Plants, like all living things, require proper nutrition to grow and develop properly. There are many nutrients that plants require and great benefit may arise from applying any one of them to crops. Proper nutrition can enhance plant growth and production as well as provide the plant with the building blocks to withstand weather conditions and other stress.
There are three main nutrients that all plants require – nitrogen (N), phosphorus (P) and potassium (K). These are known collectively as plant macronutrients. Many fertilizers are labeled with a number that represents the proportion of the N, P and K contained in the product – this number is generally in the form of 0-0-0 with the first number representing the nitrogen, the second phosphorus, and the third potassium (N-P-K).
Without adequate amounts of nitrogen, fruit and flower size and yield may be drastically reduced. As crops are harvested, soil nitrogen is depleted, risking the starvation of future progeny. It is important that plants are supplemented with proper amounts of nitrogen to enhance growth and production and improve survival. It is especially important to supplement with nitrogen if the soil is acidic or woody materials have been mixed in, as these cause nitrogen deficiencies in the soil.
In nitrogen deficiency, plants appear starved. They are thin and pale and growth is stunted. Chlorophyll development also requires adequate nitrogen, so leaves may appear yellow or pale green and they tend to remain small and drop prematurely.
Phosphorus is required for the proper growth and development of all plants, but especially seedlings. It is often recommended as a starter fertilizer to enhance the early growth of plants. That being said, it is also important to have adequate phosphorus throughout the entire lifecycle as it is required for plants to use energy and continue growing, developing and most importantly, producing fruits and flowers.
Phosphorus deficiency is the most common soil deficiency seen in North America. Root and shoot growths are both stunted, with shoots appearing spindly and leaves appearing abnormally dark in colour. In severe cases, leaves may develop a reddish purple colour. Phosphorus deficiency manifests with little to no flowers or fruit produced, delayed maturity, and winter hardiness is diminished.
Potassium, the third essential macronutrient, is responsible for proper movement of water, carbohydrates and nutrients through plant tissue. It also plays a vital role in the energy status of the plant, which affects photosynthesis. Adequate potassium enhances stress resistance and rigidity of crops, which increases survival and protects against harsh weather conditions.
Crops deficient in potassium are more susceptible to injury and disease due to its tolerance boosting effects. Also, since potassium plays a critical role in water movement, stunted growth, yield reduction, wilting, and premature defoliation are common during a potassium deficiency. Shelf life of harvested fruits may also be reduced during low potassium, and lower leaves often develop white, yellow or brown spots.
Micronutrients encompasses a large variety of different elements that may be used to enhance the growth or quality of plants.
Boron is an essential micronutrient required for proper reproductive and vegetative growth – it is responsible for root and shoot growth, pollen development, fruit and flower production, as well as proper development of roots and shoots. Boron deficiency first appears as yellowing of new leaves and can progress to the formation of thick, brittle branches and short stubby roots.
Copper is an essential metal required for proper photosynthesis. When used as a nutrient, only very small amounts are required, as copper may persist in the soil for many years. Copper deficiency affects young leaves and reproductive organs and worsens as soil pH increases. Soil without adequate copper content may cause light green or yellow leaves, reduced flowering, as well as malformed and/or necrotic leaves.
Iron is an essential micronutrient that plays a critical role in respiration and photosynthesis and is required for the proper growth of all plants. Additionally, adequate iron enhances the nutritional quality of crops. Acidic soils and waterlogged soils tend to have the highest natural iron content. Iron deficiencies are quite common and may lead to yellowing leaves and poor root formation. A certain level of iron is required for all plants in order to properly grow, however too much iron may be toxic.
Manganese is an important element that is present in small amounts in most soils. It enhances the efficiency of photosynthesis, which boosts growth, yield and quality. Manganese works synergistically with other fertilizers by optimizing the plant’s usage of the three primary macronutrients. Manganese deficiency affects the chloroplast of the plant’s cells and results in severely diminished yield and quality.
Zinc is crucial for the production of many plant growth regulators. It enhances yields, improves resistance to injury, and improves production of pollen, fruits and flowers. In zinc deficiency, growth may cease and plants become more susceptible to injury. Small, malformed leaves with necrotic spots and stunted roots are the characteristic signs of a zinc deficiency.
Secondary nutrients are those that do not fall into either the micro- or macro-nutrient category. There are two main compounds that are used as secondary nutrients – calcium and magnesium, and they are often used in combination.
Calcium is an essential second messenger that is associated with virtually all aspects of plant growth and development. It signals the growth of plant roots and shoots and is crucial for the incorporation of cell wall components. A calcium deficiency may present as leaf curling, fruit cracking, or inferior root growth.
Magnesium is the other secondary nutrient. Often calcium and magnesium are used in combination and referred to as “Cal-Mag” in commercial products. Magnesium application to deficient soil can enhance root formation, chlorophyll synthesis and pigmentation, and regulates cell turgor.