Plants require nutrients in order to grow, develop and complete their life cycle. The supply of nutrients to the plants should be balanced in order to maximize the efficiency of the individual nutrients so that these meet the needs of the particular crop and soil type.
Carbon, hydrogen and oxygen, which, together with nitrogen, form the structural matter in plants, are freely available from air and water. Nitrogen, phosphorus and potassium, on the other hand, may not be present in quantities or forms sufficient to support plant growth. In this case, the absence of these nutrients constitutes a limiting factor.
Although plants receive a natural supply of nitrogen, phosphorus and potassium from organic matter and soil minerals, this is not usually sufficient to satisfy the demands of crop plants. The supply of nutrients must therefore be supplemented with fertilizers, both to meet the requirements of crops during periods of plant growth and to replenish soil reserves after the crop has been harvested. Reserves of nitrogen in soil organic matter may be broken down and released into the soil solution (mineralization). This in turn, are depleted by growing crop plants and removed at harvest. After the growing season, mineralization continues, and may result in the leaching of nitrate nitrogen from the soil solution. Certain microbes in the soil can destroy nitrate (de-nitrification), releasing nitrous oxide and returning nitrogen gas to the air.
Source: EFMA
