referred to as anions. Consequently, positively charged cations such as
potassium (K+), calcium (Ca++), magnesium (Mg++) and ammonium nitrogen (NH4+) are
attracted and held to the surface of soil colloids much like a magnet attracts and holds iron
filings.

10. Montmorillonite clay and organic colloids have more surface area exposed than kaolinite-type
colloids and, therefore, have a higher net negative electrical charge. Thus, montmorillonitic soils
have more capacity to hold positively charged nutrient ions, or cations. This characteristic is
called cation exchange capacity (CEC). Knowledge of a soil’s CEC is basic to understanding
how to manage lime and fertilizer additions. Since kaolinite clays have less surface area
exposed, they have lower (CEC) values, meaning less capacity to hold nutrients.
CEC helps to explain why certain fertilizer elements such as positively charged potassium,
calcium and magnesium, as well as ammonium nitrogen are not as easily leached from the soil
as the negatively charged ions, or anions, of nitrate nitrogen, sulfates or chlorides.
Cations adsorbed on the surface of soil colloids, and those contained in the soil solution, are
available for plant use. Adsorbed cations, however, can be replaced by other cations present in
the soil solution through the process of cation exchange. These replaced cations may then
combine with an anion and be leached from the soil.
For example, when large amounts of a fertilizer material such as muriate of potash (KCI)
are applied to the soil, the KCI dissolves in soil moisture and disassociates into K+ and
Cl- ions. The K+ in solution tends to exchange with Mg++ adsorbed on the clay and
organic matter. The K+ is held on the soil particles, and the Mg++ combines with Cl- to
form MgCl, a soluble compound that is then leached from the soil with rainfall. As plants
remove nutrients from the soil solution throughout the growing season, the
concentrations change, and this dynamic exchange of nutrients continues.
The force by which cations are held by soil colloids will depend upon several factors. The
smaller the cation and the less water it has adsorbed, generally the tighter the cation is
held on the soil particles. Hydrogen ions, therefore, are more tightly held and more
difficult to replace than larger and more hydrated cations such as ammonium, calcium,
magnesium and potassium. Divalent cations (two charges) are generally held tighter by
soil colloids than monovalent cations (one charge). Therefore, calcium and magnesium,
divalent cations, are more difficult to replace than the monovalent cations such as
potassium and ammonium. Soils with high sand and silt content have a lower percentage
of clay and organic matter, and thus have lower CEC. This explains why coarse-textured
soils require more frequent applications of lime and fertilizer.

11. Determining Soil Cation Exchange Capacity
The cation exchange capacity (CEC) of a soil is typically expressed in terms of
milliequivalents. A milliequivalent is defined as "one milligram of hydrogen or the amount
of any other element that will displace it." When applied to soils, milliequivalents are
generally expressed on the basis of 100 grams of oven-dried soil. One milligram of
hydrogen per 100 grams of soil equates to 10 parts of hydrogen per one million parts of
soil. An acre (top 6 2/3 inches) of soil weighs about 2,000,000 pounds. Therefore, 10
parts per million of hydrogen (whose atomic number is one) equals about 20 lb/acre of
hydrogen.
This calculation provides a standard of measurement for converting the milliequivalent of
other elements to pounds per acre. The standard is one milliequivalent of hydrogen
equals 20 lb/acre of hydrogen. Since the atomic weight of hydrogen is 1, to convert a
milliequivalent of other elements to pounds per acre, multiply its atomic weight by 20.
Remember, divalent elements have two positive electrical charges and replace two
hydrogen ions; therefore, to arrive at the equivalent atomic weight of divalent cations,
divide its atomic weight by 2.
Example:
Atomic weight of calcium = 40
Valence = 2
Equivalent weight = 40/2 = 20
Therefore, one milliequivalent of calcium is equal to the equivalent weight of calcium
multiplied by 20 lb/acre of hydrogen. Calcium equivalent weight of 20 x 20 lb/acre
hydrogen = 400 lb/acre.
CEC by a Lab
One laboratory method of determining the exchange capacity of a soil is to remove all of
the adsorbed cations by leaching a weighed portion of soil with a salt solution such as
one normal ammonium acetate. All of the adsorbed cations are replaced by the
ammonium ions. All excess ammonium ions are then removed by leaching with alcohol.
The adsorbed ammonium ions are then removed from the soil by extracting with a
different salt, such as one normal potassium chloride. The potassium ions replace the
adsorbed ammonium ions. The quantity of ammonium ions in the leachate can then be

12. measured, and is then expressed as milliequivalents per 100 grams of soil — the CEC
value. This laboratory procedure is laborious and time consuming. Generally, an estimate
of the soil's CEC value is sufficient.
Estimate of CEC
An estimate of the cation exchange capacity of a soil can be made from soil test results. This
can be accomplished by dividing the pounds per acre of the element as determined by the soil
test by the milliequivalent weights of the cations. First, the equivalent weights of cations must be
converted into pounds per acre. The cations used in the calculation of CEC are hydrogen,
potassium, magnesium and calcium.
Conversion Table from Cation Weights to Pounds Per Acre
CATION
ELECTRICAL
CHARGE
ATOMIC WEIGHT
EQUIVALENT
WEIGHT
LB/ACRE OF ONE
MILLIEQUIVALENT
(M.E.)
Hydrogen 1 1 1 20
Calcium 2 40 20 400
Magnesium 2 24 12 240
Potassium 1 39 39 780
Converting Soil Test to Milliequivalents for Cations

