Biotic factors in soil formation,soil aggregation

Biological weathering,Biosphere-soil forming factor,Biological mediated soil forming process,Biotic factors influencing genesis of soil aggregation and soil structure

1. BIOTIC FACTORS IN SOIL FORMATION-AGGREGATION –SOIL STRUCTURE, SOIL DEVELOPMENT AGM 504 - SOIL MICROBIOLOGY B.KARTHIKEYAN 2019520103 SOIL SCIENCE& AGRL.CHEMISTRY AC&RI MADURAI TAMIL NADU AGRICULTURAL UNIVERSITY

2. INTRODUCTION BIOLOGICAL WEATHERING-CAUSES SOIL FORMING FACTORS – BIOSPHERE BIOLOGICAL MEDIATED SOIL FORMING PROCESS STAGES OF SOIL DEVELOPMENT SOIL AGGREGATION FLOCCULATION AND DEFLOCCULATION BIOLOGICAL FACTORS IN GENESIS OF SOIL STRUCTURE REFERENCES NUT SHELL

3. INTRODUCTION TO SOIL FORMATION

4. 1)WEATHERING Physical disintegration and chemical decomposition of rocks T YPES Physical weathering C hemical weathering B iological weathering

5. Biological weathering is the effect of living organisms, such as plants and animals, have on rocks and other inanimate objects When biological weathering occurs, the living organism breaks down the rocks through either mechanical (Biophysical) or chemical weathering (Biochemical weathering) or the use of both T here is strictly no biological weathering, they are aiding tool of physical and chemical weathering - JENNY Causes Man and Animals Higher Plants and Roots Micro- organisms BIOLOGICAL WEATHERING

6. a)Higher Plants and Roots

7. a)Higher Plants and Roots The roots of trees and other plants penetrates into the joints and crevices of the rocks. As they grew, they exert a great disruptive force and the hard rock may break apart. Roots can exert pressure up to 10.58 kg./sq. cm. when growing into a crack in rock . (e.g.) pipal tree growing on walls/ rocks Plant roots conserve moisture and thus allowing moisture and air to enter in to the rock for further action. (Biophysical weathering) The dead roots and plant residues decompose and produce carbon dioxide which is of great importance in weathering. This carbon dioxide react with water and form carbonic acid which play major role in carbonation (Biochemical weathering) .

8. b)Micro Organisms Microbial activity  breaks down rocks&minerals by altering the rock’s chemical composition, thus making it more susceptible to weathering. One example of microbial activity is lichen; lichen is fungi and algae, living together in a symbiotic relationship. Fungi release chemicals that break down rocks&minerals ; the minerals thus released from rock are consumed by the algae. As this process continues, holes and gaps continue to develop on the rock, exposing the rock further to physical and chemical weathering.

9. Man cuts rocks to build dams, channels and construct roads and buildings. All these activities result in increasing the surface area of the rocks for attack of chemical agents and accelerate the process of rock decomposition. A large number of animals, birds, insects and worms, by their activities they make holes in them and thus aids for weathering. In tropical and sub tropical regions, ants and termites build galleries and passages and carry materials from lower to upper surface and excrete formic acids.The oxygen and water with many dissolved substances, reach every part of the rock through the cracks, holes and galleries, and thus brings about speedy disintegration. Rabbits, by burrowing in to the ground, destroy soft rocks. Moles, ants and bodies of the dead animals, provides substances which react with minerals and aid in decaying process c)Man and Animals

10. The earthworms pass the soil through the alimentary canal and thus bring about physical and chemical changes in soil material. Industrialisation can cause pollution such emission of sulphur dioxide which can produce acid rain. Accelerate the chemical weathering process of hydrolysis, carbonation and solution

