Plant nutrition is the science which studies what plants eat, or more to the point which nutrients the plant takes from its surroundings, in what amounts, under what conditions and how what the plant takes is used in growth and development. This is of great importance to anyone who is interested in maximizing the genetic potential of his/her plants.
A hydroponic nutrient solution is composed of water, dissolved air and a dozen or so essential elements in their proper proportions. The essential elements, or mineral elements that must be present for proper plant growth and development are nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), calcium (Ca), sulfur (S), iron (Fe), manganese (Mn), boron (B), copper Cu), zinc (Zn), molybdenum (Mo), and chlorine (Cl). The letters in parentheses are the chemical symbols for each element. In addition to these elements, hydrogen (H), oxygen (O2) and carbon (C) are also essential elements which can be found in the air and the water.
The elements that make up a nutrient solution are broken up into two different categories depending upon their relativity to the total make-up of the nutrient solution. Hydrogen, oxygen, carbon, nitrogen, phosphorus, potassium, magnesium, calcium and sulfur are required in relatively large amounts and are so called macroelements (major elements), while iron, manganese, boron, copper, zinc, molybdenum and chlorine are required in relatively small amounts and are so called microelements (minor elements).
Hydroponic nutrients should be complete, containing every essential element, both major and minor, required by all green plants for optimum plant growth. The nutrient should be well balanced containing enough of all essential elements so no deficiency occurs, while not containing too much of any element that might lead to a toxicity. Also the nutrient should be pH balanced and buffered preventing the pH from drifting too high (alkaline) or too low (acid). The last and maybe most important requirement is that the nutrient solution be water soluble with minimal or no residue. The mineral salts used should readily dissociate into elemental ions and not contain any toxic chemicals or elements like heavy metals (lead, mercury or tungsten). This is controlled by the selection and purity of the raw ingredients used.
Nitrogen (N) a major element needed by all green plants. It is transported from older growth to new growth. Deficiency lack of lush green color, especially in older leaves. Toxicity soft, dark green leaves, long weak stems, poor root development and slow to maturation.
Phosphorus (P) an important mineral that stores energy in plants and animals, also a flowering agent. Deficiency stunted, dark green leaves. Lower leaves turn yellow and die. Leaves have brown or purple spots. Toxicity small, curled new leaves. Early maturity, large root systems.
Potassium (K) a nitrogen catalyst needed for enzyme manufacture. Needed in large quantities, although plants do not use a tremendous amount. Deficiency brown, necrotic (dead) tips and edge margins on older (lower) leaves followed by yellowing of the entire leaf. Dead brown spots on older leaves. Slender, weak stems and small seeds. Toxicity saline condition, marginal leaf burn, wilting and drying due to poor water uptake.
Calcium (Ca) helps form the structural parts of the plants (it is a major element in cell walls). Counters acidity (low pH). Deficiency new growth affected first. Root tips turn brown and die. Hard, stiff new leaves with dead edges and brown spots. Stems are stunted and woody, blossoms fall off. Little or no fruit. Toxicity rare, but can cause an alkaline (high pH) condition, wilting, iron and potassium lockup and deficiencies. Calcium is not very mobile in plants.
Magnesium (Mg) is important in photosynthesis and the chlorophyll molecule where light energy is converted to chemical energy. Chlorophyll gives plants their green color. Deficiency chlorosis (yellowing) of older leaves between the veins. Later, leaf tips curl, entire plant turns yellow and dies. Magnesium is mobile and is transported from older to newer growth. Old growth is affected first.
Toxicity edges curl on leaves, small stems, signs of potassium deficiency.
Sulfur (S) is a building block of amino acids and proteins. Used in small amounts, it aids transpiration and transport of other elements. Deficiency rare, but young leaves turn pale green with yellowing along the veins, stems turn hard and woody. Plants are stunted and spindly. Toxicity saline condition, wilting.
Iron (Fe) is an important constituent of enzymes and plays a role in photosynthesis. Iron is not very mobile in plants and can be "locked up" if the pH goes much above 7. Deficiency yellow or white chlorosis between veins of younger leaves. Stunted new growth with spindly stems. Flowers drop off before opening. Toxicity deficiencies of other elements, brown spots on leaves.
Manganese (Mn) plays an important role in photosynthesis and chloroplast membrane formation. Needed at only ½ the rate of iron, its importance cannot be understated. Manganese also enters into the chemical reactions of oxidation and reduction. Deficiency dead (necrotic) spots on younger leaves. Hard and woody stems, slow maturity. It is not very mobile in plants, so younger growth usually exhibits symptoms first. Toxicity wilting and death in all but small quantities. Note: manganese is toxic in large amounts.