13. CATION SOIL TEST LB/ACRE 1 M.E. LB/ACRE M.E./100 GRAMS
Hydrogen 50 20 2.50
Calcium 800 400 2.00
Magnesium 120 240 0.50
Potassium 250 780 0.32
To arrive at the estimated cation exchange capacity of this soil, divide the lb/acre of each
element as determined by soil test by one milliequivalent (m.e.) in lb/acre of each element. As
shown in the table at left, for calcium, divide the 800 lb/acre soil test value by the 400 m.e.
value, which yields a value of 2.0 m.e. per 100 grams of calcium. The sum of the m.e. per 100
grams for each of the four nutrients is the calculated CEC for that soil.
The proportion of adsorbed base cations (calcium, magnesium and potassium) relative to
hydrogen is expressed in terms of percent base saturation. Generally, the higher the percent
base saturation of a soil, the higher the soil pH and fertility level. In the above example, the
percent base saturation would be:
((Ca 2.0 + Mg 0.5 + K 0.32) /5.32) X 100 = 53% Base Saturation
This base saturation number is then used with the appropriate calibration database for the area
to guide fertilizer recommendations.
The table at right shows the CEC values for representative soils across the United States and
illustrates the wide range of values that can occur.
CEC Values for Representative Soils
SOIL OR SOIL COMPONENT LOCATION CEC M.E./100 GRAMS

14. CEC Values for Representative Soils
SOIL OR SOIL COMPONENT LOCATION CEC M.E./100 GRAMS
Grundy Silt Loam Illinois 23.6
Clarion Loam Iowa 19.1
Sac Silty Clay Loam Iowa 35.1
Delta Light Silt Loam Massachusetts 9.4
Cecil Sandy Loam South Carolina 5.5
Norfolk Sandy Loam South Carolina 3.0
Lakeland Sand Florida 1.5
Kaolinite Clay – 5-15
lllite Clay – 10-45
Montmorillonite Clay – 60-150
Humus – 140
Anion Adsorption
Anions are the opposite of cations, in that they contain a net negative charge. The most
common anions in soils are chloride, sulfate, phosphate and nitrate.

15. In addition to cation-adsorbing capacity, soils also have the ability to adsorb anions, but
to a lesser extent than cations. Anion adsorption is pH dependent and increases with a
decrease in soil pH. Phosphates and sulfates are adsorbed more strongly than nitrates
and chlorides. Anion adsorption is not as important agriculturally as cation adsorption.
Most agricultural soils have a pH higher than that at which anion adsorption is at its
maximum strength; and with the exception of phosphate, and to a lesser degree sulfate,
anions are largely lost from the soil by leaching.
Soil pH
Soil pH is a measure of the acidity and alkalinity in soils. pH levels range from 0 to 14, with 7
being neutral, below 7 acidic and above 7 alkaline. The optimal pH range for most plants is
between 5.5 and 7.0; however, many plants have adapted to thrive at pH values outside this
range. Because pH levels control many chemical processes that take place in the soil –
specifically, plant nutrient availability – it is vital to maintain proper levels for your plants to reach
their full yield potential.
An acid is defined as a substance that tends to release hydrogen ions (H+). Conversely, a base
is defined as a substance that releases hydroxyl ions (OH-). All acids contain hydrogen ions,
and the strength of the acid depends upon the degrees of ionization (release of hydrogen ions)
of the acid. The more hydrogen ions held by the exchange complex of a soil in relation to the
basic ions (Ca, Mg, K) held, the greater the acidity of the soil.
NOTE: Aluminum (Al) also contributes to soil acidity, but for simplicity, further discussion of soil
acidity will be limited to H as the cause of soil acidity.

16. pH Range
5.0 – 5.5 5.5 – 6.5 6.5 – 7.0
Blueberries Barley Alfalfa
Irish Potatoes Bluegrass Some Clovers
Sweet Potatoes Corn Sugar Beets
Cotton
Fescue

17. pH Range
5.0 – 5.5 5.5 – 6.5 6.5 – 7.0
Grain Sorghum
Peanuts
Rice
Soybeans
Watermelon
Wheat
Desirable Soil pH for Optimum Crop Production pH
Range
The desirable pH range for optimum plant growth varies among crops. While some crops grow
best in the 6.0 to 7.0 range, others grow well under slightly acidic conditions. Soil properties that
influence the need for and response to lime vary by region. A knowledge of the soil and the crop
is important in managing soil pH for the best crop performance.
Soils become acidic when basic elements such as calcium, magnesium, sodium and potassium
held by soil colloids are replaced by hydrogen ions. Soils formed under conditions of high
annual rainfall are more acidic than are soils formed under more arid conditions. Thus, most
southeastern soils are inherently more acidic than soils of the Midwest and far West.

