plant nutrients

The first step in Hydroponics farming is to understand the difference between soil fertilizers, and the requirements of plants. Most growers are aware of soil fertilizers such as those called by numbers 19-19-19 and 20-20-20, but what does 20-20-20 really mean?

Does it mean 20% Nitrogen (N), and 20% Phosphorous (P), and 20% Potassium (K) is the N.P.K ratio?

No, it’s not that simple.

It’s, 20% Nitrogen (N) and 20% Phosphorous Pentoxide (P2O5) and 20% Di-Potassium Oxide (K2O). (Depending on the country of origin, these units change by continent)

This translates to the actual % of the N.P.K as follows.

20% Nitrogen (N), 8.8% Phosphorous (P), and 16.6% Potassium (K).

However, a good Hydroponic nutrient contains all of these plus all the other minerals required for healthy growth. They will also be in the correct ratio to each other, according to plant type, and stage of growth, e.g. Vegetative, flowering or fruiting stage. 

The minerals required for good growth are as follows:

There are other minerals found in plant tissue when analysed, but for our purposes, these are the main requirements for Hydroponic growing, and the ones we have to monitor.

Hydroponics grower has to understand and make sure that the Hydroponics nutrients being used have all the above macro and micronutrients needed by the plant in a proportion that is needed at various stages of growth.

Take for example, the above 20-20-20 fertilizer with 20% Nitrogen (N), 8.8% Phosphorous (P), and 16.6% Potassium (K).

Researchers have determined that a tomato plant in fruiting stage needs more Potassium than Nitrogen with N:K ratio of even 1:3. Using 20-20-20 fertilizer for tomato crop in the fruiting stage might not give the best yield when compared to a Hydroponic nutrient modified in a proportion to suit the crop need.

Hydroponic farming gives best results only when the grower gives nutrients in the right proportion suiting crop, stage of growth, water pH, EC, climate conditions etc.

• Hydroponic is the act of raising plants without using soil, but rather in a water medium with nutrients.
• The plants are placed in a hydroponic system that supplies the required nutrients to the roots with the help of the water medium.
• The use of hydroponic has helped farmers to evade serious seedling diseases and pests like fungus and gnats, which mostly attack in moist soils.
• Media like coconut fibre, plugs, and peat pots have necessary nutrients and ensure that the seeds have a healthy growth.
• Rockwool or oasis can serve as a medium, the seedlings can be transplanted along with the cube into a complete hydroponic system later.
• Rapid rooters are mostly used as a medium as they have large numbers of important microbes and Mycorrhizal fungi that help in colonizing the root thus maximizing uptake of nutrients by the plant and evade serious diseases.

Other options:-

• Other than rapid rooters, there are other hydroponic options you can go for like, rock wool, coconut fibre, peat and oasis cube.
• While the rapid rooters retain a lot of water, oasis and coir retain very little water.
• The rock wool has a high PH concentration; therefore, the cubes should be rinsed in the solution of both water and vinegar to neutralize the PH before putting the seeds in the cubes to grow.
• Mix a teaspoon of vinegar in a cup half-filled with water and dip the cubes into the resulting solution shaking off the excess.
• Rock wool needs more attention because it is alkaline in nature.

Location: -

• The container should be placed where it can receive maximum light.
• If you choose to grow your seeds in the house, the convenient places are like on a table or near a window where there is partial light either in the morning or in the afternoon.
• In case you want to grow outside, then you should select a partially sunny location like a porch.
• The container should be away from heavy rainfall and winds.
• Since the container is small and portable, it should be moved from one place to another to protect it from bad weather.

Maintenance: -

• Water should be added only when the cubes start to get dry. Because much water favours the development of molds on the rock wool.
• On the other hand, if there is no water for a long time the seeds will not germinate. Thus, the cubes should be moist but not wet or dry.
• When the seedlings reach 2 inches in height, add diluted nutrient solution or fish water to the water in the container. This will greatly boost the root growth.

