REMOVAL OF NITROGEN AND PHOSPHOROUS IN SOIL

BYVAISHNAVI SUKUMAR

NITROGENWhy Nitrogen is important?

Atmosphere is 78% of nitrogen

It is an essential element for all organisms

Major component of amino acids

Fertilizers.

But plants and animals cant get it directly from the

atmosphere

So, the cycle begins

REMOVAL PROCESSES

Plant uptake

Gaseous loss

Ammonia volatilization

Immobilization

Denitrification

• Exchange

Leaching

Runoff and Errosion

Upward movement

PLANT UPTAKE

• It refers to nitrogen absorption by roots• Once nitrogen is converted into ammonium and

nitrate, these can be taken up from soils by plants

• Then used in the formation of plant and animal proteins.

GASEOUS LOSS

Ammonia Volatilization• Ammonia volatilization is the loss of nitrogen to the atmosphere as

ammonia gas 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 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

Soil pH

Type of fertilizer

Soil Temperature

Soil Moisture

Buffering Capacity:

Crop Residues

Manure

IMMOBILIZATION Immobilization is process that converts inorganic nitrogen to

organic nitrogen. It is the reverse reaction of mineralization. occurs when decomposing organic matter contains low amounts of

nitrogen. 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 nitrogen.

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 yellow coloration.

Factors leads to immobilization

Soil moisture and temperature

C:N ratio of residue

DENTRIFICATION

• 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

and pseudomonas 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, nitrogengas (N2).

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:

Waterlogged soils

Presence of nitrate

Presence of decomposable organic matter

Oxygen

Soil pH

Soil Temperature

EXCHANGE

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

LEACHING

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 disease etc

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.

UPWARD MOVEMENT

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

management practices

Proper fertilization and control of surface runoff and

erosion offer the best methods for preventing nitrogen

from getting into streams and lakes

PHOSPHOROUS

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 by plants.

Animals absorb phosphates by eating plants or plant-

eating 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.

REMOVAL OF PHOSPHOROUS FROM SOIL

METHODS

Plant uptake

• Sorption and Desorption

Precipitation and Dissolution

Mineralization and Immobilization

Leaching

Runoff and Erosion

PLANT UPTAKE

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 plants.

Soils that have higher iron and/or aluminum contents have the potential to adsorb more P than other soils.

• P-sorption results in a decrease of plant available phosphorus

• 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

pH

Temperature

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

phosphate minerals.

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 sorbed-

P 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.

LEACHING

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.

THANK YOU