GK
SOIL AND AGRICULTURE
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Clay and humus
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Gravel and sand
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Sand and calcium
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Silt and earthworms
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Detailed explanation-1: -Such soils are compact with good hydration, but little aeration; chemically they are very fertile, because of rich mineral content. Rich mineral content of black soils is due to clay, which adsorbs minerals on its surface. Clay and humus produce colloidal complex for holding water and ions and forming soil crumbs.
Detailed explanation-2: -Topsoil is dark in color because it consists mainly of decomposed organic material which makes up the substance known as humus.
Detailed explanation-3: -The thick brown or black substance that remains after most of the organic litter has decomposed is called humus. Earthworms often help mix humus with minerals in the soil. Humus contains many useful nutrients for healthy soil. One of the most important is nitrogen.