Soil Science — Part 2 MCQs with Explanations

A developed soil or mature soil has three soil horizons whose physical, chemical, and biological characteristics differ from the layers above and beneath which help in nutrient supply and proper development of the plant. The A horizon is the top layer of the mineral soil horizons, often referred to as "topsoil." The B horizon is referred to as subsoil and consists of mineral layers which are significantly altered by pedogenesis. The C horizon is below the solum horizons. The C horizon is enriched with carbonates carried below the solum by leaching.

Alkali soils are clay soils with high pH. A poor soil structure and a low infiltration capacity. Alkali soils owe their unfavorable physio-chemical properties mainly to the dominating presence of sodium carbonate, which causes the soil to swell and difficult to settle. Alkali soils are very common in semi-arid and arid climates and cover more than 25% of the earth's surface.

The phosphorous solubilizing fungi are such fungi that can act on the phosphorous present in the organic matter of the soil and make it available for plant use. The isolated phosphate solubilizing fungi belonged to the genera of Aspergillus (55.69%), Penicillium spp. (23.35%) and Fusarium (9.8%). So, out of the given options, Aspergillus is phosphorus solubilizing fungi.

A solum (plural, sola) in soil science consists of the surface and subsoil layers that have undergone the same soil forming conditions. In terms of soil horizon designations, a solum consists of A, E and B horizons and their transitional horizons and some O horizons.

Stacking of bags needs to be done in a proper format, stack the bags evenly against at least two supporting walls. Supported stacking should be used whenever possible to ensure the maximum amount of stability. The height of a stack of bags should not be more than 20 bags.

Sea surface temperature or ocean surface temperature is the water temperature close to the ocean's surface. The range of sea surface varies between 1 millimeter and 20 metres below the sea surface. The mean sea surface temperature is around 23°C, but our ranges from more than 30 degrees Celsius in warm tropical regions to less than zero degrees Celcius at high altitudes.

Vermiculite is a group of colloids that have the highest cation exchange capacity by volume basis. Vermiculite is a hydrous phyllosilicate mineral that undergoes significant expansion when heated. It is formed by the weathering or hydrothermal alteration of biotite or phlogopite. It helps to aerate the soil while simultaneously retaining water and nutrients.

The availability of P 2 O 5 is maximum at neutral pH. P 2 O 5 is listed as 'available phosphate'. The sum of the water-soluble and citrate-soluble phosphate is considered to be the amount of phosphate available to the plant and is the amount guaranteed on the fertilizer label. In acidic soil, phosphorus reacts with iron and aluminum and makes it unavailable to plants. Soil with inherent pH values between 6 - 7.5 is ideal for the availability of P 2 O 5 . Whereas pH values below 5.5 and between 7.5 - 8.5 limit phosphorus availability.

The major form of boron absorbed by plants is H 3 BO 3 (boric acid). Boron is an essential plant nutrient required by plants for its proper growth and functioning. It plays an important role in regulating plants' hormone levels and promoting proper growth. It increases flower production and retention, pollen tube elongation and germination, and seed and fruit development.

CAN is calcium ammonium nitrate, also known as nitro-limestone or nitrochalk. It is a widely used inorganic fertilizer, accounting for 4% of all nitrogen fertilizers used. It is hygroscopic, and its dissolution in water is endothermic. It accounts for roughly 8% calcium and 21 - 27 % nitrogen. It is preferred for use on acidic soils. it is mainly useful as a Top dressing for fertilizer application.

Redox potential is a measure of the ease with which a molecule will accept electrons, which means that the more positive the redox potential, the more readily a molecule is reduced. The redox potential is stimulated by the variation of a specific biological nitrification or denitrification process. The value of redox potential for nitrification should be > + 250 mV.

Among the given options, Garnet is the chromium-containing mineral. It is a member of a group of common silicate minerals that have similar crystal structures and chemical compositions. It may be colorless, black and many shades of red and green. Garnet comprises a group of silicates with may contain calcium, iron, magnesium, manganese, aluminum, chromium and many more elements in traces.

Soil fertility gradient (SFG) is the spatial pattern of variability in soil. Fertility gradients were created by applying graded doses of fertilizer N, P and K on the strips. The experiment on the Fertility gradient was proposed and conducted by B. Ramamoorthy in 1967.

