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Soil Science notes for IBPS AFO,NABARD,RRB SO
soil science

Soil Science notes for IBPS AFO,NABARD,RRB SO

By agriguru
21 Min Read
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These soil science notes are crucial for agricultural exams like IBPS AFO, NABARD, and RRB SO. Each point should be carefully studied. You can download the PDF containing these points from the Agrilearner/Agriguru WhatsApp group at 6201733962

• Soil, derived from the Latin word “Solum,” meaning ‘Floor’ or ‘Ground,’ serves as the vital interface between the atmosphere and the earth’s mantle of rocks, known as the “lithosphere”.
• Regolith encompasses all loose materials above bedrock, comprising the unconsolidated material resulting from weathered rock and soil.
• Soil Survey involves the systematic examination, description, and classification of soils.
• Pedology is the scientific study encompassing the genesis, survey, classification, and laws governing the geographic distribution of soils as a natural body.
• Edaphology focuses on the study of soils from the perspective of higher plants.=>GET IBPS AFO BOOKS <=

( Writer’s Note: If you’re preparing for IBPS AFO and NABARD exams, it’s essential to focus on soil science. In IBPS AFO exams, typically 3 to 4 questions are asked from the soil science section. So, dedicating time to studying soil science can significantly improve your chances of success in these exams.)

Rocks:

• “Rocks” are defined as aggregates of one or more minerals. For instance, limestone is an aggregation of calcite minerals.
• Unlike minerals, rocks lack a definite chemical, morphological composition, or symmetrical form.
• Rocks are classified based on their origin into three main types: Igneous rocks, Sedimentary rocks, and Metamorphic rocks.

I. Igneous Rocks:

• Igneous rocks, constituting 95% of the earth’s crust, are among the oldest rocks and are alternatively known as “crystalline,” “massive,” or “fire” rocks.
• These rocks predominantly consist of primary minerals, with over half containing “feldspar” minerals.
• Igneous rocks are further categorized based on their mode of formation into Extrusive (or volcanic) and Intrusive (or plutonic) rocks.
• Classification by chemical composition includes Acid rocks (e.g., Granite), Neutral rocks (e.g., Diorite), and Basic rocks (e.g., Basalt).

II. Sedimentary Rocks:

• Formed through the transportation and deposition of weathered sediments, sedimentary rocks are largely shaped by water, leading to their classification as clastic, aqueous, or stratified rocks.
• Based on origin, sedimentary rocks are divided into four groups: Residual sediments (e.g., Laterite, Bauxite), Mechanical sediments (e.g., Sandstone, Shale), and others.

III. Metamorphic Rocks:

• Metamorphic rocks originate from pre-existing rocks subjected to high pressure, temperature, or chemically active fluids.
• These rocks undergo profound changes in mineral composition and texture without melting entirely.
• Metamorphic rocks are classified based on texture and mineral composition, with examples including Slate, Marble, and Quartzite.

Minerals:

A mineral is a naturally occurring, homogeneous element or inorganic compound that possesses a definite chemical composition and a characteristic geometric form. The identification of minerals is often based on various physical properties such as color, luster, streak, and hardness.

• Lustre: The general appearance of a mineral in reflected light.
• Fracture: The property of a mineral to break along an irregular surface, distinct from its cleavage plane.
• Streak: The color of the powder produced when a mineral is rubbed against an unglazed porcelain plate.

Soil-forming minerals predominantly belong to the group of alumino-silicates. Minerals are classified based on several criteria including quantity (essential and accessory), origin (primary and secondary), specific gravity (light and heavy), and chemical composition (native elements, oxides, sulphates, sulphides, carbonates, halides, silicates).

Primary minerals are the original components of rocks that have not undergone chemical alteration and are formed from the crystallization of magma (molten mass).

Examples include Quartz and feldspar.

Secondary minerals result from the decomposition and/or alteration of primary minerals due to subsequent changes in the rocks. Examples include clay minerals like kaolinite and illite, excluding micas which are primary minerals.

Essential Minerals are those that constitute the chief components of a rock and are considered characteristic of it. Examples include Quartz and feldspars.

Accessory minerals occur in small quantities within rocks and are not essential for the naming or nomenclature of rocks. Examples include Apatite, pyrite, and magnetite. These minerals are not required for the formation of any specific rock.

Primary Silicate Minerals:

– Quartz: Chemical formula SiO2.
– Potash Feldspar (Orthoclase): Chemical formula KAlSi3O8.
– Soda Feldspar (Albite): Chemical formula NaAlSi3O8.
– Lime Feldspar (Anorthite): Chemical formula CaAl2Si2O8; Albite and anorthite combine to form plagioclase or soda lime feldspars.

