Function, Deficiency and Exces

Deficiency symptoms

Before we begin discussing the principles of plant nutrient systems in hydroponic systems, we need to define what we mean by "hydroponic."

Hydroponics is the process of growing plants in water containing nutrients. Examples of this type of hydroponic systems are NFT (Nutrient Film Technique) systems and deep water floating systems where the plant roots are placed in nutrient solutions. Another definition of hydroponics is growing plants without soil. According to this definition, growing plants in soilless media (potting soil) or other types of aggregate media such as sand, gravel, and coconut shells are considered hydroponic systems. Here we use the term hydroponics for growing plants without soil.

Essential nutrients

Plants cannot function properly without these 17 essential nutrients. These nutrients are needed to allow the processes important to plant growth and development to take place. For example, magnesium is an important component of chlorophyll. Chlorophyll (see picture) is a pigment that serves to capture light energy needed for photosynthesis. It also reflects green wavelengths and is the reason most plants are green. Magnesium is the center of the chlorophyll molecule. The table below lists the functions of the essential nutrients for plants.

Essential nutrients can be broadly divided into macronutrients and micronutrients . The classification macro (large) and micro (tiny) refers to the amounts. Both macronutrients and micronutrients are essential for the growth and development of plants. Macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, sulfur, calcium, and magnesium. Micronutrients include iron, manganese, zinc, boron, molybdenum, chlorine, copper, and nickel. The difference between macronutrients and micronutrients lies in the amount plants need. Macronutrients are needed in larger amounts than micronutrients. Table 1 shows the approximate content of essential nutrients in plants.

Plants obtain carbon, hydrogen and oxygen from air and water. The remaining nutrients come from the soil or, in the case of hydroponics, from nutrient solutions or aggregate media. The sources of nutrients available to plants are listed in Table 1.

Essential components of nutrient solutions, Table 1

Nutrient (symbol)	Approximate plant content (% dry weight)	Role in the plant	Source of nutrients available to the plant
Carbon (C), hydrogen (H), oxygen (O)	90+ %	Components of organic compounds	Carbon dioxide (CO ₂ ) and water (H ₂ O)
Nitrogen (N)	2–4%	Component of amino acids, proteins, coenzymes, nucleic acids	Nitrate (NO₃^-) und Ammoniak (NH₄⁺)
Sulfur (S)	0.50%	Component of sulphur-containing amino acids, proteins, coenzyme A	Sulfate (SO₄^-)
Phosphor (P)	0.40%	ATP, NADPMetabolic intermediates, membrane phospholipids, nucleic acids	Dihydrogenphosphat (H₂PO₄^-), Hydrogenphosphat (HPO₄^2-)
Potassium (K)	2.00%	Enzyme activation, turgor, osmotic regulation	Potassium (K ⁺ )
Calcium (Ca)	1.50%	Enzyme activation, signal transduction, cell structure	Calcium (Ca²⁺)
Magnesium (Mg)	0.40%	Enzyme activation, component of chlorophyll	Magnesium (Mg²⁺)
Manganese (Mn)	0.02%	Enzyme activation, important for water splitting	Manganese (Mn ²⁺ )
Iron (Fe)	0.02%	Redox changes, photosynthesis, respiration	Iron (Fe ²⁺ )
Molybdenum (Mo)	0.00%	Redox changes, nitrate reduction	Molybdat (MoO₄^2-)
Copper (Cu)	0.00%	Redox changes, photosynthesis, respiration	Copper (Cu ²⁺ )
Zink (Zn)	0.00%	Cofactor activator for enzymes Alkohol-Dehydrogenase, Carboanhydrase	Zink (Zn²⁺)
Bor (Bo)	0.01%	Membrane activity, cell division	Borat (BO^3-)
Chlor (Cl)	0.1–2.0%	Charge equalization, water splitting	Chlor (Cl^-)
Nickel (Ni)	0.000005–0.0005%	Component of some enzymes, biological nitrogen fixation, nitrogen metabolism	Nickel (Ni²⁺)

To get an idea of the quantities required, here is a fertilizer quantity recommendation from the BISZ for sugar beet in arable farming. From the quantity you can see that, for example, 90 grams of copper per 1 ha (10,000 m ² ) is only a tiny amount per square meter and a fraction of that is needed per plant. In this example: 0.009 grams per square meter. But if this element is completely missing, the plant cannot grow at all because it is essential for photosynthesis (see table above). When dry, it (copper) is no longer found due to chemical processes during drying.

