soil , water quality and pollution

WATER TECHNOLOGY CENTRE,PJTSAU
AWM-506
SOIL,WATER QUALITY AND POLLUTION
TERM PAPER PRESENTATION
SUBMITTED TO: SUBMITTED BY:
Mr . G . Kiran Reddy K . Archana
soil scientist MSc.Ag.1 st year
RAM/2020-107

LECTURE :31-IMPORTANT FUNCTIONS CARRIED OUT BY SOIL ORGANISMS-SOIL
BIOLOGICAL PROPERTIES ,MICROBIAL PROPERTIES,MICROBIAL
COMMUNITIES,SOIL MICROBIAL BIOMASS,SOIL RESPIRATION ,BOCHEMICAL
QUOTIENT,SOIL ENZYMES,NITROGEN MINERALIZATION POTENTIAL,MICROBIAL
BIOMASS TURNOVER RATE,BENEFITS OF SOIL BIOLOGICAL MANAGEMENT.
TOPIC

Introduction
1.Soil is a dynamic body.
2.It has been estimated that soil biological components
occupy only less than 0.5% volume of soil.
3.The living component of soil organic matter consists of :
• 5 to 15% of plant roots
• 85-95% of soil micro organisms among which 5-10% is
constituted by macro and meso fauna and remaining
90-95% by micro organisms.

Background on soil biology
•Soil Biology relates to the organisms within soil that carry out a wide range of
processes that are important for soil health and fertility
•These organisms decompose and recycle soil organic matter (SOM), improve
nutrient availability and soil structure, transmit or prevent diseases, and degrade
pollutants.
•The total number of organisms, species diversity and their activity will fluctuate
with changes in the soil environment.
•These living organisms can be classified by size into:
•macrofauna (> 10 mm) such as earthworms, termites and other large insects
•mesofauna (range in size from 200 um to 10 mm) such as mites and collembola
(or springtails)
•microfauna (20 - 200 um) such as protozoa and nematodes
•microflora such as fungi and bacteria

•Collectively, these groups make up the soil biota and the total mass of organisms
comprises the soil biomass
•70 - 80% of soil biota exists in the top 10cm of soil
•In 1 gram of soil, there is potentially over100,000 different species and greater
than10 million different individuals
•Different types of soil biology have different roles and functions:
•Ecosystem engineers such as ants and earthworms that primarily alter the physical
structure of soil but also have an influence on the overall rates of nutrient cycling
and energy flows.
•Litter transformers that fragment plant litter & improve availability to microbes

•Importance of soil biology:
For farmers there are 3 components to consider in terms of why soil biology
is important:
• the natural processes themselves (engineers, litter transformers & microfood
web processors)
• the impact of management on these processes
• the combined effect on plant performance
•Soil biology provides both direct and indirect benefits to the environment in
that they can:
•Decompose plant residues
•Regulate plant nutrient supply and loss (e.g. N, P, K, Fe)
•Improve soil structure (aggregate stability)
•Degrade pesticides and herbicides
•Regulate water quality (e.g. filters nutrients)
•Capture and release greenhouse gases (carbon dioxide, methane, nitrous oxide)

IMPORTANT FUNCTIONS CARRIED OUT BY SOIL ORGANISMS
1. Organic matter decomposition (By this process, plant and animal residues are broken down by micro-
organisms into more simpler compounds, other slimy compounds, other slimy intermediate products
organic acids and more resistant compound humus. All these products combinedly influence the physical
and chemical properties of soil and hence the plant growth).
(a) De-nitrification process carried out by a particular micro-organisms and causes loss of gaseous
nitrogen
(b) Development of various plant diseases
(c) Production of antibodies and other toxic substances.
(d) Competition for nutrients.
2. Inorganic transformations These processes are carried out by different groups of soil micro-organisms.
Through this process organic form of different essential plant nutrients like N, P, S, Fe etc. are transformed
into their respective inorganic forms and plants are able to absorb for their growth and development and
so this process has of vital importance).

3. Fixation of Nitrogen
(i) Bacteria Symbiotic nitrogen fixing bacteria e.g. Rhizobium
Non-symbiotic nitrogen fixing bacteria, e.g. Azotobacter, Azospirillum, Clostridium etc.
(ii) Cyanobacteria e.g. Nostoc , Anabaena etc.
(iii) Actinomycetes e.g. Frankia
4. Formation and Development of soil
(i) Decomposition of rocks and minerals
(ii) Improvement of soil structure and stability of soil aggregates
(iii) Movement of soil materials etc.
5. Production of soil enzymes (stimulates the activity as well as increases the
microbial population e.g. hydrolysis of urea by urease enzyme).