Feldspars are susceptible to attack by water containing H2CO3, a process known as carbonation. Plagioclase weathers more rapidly than orthoclase.

Micas are double silicates of K and Al, with or without iron, characterized by plate-like structures:
1. Muscovite (White Mica): Chemical formula KAl3Si3O10(OH)2.
2. Biotite (Black Mica): Occurs in both acidic and basic rocks.
3. Phlogopite: Occurs as a primary mineral in igneous rocks. Biotite is more easily weathered than muscovite.

Pyroxenes and amphiboles are double silicates of Fe, Mg, Al, and Ca:
– Pyroxene: Augite (Dark green).
– Amphibole: Hornblende (Green-black).

  • Olivines are thin silicates of Fe and Mg, examples include Fayalite and Forsterite.
  • Sedimentary rocks predominantly contain secondary minerals. Muscovite alters to hydrous mica.
  • The insoluble residual material left behind during weathering is called saprolite.
  • Exfoliation is the phenomenon of weathering due to the differential coefficient of expansion and contraction, leading to ultimate disintegration.
  • Moraine or till is the structureless mass formed from the melting of ice or glaciers in warm regions.
  • The chemical weathering of feldspar produces clay minerals.
  • Basalt decomposes more easily than granite.
  • Ease of weathering of minerals:
    Quartz > Feldspar > Micas > Olivines > Hornblende.
  • Weathering is a destructive process, whereas soil formation is constructive in nature.
  • Relief refers to the elevations and inequalities of a land surface, similar to topography used on contour maps.
  • The time taken by nature to form soil is known as pedogenic time.
  • The process leading to the development of a soil profile is called pedogenic process.
  • Humification is the decomposition of raw organic matter into humus, usually occurring in the surface or O horizon.
  • Eluviation is the process of removing constituents by percolation from the upper layer to the lower layer.
  • Illuviation is the deposition of dissolved material in the lower layers.
  • Podzolization is a humid temperate type of soil-forming process characterized by ash-like under layers.
  • Laterization is the soil formation process in tropics and subtropics, involving the removal of silica instead of sesquioxides from the upper layers.
  • Laterization and podzolization form soils belonging to the group of pedalfer.
  • Calcification occurs in areas with insufficient rainfall.
  • Soils with high saturation of Ca are called pedocals.
  • Decalcification is the removal of Ca ions or CaCO3 by leaching.
  • Cation exchange capacity is expressed as me/100 g of soil or cmol (p) kg-1 soil.
  • Soil cations are sometimes referred to as “swarm ions” due to their resemblance to a swarm of bees around a beehive.
  • The area where ions move around roots or clay particles in soils is termed the “oscillation zone.”
  • The CEC of kaolinite increases with increasing soil pH.
  • The percentage of base saturation (% BS) is calculated as Total exchangeable bases (me/100 g soil) divided by CEC, multiplied by 100.
  • Arid region soils typically have higher % BS than soils in humid regions.
  • Soils dominated by 2:1 clay minerals like montmorillonite, vermiculite, chlorite, and micas tend to have higher % BS.
  • Anion exchange is more pronounced in soils high in 1:1 clay.
  • Acid soils often exhibit low availability of Ca and Mg.
  • The availability of sulfur (S) remains unaffected by soil reactions as sulfur compounds are soluble across the entire pH range.
  • Solubility of Fe, Mn, and Al increases when pH is low.
  • Availability of B, Cu, and Zn decreases with increasing pH.
  • Availability of Mo is reduced in acidic soils.
  • “Buffering” refers to the soil’s resistance to slight changes in pH.
  • The ability to resist slight changes in pH is termed “buffer action.”
  • Horizons in a soil profile are broadly divided into four groups: A, B, C, and D.
  • AB horizons collectively form the “solum,” which, together with the parent material, constitutes the “soil profile.”
  • A “horizon” is a layer of soil approximately parallel to the land surface.
  • Diagnostic surface horizons are termed “epipedons.”
  • Soils are described as “gravelly” or “sandy” when larger mineral particles dominate and “clayey” when mineral colloids dominate.
  • Compact soils and sandy soils tend to have high bulk density.
  • Bulk density is higher in lower layers of the profile due to lower organic matter content.
  • The addition of organic matter reduces bulk density and increases pore space.
  • Leaching of Fe compounds due to high rainfall can lead to the formation of “grey” or “grey-brown” soils.
  • Hue refers to the dominant spectral colors in soils.
  • The value indicates the relative lightness or darkness of color.
  • Chroma denotes the relative purity of a color.
  • Soil consistency, expressed by the degree and kind of cohesion and adhesion, is a dynamic property of soils.
  • Non-exchangeable cations in montmorillonite include Mg, while in illite, they include K.
  • Organic matter, upon decomposition, gets modified and acquires the properties of colloids.
  • Soil survey involves the study and mapping of soils in their natural environment.
  • Remote sensing is the science and art of acquiring information about objects from a distance without physical contact.
  • Pedalfers are characterized by the accumulation of iron and aluminum in soils under high rainfall, while pedocals exhibit the accumulation of Ca in areas of low rainfall.

