Introduction

Plant growth and development depends on nutrients derived from the soil or air, or supplemented through fertilizer.  There are eighteen essential elements for plant nutrition, each with their own functions in the plant, levels of requirement, and characteristics.  Nutrient requirements generally increase with the growth of plants, and deficiencies or excesses of nutrients can damage plants by slowing or inhibiting growth and reducing yield.  Many deficiencies can be recognized by observing plant leaves.