18. Soils formed under low rainfall conditions tend to be basic with soil pH readings around 7.0.
Intensive farming over a number of years with nitrogen fertilizers or manures can result in soil
acidification. In the wheat-growing regions of Kansas and Oklahoma, for example, which have
soil pH of 5.0 and below, aluminum toxicity in wheat and good response to liming have been
documented in recent years.
Factors Affecting Soil Acidity
 Rainfall
 Nitrogen Fertilizers
 Plants
Rainfall
Rainfall contributes to a soil’s acidity. Water (H2O) combines with carbon dioxide (CO2) to
form a weak acid — carbonic acid (H2CO3). The weak acid ionizes, releasing hydrogen
(H+) and bicarbonate (HCO3). The released hydrogen ions replace the calcium ions held
by soil colloids, causing the soil to become acidic. The displaced calcium (Ca++) ions
combine with the bicarbonate ions to form calcium bicarbonate, which, be ing soluble, is
leached from the soil. The net effect is increased soil acidity.
Subsoil Acidity
Even if the top 6 inches of soil show a pH above 6.0, the subsoil may be extremely
acidic. When subsoil pH's drop below 5.0, aluminum and manganese in the soil become
much more soluble, and in some soils may be toxic to plant growth. Cotton and, to some
extent, soybeans are examples of crops that are sensitive to highly soluble aluminum
levels in the subsoil, and crop yields may be reduced under conditions of low subsoil pH.
If you’ve observed areas of stunted plants in your field, take a subsoil sample in these
areas. If the soil pH is extremely acidic (below 5.2), lime should be applied early in the
fall and turned as deeply as possible.
Liming Soil Pays
Correcting soil acidity by the use of lime is the foundation of a good soil fertility program. Lime
does more than just correct soil acidity. It also:

19.  Supplies essential plant nutrients, Ca and Mg, if dolomitic lime is used
 Makes other essential nutrients more available
 Prevents elements such as Mn and Al from being toxic to plant growth.
Limestone Increases Fertilizer Efficiency and Decreases Soil Acids
SOIL ACIDITY NITROGEN PHOSPHATE POTASH FERTILIZER WASTED
Extremely Acid — 4.5 pH 30% 23% 33% 71.34%
Very Strong Acid — 5.0 pH 53% 34% 52% 53.67%
Strongly Acid — 5.5 pH 77% 48% 77% 32.69%
Medium Acid — 6.0 pH 89% 52% 100% 19.67%
Neutral — 7.0 pH 100% 100% 100% 00.0%
LIMING MATERIALCOMPOSITIONCALCIUM CARBONATE EQUIVALENT (CCE)Calcitic
LimestoneCaCO385-100Dolomitic LimestoneCaCO3; Mg CO395-108Oyster ShellsCaCO390-
110MarlsCaCO350-90Hydrated LimeCa(OH)2120-135Basic SlagCaSiO350-70GypsumCaSO4 None

20. Liming Materials
Liming materials contain calcium and/or magnesium in forms, which when dissolved, will
neutralize soil acidity. Not all materials containing calcium and magnesium are capable of
reducing soil acidity. For instance, gypsum (CaSO4) contains Ca in appreciable amounts, but
does not reduce soil acidity. Because it hydrolyzes in the soil, gypsum converts to a strong base
and a strong acid as shown in the following equation:
CaSO4 + 2H2O = Ca (OH)2 + H2SO4
The formed Ca (OH2) and H2SO4 neutralize each other, resulting in a neutral soil effect. On the
other hand, when calcitic (CaCO3) or dolomitic lime (Ca Mg (CO3)2) is added to the soil, it
hydrolyzes (dissolves in water) to a strong base and a weak acid.
CaCO3 + 2H2O = Ca (OH)2 + H2CO3
Calcium hydroxide is a strong base and rapidly ionizes to Ca++ and OH- ions. The calcium ions
replace absorbed H ions on the soil colloid and thereby neutralize soil acidity. The carbonic acid
formed (H2CO3) is a weak acid and partially ionizes to H+ and CO2
-2
ions. Therefore, the net
effect is that more ca than H ions are released in the soil, and consequently, soil acidity is
neutralized.
IMING MATERIAL COMPOSITION
CALCIUM
CARBONATE
EQUIVALENT (CCE)
Calcitic Limestone CaCO3 85-100
Dolomitic Limestone CaCO3; Mg CO3 95-108
Oyster Shells CaCO3 90-110
Marls CaCO3 50-90
Hydrated Lime Ca(OH)2 120-135
Basic Slag CaSiO3 50-70

