Hint: Humus is a black or brown complex variable substance that forms the organic component of soil after partial decomposition of plant or animal matter.
A fertile soil would contain all of the primary nutrients needed for essential plant nutrition (like phosphorus, nitrogen, and potassium) and also other nutrients in smaller amounts (e.g., calcium, magnesium, sulphur, iron, zinc, copper, boron, molybdenum, nickel).
Humus provides a variety of nutrients and minerals that are beneficial to soil quality, the most important of which is nitrogen. Nitrogen is particularly essential for plant growth because it is mainly responsible for vegetative growth and is a plant protein component. Humus, in particular, is composed of about 60% carbon, 6% nitrogen, and minimal quantities of phosphorus and sulphur. It helps in examining soil fertility by acting as a storehouse for important plant nutrients.
One of the essential functions of humus is improving soil aeration, infiltration, and drainage by making the soil more porous. Humus less soil may become highly compacted and airless, forming tough crusts that prevent rain, air, or water penetration and also seedling emergence. Humus strengthens the composition of the soil, and humus-rich soil, along with humus' ability to hold essential nutrients, allows plants to grow more quickly.
Both Assertion and Reason are proper, and Assertion is explained correctly by the given Reason.
Therefore, the correct answer is option ‘A’.
Note: Laterite soil has a low humus content and is located in areas with high temperatures and heavy rainfall. The decomposers or bacteria in the soil are killed by elevated temperatures, resulting in lower humus content.