Important Soil Science terms

  1. Alfisols: Characterized by a clay-enriched Bt horizon.
  2. Vertisols: Known as black soils with profile inversion.
  3. Aridisols: Soils found in dry regions.
  4. Mollisols: Developed under grassland vegetation.
  5. Histols: Organic soils formed in water-saturated environments.
  6. Oxisols: Very strongly weathered mineral soils.
  7. Ultisols: Soils with low base status.
  8. Spodosols: Mineral soils with accumulation of humus and sesquioxides.
  9. Entisols: Recently developed mineral soils lacking horizonization.
  10. Bauxite reigns as the primary source of aluminum in soils.
  11. Soil displaying bluish or greenish hues often indicates poor drainage.
  12. 1:1 clay minerals boast notable porosity and permeability.
  13. Calcium and magnesium play pivotal roles in soil aggregation.
  14. Clayey soils harbor ample pore spaces facilitating air and water movement.
  15. Fungi thrive in soil, feasting on organic matter.
  16. Soil serves as a rich source of organic nutrients for plants.
  17. Inorganic soil particles exhibit lesser cation exchange capacity compared to organic ones.
  18. Saline soils are characterized by high concentrations of chlorides and sulphates.
  19. The acidity of soil solution is termed “Active acidity.”
  20. Limonite, chemically 2Fe2O3. 3H2O, signifies a hydrated form of iron oxide.
  21. Soil formation is influenced by climate and living organisms.
  22. The humus theory was proposed by the esteemed scientist von Liebig.
  23. Soil texture can be classified into twelve categories using a textural triangle.
  24. Soil structure development involves processes like flocculation and aggregation.
  25. In arid regions with poor drainage, sodium is the preferred cation for soil adsorption.
  26. Colluvial soil results from gravity-driven soil movement.

Soil Chemistry

  • Soil fertility is defined as the soil’s ability to provide the necessary nutrient compounds in appropriate quantities.
  • Soil productivity refers to the soil’s capacity to grow specific plants effectively.
  • Arnon introduced the criteria for essential elements in 1954.
  • D.J. Nicholas introduced the concept of “Functional or metabolic nutrient.”
  1. Deficiency: Occurs when an essential element is at such low levels that it severely limits yields and causes deficiency symptoms in plants.
  2. Insufficiency: Happens when the level of an essential element is below what’s needed for optimal yields or when there’s an imbalance with another nutrient.
  3. Toxicity: Arises when the concentration of either essential or other elements is high enough to significantly reduce plant growth.
  4. Excess: Occurs when the concentration of an essential plant nutrient is so high that it leads to a deficiency of another nutrient.

( Writer’s Note: Soil chemistry holds significant importance within the realm of soil science, particularly for exams such as NABARD. While it’s still relevant for IBPS AFO, its emphasis is comparatively greater in NABARD exams. Aspirants should pay special attention to this section, as it can play a crucial role in their exam preparation and success. )

Establishing the essentiality of elements:

  • Nitrogen: Theodore de Saussure
  • Molybdenum: Arnon and Stout
  • Sodium: Brownell and Wood
  • Cobalt: Ahmed and Evans

Mineralization:

