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 C O N T E N T S n -
PAGE _ l
Sources of Nitrogen ..................,....................................... 3 V
Nitrogen Fertilizers .......................................................... 5
N itrogcn Reaction in the Soil .......................................... 6
n Loss of Nitrogen ................................................................ 7 ·
Efficient Use of Nitrogen ................................................ 9 x
Amounts of Nitrogen Fertilizer to Use .......................... 10 _
l
This publication replaces Kentucky Cooperative Extension Service Leaflet 186, ~
"Nitrogen l·`ertilizers."

 Nitrogen in Kentuc y oi s
k S I
Sources, Reoctions, ond Fertilizotion
By HAROLD MILLER and GEORGE CORDER
Nitrogen is one of the major nutrients essential to plant growth.
·   An inadequate supply of available nitrogen limits crop production on
_ thousands of acres of non-leguminous cropland in Kentucky each year.
An ample supply of nitrogen promotes rapid vegetative growth and
increased yields, produces succulent crops, crisp tender leaves of
vegetables, increases the protein content of grains and foliage, pro-
motes flowering and the development of extensive root systems.
Plants growing under conditions of low available nitrogen supply
have a pale green or yellow color, grow very slowly, become dwarfed
in total growth, and “fire up” as is often seen in corn.
If the available nitrogen is high or if the available phosphorus and
. potassium are inadequate, plants are more susceptible to some diseases
and mature slowly. The stems may be weak and fall down; they llllly
fail to set fruit or the fruit may be watery and of poor quality.
SOURCES OF NITROGEN
Nitrogen in the elemental form is a colorless, odorless, inert gas.
The air over each acre of land contains approximately 35,000 tons of
nitrogen. Atmospheric nitrogen is not available to plants until it has
i undergone a change.
Bacterial fixation. Special groups of micro-organisms can take this
inert gaseous nitrogen from the air and convert it to forms that plants
can use. One group of such micro-organisms, called symbiotic nitrogen
l fixers, is found in the nodules on roots of leguminons plants—clover,
alfalfa, lespedeza, soybeans and peas—when they are properly in-
oculated. Legumes grown in association with grasses will supply some
` available nitrogen to the grass in addition to that required by the
A legume crop. Another group of soil micro-organisms, called non-
symbiotic nitrogen fixers. incorporate some atmospheric nitrogen into
their cells which is later released for plant growth.
Organic Matter. Considerable nitrogen is released when soil or-
ganic matter is decomposed. The decomposition is carried on by many
different kinds of soil organisms. A number of factors influence the rate
3

 of breakdown of organic matter as well as the amount of nitrogen re- ‘
leased. The process proceeds nore rapidly in a well aerated (well . ,
drained) soil than in a poorly aerated (poorly drained} soil. Generally, n
the rate of decomposition is more rapid as the temperature increases.
Assuming adequate moisture, considerably more nitrogen is released A
for crop growth during warm weather as compared to cool weather.
Crop residues are important sources of nitrogen for succeeding
crops when it is returned to the soil and properly managed. However, . ,
decomposition of some residues such as straw, corn stalks, and saw- . `
dust, which contain very little nitrogen relative to their carbon con- _'
tent, may reduce the amount of nitrogen available to the crop during `  ·
the initial stages of decomposition. Since these residues are high in _
carbonaceous material, the microbial population of the soil increases
rapidly during the early stages of decomposition and will compete with ‘
the growing crop for nitrogen. More nitrogen in fertilizers is needed
when large quantities of these high-carbon crop residues are added to
the soil. This competition for available nitrogen is not a factor when
crop residues having a narrow carbon—nitrogen ratio such as legumi—
nous leaves or material from young plants are returned to the soil. In
fact, these residues supply nitrogen for crops even in the early stages
of decomposition. For this reason the kind of crop residue influences -
the amount of fertilizer nitrogen required. T
More than 16 million tons of farm manures are produced annually V
in Kentucky. Assuming 1() pounds of nitrogen per ton, manure supplies
80 thousand tons of nitrogen annually which exceeds the total amount
purchased in fertilizers in 1964. Manure properly handled is a good
source of nitrogen (see Kentucky Cooperative Extension Service Cir-
cular 593, Farm Mzmures).
Commercial Nitrogen Fertilizers. ¥Vhile considerable nitrogen is
made available to crops from organic matter, farm manure, crop resi-
dues, and legumes crops, additional nitrogen is needed for tobacco,
corn, small grain, and grass sods having little or no leumes. This ad-
ditional nitrogen must be purchased in commercial fertilizers. V
Commercial nitrogen fixation processes developed by the fertilizer
industry take nitrogen from the air and convert it into various nitrogen p
compounds for use as nitrogen fertilizers. .
In Kentucky the use of commercial nitrogen increased 27%, times
from 1940 to 1964. Kentucky farmers used 2,-158 tons of actual nitrogen
in 1940 and 67,711 tons in 1964. Still much more nitrogen could be
used profitably on certain crops.
In 1964 about one-half of the total nitrogen purchased in Kentucky
was in mixed fertilizers. The amount of nitrogen in mixed fertilizers
4

