Soil Types of India — Set 4

Correct Answer: C. Loam

Loam is considered the ideal soil texture for agriculture because it has a balanced mix of sand, silt, and clay particles. This balance gives loamy soil good drainage while also retaining enough moisture and nutrients for plant growth. Loam has good aeration and allows roots to penetrate easily. Most fertile agricultural soils, including alluvial soils, tend to have a loamy texture.

Correct Answer: C. Clayey soil

Clayey soil has the highest water-holding capacity among soil textures due to the small size of clay particles and their high surface area. The numerous tiny pores between clay particles hold water by capillary action. However, excessive clay can cause waterlogging and poor aeration. The ideal situation is loamy soil, which has good water-holding capacity without becoming waterlogged.

Correct Answer: B. Sand < Loam < Clay

The correct order of water-holding capacity from lowest to highest is: Sand < Loam < Clay. Sandy soils have large particles with large pores that allow water to drain quickly. Loam has medium-sized pores that balance drainage with water retention. Clay soils have the smallest particles with tiny pores that hold water strongly through capillary forces.

Correct Answer: B. Decomposed organic matter that improves soil structure and nutrient content

Humus is the dark, stable organic matter formed by the decomposition of plant and animal matter in soil. It improves soil structure by binding particles together into aggregates, which improves aeration and water retention. Humus slowly releases nutrients as it decomposes, providing a sustained supply of nitrogen, phosphorus, and other elements. It also acts as a buffer, stabilizing soil pH and supporting microbial life.

Correct Answer: C. 6.0-7.0 (slightly acidic to neutral)

The ideal pH range for most agricultural crops is between 6.0 and 7.0, which is slightly acidic to neutral. Within this range, most essential nutrients are readily available to plants. At very low pH (acidic), aluminium and manganese can become toxic to plants. At very high pH (alkaline), micronutrients like iron, zinc, and manganese become insoluble and unavailable to crops.

Correct Answer: C. Acidic soil

A soil pH below 7 indicates acidic soil conditions. pH is measured on a scale of 0 to 14, with 7 being neutral, values below 7 being acidic, and values above 7 being alkaline. Laterite soils and Forest/Mountain soils in India tend to be acidic. Acid soils can be treated with lime (calcium carbonate) to raise the pH and improve crop productivity.

Correct Answer: C. O horizon

The O horizon (O for organic) is the topmost layer of a soil profile and consists mainly of freshly deposited and partially decomposed organic matter such as leaves and plant residues. Below it is the A horizon, which is the true topsoil. The soil profile from top to bottom consists of O, A, B, C, and R horizons. The O horizon is best developed in forest soils where organic matter accumulates continuously.

Correct Answer: A. The zone of maximum leaching and eluviation

The A horizon, also called the topsoil, is the zone of maximum leaching and eluviation where water and dissolved minerals move downward. It is rich in organic matter and biological activity and is the most important layer for plant growth. The A horizon is dark in colour due to organic matter content. It is the most weathered and biologically active zone in the soil profile.

Correct Answer: C. Zone of illuviation or subsoil

The B horizon is called the zone of illuviation or the subsoil, where materials leached from the A horizon (such as clay, iron, and aluminium oxides) are deposited. It is typically denser and less organic than the A horizon. Plant roots penetrate the B horizon to access water and minerals during dry periods. The B horizon is important for understanding soil formation and fertility.

Correct Answer: C. Partially weathered parent material

The C horizon consists of partially weathered parent material from which the soil above has formed. It is located below the B horizon and is less weathered than the overlying soil layers. The C horizon has few organisms and limited biological activity. It transitions gradually to the R horizon (bedrock) below it.