  1. Aminization: Breakdown of proteins through hydrolysis, releasing amines and amino acids.
  2. Ammonification: Conversion of released amines and amino acids into ammonium compounds.
  3. Nitrification: Conversion of ammonium ions to nitrate through biological oxidation.
  • Aminization and ammonification are carried out by heterotrophic bacteria.
  • Nitrification is performed by autotrophic bacteria:
    • NH4 to NO2: Nitrosomonas, Nitrococcus.
    • NO2 to NO3: Nitrobacter.
  • Nitrosomonas and Nitrobacter are collectively known as “nitrobacteria.”
  • High Carbon to Nitrogen (C:N) ratio inhibits ammonia release and constrains nitrification.
  • Nitrification occurs optimally at field capacity soil moisture and even below the wilting coefficient.
  • Nitrification operates within a pH range of 5.5 to 10.
  • C:N ratio exceeding 30:1 favors immobilization, while less than 30:1 favors mineralization.
  • Certain clay minerals, especially vermiculite, possess high Cation Exchange Capacity (CEC), facilitating ammonium and potassium ion fixation.
  • Ammonium fixation is greater in subsoil due to higher clay content.
  • Leaching of nitrate (NO3) is low in arid regions and high in humid areas with irrigation.
  • Denitrification reduces NO3 to N2 in poorly aerated soils, led by bacteria like Thiobacillus denitrificans and Pseudomonas denitrificans.
  • Volatilization occurs when ammonium-containing fertilizers or urea hydrolyze into NH3 gas, escaping into the atmosphere.
  • Biological Nitrogen Fixation (BNF) is catalyzed by the enzyme nitrogenase, found in various organisms.
  • Examples of symbiotic N2 fixation in legumes include:
    • Rhizopium species in Alfalfa, Clover, Soyabean, Lupini, Bean, Peas, and Vetch.
  • Non-legumes capable of N2 fixation include:
    • Casuarina (Casuarinaceae), Alnus (Betulaceae), and Frankia (Actinomycetes).
  • Rhizobium forms symbiotic associations, Azotobacter is free-living, and Azospirillum is an associate symbiont in maize, sorghum, bajra, and ragi crops.
  • BGA (Blue-Green Algae) are freeliving in irrigated rice fields, while Azolla fern hosts BGA in rice fields.
  • Mycorrhizae form symbiotic associations with plant roots across various crops.
  • The primary loss of nitrogen from soils is through uptake by crop plants.
  • Nitrogen content in plants varies from 0.2 to 4.0%.
  • Nitrogen contributes to the deep, dark green color of plants.

Phosphorus:

  • Phosphorus is often called the “key to life” due to its essential role in biological processes.
  • Phosphorus-containing calcium minerals in soils are mainly apatites, such as Ca10(PO4)6.
  • Different types of apatites include fluor apatite, carbonate apatite, hydroxy apatite, and oxy apatite, each with varying compositions.
  • Other phosphorus compounds found in soils include tricalcium phosphate (TCP), octacalcium phosphate (OCP), dicalcium phosphate, and monocalcium phosphate (MCP).
  • Among these, monocalcium phosphates are the most readily available for plants.
  • Apatite minerals are highly insoluble and thus less available to plants.
  • Phytin, a calcium-magnesium salt of phytic acid, is the most abundant organic phosphorus compound.
  • Plants prefer monovalent forms of phosphorus over divalent or trivalent forms.
  • The proportion of H2PO4 increases at pH 5.0, while HPO4 -2 predominates at pH 9.0 (very alkaline soils).
  • The optimal pH range for phosphorus availability is 6.5 to 7.5.
  • Phosphate fixation is more pronounced in 1:1 type clay minerals.
  • Gibbsite and goethite are examples of minerals contributing to phosphorus fixation.
  • The concentration of phosphorus in the soil solution is a measure of the intensity factor (I) of phosphorus nutrition.
  • Soil solution phosphorus replenishment is termed the quantity factor (Q) of phosphorus nutrition.
  • Phosphorus compounds in soils are categorized into three major groups: readily available (soil solution P), slowly available (labile P), and very slowly available (non-labile P).
  • Tropical clay soils high in iron and aluminum require a high level of Q to maintain a given I level, measured by the potential buffering capacity (PBC) = Q/I.
  • Phosphorus content in plants typically ranges from 0.03 to 0.3%, while in seeds, it can be as high as 1.5%.
  • Excessive phosphorus can lead to trace element deficiencies, particularly iron and zinc.
  • Phosphorus deficiency in plants can manifest as bronzing of leaf margins, especially in cereals.
Potassium
  • Orthoclase, chemically represented as KAlSiO3O8, is a type of potassium feldspar.
  • Minerals like kaolinite, classified as 1:1 type minerals, do not retain potassium.
  • Illite is capable of fixing potassium ions, with aluminum ions occupying the selective potassium binding sites.
  • Any potassium levels above the optimum are considered excessive and wasteful.
  • Potassium plays a crucial role in regulating water movement within plant cells.
  • Potassium deficiency can result in leaf scorching, commonly known as tip burning.
  • Decreased crop yields without obvious symptoms are termed “hidden hunger.”
  • The function of potassium is primarily catalytic in nature.
  • Secondary nutrients important for plant growth include calcium, magnesium, and sulfur.