 _ varies considerably depending on the grade purchased. The first
figure in the guaranteed analysis refers to the pounds of nitrogen in
N each 100 pounds of fertilizer. A 5-10-15 contains 5 pounds of nitrogen
in each 100 pounds, while a 10-1()-10 contains 10 pounds of nitrogen
in each 100 pounds. The 0-20-20 contains no nitrogen. Much of the
nitrogen in mixed fertilizer is in the ammonium form.
Kentucky farmers purchased 34,606 tons of elemental nitrogen as
straight nitrogen materials in 1964. These nitrogen materials are
_ ’ ’ available in three physical forms; solid, gaseous, and liquid.
NITROGEN FERTILIZERS
Solid nitrogen. The more common solid forms of nitrogen fertilizers
i are ammonium nitrate, urea, and nitrate of soda. One or more of these
, , materials is always available at your fertilizer dealer, and no special
equipment is needed to handle them. All of these nitrogen sources
produce good crop yields. Research shows that these sources of nitro-
gen are equally effective in increasing most crops yields il`: (1) rates
are used to supply the same amounts of nitrogen and   little
i volatilization loss occurs.
Gaseous form. Anhydrous ammonia is being widely used in certain
7 areas of Kentucky. At atmospheric pressure and ordinary temperature
ammonia is a gas. Under pressure ammonia gas is condensed to a
liquid and designated as anhydrous ammonia. Anhydrous ammonia
must be handled under high pressure until it is applied 4 - fi inches into
I the soil where the water. clay, and humus particles will hold it. Special
equipment is needed for handling and applying this product. The
nitrogen in anhydrous ammonia is the cheapest nitrogen source. but
the equipment for handling and applying it is relatively expensive.
Precautions must be taken to prevent the loss of ammonia to the
atmosphere during storage and application.
Nitrogen .solution.s·. Most nitrogen solutions are mixtures of ain-
monium nitrate and urea in liquid form. The behavior of these solu-
_ ` tions in plant nutrition is the same as their solid counterparts. Nitro-
gen solutions sprayed on foliage may cause some burning. Except at ·
high rates of application this burning is not serious since the plants
. will quickly recover.
g As with anhydrous ammonia. nitrogen solutions save some labor in
l handling. However, some special equipment is needed for handling
and applying them. If this equipment is not available on the farm. it
T can be supplied by custom operators.
The nitrogen fertilizers most commonly used in Kentucky react
with the soil to make it more acid. \`\`ith increased nitrogen fertiliza-
5

 tion, an adequate and more frequent liming program is essential. Be-
search shows that an application of 300 pounds of actual nitrogen per ·
acre reduced the soil pH from 5.5 to 5.0. Heavy nitorgen applications p
are a contributing factor to manganese toxicity, a common disease in A U
tobacco grown on acid soils. This disease has also appeared in corn in
Kentucky.
This is not to imply that acid-forming nitrogen fertilizer should not
be used. Generally, the cost of lime to neutralize the acidity caused by
the acid-forming fertilizers will be much less than the additional cost _ p
of nitrogen in those fertilizers that are not acid forming. ·
Some of the characteristics of the more common nitrogen materials
are summarized in Table 1. .
Table. l.— Characteristics of Common Nitrogen Fertilizers I \
Percent . , Acid Forming
tram-il.1 Nigivdgtn   Biigic Accigiiiiliitiilmg
i‘\llllIl()INTllIl
Nitrate 33.5 16.75 16.75 °° p
Urea 45.0 45.0° ° °
Nitrate of Soda 16.0 16.0 Basic Sodium
Nitrate of l’otash 13.0 13.0 Neutral Potassium
Anhydrous Ammonia 82.0 82.0 °° ,
Solutions 21.0-41.0 i °°
° l·`orms annnoniuin in the soil.
°° It requires approximately 2 pounds of agricultural limestone to neutralize the acid-
torming elleet ot each pound of nitrogen applied in these materials. A sound liming program is l
.»W·..n.il to iiisiiie goal t-mp yipltls.
i Nln·oi;i·i» trom alle solutions will lie largely iii me aiiiiamiiiim form lair may eoiaiilii a small
amoont ot nitrate nitrogen depending on the basic ingredients. .
NITROGEN REACTION IN THE SOIL A
Some crops use ammonium nitrogen to some extent, but most I
crops use the nitrate form much more readily. Nitrogen in the form of
annnoniuin reacts with the clay alld humus in the soil and is held.
The soil microbes. however, change the ammonium to the nitrate `
liorm. This change is rapid in warm weather when conditions are _ ` l
favorable for microbial activity, slower in cool weather, and practically
ceases in cold weather as the soil microbes became inactive. .
Nitrogen in the nitrate form is not held by the soil particles. lt l
dissolves in the soil solution and is free to move with the water l
through the soil.
Xlost commercial fertilizers contain nitrogen in the form of am-
monium. nitrate. or a combination of the two. \Vhile there are funda-
mental dillerenees between tllese two forms of nitrogen, research
6