11. 2)SOIL FORMING FACTORS

12. Effect of lichens, mosses and algae : Plants contribute to soil formation by helping to break down the rock. Lichens, mosses and algae grow on bare rocks and respire to produce carbon-dioxide, that react with water to form carbonic acid, which dissolves primary minerals and release the nutrients for plant growth. Algae uses atmospheric nitrogen, which is released in the soil upon the death of the algae. CO2+H2O H2CO3 CaCO3 + H2CO3 -» Ca(HCO3) 2 Insoluble Soluble 4 KAlSi3O 8 + 2H2CO3 + 2H2O 2K2CO3 + Si4Al4O10(OH) 8 + 8SiO2 Orthoclase Kaolinite It comprises all plant, man and microbiological life. These organisms improve soil productivity by decomposing rocks, minerals and organic matter. Plants BIOSPHERE

13. Addition of organic matter (effect of grasses): Plants add organic matter to the soil. Grasses, litter and plant residues create a surface layer of organic matter. Root density of grasses declines with depth. Many roots die to produce a significant amount of organic matter. Grasses are very effective at offsetting leaching by recycling soluble materials. Recycling occurs when ions are absorbed by roots and translocated up through the plant. Recycling process is especially significant for cations such as Ca, Mg, Na, K that are gradually leached from the soil.

14. Effect of forests: The horizon developed under forests is acid. The compounds of iron and aluminium are more soluble and leach faster under acid conditions. The B-horizon of such soils may therefore have illuvial deposits of organic matter and Fe and Al compounds in addition to clay deposits. Type of vegetation: Plants differ in their nutrient revival to soil. For example, the pines favor podzol formation because of low bases and their leaches are acidic. Deciduous trees bring up lime and produce brown earth. Soil protection: Plants act as a vegetative cover and reduce normal erosion rates. Thus vegetation acts as an agent of soil protection against the forces of disintegration.

15. Animals Macroorganisms : Burrowing animals, earthworms, beetles, rodents, moles, centipedes, termites dig up the soil, mix up the material and disturb the soil profile. They interrupt soil development and tend to retard horizonation . Earthworm: The organic and mineral matter is grinded and adds digestive juices. Their excretions are rich in calcium and granular in structure. Crotovinas are abandoned pathways of rodents or earthworms filled with soil and cover about 30% of the soil matrix. Wormiculture , i.e. the raising of earthworm on the farmlands and the use of their casts as manure is being encouraged. Man and soil formation Man is a destructive factor in soil formation – through exploitive land use, converts the areas under natural vegetation to agricultural land which, with time and under unprotective agriculture, get eroded

16. Micro-organisms : It includes microflora and microfauna . Microflora : Bacteria, actinomycetes, fungi and algae Microfauna : Protoza and nematodes Micro-organisms help soil development by slowly decomposing organic matter and forming weak acids. Weak acids dissolve minerals faster than water. Soil supports billions of bacteria and other micro-organisms. Micro-organisms like bacteria and fungi are responsible for processes like nitrification, sulfur oxidation. They act on mineral content of rocks. These micro-organisms usually survive best under aerobic conditions, and a temperature between 25°-30° C is optimum. These conditions are met in tropical and subtropical regions. Soil acidity (pH3.5 to 5.5) is favorable for fungi, and pH between 6.5 to 7.5 is best for bacteria. Actinomycetes thrive well in slightly alkaline condition.

17. Profile characteristics of soils developed under different vegetation

18. Orders developed under different vegetation Alfisol Mollisol Spodosol Grasslands soil. Thick, dark Ahorizon . High % base saturation coniferous soils. Usually sandy. Thick, bright white E horizon. Sub-surface layer of accumulated metal-humus complex (Bhs and Bs horizons). Forest soils. Usually an A-E-B type horizon development. The A horizon is usually less than 25 cm.