Transplanting: -

• The seedlings are ready for transplanting to a hydroponics grow system when they reach 3-4 inches in height. Look for 3 to 4 true leaves.
• Fill the net pot with clay pellets until it is half full. Which supports the plants.
• The best time of day to plant is in the late afternoon when the sun is not hot, and the wind has calmed down. By taking advantage of this time of day, the new plants have overnight to acclimate.
• Strong sun and wind are very hard on new transplants. Unless watered carefully, and in some cases provided with some shelter from the wind and sun, they can severely wilt.
• This places the plants under stress at the very beginning of their growing cycle and is not a good idea because sometimes they never bounce back and don’t thrive as well as they could have.

Growing peppers in aquaponic units: There are many varieties of peppers, all varying in colour and degree of spice, yet from the sweet bell pepper to the hot chili peppers (jalapeno or cayenne peppers) they can all be grown with aquaponics. Peppers are more suited to the media bed method but they might also grow in 11 cm diameter NFT pipes if given extra physical support.

Growing conditions: Peppers are a summer fruiting vegetable that prefers warm conditions and full sun exposure. Seed germination temperatures are high: 22–34 °C. Seeds will not germinate well in temperatures 30–35 °C lead to floral abortion or fallout. In general, spicier peppers can be obtained at higher temperatures. The top leaves of the plant protect the fruit hanging below from sun exposure. As with other fruiting plants, nitrate supports the initial vegetative growth (optimum range: 20–120 mg/litre) but higher concentrations of potassium and phosphorus are needed for flowering and fruiting. 

Growing instructions: Transplant seedlings with 6–8 true leaves to the unit as soon as night temperatures settle above 10 °C. Support bushy, heavy-yielding plants with stakes or vertical strings hanging from iron wires pulled horizontally above the units. For red sweet peppers, leave the green fruits on the plants until they ripen and turn red. Pick the first few flowers that appear on the plant in order to encourage further plant growth. Reduce the number of flowers in the event of excessive fruit setting to favour the growing fruits to reach an adequate size. 

Harvesting: Begin harvesting when peppers reach a marketable size. Leave peppers on the plants until they ripen fully by changing colour and improve their levels of vitamin C. Harvest continually through the season to favour blossoming, fruit setting and growth. Peppers can be easily stored fresh for 10 days at 10 °C with 90–95 per cent humidity or they can be dehydrated for long-term storage.

pH: 5.5–6.5

Plant spacing: 30–60 cm (3–4 plants/m2, or more for small-sized plant varieties)

Germination time and temperature: 8–12 days; 22–30 °C (seeds will not germinate below 13 °C)

Growth time: 60–95 days

Temperature: 14–16 °C night time, 22–30 °C daytime

Light exposure: full sun

Plant height and width: 30–90 cm; 30–80 cm

Recommended aquaponics method: media beds

Reference: http://www.fao.org/3/a-i4021e.pdf

Potassium is a paramount macro-element for overall survival of living things. It is an abundant mineral macronutrient present in both plant and animals tissues. It is necessary for the proper functioning of all living cells. Potassium is relatively abundant in the earth's crust making up to 2.1% by weight. Potassium is mined in the form of potash (KOH), sylvite (KCl), Carnallite and Langbeinite. It is not found in free nature.

Importance of potassium to plants

Potassium is an indispensable constituent for the correct development of plants. It is important in photosynthesis, in the regulation of plants responses to light through opening and closing of stomata. Potassium is also important in the biochemical reactions in plants. Basically, potassium (K) is responsible for many other vital processes such as water and nutrient transportation, protein, and starch synthesis.

Potassium Uptake

Bio-availability and uptake of K by plants from the soil vary with a number of different factors. The rate of respiration by plants is largely the determining factor for proper uptake and transport of potassium by plants. Its uptake is dependent on sufficient energy (ATP). Potassium plays a vital role in the translocation of essential nutrients, water, and other substances from the roots through the stem to the leaves. It is also made available through fertilizers in the form of K2O. Plant tissues analyze the form of these fertilizers and convert it into a more bio-available form. It is absorbed in the form of ions- K+.