Approximately 10% of the total incoming solar radiation is absorbed by the soil and can be used to warm it. Whereas about 70% of the total incoming solar energy is absorbed by the Earth system or we can say our environment and the remaining 30% is reflected in space.

A catena in soil science is a series of distinct but co-evolving soils arrayed down a slope. A mature catena is in equilibrium as the processes of deposition and erosion are in balance. The catena concept originated in central Uganda, by chemist W. S. Martin to describe a hill slope sequence at the Bukalasa station. The term catena was first coined by scientist Geoffrey Milne to describe these soil-topography units.

Phosphorus (P) is considered a highly mobile element within plants. It moves easily from older tissues to younger tissues where it is needed for growth. This mobility is crucial for various physiological processes, including energy transfer and photosynthesis.

CAN is calcium ammonium nitrate, also known as nitro-limestone or nitrochalk. It is a widely used inorganic fertilizer, accounting for 4% of all nitrogen fertilizers used. It is hygroscopic, and its dissolution in water is endothermic. It accounts for roughly 8% calcium and 21 - 27% nitrogen. It is preferred for use on acidic soil, but it is not acid forming fertilizer as it contains Calcium.

The enzyme responsible for the hydrolysis of urea is Urease. It catalyzes the hydrolysis of urea, forming ammonia and carbon dioxide. It is found in numerous bacteria, fungi, algae, plants and some invertebrates and also in soils, as a soil enzyme. They are nickel-containing metalloenzymes of high molecular weight.

SSP is the most popular phosphatic fertilizer after Dap as it contains 3 major plant nutrients i.e. Phosphorus, Sulphur and Calcium along with traces of other micronutrients. Free phosphoric acid in both the SSP whether it is powdered or granulated is 4% maximum. Phosphoric acid yields more available phosphorus hence it can be directly used as a fertilizer.

The micronutrient needed in the smallest amount by the plant is Molybdenum . Molybdenum is an essential component in two enzymes that convert nitrate into nitrite and then into ammonia before it is used to synthesize amino acids within the plant. It is also required by symbiotic nitrogen fixing bacteria in legumes to fix atmospheric nitrogen. The normal range for most plant tissue is between 0.3 - 1.5 ppm.

Amphibole is a primary mineral having huge importance in terms of plant nutrition. It is a group of inosilicate minerals, form prism or needle-like crystals. Amphiboles are the primary constituent of amphibolites. It is a major group of hydrous minerals that occurs in a wide range of rock types.

X-ray diffraction analysis is based on Bragg’s law , which states that "when the X-ray is incident onto a crystal surface, its angle of incidence θ, will reflect with the same angle of scattering θ. It encompasses the superposition of wavefronts scattered by lattice planes, leading to a strict relation between wavelength and scattering angle, or else to the wave vector transfer concerning the crystal lattice.

Humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a soil organic matter rich in nutrients and retains moisture in the soil. The carbon and nitrogen ratio of humus is about 10 : 1. The carbon to nitrogen ratio is significant in composting because microorganisms need a good balance of carbon and nitrogen to remain active.

The youngest fully mature leaves of the main stem are used for tissue tests in the cotton plant because these are the growing cells and show the accurate status of nutrients in the plant. Tissue analysis shows if the crop is taking up the nutrients from the soil or through the tissue from a foliar application.

Fungi is the group of microorganisms that have the highest biomass in the soil. The maximum limit is up to 790 μg C/g soil and it is found in the soil with surface organic horizons in the form of thin moss/lichen litters, in which the development of fungal mycelium is most active.

Udolls is the suborder of Mollisols in soil taxonomy. They are divided into eight suborders: Albolls, Aquolls, Rendolls, Gelolls, Cryolls, Xerolls, Ustolls and Udolls. Mollisols are the soils of grassland ecosystems or cropland. They are characterized by a thick, dark surface horizon. Mollisols are among some of the most important and productive soils in the world.

SSP is the most popular phosphatic fertilizer after DAP as it contains 3 major plant nutrients i.e. Phosphorus, Sulphur and Calcium along with traces of other micronutrients. SSP is a grey to brownish coloured material containing monocalcium phosphate and calcium in almost equal proportions. It is the least hygroscopic but needs moisture-proof packing to avoid lump formation during storage.