21. IMING MATERIAL COMPOSITION
CALCIUM
CARBONATE
EQUIVALENT (CCE)
Gypsum CaSO4 None
Site-Specific Nutrient
Management
Site-specific nutrient management is a component of precision agriculture and can be used for
any field or crop. It combines plant nutrient requirements at each growth stage and the soil’s
ability to supply those nutrients, and applies that information to areas within a field that require
different management from the field average. Site-specific management allows for fine-tuning
crop management systems along with 4R Nutrient Stewardship — the right source, rate, time
and place of nutrient use.
Site-Specific Nutrient Management
Site-specific management can be thought of as a series of layers of information about each
field, as depicted in Figure 1. Each time a measurement is made (soil tests, scouting reports,
yield data, etc.), another layer of information is added. Over time, multiple layers of information
are added and become part of the database that can guide future crop management decisions.
By geo-referencing each data point to its precise geographic location, these data layers can be
"stacked" for analysis to determine the relationship between layers for any point in the field. For
example, the relationship between nitrogen rate applied and yield obtained might be
determined, and then its variability mapped as an additional "calculated" layer of information.

22. Precision Agriculture
The systematic implementation of best management practices into a site-specific system
provides the best opportunity to develop a truly sustainable agriculture system. Managing the
right source at the right rate, right time and in the right place is best accomplished with the right
tools. Various technologies are available to help make decisions related
to nutrient management, from soil sampling to fertilizer application to yield measurement. These
tools enhance the ability to fine-tune nutrient management decisions and develop the site-
specific nutrient management plan for each field.
Identify and Quantify Variability within Fields
Variability within fields is measured by soil sampling, field scouting, physical
measurements, soil survey, and yield monitoring. Documenting this information in the
GIS database for a field provides the basis for site-specific management decisions.
Variability within fields comes from a variety of natural and man-made factors. Natural
variability is largely due to physical properties of the soil including topography, texture
and structure.
Man-made influences on soil variability include:
 Crop rotation, livestock pasture, fences, tile drainage, fertilizer and manure
application;
 Cropping systems and tillage operations affect soil tilth; and
 Compaction (a result of a combination of natural and man-made factors).
Site-Specific Equipment and
Technology
Equipment
Special equipment is not required for site-specific management. Identifying areas requiring
specific management can be done with conventional soil testing and scouting techniques.
Different fertilizer rates can be applied to different areas by staking or flagging them, and then
spreading the different areas separately. Estimates of within-field distances to identify these
areas can be documented by measuring, counting rows, pacing or other relative means. But

23. there are technology tools available that expand the capabilities for using site-specific
management more effectively.
Technology Tools
GPS, GIS-based records and data analysis, sensors and variable-rate controllers are
revolutionizing nutrient management to best meet crop needs and efficiently utilize available
resources. Site-specific sampling, variable-rate fertilizer application and yield monitors are
among the most common tools guiding today’s modern nutrient management systems.
Global Positioning System (GPS)
Most of the tools for precision agriculture involve use of data collection or controller
systems that utilize the global positioning system (GPS). Each set of data collected is
associated with its specific geographic coordinates (latitude, longitude, and elevation).
This allows the understanding of precise relationships among the different layers of data,
the resulting yield data, and other measurements. These layers can then be analyzed to
make recommendations for future decisions.
GPS systems are used on planting equipment for collecting geo-referenced planting
data, starter fertilizer application, and other inputs. With proper controllers, variable-rate
application of inputs can be added to the management plan. Each of these steps can be
added over time, increasing the value of the initial investment.
As more advanced military-technology becomes available for public use and new
technologies develop to support GPS, this tool will continue to become more valuable to
farmers in implementing site-specific management.
 Global Positioning System (GPS)
 Real-Time Kinematic System (RTK)
 Geographic Information System (GIS)
 Soil Surveys
 Intensive Soil Sampling
 Remote Sensing

24. Nutrient Management Plan
Development
The value of GPS, GIS and remote-sensing technologies comes from incorporating the data into
the management decision process. These tools can help to develop a comprehensive crop and
soil nutrient management plan that can help improve production efficiency, increase yields and
reduce potential environmental problems associated with crop production. The GIS system
provides a means to monitor and evaluate nutrient needs, crop removal, and losses to the
environment
Information Integration
Site-specific management and the technology tools available require integration of many
sources of information. Without the use of computers and GIS software, it is impractical
to try to analyze all of the information available. Site-specific systems, including yield
monitor data, generate large amounts of data that should be integrated into GIS and
used to interpret the variability to move to a higher level of production, input efficiency
and profitability.
 Taking Advantage of Information
 Information Integration
 Step-wise Implementation
 Building a Digital Nutrient Management Plan for Each Field
 Documentation of Needs, Rates of Application and Yield Responses
 Moving Forward with Site-Specific Precision Agriculture Systems
Fertilizer Use and the 4Rs
Fertilizers are a necessary component of sustainable crop production. When properly managed,
fertilizers help address the challenge of increasing production in an economically viable way
while retaining the ecological integrity of cropping systems. However, if nutrients are not
adequately available within a crop production system, fertility is mined from the soil, and the
crop will never attain optimal yields. Conversely, if nutrients are supplied in excess or without
managing risks, the possibility of nutrient movement away from the cropping system increases,