Nutrient requirement kg/ha
Nitrogen	250
Phosphor	100
Potassium	400
Magnesium	80
Sulfur	20 – 30
Calcium	60 – 80
Nutrient requirement g/ha
Bor	450 – 550
Manganese	600 – 700
Ferrum	500 – 1.500
Copper	80 – 90
Zinc	250 – 350

PH value

It is impossible to talk about plant nutrition without considering pH. Hydroponics is primarily concerned with the pH of the water used to prepare nutrient solutions and irrigate plants. pH is a measure of relative acidity, or hydrogen ion concentration, and plays an important role in the availability of plant nutrients. It is measured using a scale of 0 to 14 points, with 0 being the most acidic, 7 being the most neutral, and 14 being the most alkaline. The scale is logarithmic, and each unit corresponds to a 10-fold change. This means that small changes in values mean large changes in pH. For example, a value of 7 is 10 times higher than 6 and 100 times higher than 5. In general, the optimal pH range for growing vegetables in hydroponics is 5.0 to 7.0.

This diagram shows the relationship between nutrient availability and pH value:

Graphic: Pennsylvania State University

At the bottom of the chart, various pH levels between 4.0 and 10.0 are indicated. At the top of the chart, the relative acidity or alkalinity is indicated. Within the chart, the relative nutrient availability is represented by a bar. The wider the bar, the more relatively available the nutrient is. For example, the nitrogen bar is widest at a pH of 6.0 to 7.5. This is the pH at which it is most available to plants. Between 4.0 and 4.5, it is very narrow and not as easily available to plants.

It is also important to consider the alkalinity of the water. Alkalinity is a measure of capacity. It measures the ability of the water to neutralize the acid. This is primarily due to the combined amount of carbonate (CO3) and bicarbonate (HCO3), but hydroxide, ammonium, borate, silicate and phosphate can also contribute.

When total alkalinity is low, the water has a low buffering capacity. As a result, the pH changes slightly depending on what is added to the water. When total alkalinity is high, the pH of the water is high. To lower a high pH of the water, acid can be added to the irrigation water. The amount of acid needed depends on the alkalinity of the water.

Nutrient antagonism and interactions

For example, a hydroponic tomato nutrient solution recipe calls for 190 ppm nitrogen and 205 ppm potassium. Due to an error in calculating the amount of fertilizer to use, 2,050 ppm potassium is added. An excess of potassium in the solution can cause antagonism with nitrogen (and other nutrients) and result in nitrogen deficiency even if 190 ppm nitrogen was added. The table below lists common antagonisms.

Nutrient	Antagonist of
Nitrogen	Potassium
Phosphor	Zinc
Potassium	Nitrogen, calcium, magnesium
Sodium	Potassium, calcium, magnesium
Calcium	Magnesium, Bor
Magnesium	Calcium
Ferrum	Manganese
Zinc	Ion competition: high concentrations of heavy metals, copper and phosphate reduce the uptake rate of zinc: the cause of zinc deficiency in the plant does not necessarily have to be zinc-poor soil

Problems with nutrients

Hydroponic systems are less forgiving than soil-based systems, and nutrient problems can quickly lead to plant problems. This is why nutrient solution composition and regular monitoring of the nutrient solution and plant nutrient status are critical.

The minimum law

Carl Sprengel's law of the minimum states that the growth of plants is limited by the resource that is relatively scarce (nutrients, water, light, etc.). This means that a lack of nitrogen can also lead to the plant not being able to process other nutrients. On the other hand, too much of one component can have undesirable consequences: for example, too much lime inhibits the absorption of nutrients.

