Question

When a small amount of garden soil is put into a glass jar containing water, stirred and allowed to stand for two hours, the layers from top to bottom would be
A. Debris, water, sand and clay
B. Humus, water,clay and sand
C. Debris, clay, gravel and sand
D. Humus, clay,gravel and sand

Answer 1

Hint: Soil is a layer of complex mixture that covers the earth’s surface formed by the weathering of rocks. It mainly consists of mineral particles, air, organic material, water and living organisms which interact with each other.

Complete Answer:
- The soil consists of air and organic matter, but mostly mineral particles. There are three kinds of soil minerals available namely: sand, silt and clay. Its texture dictates the relative percentage composition of these particles in the soil.
- The largest soil particles (0.4 to 0.01 diameter) and the largest pores between particles are found in sand. Silt soil particle size ranges from 0.01 to 0.0001-inch diameter between clay and sand. Silty soil characteristics are similar to those of clay, but are moderated by the size of the larger particles.
- Clay soil has the tiniest particles of soil i.e., less than 0.0001-ich in diameter and the least amount of space between particles in water and air.
- Humus is a dark, organic substance that occurs when the matter of plants and animals decays in the soil. When much of the organic litter has decomposed, the thick brown or black layer that remains is called the humus. Humus present in soil makes it more fertiles and prevents plant diseases. The soil crumbles when humus is added to it. Movement of air and water will be eased in the loose soil. Therefore, because its scale is maximum, humus settles at the topmost and sand the lower.

Therefore the correct answer is (b) Humus, water, clay and sand.

Note: There is usually a confusion between humus and manure. Humus is made of decomposition of plants that improves the soil structure and creates a quality tilth by clumping the soil particles. Addition of humus improves the quality of clay and sand. Manure is rich in organic material. It also improves the soil structure but not as much as humus. Addition of manure helps to retain the water and nutrients in soil. Humus is low in nutrient content compared to manure.