25. potentially negatively affecting the environment. In both situations, the profitability of the
cropping system will be negatively impacted by lost yield or by lost inputs.
4R Nutrient Stewardship utilizes fertilizer best management practices (BMP) addressing the
right fertilizer source, at the right rate, the right time, and in the right place. The 4Rs provide the
foundation for a science-based framework to
achieve sustainable plant nutrition management. In short, 4R practices are good for the grower,
good for the farming community, and good for the environment.
There is an existing need to improve the adoption of fertilizer best management practices to
enhance the sustainability, efficiency and productivity of agricultural systems. Efficiency and
productivity together are interwoven with sustainability. Striving to improve efficiency without
also increasing productivity simply increases the pressure to produce more on lands less suited
to agricultural production. Conversely, squandering resources to maximize productivity can
result in increased environmental impacts and decreased profitability.
The essential plant nutrients play a vital role in providing adequate food supplies and protecting
our environment.
Nitrogen and the Environment
When soil nitrogen supply becomes low, plant stresses are immediate and yield losses
are assured. The large demand crops have for nitrogen (legumes are an exception)
means that supplemental sources must be provided for efficient and sustainable crop
production. All these sources, when added to soils enter the nitrogen transformation
cycle and are eventually converted to plant-available ammonium and nitrate-nitrogen. To
meet crop management objectives, fertilizer best management practices must ensure
that adequate amounts of nitrogen are used for profitable production levels, while
minimizing any potential negative effects on the environment. This is best achieved by
utilizing practices that address the 4Rs.
Much of the concern about nitrogen in the environment is due to the potential movement of
unused or excess nitrate-N through the soil profile into groundwater (leaching). Because of its
negative charge, nitrate-nitrogen is not attracted to the various soil fractions. Rather, it is free to
leach as water moves through the soil profile. Soil type has an influence on the amount of and
speed with which nitrate-nitrogen moves through a soil profile, with movement greater in sandy

26. as compared to clay soils. Nitrogen loss as ammonia volatilization from surface-applied sources
and as dinitrogen gas (N2) or nitrous oxide (N2O) from soil microbial activity is also a concern.
Phosphorus and the Environment
Phosphorus has been associated with environmental pollution through the eutrophication of
lakes, bays and non-flowing water bodies. The symptoms are algal blooms, heavy growth of
aquatic plants and deoxygenation. Since phosphorus is insoluble relative to other essential
nutrients, environmental degradation is associated largely with phosphorus movement when soil
erosion occurs. Except on some organic soils, very low concentrations of phosphorus are found
in drainage waters as the result of leaching. The major form of phosphorus entering surface
waters in most agricultural watersheds is particulate-phosphorus associated with either clay soil
fractions or organic matter. These fractions are the most easily eroded, and have a relatively
high surface area that contains enriched phosphorus levels compared to soil particles that have
greater resistance to erosion.

27. Sustainable Cropping Systems
Sediment-enriched phosphorus commonly contains two to six times that of soil
phosphorus levels that are left behind. High-loading in surface runoff is usually
associated with storm events. Storm flow concentrations of soluble phosphorus are often
10 times greater than base flow concentrations. Numerous research studies have shown
that conservation tillage practices reduce soil erosion and the movement of phosphorus
from agricultural lands. Conservation tillage is a BMP because it reduces erosion
considerably by absorbing the impact of falling rain and slowing water runoff. If erosion is
stopped, then phosphorus losses to the environment will beProduction demands, input
requirements and environmental impacts taken together mean the risks for making the
wrong nutrient use decisions is greater now than ever. When fertilizer BMPs result in
increased production and input use efficiency, they also reduce losses to the
environment. When making practice selection, the interconnectivity between practices
addressing source, rate, time and place should be considered.
While the scientific practices governing the 4Rs are universal, practice implementation is
site-specific; so there is not a common management plan or set of practices that will work
for everyone in every location. Crop advisors are key in the efforts to increase adoption
of 4R Nutrient Stewardship with growers.
Selecting BMPs for increasing nutrient efficiency and productivity while reducing
environmental impact begins with addressing the scientific principles behind the 4Rs.
Fertilizer BMPs should be selected based on these principles, and should then be used
in combination with other conservation practices.
reduced to acceptable minimum levels.
 Right Source
 Right Rate
 Right Time
 Right Place
Right Source:
Ensure a balanced supply of essential nutrients, considering both naturally available sources
and the characteristics of specific products in plant-available forms. Specifically, consider