Also pay attention to the symptoms of

Deficiency symptoms that often point out problems:

Here is a brief overview of the deficiency symptoms, which can vary depending on the plant genus.

Symptoms

With

Overfertilization

Upper leaves yellow

Middle leaves yellow

Lower leaves yellow

Red stems

Necrosis

Points

Shoots die

White leaf tips

Crumpled Wheatgrass

Rolled yellow leaf tips

Twisted growth

Damage caused by soluble salts

Cause: Soluble salt damage can be caused by over-fertilization, poor water quality, accumulation of salts in aggregate media over time, and/or inadequate leaching. Fertilizers are salts, and in hydroponic systems they are the most common fertilizer. As water evaporates, soluble salts can build up in aggregate media if they are not adequately leached. Irrigation water can also have high levels of soluble salts, contributing to the problem.

The symptoms: Chemically induced drought can occur when the content of soluble salts in the planting substrates is too high. The result is that the plants wilt despite sufficient watering. Other symptoms include dark green foliage, dead and burned leaf edges and root death.

Detection: Soluble salt levels can be monitored/measured by tracking the electrical conductivity (EC) of irrigation water, nutrient solutions and leachate (a nutrient solution drained from the plant container).

Correction: Soluble salts can be leached out with plain water. First, determine the cause of the high soluble salts level and correct it.

Boron

The cause: deficit in the fertilizer mixture.

The symptoms: Insufficient flower formation, the flowers are smaller and deformed. Boron deficiency affects the apical meristems (growth points). Sometimes the meristem dies completely and the side shoots start to grow (broom effect). The meristems have shorter internodes, which are often thicker and show small and deformed leaves at the tip. The shorter internodes sometimes lead to dwarfism. The stems often have breaks and cracks. The fruits are sometimes deformed and corked. Cracks or spots are also possible. Older leaves can show necrosis.

Detection: leaf analysis.

Correction : Fertilizers containing boron: Borax or boric acid, but note that boric acid is highly toxic. Alternatively: If there is a general nutrient deficiency, complete fertilizers that also contain boron can be used.

Boron toxicity

The cause: Boron toxicity is caused by too much boron applied to plants. Of the nutrients commonly applied as fertilizers, boron has the narrowest margin between deficiency and toxicity. It is easy to apply too much boron. Check the calculations of fertilizers before applying them and check again. It can also be found in irrigation water. It is important to check the boron level in a water source before use and to take into account the boron in the water when adding boron fertilizer.

The symptoms: Symptoms of boron toxicity are yellow and dead spots on the leaf edges. Reduced root growth can also occur.

Detection: Monitor the media and perform plant analysis.

Correction : Determine the source of the excess boron and correct it.

Calcium deficiency

The cause: Strong temperature changes can interrupt and hinder calcium uptake. Lack of light, cold and/or too humid environmental conditions. Fertilizer level too low. Calcium deficiency can be caused by under-fertilization, a nutrient imbalance or a pH value that is too low. It is also related to moisture management, high temperatures and low air circulation. Calcium is a mobile nutrient and is transported through the plant in the water-bearing tissues. Fruits and leaves compete for water. Low relative humidity and high temperatures can lead to an increased transpiration rate and increased transport to the leaves. In this case, a calcium deficiency can develop in the fruits.

The symptoms: The apical meristems (these are the dividing tissues of the plant) are deformed and die off without any noticeable symptoms on the oldest leaves. The upper part of the stem and flower bud may bend. Small and deformed leaves on the upper side. Unusually dark green leaves. Premature flower and fruit drop. After a deficiency, the leaves that were developing at the time of the deficiency often show a typical deformation/drying out or a white edge. This is called tip burn and is particularly common in lettuce and strawberries. Browning of the inside of a stem/head, around the growing point like in celery (black heart). Typical symptoms are also blossom end rot on peppers and tomatoes. Symptoms usually first appear as brown leaf edges on new plants or on the underside of the fruit. Blossom end rot in tomatoes and peppers. As symptoms progress, you may see brown, dead spots on the leaves. A lack of sufficient calcium can lead to rot.

