Classification of Minerals

As a traveller moving through different landscapes, you may have noticed that plants are never entirely alike - some grow lush with vivid leaves, flowers and fruit, while others nearby look stunted, discoloured or diseased, showing symptoms such as altered leaf texture, stunted growth, chlorosis (yellowing) or necrosis (tissue death). These symptoms can trace back to microbial infection, climatic stress, or a shortage of essential minerals - the subject of this chapter, which covers how minerals are classified, their functions, the deficiency diseases and symptoms they cause, nitrogen metabolism, and the special modes of nutrition some plants rely on, along with what these ideas mean for improving agricultural productivity. Plants draw their nutrients from the atmosphere, water and soil. Carbon, hydrogen and oxygen, obtained from air and water rather than soil, are called skeletal or non-mineral elements and together make up roughly 94% of a plant's dry weight, forming the backbone of its carbohydrates, fats and proteins. Every other element a plant needs is drawn from the soil as a mineral nutrient, though not every mineral present in a plant is actually required by it. To settle which minerals genuinely count as essential, Arnon and Stout (1939) proposed four criteria: the element must be necessary for growth and development; it must play a direct metabolic role rather than merely a side effect; no other element can substitute for it; and its absence must make it impossible for the plant to complete its vegetative or reproductive life cycle.