6. FEW MICRO ORGANISMS PLAY A KEY ROLE IN BIO REMEDIATION:
7. A GROUP OF SOIL MICROBES REFERRED AS PROMOTORY RHIZO BACTERIA ENHANCE
SEED GERMINATION ,ROOT DEVELOPMENT AND PLANT GROWTH:
Influence soil
structure and
various physical
properties.
Decomposition,
nutrient
recycling,
cycle.
Few microbes
help in
nitrogen
Some soil
organisms have
the ability to
form complexes
of heavy metals
while few
help in
solubilizing
to plant usable
forms.
A group of soil
microbes
as plant growth
promontory
rhizo- bacteria
(PGPR), secrete
PGH such as
IAA,GA,
and enhance
seed
germination,
development
plant growth.
Few micro
organisms play
key role in bio
remediation.

SOIL BIOLOGICAL PROPERTIES
Soil biological properties responds quickly for a change in soil quality and have been suggested better
indicators than soil physical and chemical properties which alter only after drastic change in soil quality.
Some important and measurable soil biological properties are:
1. Microbial population
2. Microbial communities
3. Microbial Biomass
4. Soil respiration
5. Biochemical quotients
6. Nitrogen mineralisation potentials
7. Microbial biomass turnover rate
8. Soil enzymes

Soil contains many micro and macro flora and fauna as long as there is a carbon source for energy.
• A large number of bacteria in the soil exists, but because of their small size, they
have a smaller biomass.
• Actinomycetes are 10 times smaller in number but are larger in size so
they are similar in biomass to bacteria in soil.
• Fungal population numbers are smaller but they dominate the soil biomass.
• Bacteria, actinomycetes and protozoa can tolerate more soil disturbance than fungal
populations so they dominate in tilled soils while fungal and nematode populations tend to
dominate in untilled.
1.MICROBIAL POPULATION:

Table1 Estimated content of organism in soil
Animal (2%) Biomass No. (kg/ha) Plant (98%) Biomass No.
(kg/ha)
• Micro: Protozoa 100 (104 -105 /gm.) Micro: Bacterial 5000 (108 -109 /
gm.)
• Nematode 2-100 (10-102 / gm.) Actinomycetes 1500 (107 -108 / gm.)
• Macro: Earthworm 50 (3.3*105 /HFS) Fungi 5000 (105 -106 / gm.)
• Myriapodas 40 (5.5*106 /HFS) Algae 10 (104 -105 /gm.)
• Insects 10-100 (50/HFS)
• Macro: Plant roots 4000
ALGAE ACTINOMYCETES PROTOZOA NEMATODES

2.MICROBIAL COMMUNITIES:
• Soil microbial communities play several important ecological and
physiological functions.
• Microbial communities play a fundamental role in plant establishment ,
that is , arbuscular mycorrhizal fungi , are obligated mutualists that
establish intimate relationships with 80% of terrestrial plant families .
• Methods such as phospholipid fatty acids(PLFA analysis), community
level physiological profile (CLPP) mainly by BIOLOG and DNA
finger printing are useful in studying soil microbial communities.

3.MICROBIAL BIOMASS:
• Soil microbial biomass is the living component of soil organic matter excluding
soil animals and plant roots larger than 5X103 µm3 (Jenkinson and Ladd, 1981).
• In other words it can be defined as the concentration of microbes in the soil. It is
an important indicator of soil health. It is said that…..
½ of microbial biomass = 10 cm top soil
• Soil microbial biomass consists of bacteria, fungi, actinomycetes, protozoa etc.
However, bacteria and fungi both are the dominant organisms with regards to
biomass and metabolic activities.

4.SOIL RESPIRATION:Carbon dioxide (CO2) release from the soil surface is
referred to as soil respiration.
• This CO2 results from several sources, including aerobic microbial
decomposition of soil organic matter (SOM) to obtain energy for their
growth and functioning (microbial respiration), plant root and faunal
respiration, and eventually from the dissolution of carbonates in soil
solution.