Detection: Leaf analysis. Fruits have a poorer shelf life.

Correction : Make sure the pH is between 5.5 and 6.5. Add calcium nitrate or calcium chloride depending on whether you need the extra nitrogen or not.

In the greenhouse: Increase the temperature. More light. Without wind, the plant's nutrient transport is reduced - ensure air movement in the greenhouse.

Ferrum deficiency

The cause: The most common cause of iron deficiency is high pH in the media and/or irrigation water. It can also be caused by nutrient imbalance.

The symptoms: Iron deficiency in plants shows itself as yellowing between the leaf veins. Note that this symptom appears first on new growth.

Detection: Monitor the media and perform plant analysis.

Correction : Correct the pH of the nutrient solution. If necessary, add iron fertilizer.

Sulphur deficiency

The cause: Too little or incorrectly proportioned fertilizer. A pH value that is too low also blocks the absorption of sulfur. At a pH value of 4.0, sulfur absorption stops completely. Too little magnesium.

The symptoms: Extensive yellowing of the leaf tissue and the leaf veins. Often the younger parts of the plant first and later the whole plant. Symptoms are more likely to appear in young or freshly growing leaves at the top of the plant. Sulfur is an immobile nutrient. This means that sulfur can only be re-disposed (transported) relatively slowly by the plant. Lime green to yellow discoloration on leaves is characteristic of sulfur deficiency. It starts at the leaf stalk and moves to the leaf edges and tip. As the disease progresses, the entire leaves first turn yellow, then later brown and necrotic and then die completely. Sometimes purple/reddish leaf stalks on the affected leaves or even a purple stem. The symptoms of a mild deficiency are usually limited to the top of the plant. The middle part of the plant is hardly affected, lower leaves almost never.

Detection: leaf analysis.

Correction : increase the fertilizer dose. Correct the pH: keep it well above 4.0. 5.5 to 6.5 is a good average for many plants. Enrich the soil with Epsom salt / magnesium sulfate / MgSO₄ : one teaspoon per 2 liters of water (approx. 1% concentration).

Nitrogen deficiency

The cause: Nitrogen deficiency can be caused by under-fertilization, nutrient imbalance or excessive leaching.

The symptoms: Typical first symptoms of nitrogen deficiency are light green foliage and a general stunting of the plants. Wilting and dead and/or yellow leaf edges can also be observed. Yellowing of the entire leaf, including the leaf veins, can be seen. The older leaves turn yellow first, but the nitrogen deficiency quickly leads to a general yellowing. Necrosis or deformation of leaves or stems does not appear in the initial stage.
General growth retardation.

Detection: Measuring/monitoring the electrical conductivity (EC) of nutrient solutions can help prevent nitrogen deficiency. Adjust the EC value if it is too low or too high.

Correction : Determine the cause and correct it. This may mean adding more nitrogen to the nutrient solutions. It may also mean there is too much of an antagonistic nutrient in the nutrient solution.

Potassium deficiency

The cause: incorrectly dosed nutrient solution. Plant consumption higher than calculated: a potassium deficiency often occurs in crops that bear a large amount of fruit.

The symptoms: Wilting of the plants even at moderate temperatures. Leaf edge necrosis on the oldest leaves. Browning and curling of the lower leaf tips and yellowing (chlorosis) between the leaf veins. Purple spots may appear on the underside of the leaves. Yellowing: Yellowing also begins on the edges of the oldest leaves and develops towards the middle of the leaf. In some cases the leaf edge is not affected and the necrosis begins inside the leaf between the leaf veins.

Detection: Nutrient analysis and/or perform plant analysis.

Correction : Re-dose. Check antagonist concentration: nitrogen, calcium, magnesium

Note: Too much potassium can cause severe stunting, redness, and poor germination. Excessive amounts of potassium can also make it difficult to absorb other ions such as calcium.

Copper deficiency

The cause: incorrect fertilizer composition.

The symptoms: White discoloration in the tips of the younger leaves. The leaves curl up in a corkscrew shape. Later they may die (necrosis).
The youngest leaves have difficulty unfolding. The youngest leaves curl up and wilt. Necrosis at the youngest growing points and the leaf margins of the youngest leaves.