Calcium (Ca):

  • Calcium is primarily found in minerals like basic plagioclase.
  • It’s the most prevalent cation in all soils, often in the form of calcite (CaCO3).
  • Light-textured soils tend to lose more calcium compared to heavy soils.
  • Calcium is crucial for cell wall formation.
  • Symptoms of calcium deficiency include:
    1. Stunted development of terminal buds.
    2. Dieback in fruit trees.
    3. Chlorotic leaves with red-brown spots in guava trees.
    4. Loss of color in young leaves of brassica species.

Magnesium (Mg):

  • Adding large amounts of magnesium salts to soils containing montmorillonite can change the minerals to vermiculites.
  • It’s typically low in acidic soils.
  • Dolomite limestone is a rich source of magnesium.
  • Magnesium is a component of chlorophyll and helps maintain a dark green color in plants.
  • Excessive magnesium in sandy soils may lead to potassium deficiency.

Sulfur (S):

  • Sulfur behaves similarly to nitrogen in many aspects.
  • Sulphates are found in subsoils containing 1:1 clays.
  • Mustard and onion plants are known to contain sulfur in their oils.
  • Sulfide production in paddy soils can lead to a condition known as “Akhiochi” or H2S injury.
  • H2S injury causes bubbles to emerge from affected areas and turns the soil black.
  • “Akhiochi” disease occurs in soils lacking iron.

Micronutrients, as classified by Viets in 1962, are categorized into different pools based on their availability and forms in soil:

  • Pool A: Water-soluble ions, typically non-existent for copper (Cu) and zinc (Zn), very small for iron (Fe) and manganese (Mn). Low redox potential and low pH increase Mn and Fe but not Cu and Zn.
  • Pool B: Cations exchangeable by NH4, small for Cu and Zn.
  • Pool C: Cations exchangeable only by strong chelating agents like EDTA, DTPA.
  • Pool D: Micro-nutrient cations held in secondary clay minerals.
  • Pool E: Cations held in primary minerals.
  • Chlorides mostly occur in Pool A and Pool E, borates in Pool E, while molybdates occur in all pools.
  • Micronutrients are more concentrated in the surface soil.
  • Presence of moisture reduces the availability of Cu and Zn and increases Fe and Mn.
  • Low Si/Mg ratio leads to Zn fixation in soils.
  • Higher CaCO3 content reduces availability of Fe, Mn, Zn, Cu, and increases Mo availability.
  • Boron is more available in coarse soils, and its deficiency is common in dry areas.
  • Antagonism effect affects micronutrient availability (e.g., Mn vs. Fe, Fe vs. Zn, Cu vs. Mo).

Boron:

  • The only non-metal among micronutrients.
  • Tourmaline is the main boron-containing mineral found in most soils.
  • Boron fixation is higher in fine-textured soils.
  • Borax (Na2B4O7.10H2O) is a boron source.
  • Indicator plants for boron deficiency include sunflower, cabbage, cauliflower, and sugar beet. Deficiency causes heart/crown rot in sugar beet and topsickness in tobacco.

Copper:

  • Copper deficiency leads to exanthema and dieback in citrus, and empty glumes in wheat.

Iron:

  • Structural constituent of pigments in microorganisms.
  • Various forms like Fe-EDTA, Fe-HEDTA, Fe-DTPA, Fe-EDDHA cater to different soil pH levels.
  • Deficiency causes white foliage in nurseries.

Manganese:

  • Legumes show manganese deficiency.
  • More prevalent in red soils.
  • Constituent of nitrite-reductase and hydroxylamine reductase.
  • Deficiency symptoms include “Pahala blight” in sugarcane and “Grey speck” in oats.
  • Paddy is highly susceptible to Mn deficiency, with symptoms appearing early on the third emerging leaf.
  • Mn toxicity is common in acid soils.

Molybdenum (Mo):

  • Molybdenite (MoS2), Wulfenite (PbMoO4), and Powellite (CaMoO4) are minerals containing molybdenum.
  • It is a constituent of “nitrate reductase.”
  • Deficiency leads to “whip tail” in cauliflower.
  • Molybdenosis, characterized by “teartness,” refers to the toxicity of molybdenum on animal health.

