Soil Organisms, functions and their role in Soil fertility

Soil Organisms, functions and their role in Soil fertility
Soil Organisms
Classification of soil organisms
Classification of Bacteria
Soil flora
Nitrogen fixing systems
Soil fauna
Interaction among soil organisms
Role of organism in soil fertility
Soil fertility evaluation by biological tests-
Harmful Activities of Soil Organisms 
Soil flora (Plant kingdom)
1) Macro-flora - Plant roots, Macro -algae
2) Micro-flora - Bacteria, Actinomycetes
Fungi, Algae
Soil fauna (Animal kingdom)
1) Micro fauna - protozoa, nematodes
2) Macro-fauna - Earthworms,Termites,
Ants,Grubs

1. Institute of Agricultural science RGSC BHU SSC-411-(0+10)10 Topic:- Soil Organisms, functions and their role in Soil fertility Submitted to: Submitted by: Dr. Ashish Latare Anup Kumar (Assistant professor) B.sc.(Ag) 4 th year ID No.:- 16311 Ex Roll No:-16230AGC008

2. CONTENT Soil Organisms Classification of soil organisms Classification of Bacteria Soil flora Nitrogen fixing systems Soil fauna Interaction among soil organisms Role of organism in soil fertility Soil fertility evaluation by biological tests- Harmful Activities of Soil Organisms 

3. Soil Organisms The organisms that live in the soil are called soil organism. Micro organisms are numerous in number with monopolized biological activity in soils (60-80% of total biological activity).The study of living organisms in soil is called Soil biology. The organisms in the soil, not only help in development of soils but carryout a number of transformations facilitating the availability of nutrients to the plants. In the absence of the activities of these organisms, in soil, life on earth would have come to a halt, as all available nutrients would have ended up locked in the organic, disrupting the nutrient cycles.

4. Continued….. The soil is teeming with millions of living organisms which make it a living and a dynamic system. Under microscope it reveals a complex arrangement of soil particles and pore spaces filled with air and water. It is in these pore spaces that plant roots and millions of organisms develop, ranging from microscopic to macroscopic in size. The soil organisms are classified into two broad groups , viz. soil flora and soil fauna, important groups as follows

5. Classification of soil organisms: Soil flora (Plant kingdom) 1) Macro-flora - Plant roots, Macro -algae 2) Micro-flora - Bacteria, Actinomycetes Fungi, Algae Soil fauna (Animal kingdom) 1) Micro fauna - protozoa, nematodes 2) Macro-fauna - Earthworms,Termites , Ants,Grubs

6. Classification of Bacteria Heterotrophic 1) nitrogen fixing- a) Symbiotic( Rhizobium ) b) Non-Symbiotic- Aerobic( Azatobactor ) Anaerobic( Clostridium) c) Associative symbiotic - Azospirillum 2) Non-nitrogen fixing- a) Aerobic- Ammonifiers b) Anaerobic- Denitrifiers Autotrophic-a) Chemoautotrophic( Thiobascillus ) b) Photoautotrophic ( Chlorobium )

7. SOIL FLORA 1 ) SOIL MACROFLORA- Eg . Roots of higher plants Functions in soil- The dead plant contribute to the formation of the soil organic matter which , provides food, energy and nutrients to microorganisms and also higher plants – a process of cycling of plant nutrients .

8. Continued….. Decay of plant roots add O.M. to soil , thereby changing soil properties viz. soil aggregation , CEC,water and nutrient retention capacity, etc. of soil. While proliferating , the roots exert tremendous pressure on surrounding particles. When roots decay , the vacant space makes room for water and air to move it as well as more food to the microbes, influencing therby microbial activity in soil.

9. 2) SOIL MICROFLORA- a) Bacteria : Bacteria are primitive ,very minute, unicelluar organisms. They are known for rapid proliferation. Size varies from 0.5 to 1 micron in diameter and 1 to 10 micron (length). They have flagella and are motile. They are most abundant in soil. 300 to 3000 kg of live weight of bacteria/ha., 0.01 to 0.4 % of total soil mass

10. Continued….. Shape may be round ( cocci ), rod like (bacilli) or spiral ( spirilla ). In the soil, the rod shaped ones seem to predominate. Bacterial population vary from few billion to three trillion in each kilogram of soil.   Types on the basis of temp. Psychrophiles - <10 C Mesophiles - 20 C-40 C Thermophiles - >40 C The genera –Pseudomonas, Azotobacter , Bacillus, Agrobacterium , Arthrobacter - are most abundant .The genus Bacillus has largest species followed by Pseudomonas.

11. Functions of Bacteria – Biological fixation of N. Symbiotic and non-symbiotic N-fixation. Decomposition of carbohydrates and lignins . Decomposition of proteins with the liberation of ammonia or ammonification , nitrification ,and denitrification . transformation of C,N,P,S,Fe,Mn .

12. Fungi They are longer than bacteria , aerobic and heterotrophic in nature (Saprophytic in nature). Fungi are broadly grouped in to yeasts, molds and mushrooms, out of which molds and mushrooms are important in soils. Fungi dominates in acid soils.

13. Continued….. Important molds in soils are Penicillium , Mucor , Fusarium and Aspergillus . Prefer acid medium (4.5-6.5). Some fungi can tolerate even pH 9.0. Mushroom fungi are found in forests and grasslands. Mushroom fungi are not widely distributed like molds, but are of much significance especially in breaking down of woody tissue.