• Soil respiration is one measure of biological activity and
decomposition.
• It can be measured by simple field methods or more sophisticated
field and laboratory methods.
• During the decomposition of SOM, organic nutrients contained in
organic matter (e.g., organic phosphorus, nitrogen, and sulfur) are
converted to inorganic forms that are available for plant uptake. This
conversion is known as mineralization.
• Soil respiration is also known as carbon mineralization.

5.BIOCHEMICAL QUOTIENTS:
• Ratios of different soil biochemical properties referred to as quotients are
preferred for precise assessment of soil biological conditions.
• Biochemical quotients like metabolic quotient qCO2 microbial quotient,
mineralization have been proposed . Among these qCO2 is widely used for
measuring soil biological health.
6.SOIL ENZYMES:They are proteins with catalytic properties owing to their power of
specific activation that cause biochemical reaction to faster rates.
Soil enzymes increase the reaction rate at which plant residues decompose and release
plant available nutrients. The substance acted upon by a soil enzyme is called the
substrate.
• Sources of soil enzymes include living and dead microbes, plant roots and residues,
and soil animals.
• Soil enzymes play an important role in organic matter decomposition and
nutrient cycling

Specific problems that might be caused by poor function: Absence or suppression
of soil enzymes prevents or reduces processes that can affect plant nutrition.
Poor enzyme activity can result in an accumulation of chemicals that are
harmful to the environment; some of these chemicals may further inhibit
soil enzyme activity.

7.NITROGEN MINERALISATION POTENTIAL:
• Nitrogen mineralization is the process by which organic N is converted to plant-
available inorganic forms.
• Soils regularly amended with organic wastes will accumulate organic N until
they reach a steady-state condition, a concept useful for planning N
management strategies.
• The fraction of organic nitrogen released in a given time is usually termed as potentially
available N for the crops.
• The most widely used method for the determination of mineralizable available N in
India is based on determination of alkaline permanganate oxidizable organic N.

8.MICROBIAL BIOMASS TURNOVER RATE:
• The rate of decomposition or turnover of microbial biomass is assumed to be
proportional to the mass of organisms.
• It is associated with plant nutrient transformations and continuously changes with
time in response to soil management practices.
• Estimation of microbial biomass C, N, P turnover is time consuming and requires
isotopic labelling with C14, N15 ,P32 of soil micro organisms and turn over rates
are then computed.

How to manage soils to improve soil biology:
1. Manage soil pH
2. Use organic fertilizers
3. No-till , stubble retention and direct drill
4. Crop rotations
5. Minimize use of pesticides
6. Maintain and conserve ground cover
7. Adopt appropriate grazing management strategies

BENEFITS OF SOIL BIOLOGICAL MANAGEMENT:
•Active soil biology is essential to improve and sustain agricultural production - a
healthy soil is one that is full of life where organic material and nutrients are
recycled.
•In dryland environments, biological sources within the soil can provide up to 80% of
total nitrogen requirement of crops when conditions are optimized.
•Soil organic matter has declined significantly in many soils since they were
cultivated for cropping - consequently these soils may be less able to supply
nutrients to meet plant demand through microbial activity.
•High levels of organic carbon helps to maintain agricultural production through its
positive role in maintaining soil health, raising fertility, reducing erosion and
encouraging soil biota
•Soil biology also plays a key role in the carbon cycle where soil biota assimilate
carbon and act as a large carbon sink as well as providing a substrate carbon
source upon their death for other soil biota.

•Soil biology also plays a key role in the carbon cycle where soil biota assimilate
carbon and act as a large carbon sink as well as providing a substrate carbon
source upon their death for other soil biota
•The processes that are mediated by soil biology impact on plant (and animal)
production systems by modifying the soil physical, chemical and biological
environment within which plants grow and persist .
1. Decomposing plant residues
2. Regulates nutrient supply
3. Improves soil structure
4. Degrades chemicals inputs
5. Biocontrol
6. Greenhouse gases

1.Decomposing plant residues:
• The process of converting plant residues (and other organic residues/wastes) into
humus is facilitated by enzymes, either contained within the soil organisms or
secreted by either living or dead soil organisms into the soil matrix.
• Fungal hyphae grow on plant residues - secreting a range of
enzymes that break down these residues and release plant
nutrients and gases .
• Bacterial colonies remain attached to plant and soil surfaces
and also secrete enzymes to release plant nutrients.
• The nutrients produced can be re-used by the microbes and
are then respired or transformed into humus, taken up by living
plants or lost through volatilization or leaching.

