Question

Consider the following zones :

Which of these does not relate to the zone of aeration in the soil profile?

• A. 1 and 2
• B. 2 and 3
• C. 4 only
• D. 1 only

Answer 1

The correct option is D 1 only

(i) Soil-water zone: The soil-water zone extends from the ground surface down upto the major root zone. The soil in this zone becomes saturated either during irrigation or when rainfall occurs. However, the soil in this zone remains saturated only for a short duration after irrigation or rainfall, because the excess water drains through the soil under the influence of gravity. The excess water which cannot be retained by the soil is known as gravitational water.

(ii) Intermediate zone: The intermediate zone extends from the lower edge of the soil-water zone to the upper limit of the capillary zone. This zone usually contains non-moving vadose water which is held by molecular and surface tension forces in the form of hygroscopic and capillary water.

(iii) Capillary zone: The capillary zone extends from the water table upto the limit of capillary rise of water. This pore space may be considered to represent a capillary tube and hence just above the water table almost all pores contain capillary water which constitutes this zone.

(iv) Saturation zone: In the zone of saturation all the interstices are filled with water under hydrostatic pressure. The zone of saturation is bounded at the top by either a limiting surface of saturation called a water table or overlying impermeable strata and extends down to underlying impermeable strata.