Zinc (Zn):

  • Zinc retention in soils compared to other cations follows the order: H > Zn > Cu > Mg > K.
  • Sphalerite (ZnS) is a mineral containing zinc.
  • Zinc is required for the synthesis of ‘tryptophan.’
  • It is a component of alcohol dehydrogenase and galactose oxidase enzymes.
  • Deficiency in rice leads to ‘khaira.’
  • Zinc deficiency causes ‘little leaf‘ in cotton and ‘white bud‘ in maize.
  • The critical pH range for zinc availability is 5.5 to 6.5.

Problem soils present various challenges that affect plant growth and crop productivity:

  1. Leaching is a significant issue in humid regions, while salt accumulation poses problems in arid and semi-arid areas.
  2. Soil becomes saline when annual evaporation exceeds precipitation.
  3. Beans are susceptible to damage from chloride in the soil solution under equal osmotic pressure, whereas sulfates do not harm crops.
  4. Grasses exhibit higher tolerance to chlorides compared to sulfates under equal osmotic pressure.
  5. At very high osmotic pressure, magnesium becomes more toxic than calcium and sodium.
  6. Acid soils, such as laterite and ferruginous red soils, hinder normal plant growth due to their high acidity.
  7. High soil acidity leads to the solubilization and toxic availability of aluminum, manganese, and iron.
  8. Bacteria and actinomycetes activity are adversely affected in acid soils, while fungi thrive in acidic pH.
  9. Most micronutrients are available in acid pH except molybdenum, which is deficient in leguminous crops.
  10. In saline soils, increasing osmotic pressure reduces water availability to plants.
  11. High exchangeable sodium in alkali soils reduces the availability of calcium and magnesium.
  12. Reclamation methods for problem soils include using good quality irrigation water for saline soils and gypsum, pyrites, and molasses for alkali soils.
  13. Salt-tolerant varieties of various crops have been developed to cope with problem soils.
  14. High seed rates and closer spacing are attempted under saline conditions compared to normal conditions.
  15. Ammonium sulfate and calcium ammonium nitrate (CAN) are preferred over urea in alkali soils.
  16. Leafhopper damage in alfalfa can sometimes be confused with boron deficiency.

Nutrient Deficiency Symptoms:

  • Yellowing or chlorosis can indicate deficiencies in nitrogen (N), magnesium (Mg), iron (Fe), and manganese (Mn).
  • Older leaves typically show signs of nitrogen and magnesium deficiency, while younger leaves are affected by iron and manganese deficiencies.
  • Molybdenum (Mo) deficiency in legumes may resemble mild nitrogen deficiency.

Soil Testing Methods:

  • Phosphate: Bray’s modified test
  • Potassium (K): Sodium cobaltinitrite test
  • Mehlich technique for available potassium oxide (K2O)
  • Cunninghamella plague method for phosphate (P)

 

indicator plant soil science

Indicator Plants:

  • Nitrogen (N): Cauliflower, cabbage
  • Potassium (K): Potato
  • Magnesium (Mg): Sorghum (CSH – 1)
  • Manganese (Mn): Rice (IR – 8)
  • Molybdenum (Mo): Tomato, cauliflower
  • Phosphorus (P): Rape seed
  • Calcium (Ca): Cauliflower
  • Zinc (Zn): Hybrid maize
  • Copper (Cu): Wheat
  • Boron (B): Hybrid maize, sunflower

Techniques:

  • Sunflower pot cultural technique for boron assessment
  • Sackett and Stewart technique (Azotobacter test for phosphorus (P) and potassium (K))
  • Mulder’s Aspergillus niger test for copper (Cu) and magnesium (Mg)
  • Fertility gradient approach of “Rammoorthy” for soil fertility assessment

Testing Nutrients in Soil:

  • To check nitrogen (N), we use a purple liquid called alkaline KMnO4.
  • For phosphate (P2O5), we use a solution made with baking soda.
  • To measure potassium oxide (K2O), we use another solution made with ammonium acetate.
  • We also check for organic carbon using a quick test.

Understanding Soil Science and Farming:

