Soil Science and Fertilizers

Fertilizers require essential nutrients: nitrogen, phosphorus (as phosphate), and potassium (potash). Apatite provides phosphate (P), sylvite provides potassium (K). Gypsum is calcium sulfate used in plaster, halite is table salt (NaCl), calcite is in cement, and cassiterite/albite are not fertilizer minerals.

Both green manure (decomposing plant material turned into soil) and biofertilizers (microbial inoculants that enhance nutrient availability) are biological materials used to maintain and improve soil fertility. Bioinsecticides control pests but do not directly enhance soil fertility.

Trees derive approximately 90% of their biomass from atmospheric carbon dioxide through photosynthesis, not from soil nutrients. This scientific fact surprises many people. Only about 10% comes from soil minerals and water. The massive trunk, branches, and leaves are mostly built from carbon extracted from air CO2, not from soil.

Onions get their smell from sulfur compounds they synthesize, not by 'soaking up sulfur from soil.' They produce these compounds through their own metabolic processes.

Both green manure and biofertilizers are biological materials used to enhance soil fertility. Green manure involves growing plants and plowing them back into the soil, while biofertilizers contain living microorganisms that fix nutrients. Bioinsecticides are used for pest control, not soil fertility.

Earthworms improve soil fertility through burrowing, which aerates the soil and enhances water infiltration. Their digestive process converts organic matter into nutrient-rich castings (vermicast) that boost soil nutrient content and structure. Beetles and roundworms don't contribute to soil fertility in the same way, while ringworm is actually a fungus that causes infection.

Humus is the correct botanical term for decayed organic matter in soil. It's dark, nutrient-rich material formed by decomposed plant and animal matter.

Plants absorb nitrates (NO3-) from soil through their roots and reduce them to form free nitrogen (N2) as part of their metabolic processes. They do not convert nitrates to urea (animal waste), ammonia (intermediate form), or directly to proteins (which are built from amino acids).

"Compost" is a mixture of decaying organic matter, such as leaves and manure, used to fertilize soil. Distractors like "small stream" (brook) are incorrect.

An exigency refers to an urgent need, pressing situation, or emergency that requires immediate attention or action. It's derived from 'exigent' meaning demanding. The other options are completely unrelated - option B describes manure/compost, C describes plant anatomy (a leaf whorl), and D simply means excessive or too much.

Organic food is defined by being grown without synthetic chemicals. "Without" is the only preposition that clearly indicates the absence of inorganic substances. "Except" would imply they are used in some cases, which contradicts organic principles. "Rather" and "instead" don't convey the necessary meaning of absence in this context.

India has no significant domestic potash reserves and must import 100% of its potash fertilizer requirements. Unlike nitrogen and phosphatic fertilizers where India has some domestic production capacity, potash dependence is complete.

This is the correct option as this statement is false. The survival of all the living things is dependent on each other.

A mulch is a layer of material applied to the surface of an area of soil. Its purpose is to conserve moisture and to improve the fertility and health of the soil. A mulch is usually but not exclusively organic in nature. This is not a FYM.

This is the correct option. Plants get some nutrients like nitrogen, chlorine and phosphorus from the soil.