Gypsum is a naturally occurring mineral with the chemical formula CaSO4·2H2O. It serves as an important source of calcium and sulphur for plant nutrition. The sulphur content in pure gypsum is approximately 18%. Beyond its role as a fertilizer, gypsum is widely used in agriculture to improve soil structure, particularly in sodic soils, by replacing exchangeable sodium with calcium, thereby enhancing water infiltration and root growth.

Electrical conductivity (EC) is a standard measure of soil salinity, reflecting the concentration of soluble salts. In the classification of salt-affected soils, alkaline (or sodic) soils are characterized by high exchangeable sodium percentage but typically maintain an EC of less than 4 dS/m. This metric is crucial for assessing soil health, nutrient availability, and water management strategies.

Environmental science is an interdisciplinary field that integrates natural sciences to address environmental challenges. It encompasses the study of physical, chemical, biological, social, and economic factors that constitute the surroundings of living organisms. By combining these diverse perspectives, the field provides a comprehensive, quantitative approach to understanding environmental systems, human impact, and the complex interactions between humanity and the natural world.

A pedon is defined as the smallest sampling unit that displays the full range of genetic horizons and properties of a particular soil body. It is a three-dimensional volume, typically ranging from 1 to 10 square meters in surface area. When multiple pedons with similar characteristics are found together in a landscape, they are collectively referred to as a polypedon, which serves as the basis for soil mapping and classification.

Specific gravity is defined as the ratio of the density of a substance to the density of water at a reference temperature, typically 4 degrees Celsius. For concentrated sulfuric acid of analytical reagent (AR) grade, the density is approximately 1.84 grams per cubic centimeter, which corresponds to a specific gravity of 1.84. This high density is a characteristic property of concentrated mineral acids used in laboratory and industrial applications.

Pegmatitic rocks are igneous rocks with exceptionally large crystals, typically greater than 1 cm in size. This coarse-grained texture occurs because the magma cools very slowly in a water-rich environment, allowing ions to migrate and form large mineral crystals. This is distinct from plutonic rocks, which are generally coarse-grained but not necessarily of pegmatitic size.

Alkali soils, also known as sodic soils, are characterized by a high concentration of exchangeable sodium and a high pH. Sodium carbonate (Na2CO3) is the primary salt responsible for these conditions. Its hydrolysis leads to the formation of hydroxyl ions, which increase the soil pH and cause dispersion of soil colloids, resulting in poor soil structure and reduced permeability.

Plants absorb sulphur primarily in the form of sulphate ions (SO4^2-), often written as SO-2 in shorthand. This inorganic form is soluble in soil solution and is readily taken up by plant roots to synthesize essential amino acids like cysteine and methionine.

The C:N ratio is a critical factor influencing the microbial decomposition of organic matter in soil. Microorganisms require nitrogen to build their cellular structures during the breakdown of carbon-rich materials. When residues have a wide C:N ratio, nitrogen becomes a limiting factor, forcing microbes to scavenge nitrogen from the soil, which significantly slows down the decomposition process compared to residues with a narrower, more balanced C:N ratio.

A gypsum block is an indirect sensor used to estimate soil moisture by measuring the electrical resistance between two internal electrodes. As the soil dries, the water content within the gypsum block decreases, increasing its electrical resistance. These blocks are most effective for monitoring soil water potential within the range of 1 to 15 bars, which corresponds to the typical range of plant-available water in many soil types.