  • In dark soils, we calculate phosphorus levels differently based on how much clay is in the soil.
  • Cattle can get sick if they don’t get enough magnesium (Mg) from the grass they eat.
  • Plants might not get enough iron (Fe) during dry summers.
  • Some fruits like date palms and coconuts can handle salty soil.
  • We classify irrigation water into four groups based on how salty it is.
  • Dark blue liquid in plants might mean there’s too much nitrogen.
  • Potassium sticks to soil particles in three places.
  • Some fertilizers with lots of sulfates can stop plants from using a nutrient called molybdenum (Mo).
  • Water with too much boron can’t be used for farming.
  • The best mix of calcium (Ca) and magnesium (Mg) in soil is 7 parts Ca to 1 part Mg.
  • Some soils need a special boron compound to fix boron shortages.
  • Too much sodium in soil can make it hard for plants to grow.
  • Soybeans need a lot of calcium to grow well.
  • Nitrifying bacteria need calcium and phosphorus to survive.
  • Ferns need aluminum, and green algae like Scenedesmus need vanadium.
  • Certain soils can hold onto nutrients better than others.
  • Phosphorus helps plants grow when there’s not a lot of carbon around.
  • Potassium makes plants strong and helps them fight off diseases.
  • Scientists use a special method to see how much nutrients are in soil.
  • If plants are missing some nutrients, their leaves will show it first.
  • Putting organic stuff in soil can help keep phosphorus from disappearing.
  • Lettuce is often grown to test how good soil is for farming.
  • Manganese in soil is different depending on how acidic it is.
  • Zinc can turn into something else in certain soils and help crops grow better.

Manures and fertilizers are essential for keeping soil healthy and fertile:

1. Manuring:

  • This process improves soil fertility by adding nutrients in different forms.
  • Manures mostly come from organic sources like animal waste and plant residues.
  • Decomposing manures helps balance the carbon-to-nitrogen ratio to around 25:1.
  • Urine is a significant nitrogen source in farmyard manure (FYM).
  • Old and unhealthy animals produce FYM rich in nutrients.
  • Government farms and advanced countries often use the “byre system” to collect FYM.

2. Composting:

  • Composting is a way to turn organic materials into nutrient-rich manure quickly.
  • It involves accelerating the fermentation process under controlled conditions.
  • Earthworms like Eisenia foetida are sometimes used to speed up composting.
  • The ADCO method and the Bangalore method are popular composting techniques.
  • CuSO4 powder can be added to reduce bad odors caused by certain compounds in compost.

3. Sewage and Drainage:

  • Sewage refers to the wastewater taken out of cities, including night soil, through underground pipes.
  • Sewerage is the pipe system in cities used to drain wastewater.
  • Sullage is the wastewater from cities that doesn’t contain night soil, often drained through open channels.
  • Effluent is the liquid floating on top of drainage water after settling.
  • Sludge is the solid material that settles at the bottom of tanks containing drainage water.
  • Adding salts like FeCl2 and FeSO4 to drainage tanks can activate certain bacteria to help settle sludge.

4. Green Manure:

  • Green manure crops are grown to improve soil fertility when plowed into the ground.
  • The best time to incorporate green manure into soil is during flowering.

5. Binding Agents:

Tisdell and Oodes (Tisdell and Oodes are scientists who proposed a classification system for binding agents in soil.) identified three binding agents that help improve soil quality.

  1. Binding Agents:
  • Transient binding agents include substances like gums and mucilage.
  • Temporary binding agents are found in fine plant roots and fungal hyphae.
  • Persistent binding agents, along with substances like iron and aluminum oxides, act as permanent binding agents.
  • These binding agents help improve soil structure and stability.
  1. Daincha:
  • Daincha is a crop grown to break up hard, deep layers of soil.
  • It is not used as fodder and is suitable for sodic or alkali soils.
  1. Composting:
  • Pourdrette refers to a form of night soil.
  • The largest compost plant is located in Tel Aviv, Israel.
  • Bone meal is effective in soils with high iron and aluminum content.

Fertilizer Production Imp topic Soil science :

  • Continuous use of inorganic fertilizers can lead to soil salinity, known as exosmosis. This can be countered by adding organic materials.
  • Blood meal, obtained from drying blood, can be red or black depending on the drying method.
  • Guano, a fertilizer from seabird droppings, is treated with sulfuric acid to convert organic nutrients into inorganic forms.
  • Chile saltpeter (NaNO3) is a rich source of nitrate deposits.
  1. Nitrogen Fertilizers:
  • The Haber-Bosch process combines nitrogen (N2) and hydrogen (H2) under specific conditions to produce ammonia (NH3).
  • The source of atmospheric nitrogen (N2) is used in this process.
  • Different sources, like water or natural gas, are used to provide hydrogen (H2) for the process.
  • Ammonia contains 82% nitrogen (N).
  • Ammonium sulfate ((NH4)2SO4) is manufactured using processes like the coke oven gas process or the gypsum process.
  • It’s important to monitor ammonium sulfate for toxic impurities like thiocyanates.
  • Ammonium sulfate can create acidity in soil, requiring lime for neutralization.