Functions of Potassium in plants

Potassium (K) essentially plays a major role in plant physiological processes. Therefore, it is required in large amounts for proper growth and reproduction in plants. It is considered vital after nitrogen as far as nutrients needed by plants are concerned. It is also termed "the quality nutrient" for its contributing factor in a number of biological and chemical processes in plants. Here is why Potassium is important in plants:

• Potassium regulates the opening and closing of stomata thus regulating the uptake of CO2 thus enhancing photosynthesis.
• It triggers activation of important biochemical enzymes for the generation of Adenosine Triphosphate (ATP). ATP provides energy for other chemical and physiological processes such as excretion of waste materials in plants.
• It plays a role in osmoregulation of water and other salts in plant tissues and cells.
• Potassium also facilitates protein and starch synthesis in plants.
• It activates enzymes responsible for specific functions.

Potassium deficiency in plants

Regardless of its availability from soils, potassium deficiency may occur and might start from the lower leaves and progress towards other vital parts of the plants. Deficiency might cause abnormalities in plants affecting reproduction and growth. Severity depends on with the type of plant and soil. Some of the potassium deficiency symptoms may include:

• Chlorosis: May cause yellowing of leaves, the margin of the leaves may fall off, and also lead to shedding and defoliation of the leaves.
• Stunted growth: Potassium being an important growth catalyst, its deficiency or insufficient might lead to slow growth or poor developed roots and stems.
• Poor resistance to ecological changes: Reduced availability of potassium will directly result in less fluid circulation and translocation of nutrients in plants. This will directly make plants susceptible to temperature changes.

Importance of potassium in agriculture

Potassium is important in agriculture and soil gardening. It is used as a constituent in artificial fertilizers. Potassium fertilizers have been seen to increase crop yields, enhance production of grains rich in starch and protein content of plants. Additionally, potassium fertilizers may help improve plants immunity to weather changes, diseases, and nematodes.

Potassium is majorly used in hydroponics to improve root growth and enhance drought tolerance. It also enhances the building of cellulose and thus reduces lodging.

What is pH?

pH is a measure of the relative concentration of hydrogen ions (H+) to hydroxide ions (OH-). The greater the number of H+ ions in relation to OH- the more acidic the solution becomes. The greater the ratio of OH- ions to H+, the more basic the solution becomes. PH is measured on a scale of 1-14. A reading below 7 means that there are more H+ ions and a reading above 7 indicates more OH- ions. At pH 7 there are the same number of H+ ions as OH- ions so the pH is neutral, neither acid nor base.

Acids and Bases

Any substance that increases the concentration of hydrogen ions (lowers the pH) when added to water is called an acid. A substance that reduces the concentration of hydrogen ions (raises the pH) when added to water is called a base or an alkali. Some substances enable solutions to resist pH changes when an acid or base is added. These substances are called buffers. Buffers are very important in helping to maintain a relatively constant pH in a feeding solution and in the root zone after the water has been applied to the crop. Most greenhouse water supplies have sufficient alkalinity that they require routine acid addition to correct the pH to the normal 5.8-6.2 feeding range. At this level, the irrigation water tends to have a neutral effect on media pH, although this depends on the buffering capacity of the media. Some growers use very pure water from rain and surface sources. In these situations, they may need to apply a combination of acid and base materials to stabilize and buffer the pH.

Why does pH Matter?

Improper management of media pH can result in poor growth and reduced plant quality in greenhouses and nurseries. The pH or soil reaction has a primary influence on the solubility and availability of plant nutrients. Many crops have a narrow range of pH tolerance. If the pH of the soil medium falls above or below this tolerance zone, they may not grow properly due to nutrient deficiency or toxicity.

The availability of most fertilizer elements is affected to some extent by the media pH. Calcium and magnesium become more available as the pH increases, while iron, manganese, and phosphorus become less available. A one-unit pH drop can increase the solubility of manganese by as much as 100 times, and the solubility of iron by as much as 1000 times.

Why Adjust Irrigation pH?