The honeycomb structure is found in Phyllosilicate , also termed sheet silicates. The basic structure of the phyllosilicates is based on interconnected six-member rings of SiO 4 -4 tetrahedra that extend outward in infinite sheets. Three out of the 4 oxygens from each tetrahedral are shared with other tetrahedra.

Lateralization is the process of the accumulation of iron and aluminium oxides in the soil. It is also termed tropical weathering and is a prolonged process of chemical weathering that produces a wide variety in the thickness, grade, chemistry, and ore mineralogy of the resulting soils. Typical laterite is porous and claylike. It contains the iron oxides minerals goethite, HFeO 2 ; lepidocrocite, FeO(OH); and hematite, Fe 2 O 3 . It also contains titanium oxides and hydrated oxides of aluminum, the most common and abundant of which is gibbsite, Al 2 O 3 · 3H 2 O.

Triple super phosphate contains about 40 - 48% soluble monocalcium phosphate [(H 2 PO 4 ) 2 • H 2 O] . when it dissolves in water, its phosphorus is negatively charged (-1). TSP fertilizers are preferred as starter fertilizers for low soils. It can be used for all plants that are grown in soils with low or moderate phosphorus availability. When phosphorus is applied less than required or applied phosphorus has low efficiency due to soil conditions.

Soil gases are the gases found in the air space between soil components. The spaces between the solid soil particles, if they do not contain water, are filled with air. The primary soil gases are nitrogen, carbon dioxide and oxygen. Oxygen is critical because it allows for respiration for both plant roots and soil organisms. The percentage of oxygen in the soil air is about 20.6.

Nutrient uptake is the amount of each nutrient required for the crop to complete its life cycle at a given yield level. The rate of nutrient uptake is independent of the rate of water uptake, but the concentrations of nutrients at root surfaces depend strongly on soil water content. Nutrient uptake by crops is fastest during Active growth.

Nitrosomonas and Nitrobacter are chemoautotrophic organisms found in soil and water and are responsible for the oxidation of ammonium to nitrite by Nitrosomonas and nitrite to nitrate in the presence of Nitrobacter. These are obligate autotrophs that can obtain energy only by the oxidation of inorganic substrates and that cannot assimilate simple organic substrates, such as acetate, in the same way as carbon dioxide.

In tree crops, fertilizer is not added near the trunk because of the presence of fewer roots in that area. When it comes to fertilizing trees arborists often recommend deep root fertilization. Deep root fertilization is a specialized application method used to help restore trees that are struggling or showing signs of decline, it also improves soil aeration.

Sedentary soil is soil remaining on the rock from which it has developed or on which they are situated. Black soil is an example of sedentary soil. Black soils are mineral soils that have a black surface horizon, enriched with organic carbon. It is the third major group of soil found in India.

Geological erosion is also known as Natural erosion. It is the action of surface processes that removes soil, rock or dissolved material from one location of the Earth’s crust, and then transports it to another where it is deposited by the action of wind or water. The geological type of erosion contributes to the formation of soils and their distribution on the earth's surface.

Ultisols are strongly leached, acid forest soils with relatively low native fertility. They are found primarily in humid temperate and tropical areas of the world. Alfisols are moderately leached soils that have relatively high native fertility. These are primarily found in temperate humid and subhumid regions of the world. Alfisols have at least 35% base saturation, meaning calcium, magnesium, and potassium are relatively abundant. This is in contrast to ultisols, which are the more highly leached forest soils having less than 35% base saturation. That means Ultisol is comparable with alfisol except for having low BS% where BS is base saturation.

Fe-EDDHA is the Fe-chelate suitable for application to crops grown on calcareous soils. This chelated iron helps in correcting iron deficiency in flowers, vegetables, shrubs, and trees. EDDHA is a chelate that protects nutrients against precipitation in a wide pH range of 4 - 9. And the availability of iron to plants is reduced through preci[piatation of iron at high pH, or by high concentrations of phosphorus.

Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. It is a common material, making up to 45% of average modern mud, found in many river deltas and as wind-deposited accumulations. Silt is made up of rock and mineral particles that are larger than clay but smaller than sand. It ranges from 0.002 to 0.05 mm in diameter.

FYM stands for Farmland Manure and is an important organic resource for agricultural production in livestock-based farming systems in the semi-arid tropics of India. It contains well-decomposed farmyard manure with 0.5% nitrogen, 0.2% P 2 O 5 and 0.5% K 2 O .