28. nutrient supply in plant-available forms, ensure the nutrient suits soil properties, and recognize
the synergisms among elements.
Fertilizer Best Management
Practices that Address the 4Rs
 YIELD LEVEL
 TIMING OF APPLICATION
 SPLIT- OR MULTIPLE NITROGEN APPLICATIONS
 ADEQUATE & BALANCED NUTRIENT SUPPLY
 USE OF INHIBITORS
 CORRECT METHOD OF APPLICATION
 CREDITS
 SOIL & TISSUE TESTING
 IRRIGATION WATER CREDITS
 EROSION CONTROL
 USE OF COVER CROPS
 LIMING TO CONTROL SOIL ACIDITY
Split- or Multiple Nitrogen Applications
Consider split-nitrogen applications according to plant growth stages and crop needs for
both small grains and row crops. Preplant, starter, top-dress, side-dress and fertigation
are some of the fertilizer application timing options. Plant-soil analyses can be helpful to

29. determine additional nitrogen needs. Timeliness of application is essential to be sure
crop yields do not suffer from nitrogen deficiency.
Agronomic Comparisons of Fluid and
Dry Fertilizers
Experimental data from a wide range of studies overwhelmingly supports the conclusion that
there are essentially no differences among the liquid, suspension and dry fertilizers when they
are compared over the long term under conditions of similar nutrient rates, placements and
chemical forms. The last is particularly important when comparing phosphate fertilizers. For
instance, it would not be valid to compare a highly water-soluble phosphate in fluids with a solid
phosphate of low water solubility. However, when solids such as diammonium phosphate
(DAP), monoammonium phosphate (MAP) or ammonium polyphosphate were compared with
fluids such as 10-34-0, 8-24-0 or 11-37-0 under similar conditions, long-term studies have
shown these to be essentially equal in nutritive value. Similarly, long-term studies have shown
solid urea or ammonium nitrate to be virtually equal to nitrogen solutions, such as urea-
ammonium nitrate. Essentially, the same conclusions would be reached with dry and fluid NPK
mixes.
Cautions in Comparing Fertilize
For valid comparisons, studies should be conducted for several years at the same location
using the same experimental design to ensure that the variability inherent in field studies does
not lead to faulty interpretations. If data are selected from one study, for one year, at one
location, evidence can be cited to prove that solids are better than fluids, or vice versa, or that
polyphosphates are better than orthophosphates, or vice versa.

30. Care must be exercised in comparing any solid or fluid fertilizers under field conditions. For
example, concentrated superphosphate, 0-46-0 or CSP, can’t be compared directly with 10-34-0
solution or solid monoammonium phosphate, 11-48-0 or MAP, because the latter two contain
nitrogen.
For valid comparisons, studies should be conducted for several years at the same location
using the same experimental design to ensure that the variability inherent in field studies does
not lead to faulty interpretations. If data are selected from one study, for one year, at one
location, evidence can be cited to prove that solids are better than fluids, or vice versa, or that
polyphosphates are better than orthophosphates, or vice versa.
Care must be exercised in comparing any solid or fluid fertilizers under field conditions. For
example, concentrated superphosphate, 0-46-0 or CSP, can’t be compared directly with 10-34-0
solution or solid monoammonium phosphate, 11-48-0 or MAP, because the latter two contain
nitrogen.
Fluids and Solids are Equal
Agronomically
The relative equality of fluid and dry fertilizers should not be too surprising in light of the fact that
the chemical constituents of the two physical forms are usually identical.
The matter of equality of various physical forms is even more predictable when one considers
the limited variety of chemical forms presented to the plant root. Although a farmer may apply
fertilizer nitrogen as anhydrous ammonia, urea, ammonium nitrate, urea-ammonium nitrate,
calcium nitrate or several other forms, the same farmer may be assured that, within a fairly short
time, the roots of his crops will be confronted mainly with nitrogen in the nitrate form (NO3). This
is because various soil enzymes rapidly convert urea nitrogen to ammonium forms, and then
soil microbiological processes fairly rapidly convert the ammonium forms to nitrate. So, for most
of the growing season, plant roots "see" mainly nitrates unless a source of ammonium nitrogen
is supplied during the season.
Despite the fact that farmers are offered a wide array of phosphorus-containing
fertilizers, these farmers are assured that their crops are really confronted with a very limited
variety of chemical forms of phosphorus. First, the phosphorus in most fertilizers is present in
the orthophosphate form. When an orthophosphate-containing fluid fertilizer is applied or an

31. orthophosphate-containing dry fertilizer dissolves in the soil solution, the plant roots are
confronted mainly with two phosphate species (H2PO4- and HPO4
=
). If a fertilizer material
containing polyphosphates is applied, the polyphosphate is fairly rapidly converted in most
agricultural soils to the orthophosphate form. So, regardless of the physical or chemical form of
phosphate fertilizer, after a short while in the soil, plant roots "see" only two very similar forms of
phosphate.
Potassium fertilizers are even more uniform than either nitrogen or phosphate fertilizers. The
dominant source of potassium for both fluid and dry fertilizers is potassium chloride. Even when
other sources are used, such as potassium phosphate or potassium nitrate, it is the potassium
ion (K+) that the plant root deals with in the soil solution.
Implications of Equality
Fluid and dry fertilizers of comparable chemical constituency are essentially equal
agronomically when applied at equivalent nutrient rates under similar placements at the
same time. This equality of the various forms of both fluid and dry fertilizers is a powerful
management tool. It frees the farmer to choose from a wide variety of materials using a
multiplicity of non-agronomic factors as criteria for the decision.
Soil Testing
The purpose of soil testing in high-yield farming is to determine the relative ability of a soil to
supply crop nutrients during a particular growing season, to determine lime needs, and for
diagnosing problems such as excessive salinity or alkalinity. Soil testing is also used to guide
nutrient management decisions related to manure and sludge application with the objective of
maximizing economic/agronomic benefits while minimizing the potential for negative impacts on
water quality
Sampling
The soil testing program starts with the collection of a soil sample from a field. The first basic
principle of soil testing is that a field can be sampled in such a way that chemical analysis of the
soil sample will accurately reflect the field’s true nutrient status. This does not mean that all of

