The Role of Fertilizers

The role of fertilizers

Refer to the Chemical Industries Resource Pack for more information.

Plants are only able to absorb nutrients from the soil when they are dissolved in water so that their root systems can absorb the nutrients. Nitrogen gas (\(\text{N}_{2}\)) for example, cannot be absorbed in the gas form, and needs to be changed into an ion that is soluble in water, for example the nitrate ion (\(\text{NO}_{3}^{-}\)). In the same way phosphorus is absorbed as phosphate ions (\(\text{PO}_{4}^{3-}\)).

Plants will grow best in soil that is able to provide sufficient nutrients to them. Natural processes, like the nitrogen cycle, replace nutrients in the soil. However, these natural processes of maintaining soil nutrients take a long time. As populations grow and the demand for food increases, the soil has to supply nutrients faster than the natural processes can sustain. This places more and more strain on the soil to be able to produce a crop.

Often, cultivation practices don’t give the soil enough time to recover and to replace the nutrients that have been lost. Today, fertilizers play a very important role in restoring soil nutrients so that crop yields can stay high. Some of these fertilizers are organic (e.g. compost, manure and fishmeal), which means that they started off as part of something living. Industrial (commercial) fertilizers are inorganic (for example ammonium nitrate (\(\text{NH}_{4}\text{NO}_{3}\)) or super phosphates (\(\text{Ca}(\text{H}_{2}\text{PO}_{4})_{2}\)) and have the advantage of being in a soluble form that can be absorbed by a plant immediately.

fertilizers usually provide the three major plant nutrients (nitrogen, phosphorus and potassium). fertilizers are in general applied to the soil so that the nutrients are absorbed by plants through their roots.

Examples of (a) organic (compost) and (b) inorganic (industrially made) fertilizers indicating the NPK ratio that will be discussed later. Photos by Kessner Photography on wikipedia and Elvera Viljoen in the UCT Chemical Engineering Chemical Industries Resource pack.