Fertilisers

Ensuring adequate levels of mineral nutrients is important to maintaining the health and vigour of plants. Plants need 17 essential elements for proper growth and development. Three of these elements (carbon, hydrogen and oxygen) are provided by air and water; the remaining elements are provided by soil. Each essential element

Plants need 17 essential elements for proper growth and development. Three of these elements (carbon, hydrogen and oxygen) are provided by air and water; the remaining elements are provided by soil.

Each essential element fulfils one or more critical physiological functions in plants. If plants are not able to take up adequate amounts of essential elements, their growth will be reduced and they may show visible signs deficiency such as chlorosis (yellowing) or necrosis (dead areas in leaves). Nutrient deficiencies may be caused by an inadequate supply of nutrients in the soil or, in some cases, by reduced nutrient availability associated with other factors, often high soil pH. Nutrient elements that are needed in the largest quantities are termed macronutrients. Micronutrients, in contrast, are elements needed in very small or trace amounts. When analytical laboratories run a foliar analysis to determine the chemical composition of leaves, macronutrients are usually expressed as a percent (%) of leaf dry weight, whereas micronutrients are expressed in parts per million (ppm).

Nutrient deficiencies may be caused by an inadequate supply of nutrients in the soil or, in some cases, by reduced nutrient availability associated with other factors, often high soil pH. Nutrient elements that are needed in the largest quantities are termed macronutrients. Micronutrients, in contrast, are elements needed in very small or trace amounts. When analytical laboratories run a foliar analysis to determine the chemical composition of leaves, macronutrients are usually expressed as a percent (%) of leaf dry weight, whereas micronutrients are expressed in parts per million (ppm).

Nitrogen deficiencies may occur in plants since it is the element that is needed in the largest amounts, yet it is lost from the soil over time through leaching. Also, raking and removing leaves each fall interrupts the natural re-cycling of nitrogen that occurs in native forests. Iron and manganese deficiencies are common in specific landscape trees and are associated with alkaline soil pH. In both cases, soils may contain adequate amounts of the element, but availability and uptake are reduced by alkaline soil conditions.

Visual symptoms. Certain nutrient deficiencies can be identified by characteristic symptoms. Nitrogen deficiencies are often characterized by leaf chlorosis. Leaves deficient in phosphorus may take on a purplish cast. Trees that are deficient in potassium may show marginal necrosis. However, not all nutrient deficiency symptoms are unique and similar symptoms may be caused by different elements. For example, interveinal chlorosis can indicate magnesium, manganese or iron deficiencies. Moreover, some symptoms that resemble nutrient deficiencies may be caused by pest-related issues or other environmental stresses such as drought stress or poor soil drainage. Therefore, visual deficiency symptoms should be viewed as “one piece of the puzzle” when identifying potential nutrient problems and are best used in conjunction with soil or foliar testing