Which transport process is driven by the bulk movement of water carrying dissolved substances through the soil?

• A. Diffusion
• B. Osmosis
• C. Capillary rise
• D. Mass flow

Answer: (D)

The main idea is that nutrients move with the water itself as it flows through the soil. This bulk movement of water transports dissolved substances along with it, a process known as mass flow. It’s driven by water fluxes from rainfall, infiltration, drainage, and plant water uptake, so nutrients carried in the moving water are delivered to roots and redistributed with the water that moves through the soil profile.

This differs from diffusion, which is the spreading of solutes from areas of higher concentration to lower concentration due to random molecular motion, not because the water is moving as a bulk. Osmosis involves water moving across a semi-permeable membrane to balance water potentials, not the general transport of dissolved nutrients through soil. Capillary rise describes water moving upward in small pores due to capillary forces, which explains some upward water movement but does not define the main mechanism by which dissolved substances are transported with the bulk flow of soil water.