Nutrients must come in contact with the root surface in order to be absorbed by the root. There are three ways in which soil nutrients can reach the root surface: diffusion, mass flow and root interception.
The movement of nutrients in the soil solution along a concentration gradient. As crops take up nutrients, an area of lower nutrient concentration is created around the root zone. Nutrients then move from areas of higher concentration outside the root zone into the root zone along this concentration gradient.
The movement of nutrients in soil solution to the surface of the roots through the flow of water.The flow of the water is a result of wetting and drying or transpirational water uptake by the plants. The rate at which nutrients are taken up by mass flow is determined by the water in the soil and by the amount of water being taken up by the crop.
The movement of roots through the soil and the absorption of nutrients as the roots
come in contact with nutrients. Nutrient uptake by root interception is enhanced by a growing root system and by mycorrhizal infections.
Mass flow and diffusion supply a significant portion of the macronutrients to the root surface, but are negatively influenced by a number of soil factors, such as clay content and moisture levels. Clay can prevent the easy movement of nutrients into the soil solution, thus preventing the movement of nutrients to the root surface. Low moisture levels leads to reduced transpiration by crops, meaning that less water is taken up from the soil and therefore less nutrients.