Different types of soils

SUBMERSED SOILS - ORGANIC SOILS Based on organic content, soils grouped into mineral soil and organic soil The mineral soils - organic matter - from trace to 15-20% In organic soils - organic matter to 90-95% For cultivation - 80% organic matter It forms around lesser than <5% of the total soil components Organic soils are useful in intensive production of crops, particularly vegetables

TYPES OF SOILS AND CHARECRSTICS Wet lands Methane and hydrogen sulfide formation Saline soils Alkali Soils Acid sulphate soils Iron Pyrites Soil reclamation

PEAT SOIL: The organic materials that accumulate in swamps and marshes are called peat. Types of peat soils Sedimentary peat Fibrous peat Woody peat PEAT SOIL

Sedimentary peat - usually accumulates in deeper water Plant material - water lilies, pond weeds etc Plankton humify completely, soil is highly colloidal, characteristically compact and rubbery, olive green in color Moisture capacity is as high as 4-5 times of dry weight It absorbs water very slowly and persistently remains hard and lumpy condition Sedimentary peat is undesirable for agriculture cultivation

Fibrous peat By decomposition and deposition of sedges, mosses grass, weeds etc Has high water holding capacity A very good field soil – greenhouse, nurseries, gardens, flower beds etc Usually lies above the sedimentary peat

Wood peat Is a swampy deposit accumulating at the surface above the fibrous peat Soil is brown or black in color Has well disintegrated and decomposed Water holding capacity is lower than that of fibrous peat soil is less useful in green house and nurseries and it is useful for growing vegetables

ConstituentsPeat SurfaceMineral Surface 1. Organic Matter() 2. Nitrogen (N) 3. Phosphorous (P) 4. Potassium (K) 5. Calcium (Ca) 6. Magnesium (Mg) 7. Sulphate (S) Chemical composition peat (% based on Dry matter)

PHYSICAL PROPERTIES OF PEAT SOILS 1. Color:Dark Brown 2. Bulk density :Lower than Mineral soil 3. Water capacity:High 2-3 times 4. Structure:Highly adsorptive, low plasticity & cohesion highly porous, easy for cultivation 5. Buffering:Residential to pH change 6. Lime loss:High as cat ion is very active 7. Strength of acid:Lower pH 8. Colloidal nature:Surface area increases due to soil colloids

USES OF PEAT SOILS As a manure – used in nurseries, green house and lawns As a bedding material-used in stables litters, poultry houses, As a packing material-as it is a good insulation capacity. As a fuel-as rich in carbon coal like Dutch, Germen peat. Industrial purpose Field soils- United States for soil amendments

BOG LIME: Deposition below the peat soils at varying depth by a soft impure calcium carbonate called bog lime or marl Marl - formed due to the deposition and decomposition of mollusks shells, aquatic plants such as mosses, algae (chara) Marl is a white grey, soft crumbly material offers full of shells Marl may be dugout, dried and pulverized and used as agricultural lime It is an alkaline peat soil and it is not desirable for aquaculture activities

Peat V/S Muck soil The oxidized material is called muck to distinguish it from the unoxidized peat Muck - higher percentage of mineral matter than peat – because of the decomposition of organic material The acidity or alkalinity of a soil depends largely on the balance between the negatively charged micelles and basic cations (mostly (Ca ++, Mg ++ K + NH 4 + and Na +) The cat ions are called bases - enough OH - ions present to make the soil alkaline

The soil is said when the reverse situation occurs and many of the negative charges of the micelles are offset by H + and A1 +++ ions (CO 3 --, SO , Cl - NO 3 -) Cat ions in mineral structures of soil are gradually made available by weathering processes The rate of release however is different for cat ions and minerals The cat ions thus released may held by cat ion exchange or they move into solution

Weathering processes in arid regions is slower, and less material enters the soil solution than in humid regions soils The solution is more concentrated in the arid region soils – because of increased salt content than water content Dissolved materials - collect at the bottom of the ‘B’horizon as salts Ca ++, Mg ++, Na +, K + - combin with CO 3 --, SO 4 — Anions - move back upward in the profile along with water moving by capillary action when the upper horizons are drier than the lower ones Ex:Sodium

Cat ion absorbed by cat ion exchange on the soil colloids depends on Available supply of each cat ion Intensity of leaching action Strength of cat ion absorption Leaching - makes soil more acidic because H + ions replace some of the basic cat ions on the micelles Erosion looses - can remove large amounts of plant nutrients, volatization in wet soils reduces nitrogen gas, hydrogen sulfide and methane etc

The strength of the attractive force between a cat ion and micelle depends on the change of the cat ion Single changes – H +, Na +, K +, NH 4 + Double changes – Ca ++, Mg ++ Triple charges – Al +++ Hence, Al +++ > Ca ++ > Mg ++ > K + > NH 4 + > Na + Soil of pH above 8 have high % of sodium ion and most soil values below 4.0 contains sulfuric acid

ALKALINE SOILS Soils with pH more than alkaline soils Formation of alkaline soils Alkaline soils - formed in arid regions where enough precipitation to leach bases (Ca ++ Mg ++ K + Na +) from the soil Ground water carries bases into soils in low topographic positions and leaves the bases there when it evaporates

PROBLEMS WITH ALKALINE SOILS Chemical Problems Iron deficiency is the common problem. Alkaline soils contains high concentrations of soluble salts Osmotic concentration becomes higher in soil solution. Reduce the response of plants to fertilizers Physical Problems Results the high dispersion of the soil colloids Makes soil low permeable