Correction : Add special copper fertilizer.

Magnesia deficiency

Cause: Magnesium can be caused by a high pH of the medium and/or a nutrient imbalance between potassium, calcium and nitrogen.

The symptoms: Yellowing of the leaf tissue. The leaf veins remain green. This yellowing begins on the oldest leaves. Look for yellowing between the leaf veins as a symptom of magnesium deficiency: chlorosis or yellowing. Magnesium deficiency usually shows up first on the lower to middle leaves, which makes it easier to distinguish from iron deficiency. Premature leaf drop of the affected leaves. Sometimes the discoloration can be more brownish than yellow.

Detection: Nutrient analysis and perform plant analysis.

Correction : Correct the pH of the nutrient solution. If necessary, add magnesium fertilizer. Check the dosage of competing cation suppliers (K, Ca and N).

Manganese deficiency

Cause: Too little or no fertilizer. Manganese deficiency is somewhat similar to iron deficiency: chlorosis between the leaf veins. Light green net on the leaves. It can also be confused with magnesium deficiency. With a manganese deficiency, the leaf veins (including the smaller veins) remain green, but the green stripes remain very narrow.
With a magnesium deficiency, these green stripes around the veins are wider and the finest leaf veins also turn yellow.

The symptoms: Distinct network of green veins. Sometimes occurs on young, but already fully developed leaves (middle leaves).

Correction : Add special manganese fertilizer. Increase fertilizer dosage.

Molybdenum deficiency

The cause: Too little or no fertilizer. Many symptoms of a molybdenum and nitrogen deficiency are similar. The plant cannot use and process nitrogen without molybdenum.

The symptoms: The plants are smaller and show a pale green color. The discoloration can develop into yellowing first on the edges and then between the main veins. The leaf disk disappears almost completely, only the main vein of the leaf remains with small pieces of leaf. This main vein is usually also wavy. (whipstick symptoms). The leaves remain smaller and sometimes take on a spoon-like shape: wavy edge and curved main vein.

Correction : Add special molybdenum fertilizer.

Phosphorus deficiency

The cause: The pH value may not be in the optimal range of 5.5 to 6.5. There may also be an imbalance of nutrients. Check the antagonist zinc dosage. In cold periods, a build-up of sugar in the leaves can show the same symptoms as a phosphorus deficiency.

The symptoms: stunted and spindle-shaped growth, reduced leaf size and reduced number of leaves. Dull grey-green leaves with red pigments in the leaves. The phosphorus deficiency is mainly evident in the characteristic reddish to purple leaf discolouration, first on older leaves, and often the leaf veins are also affected.

General growth retardation. Poor root development. Smaller plants than usual.

Detection: pH control and dosage monitoring. Nutrient analysis.

Correction : Correct the pH value of the nutrient solution. If necessary, reduce the zinc content in the nutrient solution.

Note: An excess of phosphorus can result in a deficiency of trace elements such as Zn, Fe or Co.

Zinc deficiency

The cause: Possibly too high a phosphorus content in the nutrient solution or too little zinc in the nutrient solution.

Symptoms: The following symptoms may occur: Chlorosis: yellowing of the leaves. Depending on the species, young leaves may be the most affected, while in others both old and new leaves are chlorotic. Necrotic spots: partial or total death of leaf tissue in areas of chlorosis. Leaf bronzing: chlorotic areas may turn bronze. Retarded plant growth: this may occur as a result of a decrease in growth rate or a decrease in the internode (the length of the shoot between two nodes). Dwarf leaves: small leaves that often show chlorosis, necrotic spots or bronzing. Malformed leaves: leaves are often narrower or have wavy edges.

Detection: Monitor media and/or perform plant analysis.

Correction : Correct the pH value and/or the amount of phosphorus if you know that there is enough zinc in the nutrient solution. Otherwise, add zinc in small doses. Remember: copper and phosphate reduce the absorption of zinc!

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Fertilizer: Essential Nutrients, Function, Deficiency and Exces