2.Regulates nutrient supply:
• Nitrogen cycle
• Nitrogen fixation
• Phosphorous supply
.

4.Degrades chemical inputs:
• Agricultural pesticides are degraded in the soil principally by the action of
microorganisms, a process termed biodegradation, where biodegradation is defined
as the breakdown of a substance to smaller products caused by microorganisms or
their enzymes.
• The rate at which different pesticides are biodegraded varies widely but generally
degradation is faster in soils with high microbial diversity and activity.
• Some pesticides such as DDT have proven to be recalcitrant. Consequently they
remain in the environment for a very long time and are known to accumulate into
food chains decades after their application to soil.
• Pesticides which are more readily biodegradable, such as the organophosphates,
are now used in preference to the more persistent chlorinated pesticides.

5.Biocontrol:
• Many soils support microbes that are deleterious to plant growth; the
symptoms can be visible (clinical) or invisible (sub-clinical).
• Organisms identified as potential biocontrol agents in suppressive soils include
the soil fungi, Trichoderma spp , Penicillium spp and Metarhizium spp and the
bacteria, Pantoea, Exiguobacterium and Microbacterium.
• Reported modes of action of the suppressive microorganisms are production of
antibiotics, competition for infection sites on the roots, competition for space
and nutrients in the rhizosphere and parasitism of the pathogens.
• These beneficial organisms should be encouraged through management such
as crop rotations and maximizing the return of residues (carbon source) to the
soil in order to restore a balance between the soil biota in the soil so that
pathogens do not dominate.

 A suppressive soil does not result in the elimination, but the control of disease
forming organisms. Farmers should be trying to achieve a level of suppression
(microbial balancing) that prevents disease. But suppression is relative - a soil
may be suppressive, but disease at a lower level is still experienced.

6.Green house gases:
 Primary industries are significant emitters of greenhouse gases. Agriculture is the
third largest contributor to total greenhouse gas emissions. Therefore, this sector
has an important role to play in reducing emissions.
 Nitrous oxide emissions are produced by a range of nitrifying bacteria in the soil,
where they convert nitrate into nitrous oxide.
 These losses are greatest when soils are warm and waterlogged, and in those with
high nitrate contents.
 Thus it is important to apply nitrogen fertilisers only at times, and in quantities and
forms, useful to plants as overuse of fertiliser can drastically increase levels of
denitrification.

 Nitrous oxide is a more potent greenhouse gas than carbon dioxide. One unit of
nitrous oxide is equivalent to 310 units of CO2.
 Conventional tillage systems also release more CO2 into the atmosphere than
no-till systems as the incorporated residues turnover more quickly and result in
more carbon being respired by the microbial community.
 No–till systems tend to lock up more carbon in the form of organic matter. A
large soil microbial community can also tie up carbon and nitrogen that might
otherwise be released into the atmosphere as greenhouse gases.

Article:
 Influence of P-solubilizing bacteria on crop yield and soil fertility at
multilocational sites:
• Inoculation of P. cypripedii and P. plecoglossicida significantly increased the yield
and total P uptake in maize and wheat crop and improved the soil fertility during
two year of field study but the effects were more pronounced and significant when
RP was supplemented along with inoculation. This is an early report on P. cypripedii
and P. plecoglossicida (isolated from an organic field) for their significant effect as a
bio-inoculant along with RP fertilization on improvement of yield and soil fertility at
different sites in different agroclimatic regions with different physiochemical
properties of soil. In long term, this approach would ensure cost effective,
sustainable and environmental friendly production system for maize and wheat crop
at several sites comes under different agroclimatic regions.
Gurdeep Kaur, M. Sudhakara Reddy
Punjab, India (2013).

• A significant increase in grain yield
and total P uptake in seed, shoot
and root of maize and wheat crop
was observed by introduction of P.
cypripedii and P. plecoglossicida
during two year of field study
compared to control (Figs. a and
b). Stimulatory effects of PSBs on
yield and P uptake were found to
be more pronounced when
inoculated along with RP
fertilization. Enhancement in yield
and P uptake in maize and wheat
was more pronounced and
significantly higher at sub
mountain undulating region
compared to central plain region
and sub mountain undulating
central region.

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