| Hydroponics literally means "working water" | | | | sometimes in adequate concentration for our needs, |
| (hydro=water, ponics=work). Practically, it means | | | | especially in well-water. If the concentration is higher |
| growing plants without using soil, delivering nutrients | | | | than required, the source water should be |
| only by a aerated nutrient solution. | | | | pre-treated. |
| Hydroponics systems can be either closed or open | | | | Calcium nitrate is the only fertilizer appropriate for |
| systems. In closed systems the same hydroponic | | | | calcium addition to hydroponics irrigation water. |
| nutrient solution is recirculated and the nutrient | | | | Magnesium nitrate and magnesium sulfate are both |
| content is monitored and adjusted. | | | | appropriate sources for magnesium addition. Note |
| Keeping the nutrient balance in such systems is a | | | | that calcium nitrate and magnesium nitrate also |
| challenge and the hydroponic nutrient solution has to | | | | contribute nitrogen to the solution. |
| be sampled and analyzed every week. The nutrient | | | | Sulfur |
| solution composition has to be adjusted according to | | | | Sulfur is present in a wide range of concentrations in |
| the results. | | | | various water sources, and plants growing in |
| In open systems a fresh nutrient solution is | | | | hydroponics can tolerate relatively high concentration. |
| introduced for each irrigation cycle. | | | | But sulfur excess might have untoward effects and |
| Inert growing media are usually used in hydroponics. | | | | even limit nitrate uptake. |
| Unlike soil, that stores nutrients and directly interacts | | | | Micro-nutrients |
| with the plant, the growing media used in hydroponics | | | | Iron, manganese, zinc and copper can be provided in |
| have little effect, if any, on the plant nutrition. As a | | | | the sulfuric form, but their availability is greatly |
| result, the only source of nutrients is the nutrient | | | | decrease in pH greater than 6.5. The chelated forms, |
| solution, and therefore you have total control over | | | | may also be used, because they are available for |
| your plant nutrition. | | | | uptake in a wider range of pH. Some growers regard |
| While soil allows more tolerance for inaccuracy, | | | | EDTA as harmful for plants, and avoid its use. |
| hydroponics leave very little room for errors. Because | | | | Molybdenum is usually provided using sodium |
| changes are rapid and mistakes can be very costly, | | | | molybdate. The presence of sodium in this fertilizer |
| hydroponics growers should make highly educated | | | | should not be a cause for alarm. Because |
| and accurate decisions. | | | | molybdenum is needed in minute quantities, very |
| Close monitoring of Water content is extremely | | | | small amounts of this fertilizer are usually used, and |
| important in hydroponics | | | | the sodium addition is negligible. |
| Naturally, water plays a major role in hydroponics, | | | | Boron can be provided through boric acid or solubor. |
| making their quality and content - paramount. | | | | Solubor also contains sodium, but again, quantities are |
| There are several key questions that should be | | | | small enough as to not have a significant effect on |
| addressed when dealing with this issue: | | | | sodium concentration in the solution. Range for |
| Which nutrients are required? Are they all present in | | | | adequate boron levels is very narrow (0.2-0.5 ppm) |
| the correct concentration in your hydroponic solution? | | | | and can easily be missed, resulting in either deficiency |
| - What are the ratios between the nutrients? Do | | | | or toxicity. Therefore boron supplements should be |
| some nutrients affect the availability of others? | | | | carefully added. Well water often contain sufficient |
| - What is the total concentration of minerals in the | | | | boron levels, so no boron addition is needed. |
| solution? | | | | Harmful elements - Sodium - Chloride |
| - Are there any harmful elements in the water? | | | | Chloride is required by plants in minute quantities and |
| What is their concentration? | | | | most water sources contain chloride concentration |
| - What is the pH of the hydroponic solution and how | | | | well above and beyond plants require, so chloride |
| does it affect nutrient uptake by the plant? | | | | deficiency is extremely rare. Chloride related problems |
| First Step - Source Water Analysis | | | | are more commonly those of toxicities rather than of |
| Hydroponics solution consists of minerals in the | | | | deficiencies. Therefore, using fertilizers which contain |
| source water and the nutrients added with fertilizers. | | | | chloride is uncommon in hydroponics. |
| The choice of fertilizers type and amount added | | | | Sodium can be very harmful in recirculating systems, |
