Part III: Theoretical background 12 Plant nutrients The elements that plants need to survive are called nutrients. Nutrients are usually adsorbed from the soil solution in the form of ions. Ions are dissolved salts (nutritive salts) that have an electrical charge. | Part III Theoretical background 12 Plant nutrients The elements that plants need to survive are called nutrients. Nutrients are usually adsorbed from the soil solution in the form of ions. Ions are dissolved salts nutritive salts that have an electrical charge. Positively charged particles are called cations . ammonium NH4 and negatively charged particles are called anions . nitrate NO3- phosphate H2P04- . These ions will be mentioned again later. The nutrients that a plant requires to progress through an entire growth cycle are called the essential nutrients. A deficiency of any one of these will have consequences for the plant such as limited growth or a lack of flowers seeds or bulbs. In addition to the essential nutrients plants absorb other nutrients that they do not need . sodium Na or that can even be harmful . aluminium Al or manganese Mn . Plants do not need equal amounts of each nutrient. For this reason the essential nutrients are divided into two groups. The macro-nutrients which plants need large amounts of carbon C hydrogen H oxygen O nitrogen N phosphorus P potassium K calcium Ca sulphur S magnesium Mg The micro-nutrients which plants need only small amounts of iron Fe manganese Mn Contents 55 boron B zinc Zn copper Cu molybdenum Mo The functions of the macro-nutrients will be discussed briefly below. The micro-nutrients are just as important for the plant but they are needed in such small amounts that a deficiency of one or more of them occurs only in special circumstances. The macro-nutrients Nitrogen Nitrogen is an important building block of proteins in the plant. It promotes the growth of stalks and leaves. With sufficient nitrogen the leaves become big and succulent with insufficient nitrogen the plant s growth is severely inhibited and its leaves are small and fibrous. Nitrogen is also needed for the green colour of the plant. If a deficiency of nitrogen occurs the older leaves turn pale-green to yellow and the young leaves .