 generally shows no significant differences in crop response between
l the two forms if they are retained i11 the soil. \Vl1Cll nitrogen is needed
_- - il] early spring before the soil is warm enough for the soil microbes to
be active in converting the Zll]]lTlOITllllD to nitrate nitrogen, a fertilizer
containing some nitrate nitrogen 1nay be desireable.
LOSS OF NITROGEN
_ ‘ ’ A11 understanding of the reactions of nitrogen fertilizers in the soil
is essential to the proper application and elhcient 11se of these lHU.tCl`ltllS.
Nitrogen can be lost or made unavailable to the growing crop in
V several ways. Nitrogen can be lost by volatilization, denitrification,
· leaching, and erosion. It may be tied-up temporarily by the soil
microbes.
Volatilizafion. Ammonia is a gas which will escape to the at1nos-
phere. For this reason certain precautions 1HllSt be taken \’Vll€l1 ap-
plyi11g nitrogen fertilizer in tht? i1l]]U]Ol1lL`l form or those that are
converted to ammonia.
Anhydrous ammonia is handled as a liquid under pressure. \Vhen
the pressure is released ammonia gas is formed. To prevent the loss
_ of ammonia (82 percent nitrogen) to the atmosphere it l]lllSt be re-
leased at a depth of 4 inches or ll]()l`C in the soil and preferably in a
well prepared seedbed. \Vhecls may be attached behind the appli-
cator knives to close the furrows left by the knives. Tl1is helps seal
1 the ammonia in the soil. \Vhcn applied in this manner the ammonia
quickly reacts with water to form ammonium nitrogen which is held
by the soil colloids. The higher tl1e sand co11te11t of the soil, the deeper
the 1ll’T`1IUOIll[l must be applied.
\Vhen urea is applied to the soil, it quickly converts to ammonia.
Recent research at Kentucky and other experiment stations shows
that considerable a1no11nts of nitrogen may be lost by volatilization of
ammonia when 11rea or solutions containing urea are applied as a top-
drcssing. The rate of yolatilization loss increases with high temper-
l l ature, high pH, and high 1noist11re. The loss is avoided if the urea or
solution containing urea is mixed with tl1e soil either by plowing or
disking within a day or two after it is applied.
  Apparently there is less loss when these materials are applied
` as a top dressing on cultivated or bare soil than when topdressings
are made on fields having a vegetative cover. This is caused, no doubt,
by 1nore of the material being in contact with soil particles o11 culti-
vated soils; therefore. as ammonia is formed more of it reacts with the
soil colloids, reducing tl1e volatilization loss.
7

