Why do clay soils need more water than other soils?

Why do clay soils need more water than other soils?

• A. Water is held more tightly by the small pores
• B. They drain slowly
• C. They have large pores
• D. They require more sun

Answer: (A)

Clay soils need more water because their very small pore spaces hold onto water more tightly. The tiny pores create strong capillary forces and a large surface area on clay minerals, so water molecules cling to the particle surfaces and within those pores. That means a larger portion of the water in clay soil is held in a form that is not easily available to plant roots. As a result, to keep the root zone properly moist, you typically need to apply water more frequently or in additional amounts to overcome this strong binding. The other ideas don’t fit as well: slowly draining is true for clay, but it doesn’t directly explain needing more water; having large pores is the opposite of what clay has; and sun exposure doesn’t determine how much water the soil can hold.

Clay soils need more water because their very small pore spaces hold onto water more tightly. The tiny pores create strong capillary forces and a large surface area on clay minerals, so water molecules cling to the particle surfaces and within those pores. That means a larger portion of the water in clay soil is held in a form that is not easily available to plant roots. As a result, to keep the root zone properly moist, you typically need to apply water more frequently or in additional amounts to overcome this strong binding.

The other ideas don’t fit as well: slowly draining is true for clay, but it doesn’t directly explain needing more water; having large pores is the opposite of what clay has; and sun exposure doesn’t determine how much water the soil can hold.