Topsoil contains which of the following?
(a) Humus and living organisms only.
(b) Humus and soil particles only.
(c) Humus, living organisms, and plants.
(d) Humus, living organisms, and soil particles

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Detailed Solution

Soil not only supports vegetation but also plays a key role in the pedosphere, where it interacts with climate (water, air, temperature), soil organisms (microbes, plants, animals), organic residues, mineral material, and the surrounding landscape.

As soil forms, its profile gradually deepens and develops distinct layers called horizons. The topmost horizon is usually dark brown in color due to the high content of humus. Humus is produced by the decomposition of dead and decaying organic matter with the help of soil bacteria, mixed with soil particles. This fertile layer is typically 2 to 8 inches deep.

In earlier times, agronomists viewed soil mainly as a medium for crop productivity, focusing on its chemical, physical, and biological properties. Meanwhile, pedologists and geologists studied soil in relation to landscape character and history. Today, both approaches are integrated in the fields of landscape and environmental sciences.

Correct Answer: Humus, living organisms, and soil particles.

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