Phosphorus is a mobile macronutrient, and its availability in soil is related to the soil pH. Phosphorus deficiencies are tough to diagnose by eye because a plant that is deficient in this macronutrient may not be visible. A visible deficiency will present as stunted growth or a dark green to purple coloring, but the best way to tell if there is a deficiency is by a soil test.
Phosphorus is essential to root growth, and plays a role in the storage and transfer of energy.
However, Phosphorus in the soil is relatively immobile which makes it harder for the plant to uptake. While applying Nitrogen fertilizers may result in some substantial visual changes, Phosphorus application results may not be apparent. Even though the visual response of Phosphorus is low, this macronutrient is still very important for plant life.
This macronutrient plays several important roles in plants such as regulation of water and energy, opening and closing of the stomata, as well as the transport of nutrients. Potassium is also mobile in the plant. Potassium deficiencies may present as yellow or brown spots on the edges of leaves, but are usually really difficult to distinguish by eye. Likewise, an application of Potassium will typically show little to no visual response.
Potassium and Nitrogen have an important connection, because Nitrogen stimulates rapid soft growth, and Potassium balances this by supporting the growth of firmer tissues. Applications of Potassium without sufficient Nitrogen may lead to decreased Nitrogen content in younger plants.
Deficiency symptoms of Chlorine, specifically the chloride ion, are rare, but show as wilting of new leaves, chlorosis, and necrosis. This micronutrient is very mobile in soils. Chlorine plays a role in the stomata functions, osmotic regulations, and maintains a cation/anion balance. Plants are exposed to Chlorine by rainwater, air, irrigation, plant waste, animal manure, and from some fertilizers.
Copper is a micronutrient responsible for enzyme activation and is also involved in the chemical reactions for photosynthesis and respiration. A copper deficiency will present in the youngest plant tissue as chlorosis, and there may be a reduction in plant growth. Most soils contain enough Copper for healthy plant growth and a deficiency is rare but can occur in soils that have higher organic matter.
Iron is a micronutrient that is essential for photosynthesis and metabolic processes and if Iron is not present, then chlorophyll cannot be produced. An Iron deficiency may occur in soils that have a pH of over 7.0. As pH increases, the availability of Iron decreases. This micronutrient is not mobile, so a deficiency shows as yellowing of the younger leaves. Iron deficiencies are best to be corrected by foliar application. Iron deficiency is the most common micronutrient deficiency in turfgrass.
Iron toxicity can also occur, and when this happens the turf may turn a very dark green or black color for a few days, but generally there is no permanent damage.