Boron (B) is needed in small amounts. Boron aids in cell division and in transporting sugars through cell walls. It also aids in forming the amino acids thymine and cytosine, important to DNA synthesis. Deficiency affects new growth first. Black, brittle areas on leaf tips. Small, burned leaves with dead spots. Stubby brown and dead root tips. "Heart rot" in beets and "stem crack" in celery. Toxicity above 10 PPM, dead leaf margins, wilting and quick death of the plant.
Copper (Cu) is needed in only small amounts. This metal aids in plant metabolism and general health. It helps ward off disease and pests, aids in the utilization of iron and the manufacture of enzymes. Deficiency dark green, spindly young leaves. Plants are susceptible to disease and insects, wilt easily and exhibit stunted growth. Toxicity dark roots, leads to an iron deficiency (interveinal chlorosis on young leaves).
Zinc (Zn) is needed in small amounts for growth and chlorophyll synthesis. Deficiency short stem internodes and a condition called "little leaf" or "rosetting" where the young leaves are spindly and twist around each other. Reduced or no bud formation. Mottled dead spots between veins. Toxicity related to an acid pH, splotchy mottled leaves and wilting.
Chlorine (Cl) this element controls water uptake and transpiration. Stimulates photosynthesis and is a major constituent of the anthocyanin molecule. Deficiency plants wilt easily. Bronze colored leaves with dead or chlorotic spots, stunted roots with club-shaped tips. Toxicity saline poisoning, small dark leaves, burned margins and wilting.
Molybdenum (Mo) a catalyst needed in small quantities. It is involved in nitrogen fixation (assimilation) and in the manufacture of enzymes. Deficiency causes nitrogen deficiency. Plants are light green, malformed and stunted. Causes the "whiptail" disease where young leaves are long, narrow and severely twisted, but not tightly bunched as in "rosetting" caused by zinc deficiency. Toxicity very toxic to plants above 100 to 200 parts per billion (not much!). Causes iron and copper lockup and improper nitrogen utilization.
Cobalt (Co) a constituent of vitamin B-12 and required for the fixation of nitrogen and DNA synthesis. Deficiency causes pernicious anemia (lack of vitamin B-12) and improper nitrogen assimilation. Toxicity all but the smallest amount causes quick wilt and death.
What is the NPK and how is relevant to a hydroponic nutrient? The NPK is the ratio of the levels of nitrogen, phosphorus and potassium. Note that the NPK is important in choosing the right nutrient for the proper stage of growth exhibited by your plants.
The nutrient solution in hydroponics, like the in-the-soil solution for traditional soil gardeners, provides the plant roots with water and essential elements. In hydroponics, the essential elements are added to the nutrient solution, using fertilizer (mineral) salts.
There are a number of hydroponic nutrients on the market these days but they mostly fall into one of four categories they can be either liquids or powders, and these can be either a one or two part formulas. Most hydroponic retail centers offer a wide range of powder and liquid, one and two part, grow and bloom nutrients.
Powder nutrients are more concentrated than liquids and are usually less expensive. Powders should be dissolved in hot water to make a liquid concentrate, and not be used by adding the powder directly to the tank. This should be done to insure that the powder dissolves completely. If a liquid concentrate is to be made from a two-part powder formula, it is essential that the final volume of the two solutions be the same.
Liquid nutrients are more popular with most hydroponic gardeners because they are easier to use. Liquid nutrients can be added directly to the tank, while powders should be mixed separately then added to the tank. Also another thing to remember is that liquids should be shaken well before dilution, to get an even mix of nutrient chemicals by getting the sludge moving.
The strength of a nutrient solution is measured by its electrical conductivity (EC) and is of critical importance. Too high an EC results in vegetative growth at the expense of fruit or flower production and too low an EC produces weak, unproductive plants.
The EC can be expressed as TDS (total dissolved salts) or ppm (parts per million) depending upon the meter that is used. TDS is the concentration of s solution as the total weight of dissolved solids. These meters are widely used by hobbyists, and actually measure the electrical conductivity of a solution. They do this by measuring the amount of electric current a solution carries. The meters use a built-in conversion factor to express the electrical conductivity in TDS/ppm. The conversion factor for true TDS/ppm is expressed as:
True TDS/ppm = 640 x EC (mS/cm)
EC (mS/cm) x 640 = 640 True TDS/ppm
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