32. the samples must, or will, show the same test results, but rather that the results must reflect true
variations within the field. Remember that the soil test recommendations for lime and fertilizer
can never be more accurate than the accuracy of soil sampling.
Note: A separate chapter in the EFU Guide is devoted to soil sampling.
ACTORS AFFECTING
NUTRIENT AVAILABILITY
N P K S
CA AND
MG
MICROS
Soil pH X X X X X X
Moisture X X X X X X
Temperature X X X X X X
Aeration X X X X X X
Soil Organic Matter X X X X X
Amount of Clay X X X X X X
Type of Clay X X X X
Crop Residues X X X X X X
Soil Compaction X X
Nutrient Status of Soil
Soil Test Parameters
In addition to extracting solutions, several other parameters of each soil test are important in
determining the final number that is printed on a soil report for any one soil sample. These
parameters include:
 Ratio of soil to extractant

33.  Shaking time, action and speed
 Method of expressing the results
(e.g., lb/acre, ppm, index systems)
 "Cut-off" levels for high test results
 Overall techniques used in the lab
The extractants containing the dissolved plant nutrients are analyzed to determine the
concentration of the plant nutrient(s). Results are usually reported as parts per million (ppm), or
pounds per acre (lb/acre). For most nutrients, ppm may be converted to lb/acre by multiplying
by two (40 ppm of potassium = 80 lb/acre). For nitrate, sulfate and chloride, essentially all the
nutrient forms present in the soil are extracted, and depth increments, other than the standard
6- to 7-inch surface layer, are sampled. For these measurements, ppm is converted to lb/acre
by the following formula: lb/acre = ppm x 0.3 x depth increment in inches. For example, a 10
ppm nitrate N test on a soil sample taken
to a 24 inch depth would convert to 72 lb/acre (10 ppm x 0.3 x 24 inches). In this case, 72
lb/acre of nitrate nitrogen were present in the top 24 inches of the soil sampled.
Extracting available plant nutrients helps give an educated estimate as to the amounts of plant
nutrients that will be available to a particular crop during the growing season. The amount of
plant nutrients extracted will depend on the strength of the extracting solution and various other
parameters. Soil test values are a relative number and should be interpreted as low, medium or
high for a particular nutrient.
Calibration and Interpretation
Perhaps the greatest challenge in soil testing is calibration of the tests. It is essential that the
results of soil tests be calibrated against crop responses from applications of the plant nutrients
in question. This information is obtained from field and greenhouse fertility experiments
conducted over a wide range of soils. Yield responses from rates of applied nutrients can then
be related to the quantity of available nutrients in the soil.
The results of long-term soil test calibration studies on different soil types are then utilized to
establish recommended amounts of plant nutrients to apply to a particular crop at a given soil
test level. For instance, if the soil test P level is in the range of 0–10 ppm (which is low), the P
recommendation for a 150 bu/acre corn crop may be 100 lb/acre of P2O5; whereas, if the soil
test P level is above 40 ppm (very high), the recommendation may be 0 to 20 lb/acre.

34. In this example to the right, more than 85 percent of the fields testing very low in a particular
plant nutrient may give a profitable yield response to the added nutrient. At the very high level,
there is only a 15 percent probability of a profitable yield increase to the added nutrient. These
values are arbitrary, but they illustrate the idea of expectation of response.
The tools of site-specific precision management now allow growers to manag
The tools of site-specific precision management now allow growers to manage more
homogenous areas within fields. Some of those areas have much higher yield potentials than
the database with which most of today’s soil tests were calibrated. This lack of calibration for
high-yielding areas is one of the factors driving interest in using yield monitors and global
positioning satellites to conduct strip trials to determine the adequacy of existing soil fertility
programs. New precision ag tools have the ability to develop algorithms that allow for
management of multiple site-specific zones within individual fields. This means a balanced crop
nutrition prescription can be delivered to each square foot of every field.
When interpreting soil test results, several things should be kept in mind:
 The chances of getting a profitable response to fertilization are much greater on a soil
that tests low in a given nutrient than on one that tests high.