 Where herbicides or insecticides are applied in nitrogen solution,
the savings in labor over applying dry materials probably would -
more than offset the nitrogen loss due to volatilization.
Very little volatilization loss of nitrogen as ammonia from dry ‘- A
materials is reported except when urea is applied as a topdressing on ·
very high pH soils. V
Denitrifieution. Under conditions of poor aeration or a low supply
of free oxygen, adequate energy material such as soil organic matter,
and a supply of nitrates, anaerobic bacteria will reduce nitrates to p g
nitrous oxide or elemental nitrogen. These nitrogen gases will escape ~
to the atmosphere and be lost to crops. In low wet areas of a field or
during periods of heavy rainfall where the soil stays saturated for ·
few days considerable loss may occur by this process. W/here nitrogen
deficiency symptoms results from such conditions, sidedressing with a
nitrogen fertilizer will be profitable.
Lcaclzing. Leaching probably accounts for the greatest nitrogen
loss under Kentucky climatic conditions. Any nitrogen in the nitrate
form goes into the soil solution and moves with the water in the soil.
ln the winter and early spring as the water moves through the soil
profile, nitrate nitrogen will be carried out in the drainage water and
lost. The annnonium forms of nitrogen are held by the soil colloids and
not subject to leaching loss. However, the ammonium is converted to V
the nitrate form of nitrogen by soil micro-organisms when the soil tem-
perature is above   degrees. At temperatures of 32-50 degrees the rate
of change is slow, but when the soil temperature is above 60 degrees r
the change takes place rapidly.
During the late spring, summer and fall months rapid transpiration
of moisture by the growing crop and evaporation from the soil surface
removes soil moisture rapidly. Since water is being removed rapidly
during this period, there is seldom sufficient precipitation for water
to move through the soil profile except in sandy soils. For this reason
the leaching loss of nitrogen during this period is negligible on silt
loam and heavier soils.
\\’ith the variable winter temperatures existing in the state there ·
is evidence that some nitrogen will be lost by leaching even where the
ammonia forms of nitrogen are applied in the fall. For this reason
maximum crop response is not obtained in Kentucky when nitrogen y
fertilizers are applied in the fall for next year`s crops.
Erosion. (Ionsiderable nitrogen is lost each year by erosion. Most
of the organic matter in the upland soils is in the surface. 6-8 inches.
\Vith poor conservation practices, erosion removes the organic matter
with the nitrogen as well as the other plant nutrients it contains.
8

 EFFICIENT USE OF NITROGEN
` Nitrogen is not a substitute for other elements essential to plant
__ _ growth. To obtain the maxium response from nitrogen applications.
a proper balance of those elements needed by the plant must be
available in the soil.
Since nitrogen is lost from the soil more readily than the other
plant nutrients, particularly through leaching, it should be applied at
rates to meet the needs of the crop each growing season. Other soil
e , amendments, such as agricultural limestone, phosphate and potash
` fertilizers can be applied at heavier rates to meet the cropping needs
for several years since leaching losses of these nutrients are minimal
· in the silt loams and heavier soils. On sandy soils smaller and more
frequent applications of all fertilizers should be made.
Fertilizer placement is not usually so important with nitrogen as
with other plant nutrients since nitrogen in the nitrate form moves
with the soil moisture and will be carried to the plant roots during
periods of adequate rainfall. Topdressings of nitrogen feritlizers are
usually effective. However, where extended dry periods follow a top-
dressing, the nitrogen may not be carried into the root-feeding zone.
\Vhen nitrogen fertilizer can be worked into the soil without additional
cost, it is a good practice to do so.
V Based on available research little evidence exists that one source of
commercial nitrogen is preferable to another. The eos! of actual nitro-
gen applied to the land should determine which material is the best
buy when proper precautions are taken against volatilization loss.
Costs of nitrogen materials varies from one area to another and from
one season to the next. Table 2 shows the amount of the different
materials required to supply different rates of nitrogen per acre. Low
nitrogen rates are shown in the table, hrrt by doubling or combining
these rates the amount of material required for heavier rates can
easily be calculated.
Table 2.-— Amount of Material Required to Supply the Desired Rate of Nitrogen
Material Nitrogen 20 30 40 50
Arrrrrroniurn nitrate 33.5 60 90 119 140
Urea 45.0 45 67 80 l 11
Nitrate of Soda 16.0 125 188 250 318
Nitrate of Potash 13.0 154 231 308 $85
Anhydrous annnonia 82.0 24 37 49 61
Solutions° 30.0 67 100 133 167
° Nitrogen content of solutions may vary widely. The grrarantrwd analysis shows the pounds
or nitrogen in r-ao] roo pmmrrs or saramm. ria- rates srrawa in uw carrie are are poamrs or an
130-percent solution required.
9

 AMOUNTS OF NITROGEN FERTILIZER TO USE
The amount of nitrogen fertilizer required per acre depends 0n the
kind of crop grown, residues and manure, soil fertility, soil aeration, `
expected yield, available moisture, and other factors. General nitrogen _ _
fertilizer recommendations for various Crops grown in different Crop- I
ping systems are shown in Table B.
10

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COODf‘l`&lll\’L‘ Extension Work in Agriculture and Home Economics: College of Agriculture
ginri Ilmnv Rumiuiiiics. University of Kentucky. Lexington. and the United States Depart-
nwnt of .·\;;i·ivultni·e·, ¤~<»npei·;iting. William A. Scziy. Dean and Director. Issued in further-
nnce of the Acts of l\I;13‘ 8 amd June 30, 1914.
Issued 9-66, SM; IOM-3-67