By carefully modifying the pH and alkalinity of your irrigation and feed solutions, you can help maintain the desired plant growth and quality. There are other reasons to monitor and control pH in your irrigation water and nutrient solutions: 1) Solution pH affects the availability of nutrients. 2) Correct pH helps ensure dissolved fertilizer concentrates remain in solution when mixed in the water supply. 3) Acid injection can be used to neutralize excess alkalinity in water supplies.

Understanding The pH Scale

The pH scale measures the relative concentration of Hydrogen Ions (H+) and Hydroxyl ions (OH-) in a solution. Technically, the pH of a solution is defined as a negative logarithm of the hydrogen ion concentration. The ‘p’ is the mathematical symbol for a negative logarithm and the ‘H’ is the symbol for hydrogen. The pH scale measures this, and places a value on it ranging from 0 to 14. Since it is a log scale, each number on the scale is 10 times greater (or smaller) than the next. A lower pH number corresponds to a higher concentration of hydrogen ions (H+) relative to hydroxyl ions (OH-). A higher pH number corresponds to a relatively lower concentration of hydrogen ions

Measuring pH

There are several methods available for measuring pH, but the most useful and practical is an accurate pH meter. Follow the instructions included to preserve the accuracy and life of your instrument. These meters typically use a liquid filled glass probe, although some are now using flat sensor technology.

Water and nutrient solution samples can be measured directly or preferably after a few hours of settling time. Dissolved CO2 in water supplies can cause slightly lower readings until the sample has come to equilibrium with the air. When testing media, freshly mixed samples of media should be watered and allowed to stand for 24 hours before a reading is taken to release some of the lime and fertilizers. The preferred method for testing media pH is to obtain several representative samples of a crop and to measure each separately. Multiple measurements give greater accuracy in reading, and shows the degree of variability of pH across several locations. A saturated media extract or a 1:1 soil to distilled water ratio is fine for measuring media pH.

Factors Affecting pH

These variables can affect the final pH, the rate of pH change, and the amount of modifying action required. They include the effects of:

• Soil temperature
• Fertilizer materials (may raise, lower or buffer pH)
• Soil amendments such as gypsum, sulfur and lime
• Root volume & metabolic activity
• Soil microorganisms
• pH and alkalinity of the irrigation water
• Leaching fraction
• Buffering capacity of both the soil medium and the irrigation source
• Media cation exchange capacity

With all of the emphasis on N-P-K in agriculture, calcium and magnesium are sometimes overlooked. Calcium and magnesium are essential macro-elements, used in relatively large quantities. In fact, plants take up more calcium than phosphorus!

ROLES OF CALCIUM IN PLANTS

CALCIUM IN HYDROPONIC NUTRIENT SOLUTIONS

In hydroponic systems, adequate levels of calcium are usually maintained with calcium nitrate or other calcium salts. Therefore the lowering of calcium levels in the plant tissue and the occurrence of deficiency symptoms usually result from the influence of other factors which impede either calcium uptake or its distribution within the plant. Calcium uptake may be reduced by the competitive effects of a high concentration of other cations such a potassium, sodium, magnesium or ammonium in the solution. And since calcium moves in the xylem tissue, its uptake is also affected by low root temperature and by restricted water movement through the plant caused by high salinity in the media or excessive humidity in the atmosphere.

Higher EC levels in the nutrient solution reduce the uptake of calcium, unlike nitrogen and potassium which increase in concentration in leaf tissue with higher EC levels. Reducing the EC of the nutrient enhances water uptake and with this, more calcium can be taken up and transported within the plant to developing tissue.

CALCIUM DEFICIENCY SYMPTOMS

REMEDIES

The simplest means of preventing calcium deficiency disorders such as tipburn and blossom end rot is to maintain adequate calcium levels in a balanced nutritional solution with the correct EC level. Use 0.75% - 1.0% calcium nitrate solution as foliar spray in acute cases. As always, moderation is always recommended when using additives. Start with very low dosages, see how the plants respond and add more if necessary. Keeping the plants stress free, providing gentle air movement across the leaf source to encourage transpiration and preventing excessive temperatures all help drive calcium into leaf tips and developing fruits.