Ammonium Chloride (NH4Cl):

  • Popular in Japan and Southeast Asia.
  • Prepared by direct neutralization process or dual salt process.
  • In the dual salt process, NH4Cl is salted out by NaCl using the common ion effect.

Calcium Ammonium Nitrate (CAN):

  • A mixture of NH4NO3 and CaCO3.
  • Fine granules coated with soapstone powder (MgSiO3) for improved flow and conditioning.

• Urea:

  • Contains nitrogen in organic, non-ionic (amide) form.
  • Used for 82% of nitrogen requirement in Indian crops.
  • At temperatures over 100°C, urea produces a toxic byproduct called biuret, which has less nitrogen.
  • Biuret content in urea should not exceed 1.5%, and for cattle feed, it should be less than 0.5%.

• Phosphorus Fertilizers:

  • Ammonical fertilizers are not recommended for acidic soil as they increase acidity.
  • Paddy prefers ammonical fertilizers as it uptakes nitrogen in the NH4+ form.
  • Phosphate added to soils is initially in the unavailable PO4^3- form, which converts to available forms like H2PO4^- and HPO4^2-.

• Rock Phosphate:

  • Primary minerals form magmatic rock phosphate, while teeth and bones form organogenic rock phosphate.
  • Morocco has significant organogenic rock phosphate deposits.
  • Rock phosphate is the primary raw material for phosphatic fertilizer production.
  • It is treated with H2SO4 to produce Single Super Phosphate (SSP) or with H3PO4 to produce Triple Super Phosphate (TSP).
  • H3PO4 can be directly used as a liquid fertilizer.

• Single Super Phosphate (SSP):

  • Produced by Dean process or continuous rock acidulation process.
  • Contains calcium dihydrogen phosphate (Ca(H2PO4)2) and gypsum.
  • Available in 14% P2O5 and 16% P2O5 (7% P) grades in India.

• Triple Super Phosphate (TSP):

  • Does not contain gypsum and is completely soluble in water.

• Basic Slag:

  • By product of the steel industry, also known as Thomas slag.
  • Used as a phosphorus fertilizer.

Pelophos: It’s a fertilizer made by enriching basic slag with rock phosphate. This mixture is sold under the trade name “Pelophos.”

Potassium Minerals:

  • Carnalite: A mineral containing potassium chloride and magnesium chloride.
  • Kainite: Another mineral with potassium chloride and magnesium sulfate.
  • Schoenite: Contains potassium sulfate and magnesium sulfate.
  • Sylvite: Pure potassium chloride.
  • Sylvinite: A mixture of potassium chloride and sodium chloride.
  • Langbeinite: A mineral consisting of potassium sulfate and magnesium sulfate.

Preparation Methods:

    • KCl Production: Mainly through a process called floatation.
    • K2SO4 Production: Made from minerals like langbeinite and sylvite using the Mannheim process.

Fertilizer Classification:

    • Complete Fertilizer: Contains all three major nutrients (N, P, K).
    • Multi-nutrient Fertilizer: Contains two nutrients.
    • Complex Fertilizers: Have a homogeneous composition, while mixed fertilizers have a heterogeneous one.

Specific Fertilizer Types:

    • Ammonium Phosphate: Commercially known as Factammophos.
    • Nitrophosphate: Sold under the trade name Suphala.

Bulk Blended Fertilizer (BBF): It refers to the practice of mixing straight fertilizers in large quantities.

Drillability: This term encompasses all properties affecting the flow of fertilizers through distribution equipment.

Crystallization and Mixing:

    • Crystal Knitting: It’s a process where new compounds form due to crystallization under pressure.
    • Double Decomposition: Refers to a reaction between two compounds without a common ion.

Choice of Fertilizers:

    • NH4+ fertilizers are preferred in neutral to slightly alkaline soils.
    • NO3- fertilizers are suitable for acidic soils (pH 5.0), while NH4NO3 works for soils with a pH range of 5-7.
    • KCl has a higher salt index compared to K2SO4.

Nutrient Availability and Soil pH:

    • Ca and Mg deficiencies are common in acidic soils, while S deficiencies occur in alkaline soils.
    • Calcium is essential for root development and is often referred to as a root developer.

Soil Management:

    • In delta regions, silt is indirectly added to the soil through the inundation of fields with floodwaters rich in silt, a process known as “wrapping.”

Please don’t overlook the PDF containing Soil science topics It’s included in the General Agriculture book by Agriguru, and it’s particularly crucial for IBPS AFO preparation. Be sure to download it to enhance your study material and boost your chances of success in the exam. Special thanks to agrilearner

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