Most gardeners will tell you that N, P and K are the initials of three plant nutrients or simply, “fertilizer.” They are much more than that; they are three elements on the periodic table (PT). How many can list the rest?
For those like me, who may have passed his tenth-grade PT pop-quiz but would now fail miserably, you can find hundreds of examples on the internet. I downloaded a small free program from Custom Fit Software. Find one if your memory is as bad as mine.
OK, this is a gardening column so let’s stick to the elements needed for plant growth. The number considered essential now varies from 16 to 20 or more, depending upon the definition of essentiality. In high school I memorized them using the little ditty, "See Hopkin's café, mighty good; mob comes in" -- (C H O P K N S Ca Fe Mg Mo B Cu Mn Zn). But when I asked a younger brother, he remembered a different mnemonic – "See Hopkin's cafe manager if Nana calls" – (C H O P K N S Ca Fe Mg I Fe Na Ca).
We laughed at the differences but the truth is plants take up most of the 90 or so mineral elements and it wouldn't surprise me if all are if not essential, certainly beneficial as we continue to discover how these elements are utilized for growth, reproduction and complex applications we have just begun to understand, such as chemically repelling herbivorous insects or attracting pollinators.
The major compound in all plants is water. After the water is removed, the bulk of the dry plant material consists of carbohydrate compounds containing the elements C, H, and O.
C, the fourth most abundant element in the universe is considered by many scientists 'the' essential element of life on Earth. The backbone of all organic substances, it is what most of the physical plant is made of. Plants take it from the CO2 in the air, the same CO2 that is being blamed for global warming. We need less driving and more gardening.
H may be the simplist element but it's number one on the PT and essential to plants for building sugars (add C and you get carbohydrates). It is a major component of organic molecules, which are the building blocks of all organisms. Water -- H2O, supplies H to the plant.
O is for cellular respiration; also from H2O.
Plants obtain the rest of the essential elements from the soil and those needed in the greatest amount are called macronutrients, which include the most popular N, P and K. These three elements are those most rapidly removed from the soil by plants.
P is essential in virtually every metabolic process including fruit, flower and seed formation, protein synthesis, and cell division. P deficient plants are characterized by stunted growth, dark green leaves with a leathery texture, and reddish purple leaf tips and margins.
K is absorbed by plants in larger amounts than any other mineral element except N and, in some cases, Ca. It helps in the building of proteins, photosynthesis, fruit quality and reduction of diseases. Compost and cover crops are the best K sources. Deficient plants exhibit chlorosis (loss of green color). In severe cases, the whole plant turns yellow, and the lower leaves fall off.
N is a constituent of amino acids, which are required to synthesize proteins and other related compounds, it plays a role in almost all plant metabolic processes. N is probably the nutrient most likely to be deficient in a plant, causing stunted and poorly developed plants. Excess N in our environment is a subject for another day.
S promotes activity and development of enzymes and vitamins and helps in chlorophyll formation. It improves root growth and seed production. S is an essential ingredient in many of the amino acids.
Ca is a part of cell walls and is involved in production of new growing points and root tips. It also regulates transport of other nutrients into the plant. A deficiency in tomatoes and peppers causes blossom-end rot. In peanuts, low Ca causes "pops," a condition that prevents nuts from developing.
Mg is a constituent of the chlorophyll molecule, which is the driving force of photosynthesis and is essential for the metabolism of carbohydrates. It regulates uptake of the other essential elements and enhances the production of oils and fats. On grain crops Mg deficient leaves have light green to yellow stripes that run parallel with the blade. In severe cases, the entire leaf turns yellow. Mg deficiency is the common cause of "grass tetany" in ruminant animals.
Fe is essential for formation of chlorophyll and necessary for photosynthesis. Fe deficiency can result in interveinal chlorosis and necrosis.
Mo is important in building amino acids. The most well-established function of Mo is in nitrate reductase, an important enzyme that converts nitrate, NO3-, to ammonium, NH4+.
B helps in regulating other nutrients, aids production of sugar and carbohydrates and is essential for seed and fruit development. B deficiency causes necrosis in young leaves and stunting.
Cu is important for reproductive growth, aids in root metabolism and helps in the utilization of proteins. Cu is also important for photosynthesis. Symptoms for Cu deficiency include chlorosis.
Mn functions with enzyme systems involved in breakdown of carbohydrates, and nitrogen metabolism. Mn deficiency may result in coloration abnormalities, such as discolored spots on the foliage.
Zn is essential for the transformation of carbohydrates and in the regulation of sugars. It is required in a large number of enzymes and plays an essential role in DNA transcription. A typical symptom of Zn deficiency is the stunted growth of leaves, commonly known as "little leaf."