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.