| greatly depend on the initial content of source water. | | | | since it builds up with time in the hydroponic solution. |
| Therefore, testing the source water prior to | | | | Threshold concentration of sodium and chloride for |
| preparing a fertilizer formula is imperative. | | | | most hydroponics grown plants is 75 ppm. |
| For example, your source water may contain an | | | | Electrical Conductivity (EC) |
| sufficient amount of calcium for your crop nutrition. In | | | | Electrical conductivity is a measure of the total salts |
| this case, you should not use calcium nitrate, not only | | | | dissolved in the solution (learn more about EC). It is |
| because it is redundant, but also because any calcium | | | | used for monitoring daily applications fertilizers. Note |
| addition might precipitate with other elements in the | | | | that the EC reading doesn't provide you with |
| hydroponic solution, such as phosphorus, or interfere | | | | information regarding the ratios between nutrients. |
| with uptake of others. | | | | In closed hydroponics systems, with recirculating |
| Additionally, source water may contain too large | | | | solution, nutrients which are not absorbed by the |
| amounts of harmful elements, such as sodium, | | | | plants (such as sodium, chloride, fluoride etc.) or ions |
| chloride, fluoride or excess of boron, rendering it | | | | released by the plant, build up in the hydroponic |
| unsuitable for hydroponics. This can be solved by | | | | solution. In this case you need more information |
| pre-treating the source water with desalination or | | | | about the solution content, that EC cannot provide. |
| ion-exchange. | | | | Frequent water analysis tests will help you decide on |
| Source water analysis must contain at least the | | | | the timing for replacing the nutrient solution or dilute |
| following information: | | | | it with good quality water.pH |
| EC, pH, calcium, magnesium, chloride, sodium, sulfur | | | | The optimal pH range for the nutrient solution is |
| and bicarbonate levels. | | | | 5.8-6.3. micro-nutrients are more available in lower pH, |
| If your water source is a bore hole/well, it would also | | | | but when pH levels drop below 5.5, you run the risk |
| be wise to test for boron, manganese and fluoride | | | | of micro-nutrients toxicity, as well as impaired |
| levels. | | | | availability of calcium and magnesium. In hydroponics, |
| The Essential Plant Nutrients | | | | especially in closed systems, the roots readily affect |
| There are 13 mineral nutrients that are essential for | | | | the hydroponic solution pH, so pH tend to fluctuate. |
| completion of the plant's life cycle. Macro-elements | | | | Appropriate products for acidifying the hydroponic |
| are required in large quantities: nitrogen, potassium, | | | | solution are sulfuric acid, phosphoric acid and nitric |
| phosphor, calcium, magnesium, sulfur. Micro-nutrients | | | | acid. The preferred one is sulfuric acid because the |
| are required in very low concentration: iron, | | | | EC control and pH control are kept separate. This |
| manganese, zinc, copper, molybdenum, boron, | | | | makes the grower's job much easier. |
| chlorine. | | | | Ammonium/nitrate is one of the major factors |
| All of these nutrients should be provided in the | | | | affecting the pH of the nutrient solution |
| hydroponics solution, in the right concentrations, and | | | | Nutrient balance |
| in adequate ratios. | | | | Several nutrients compete with each other over |
| According to the law of "limiting factor" , if one | | | | uptake by the plant, so keeping adequate ratios is |
| nutrient is deficient, other nutrients cannot | | | | important for avoiding deficiency. For example excess |
| compensate for the deficiency, and the crop may | | | | of potassium compete with calcium and magnesium |
| suffer, resulting in decreased quality and/or yield. | | | | absorption. A high iron/manganese ratio can result in |
| Nitrogen, phosphorus and potassium | | | | manganese deficiency, and high sulfur concentration |
| Most water sources contain only very small amount | | | | might decrease the uptake of nitrate. |
| of these nutrients, if at all, therefore they must be | | | | As mentioned in the beginning of this article, the |
| provided using fertilizers. | | | | nutrient balance in a closed hydroponics system |
| Commonly used soluble fertilizers are MAP, potassium | | | | changes frequently and has to be closely monitored |
| sulfate, ammonium nitrate, potassium nitrate. | | | | and managed. Harmful minerals like sodium, chloride |
| Calcium and magnesium | | | | and fluoride build up in the solution and might reach |
| These elements are usually found in source water, | | | | toxic levels. |