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REMOVAL OF NITROGEN AND
PHOSPHOROUS IN SOIL
Why Nitrogen is important?
Atmosphere is 78% of nitrogen
It is an essential element for all organisms
Major component of amino acids
But plants and animals cant get it directly from the
So, the cycle begins
Runoff and Errosion
It refers to nitrogen absorption by roots
• Once nitrogen is converted into ammonium and
nitrate, these can be taken up from soils by
• Then used in the formation of plant and animal
Ammonia volatilization is the loss of nitrogen to the atmosphere as
Ammonia production and loss is typically associated with urea
hydrolysis in soils.
In urea hydrolysis, the ph of urea is increased drastically and the
proportion of nitrogen in the ammonium form is shifted towards
Ammonia is then released into the atmosphere and no longer available
to the plant.
Movement of urea into the soil prior to hydrolysis is an effective way to
minimize ammonia volatilization.
Factors leads to volatilization
Type of fertilizer
Immobilization is process that converts inorganic nitrogen to
It is the reverse reaction of mineralization.
occurs when decomposing organic matter contains low amounts of
Also occurs if the source of organic matter has a high C:N ratio
Microorganisms which need nitrogen to live, scavenge the soil for
nitrogen when plant residues contain inadequate amounts of
As inorganic ammonium and nitrate are incorporated into the cells
of living microorganisms, the total N levels in the soil are reduced
When nitrogen is immobilized in the soil, there may be little
nitrogen available for crop growth.
As a result, plants can suffer from nitrogen deficiency and develop a
Factors leads to immobilization
Soil moisture and temperature
C:N ratio of residue
It is one source of N loss from the soil.
Is the biological process in which nitrate is converted to
atmospheric N2 mediated by denitrifying m.organisms.
Reduction is accomplished by facultative heterotrophic organisms
Denitrifying bacteria's are thiobacillus, paracoccus,micrococcus
Denitrification occurs when oxygen levels are depleted and nitrate
becomes the primary oxygen source for microorganisms
When bacteria break apart nitrate(NO3-) to gain the oxygen (O2),
the nitrate is reduced to nitrous oxide (N2O), and, in turn,
Since nitrogen gas has low water solubility, it escapes into the
atmosphere as gas bubbles.
Free nitrogen is the major component of air, thus its release does not
cause any environmental concern
Soil conditions that lead to Denitrification:
Presence of nitrate
Presence of decomposable organic matter
It refers to cation and anion exchange
Such as ammonium, are attracted to soil particles that
have a cation exchange capacity.
Ammonium is largely mobile .
Losses of ammonium
Leads to Nitrogen loss
When soil becomes excessively wet through rainfall, the soil
will reach a point where it cannot hold any more water.
This happens because the air spaces between soil particles
become filled with water
As these air spaces fill, gravity will cause water to move
down through the soil profile.
As water moves down through the soil, nitrogen can be
carried with it.
Nitrate is very mobile and easily leaches with water.
Heavy rains can cause nitrates to leach downward in the soil
below the root zone
Once nitrates get into the groundwater, can be toxic to
newborns, causing anoxia, methemoglobinemia, or blue-baby
FACTORS LEADS TO LEACHING
High rainfall intensity and distribution
Highly irrigated fields
Coarsely textured soils
RUNOFF AND ERROSION
Runoff and erosion losses may include nitrate, ammonium,
and organic nitrogen
when nitrogen fertilizers are applied to soils and rain or
irrigation water is applied, the water dissolves and runsoff the
surface finally these ions move with it.
Soil erosion moves more nitrogen
When erosional soils are deposited in rivers and lakes,
microbial activity will slowly convert nitrogen compounds
into soluble forms.
Nitrate can also move upward, especially in semi-arid
and arid regions.
Upward movement of nitrate and other soluble ions
occurs when evaporation exceeds precipitation, causing
water to move upwards.
Prevention of Nitrogen Loss
The best way to prevent losses of nitrogen from
agricultural lands is through good soil and water
Proper fertilization and control of surface runoff and
erosion offer the best methods for preventing nitrogen
from getting into streams and lakes
WHAT IS PHOSPHOROUS AND
WHY IT IS SO IMPORTANT?
Phosphorus cycle is the movement of phosphorus from the
environment to organisms and then back to the environment.
Phosphorus is mainly found in water, soil, and rock.
Phosphorus is essential for life.
◦ Component of DNA
◦ Building block of our bones and teeth.
Unlike the other cycles, phosphorus cannot be found in air in
the gaseous state
Phosphorus is most commonly found in rock formations and
ocean sediments as phosphate salts
Phosphate salts that are released from rocks through
weathering usually dissolve in soil water and will be absorbed
Animals absorb phosphates by eating plants or planteating animals.
When animals and plants die, phosphates will return to
the soils or oceans again during decomposition.
After that, phosphorus will end up in sediments or rock
formations again, remaining there for millions of years.
Eventually, phosphorus is released again through
weathering and the cycle starts over.
Sorption and Desorption
Precipitation and Dissolution
Mineralization and Immobilization
Runoff and Erosion
Plant roots absorb phosphorus from the soil solution.
Absorb phosphorus in the form of orthophosphate, but
can also absorb certain forms of organic phosphorus
Phosphorus moves to the root surface through diffusion.
The presence of mycorrhizal fungi, which develop a
symbiotic relationship with plant roots and extend
threadlike hyphae into the soil, can enhance the uptake
of phosphorus in plant
SORPTION AND DESORPTION
Sorption is the chemical binding of plant available P
to soil particles, which makes it unavailable to
Soils that have higher iron and/or aluminum
contents have the potential to adsorb more P than
P-sorption results in a decrease of plant available
Desorption is the release of adsorbed P from its
bound state into the soil solution
Adsorption occurs quickly whereas desorption is
usually a slow process.
Factors that affect P-sorption
Soil Mineral Type
Amount of clay
PRECIPITATION AND DISSOLUTION
Phosphorus can become unavailable through precipitation,
Which happens if plant available inorganic P reacts with
dissolved iron, aluminum, manganese , or calcium to form
Dissolution of phosphate minerals occurs when the mineral
dissolves and releases phosphorus
Mineralization and Immobilization
Mineralization is the microbial conversion of organic
P to H2PO4-or HPO42-, forms of plant available P
known as orthophosphates.
Immobilization occurs when these plant available P
forms are consumed by microbes, turning the P into
organic P forms that are not available to plants..
During immobilization there is not enough P to
sustain both plants and microorganisms; and so,
microorganisms scavenge the soil for P
The microbial P will become available over time as
the microbes die
RUNOFF AND EROSSION
Runoff is a major cause of P loss from farms.
Erosion by wind can carry particles that contain sorbedP to water systems, where phosphorus may later desorb
Sediments containing phosphorus can also contaminate
ground and/or surface waters
Phosphorus availability is reduced by the removal of
plant material during harvest.
Phosphorus leaching can occur if the soil reaches
maximum phosphorus holding capacity, especially when
P fertilizers are over applied.
Sandy soils are most susceptible to phosphorus leaching
The consequence of phosphorus leaching is the
contamination of ground water reserves.