19. Fundamental Pedogenic Processes Humification b. Eluviation/Emigration c. Illuviation /Immigration Humification It is the process of transformation of raw organic matter into humus. When raw organic materials are added in soil, their decomposition by various organisms produces simple organic acids. Further bacterial polymerization of these organic acids produces a dark brown colloidal substance resistant to microbial attack called humus. M ULL HUMUS developed under deciduous woodland, where base rich plants are actively breakdown by soil biota M OR HUMUS develops beneath coniferous woodland under cool wet climatic condition. Breakdown slows due to absence of soil biota. 3)SOIL FORMING PROCESS

20. Calcification Decalcification Podzolization Laterization Specific Pedogenic Processes (a) Zonal Soil Forming Processes b) Intrazonal Soil Forming Processes 5. Gleization 6. Salinization 7. Alkalization 8. Pedoturbation The soil forming processes that are occurring under the prevailing conditions of climate and biosphere (active factors) These pedogenic processes are more influenced by certain local conditions such as relief or parent material than climate and vegetation

21. 1)PODSOLISATION Climate : Cold–humid Vegetation : Coniferous (acidic nature) Parent material : Sandy (siliceous) It is a type of eluviation in which humus and sequioxides become mobile, leach out from upper horizons and become deposited in the lower horizons.It requires high content of organic matter and low alkali in the parent material. The process increases the proportion of silica in A-horizons. 2) LATERISATION Climate : Warm–humid Vegetation: Broad leaf tropical vegetation (basic nature) Parent material : Basic parent materials ( pyroxene, amphibole, biotite, chlorite ). It is reverse process of podsolisation

22. 3)GLEIZATION This process results in the development of a gley horizon (g) in some part of profile due to poor drainage condition . Under such condition, iron compounds are reduced to soluble ferrous forms. This is responsible for the production of typical bluish to grayish horizons with mottling of yellow and reddish brown colours . Example for iron reducers Geobacter  sp.,  Rhodoferax   ferrireducens , Geothrix fermentans ,  Ferribacterium limneticum , Geoglobus ahangari , and  Shewanella  sp. The term  glei of Russian origin, which means blue, grey or green clay.

23. 4)PEDOTURBATION It is the process of mixing of the soils. Mixing to some extent takes place in all soils. Faunal pedoturbation : Mixing by animals such as ants, earthworms, moles, rodents and man himself. Floral pedoturbation : Mixing by plants, as in tree tipping that forms pits and mounds. Argillo pedoturbation : Mixing of materials in solum by churning process caused by swell - shrink clays as is observed in deep black cotton soil.

24. STAGES OF SOIL DEVELOPMENT Formation of 1 cm soil its nearly take 1000 years time period

25. Aggregates is the naturally occurring, arrangement of soil particles into peds. T hat result from pedogenic process. The grouping or arrangement of individual soil particles into a larger grouping. The soil peds are a cluster or grouping of sand, silt, clay, organic material, biological slimes, and fungal masses. Single particles when assembled appear as larger particles. These are called aggregates Peds aggregates SOIL AGGREGATION

26. SOIL AGGREGATION The initial stage in the aggregation is the process of flocculation . Individual colloids typically exhibit a net negative charge which results in an electrostatic repulsion.

27. In the presence of natural or artificial binding agents clay particles become more strongly cemented together forming stable soil aggregates. These binding agents may be: 1)Inorganic – Fe & Al oxides, carbonates, amorphous gels and sols; or 2)Organic – polysaccharides, hemicellulose,and other natural or manufactured organic polymers. G LOMALIN produced by arbuscular mycorrhizal fungi (AMF) called as super glue of soil

28. When individual tiny soil particles especially fine clay, aggregate together into small clumps of floccules, the phenomenon is called flocculation It aids in the formation of stable aggregates Separation of compound particles to individual components by chemical or physical means is called deflocculation or dispersion FLOCCULATION AND DEFLOCCULATION

29. By the reduction of the forces of electrostatic repulsion allows the particles to come closer together. + Flocculation MECHANISM OF AGGREGATION

