The plant takes up nutrients in the soil through its roots and in particular its root hairs. To be taken up by a plant, a nutrient element must be located near the root surface; however, the supply of nutrients in contact with the root is rapidly depleted within a distance of ca. 2 mm.
There are three primary mechanisms whereby nutrient ions dissolved in the soil solution are brought into contact with plant roots.
- Mass flow of water
- Diffusion within water
- Interception by root growth
All three mechanisms operate simultaneously, but one mechanism or another may be most important for a particular nutrient. For example, in the case of calcium, which is generally plentiful in the soil solution, except when aluminum over-competes for calcium on cation exchange sites in very acid soils.