35.  This does not rule out the possibility of a profitable response from nutrient application at
a high level of fertility or lack of a profitable response on soils of low fertility.
 Soil tests are better at predicting the probability of a profitable response to nutrient
application than predicting the actual quantity of nutrient that will be needed in any one year.
 Research in the United States and Europe shows that in any one season, a soil testing
low in a nutrient often will not yield as well as a soil testing at an optimum level, no matter how
much fertilizer is applied that year.
 Interpretation of soil test results and recommendations often becomes a matter of how to
improve the fertility status of soils testing less than optimum. How much will be needed to
change the soil from low to medium or high in that element? What will be the most economical
level at which to maintain the nutrient status of the soil?
 With top-level management practices, yields increase and the probability of a response
at any given soil test likewise increases.
 Wise use of soil testing incorporates a long-term approach to fertility management, in
which site-specific soil test target levels are established for each field and nutrient management
plans developed to reach and maintain the target levels.
Recommendations
The goal of soil testing is to help farmers achieve economical optimum yields while protecting
the environment. The basic philosophy of soil test fertilizer recommendations is:
 Base them on soil test results;
 Recommend that lower-testing soils be built up to higher test levels by adding extra
fertilizer;
 Apply maintenance amounts of plant nutrients to higher-testing soils to keep them there
and to keep productivity high; and
 Do not apply specific nutrients to soils testing very high in these nutrients.
Individualized fertilizer recommendations use site- and grower-specific information, rather than
laboratory-generated recommendations based on assumptions and generalizations. Computer
programs are available that help personalize recommendations by considering the following:

36. Soil Test Calibration Relevancy
How appropriate is the calibration used in the standard recommendation for the field in
question? Unusual soil types, a different climate, no-till or ridge-till culture, crop variety, cropping
history and field variability are examples of factors that could cause differences.
Yield Potential
Yield potential determines the economic value of each percentage change in relative yield and
may influence the shape of the calibration curve.
Fertilizer Placement
Band placement often reduces lost yield as sub-optimal soil test levels are built to optimum
levels because the short-term recovery of applied fertilizer by crop plants is improved. Some
recommendation systems reduce the rate recommended when banding is used, compared to
broadcast. However, rate studies have shown the optimum rate when banding is sometimes
equal to or greater than the optimum broadcast rate. It is wise to build soil test levels to optimum
regardless of placement method used.
Farmer Financial Circumstances
The financial objective of farmers, like other investors with limited capital, is to maximize the
return on the last dollar invested after considering all possible investment alternatives and their
associated risks. Therefore, cash flow influences fertility management decisions.
Uniform and Balanced Nutrient Distribution
Balance recommendations to ensure each nutrient is used efficiently.
Land Tenure (Period of Time the Grower Will Farm the
Field)
Soil test phosphate and potassium are capital investments, and buildup costs should be
amortized over the expected time of ownership or operation. The longer the period of time
benefits will be accrued from buildup, the lower the cost of buildup becomes and the higher the
optimum soil test level becomes. Landowners and operators, as well as the environment,
benefit from the development of agreements in which the costs and returns of soil test buildup

37. are equitably shared. Such agreements can help avoid the loss of productivity and accelerated
erosion typical of run-down farms having impoverished soil fertility.
Soil Test Buffer Potential
Soil test buffer potential is the quantity of fertilizer required to change the soil test level, and is
usually expressed as pounds of P2O5 or K2O required per ppm of soil test level change. Some
low-pH and some high-pH soils fix applied phosphate readily, and increasing soil test phosphate
is more costly, decreasing the optimum soil test level. Soil test phosphate and potassium levels
are usually easier to change in sandier soils than on medium or fine-textured soils, except with
very sandy soils, where potassium leaching becomes significant.
Recommendations When Levels Are
High
Once soil tests are interpreted, possible approaches to a nutrient management plan may include
the following:
 Sufficiency: Add necessary rates of deficient nutrients so yields are not limited in present
crop.
 Build-Maintenance: Add enough of needed nutrient(s) to supply present crop need, and
gradually increase soil supply to non-limiting level. Replace crop harvest–removed nutrients to
keep plant nutrient levels at non-limiting levels.
If soil tests high in a plant nutrient, applying more of that nutrient is not recommended, at least
for the current crop. This is especially true if there is an abundance of the nutrient present to the
extent that there is almost no chance of response even if the nutrient was not applied for several
years. However, some laboratories assign the value high to a level that points to little or no
response to applications of that nutrient that year.
Failure to apply any of these nutrients will result in soil test depletion. Also, under some
conditions, crops will respond profitably to a nutrient even with a high test. For example, on
early-planted corn, the addition of N, P and K as a row application may produce response on
soils testing high.

38. Fertilizer application when soils test in the high range is influenced substantially by the factors
discussed in the section on individualization of recommendations. Maintenance in the high soil
test category will be appropriate for some growers and sites but not for others.
SOIL TEST CLASS PROBABILITY OF RESPONSE
Very Low Profitable response in all but rare cases
Low Profitable response in most seasons
Medium Average response over years is profitable
High Occasional profitable responses
Very High
.