30. Soil organic matter consist of polysaccharides,hemicellulose as well as number of other natural polymers which are poly electrolytic in nature and have multiple charges.It also contaion fats,oils and waxes . These materials are attached to clay surfaces by means of 1)cation bridge Clay - _ + Ca + _ - OOC-R-COO - _ + Ca + _ - Clay (carboxyl group) 2)Hydrogen bonding Clay - _ + H- OOC-R-COO-H + _ - Clay (carboxyl group) 3)Vander walls forces 4)Anion exchange or ligand exchange mechanism clay - + - HO-R-OH - Clay-R-Clay + OH - (Alcoholic group) That’s why organic matter acts as very good binding agent Functional groups of humus

31. As this process continues, the flocs become larger and larger forming the more refined structural units.

32. Aggregation of soil particles can occur in different patterns, resulting in different soil structures. The circulation of water in the soil varies greatly according to structure, Therefore, it is important for you to know about the structure of the soil Arrangement of primary particles and their aggregates into certain definite pattern is called as soil structure SOIL STRUCTURE

33. Soil Structural Types Soil Structure Size/ Class Very Fine (Very Thin) Fine (Thin) Medium Coarse (Thick) Very Coarse (Very Thick)

34. By definition, the grade of structure is the degree of aggregation , expressing the differential between cohesion* within aggregates and adhesion* between aggregates. As these properties vary with the moisture content of the soil, grade of structure should be determined when the soil is neither unusually moist nor unusually dry. There are four major grades of structure rated from 0 to 3 as follows: Soil Structure Grade Structureless = 0 Weak = 1 Moderate = 2 Strong = 3

35. BIOTIC FACTORS AFFECTING SOIL STRUCTURE Organic matter : Organic matter improves the structure of a sandy soil as well as of a clay soil. In case of a sandy soil, the sticky and slimy material produced by the decomposing organic matter and the associated microorganism cement the sand particles together to form aggregates . In case of clayey soil , it modifies the properties of clay by reducing its cohesiveness . This helps making clay more crumby Some of the decomposition products of organic matter and the associated microbial tissue act as cementing agents. Thus it has a stabilizing effect. Organic matter helps in the granulation of clay.

36. Plants, Roots and Residues: Plant foliage protects soil aggregates against the disintegrating action of raindrops. Root hairs penetrate clods, thus breaking the soil clods into desirable aggregates. Root excretions, water sorption by roots and pressure exerted by root penetration are conducive to formation of stable aggregates. Grasses and legumes can restore deteriorated soil structure. Soil Organisms Decomposition of organic matter by micro-organisms produces humic acids, polysaccharides that impart stability to aggregates. Thus soil micro-organisms are indirectly helpful in formation of stable aggregates. Macro-organisms like rodents and earthworms help soil aggregation by burrowing, turning and mixing the soil. Earthworm’s activity has a remarkable effect in the formation of stable aggregates. They excrete surface casts and form burrows, which promotes granulation.

37. Microbes : Algae, fungi, actinomycetes and fungi keep the soil particles together. Fungi and actinomycetes exert mechanical binding by mycelia , Cementation by the products of decomposition and materials synthesized by bacteria

38. REFERENCE INTRODUCTORY SOIL SCIENCE –D K DAS T EXT BOOK OF SOIL SCIENCE – R.K.MEHRA SOIL GENESIS AND CLASSIFICATION(ISSS) - s.k. singh and p. chandran SOIL PEDOLOGY – J.SEHGAL FACTORS OF SOIL FORMATION- HANS JENNY FACTORS OF SOIL FORMATION Biota - A H Jahren, Johns Hopkins University, USA FACTORS OF SOIL FORMATION/HUMAN IMPACTS -J Sandor, C L Burras , and M Thompson, Iowa State University, Ames, IA, USA ABIOTIC AND BIOTIC FACTORS INFLUENCING THE EFFECT OF MICROPLASTIC ON SOIL AGGREGATION -Anika Lehmann 1,2,* , Katharina Fitschen 1 and Matthias C. Rillig 1,2 SOIL BIOTA, ECOSYSTEM SERVICES AND LAND PRODUCTIVITY- Edmundo Barrios , Colombia