Soil Science - Study Mode

[#616] The solum is comprised of
Correct Answer

(A) A, B and E horizons

Explanation

Solution: The solum (plural-sola) in soil science consists of the surface and subsoil layers that have undergone the same soil-forming conditions. The base of the solum is the relatively unweathered parent material. A surface layer that is 10 cm thick overlying bedrock can be called a solum. The solum is comprised of A, B and E horizons.

[#617] A-horizon of the soil is also known as
Correct Answer

(D) Top soil

Explanation

Solution: The A horizon is the top layer of the mineral soil horizons, often referred to as ‘top soil’. This layer contains dark decomposed organic matter, which is called "humus." A horizon contains less clay or pedogenic oxides. The A is a surface horizon, which is the home for various microorganisms as well as earthworms, thus it is the zone in which most biological activity occurs.

[#618] Lignin theory is given by
Correct Answer

(A) Waksman

Explanation

Solution: Lignin's theory is given by Waksman in 1932 . According to this theory, lignin is incompletely utilized by microorganisms and the residuum becomes part of the soil humus. Modification in lignin includes loss of methoxyl groups with the generation of o-hydroxy phenols and oxidation of aliphatic side chains to form COOH groups. The modified material yield first humic acids and then fulvic acids. This pathway is exemplified by Waksman’s lignin-protein theory .

[#619] Puddling is possible when clay % is
Correct Answer

(C) > 20%

Explanation

Solution: Puddling refers to the tillage system, in which the soil is repeatedly plowed and harrowed under submerged conditions, to make it soft for transplanting and less permeable to water. It decreases the macroporosity of clay soils and increases their microporosity thereby causing an increase in the water-holding capacity of the puddled soil. Puddling is possible when clay % is greater than 20%.

[#620] The maximum concentration limit of urea for spraying is
Correct Answer

(C) 4%

Explanation

Solution: Urea is the most important nitrogenous fertilizer in the country because of its high N content (46%), which is required for the growth and development of the crop. The maximum concentration limit of urea for spraying is 4%. Concentration should always be kept in mind before spraying any insecticide or fertilizer as excess may harm to an extreme extent the crops.