14. Functions of fungi- A mutually beneficial (symbiotic) association between numerous fungi and the roots of higher plants is called ‘ Mycorrhizae ” (fungus root), is useful in adsorption of nutrients. Eg . VAM-fungi Fungi decomposes almost anything in organic that cannot tackle by bacteria.They decompose carbohydrates,celluloses,sugars,proteins,fats and lignins .

15. Actinomycetes Thread / Filamentous bacteria. Next to bacteria in abundance. A common genus is streptomyces . Actinomycetes have transitional charecteristics between bacteria and fungi, sometimes called fungi-like bacteria. They are more abundant in dry and tropical soil.

16. Functions of Actinomycetes Actinomycetes can degrade all sorts of organic substances such as celluloses, polysaccharides, proteins,fats,etc . But, they are slower activity than bacteria and fungi.For this reason , organic residues first attacked by bacteria and fungi, later on actinomycetes . It produce very little mycelium ,so less contribute to humus .

17. Algae Charecteristics - Chlorophyll containing organism, Aerobic, Photoautotrophic. Blue green algae(BGA) , also called cynobacteria are free living N-fixer ‘Heterocyst’ cells found in which N-fixation done.It provide anaerobic environment Algae in rice field

18. Continued….. Soil algae have been divided mainly into four classes,viz . Ex:-a) Blue green algae/ Cynophyta -(Anabaena, Nostoc ,)- dominates in tropical soil b) Chlorophyta -grass green algae-dominates in temperate regions. c) Xanthophyta - yellow green algae d) Bacillariophyta - golden-brown algae or diatoms Use in agriculture- Azolla -anabaena symbiosis can increase 10-15% rice yield  

19. Nitrogen fixing systems N- Fixing System Organism Involved Plant Involved Site of fixation Nitrogen kg N/ha/year Legumes ( Symbiotic) Rhizobium (bacteria ) Legumes Nodules 50-100 Non- legumes ( Symbiotic) Frankia ( Actinomycetes ) BGA(Anabaena) Alnus Casuarinas Azolla (Fern) Nodules Leaf 50-100 Associative symbiotic Associative symbiotic Non- legumes Rhizosphere 5-30 Non- Symbiotic BGA Azatobacter , Beijerinckia , (aerobic) Clostridium (anaerobic) Not Soil & Water 10-50 5-30 5-20

20. B) SOIL FAUNA 1) SOIL MACROFAUNA- Earthworms- These having slender cylindrical bodies with varing diameters. These feed on dead organic tissues and soil materials . Mineral soil constituents are digested and decomposed in digestive system. Their excretaare richer in bacteria and available mineral nutrients. They are more common in fine texture soil

21. Continued….. Ants- Ants are the most widespread species of insects in soil, and consume plant residues. B ut are more active in humifying insects than plants.

22. Others macrofauna are- Termites,Grubs , Slugs,Snails,Centipedes , Millipedes etc

23. 2) SOIL MICROFAUNA- 1 ) Soil protozoa- are unicellular but larger than bacteria, size varing from few microns to few cm, found in all arable soils. Functions- The role of protozoa in soil is not definitely known. As they feed on bacteria and actinomycetes , they probably help to maintain a favourable balance of the microflora in soil.

24. 2) Nematodes- Also called eelworms, thread worms or round worms. There are various types of nematode found as- saprophytic(feed on decaying O.M.), predatory(feed on earthworm) and parasitic (feed on roots of higher plants), this one (parasitic) cause lossof vigour of root system and make plants growing in nematode infested soil soil liable to diseases.

25. 3) SOIL VIRUSES These are ultramicroscopic obligate parasite( have head-tail structure , with diameter 0.05 to 0.1 micron) always requiring a living host for their multiplication . They are much smaller than bacteria , only visible through electron microscope . The viruses in soil is known as bacteriophases . When they parasitize and destroy a bacterium of agricultural importance like Rhizobium , they attain economic importance.

26. Interaction among soil organisms- Soil organisms interact with each other, with the plant roots, and with the environment . Some interactions are as follows- The association existing between one organism and another whether of symbiotic or antagonistic influences the population and activity of soil microbes. The predatory habit of protozoa and some mycobacteria which feed on bacteria may suppress or eliminate certain bacteria. A ctivities of some of the microorganisms are beneficial to each other. For instance organic acids liberated by fungi, increase in oxygen by the activity of algae, change in soil reaction etc. favours the activity or bacteria and other organisms in soil.  

27. Role of organism in soil fertility Soil microbes break down organic matter. Soil microbes recycle nutrients. Soil microbes create humus. Soil microbes create soil structure. Soil microbes fix nitrogen. Soil organisms promote plant growth. Soil microbes control pests and diseases.

28. Soil fertility evaluation by biological tests- Neubauer seedling method Standard and Demont technique Microbiological methods Sacket and Stewart technique Melich Cunninghamella - plaque test Mulder Aspergillus niger-test

29. Harmful Activities of Soil Organisms   Rodents, snails, slugs, termites, insect larvae and nematodes cause great damage to plants. Mainly fungi, but bacteria and actinomycetes ,also, are responsible for many soil borne diseases of crop plants .   Offer lot of competition to higher plants. Under conditions of poor drainage, depletes the available oxygen and hampers the normal growth of plants. Under anaerobic conditions, bacteria transform some of the nutrients to unavailable form (k & Zn etc.) and some nutrients to be available in toxic levels ( Fe & Mn etc.)

30. “There can be no life without soil and no soil without life; they have evolved together.” -Charles E. Kellogg