Types of alkaline soils High lime soils Saline soils Sodic soils Saline sodic soils High lime soils Soils occur is humid regions Most soil high in lime i.e. CaCO 3 soluble is low The Soil pH is always between 7.5 and 8.0 because buffering action of CaCO 3 High lime soils are deficient in nutrients

Saline soils Soils have high content of soluble salts Saline soils have high electrical conductivity 4 millimhos/cm (2 mmohs/cm is normal) Soil less than 15% of the cat ion exchange capacity due to sodium ions pH is usually between Such soils are sometimes called “white alkali soils” because of excess salts of chlorides and sulphates of sodium, calcium and magnesium helps to form white crust formation

Sodic soils Soils have more than 15% cat ion exchange sites occupied by Na + ions Low in soluble salts, pH always above 8.5 due to Na + ions in solution Have highly dispersed soils, very low permeability and practically no plant growth Sodic soils are chemically called black alkali

Saline-Sodic soils Soils contain the high salt content (More than 4 milli mhos/cm in solution) Higher percentage of Na + ions (more than 15% on the cat ion exchange sites) pH values between 8.0 and 8.5 Saline soils can be reclaimed simply by leaching where as saline-sodic soils deteriorate if they are leached without a soil amendment

RECLAMATION OF SOILS Reclamation of alkaline soils Alkaline soils need good drainage Good drainage system prevents accumulation of soluble salts High lime soils Eradication - Adequate drainage and proper fertilizer will help the soil to grow plants Addition potassium fertilizer may be applied. Apply manures as they are sources of potassium

Saline Soils Good drainage is the best solution – Excess salts can be removed by irrigation Saline sodic soils Add Gypsum and sulfur

II.CONVERSION Na + + CaSO 4 Ca Na 2 So 4 ↓ SodiumGypsum Soluble can be leached by drainage 2Na + Co 3 --+CaSo 4 CaCo 3 ↓+2Na ++ So 4 -- Sulfur: 2S H 2 O 2H 2 So 4 ↓ Microbial action H 2 So 4 + Na ++ Co Na ++ So H 2 O+Co 2 ↑ H 2 So 4 + CaCo 3 CaSo 4 + H 2 O+ CO2↑

III. CONTROL Retardation of evaporation Irrigation Grow salt resistant crops Use farm manure

ACID SULPHATE SOILS Soils – has iron pyrite (FeS 2 ) or closely related sulfide compounds Iron pyrite - accumulate especially in soils of coastal areas Decomposition of organic matter in the sediments - oxygen depletion and iron oxides in soils - under anaerobic conditions reduced to form ferrous iron (Fe ++ ) Brackish waters in the coastal wetlands have high sulphate concentration This soil under anaerobic condition due to microbial activity it produces sulfides (H 2 S - ) and elemental S o

Iron sulfides and sulfur react to produce Iron pyrite. Fe 2 O 3 + 4SO CH 2 O + ½O 2 2FeS 2 +8HCO H 2 O (Ferric Iron) (Sulphate) (Organic) (Ironpyrite) Iron pyrite is stable as long as it is in an anaerobic environment It is a common phenomenon that the coastal water will have upto 5% of sulfide in the total sulphur When sulfide soils are exposed to atmosphere, it oxidizes to from sulphuric acid (H 2 SO 4 ) soil contains more than about 0.75% of total sulfur are known potential acid

SULPHATE SOILS Such oxidized sulfide bearing soils are termed acid sulphate soils Sulfuric acid dissolves aluminium, Mn, Zn and copper from the soil Acidic runoff from acid sulfate soils or mineral soils can produce potentially toxic metal ions The amounts of acid produced in acid sulphate soil depend on the amount and particle size of iron pyrite The presence or absence of exchangeable bases and carbonates with in the pyrite bearing materials

Acid sulphate soil - pH of below of 3.5 A yellowish material of jarosite - seen in the surface layer of brackish water ponds in strong acid sulphate soils Yellow deposits of elemental sulfur are often visible and the odor sulfur is apparent Soil acidity results from a lack of exchangeable cat ion The quantity of those absorbed metallic cat ions controls the exchange base saturation and there by indirectly determines the H + ions concentration of soil solution

Soil acidity - reclaimed by adding metallic cat ions- calcium and magnesium Commercial Oxidizer of lime - commonly used as burnt lime / quicklime / Oxides of calcium (Calcite) CaCo 3 +heatCaO+Co 2 ↑ (Dolamite) CaMg (Co 3 ) 2 +heatCaO+MgO+2Co 2 ↑ Burned lime contains oxides, Ca ++ and Mg ++ with small amounts of hydroxides (OH) CaO+MgO+2H 2 OCa (OH) 2 +Mg(OH) 2

EFFECTS OF LIME ON THE ACIDIC SOILS Physical Effects Increases granulation Decomposes the soil organic matter and produce humus which increase the granulation of soil Biological Effects Lime stimulates the heterotrophic soil organisms Soil organism increases the production of organic matters and nitrogen content of acid soil Soil organisms stimulate the enzymatic process which favors the formation of humus etc

Chemical Effects Decreases the concentration of H + ions, Increases the concentration of OH - ions, Decrease the solubility of Fe, +++ Al +++, Mn + Increases the availability, Po 4 -, Mo - in the soil Increases exchangeable Ca ++,Mg ++ ions Increases the percentage base saturation Increases the availability of K +