Nutrient Management

In today’s article, I want to cover in brief 3 aspects of how nutrient interactions happen within the plant.

1. Antagonistic and Stimulant nutrients
2. Law of minimum
3. Mobility of nutrients

Antagonistic and Stimulant nutrients:

Antagonistic nutrients have a negative effect on the uptake of other nutrients. Possibly you have seen that an excess of Phosphorus (P) creates an imbalance with Iron (Fe) and Zinc (Zn)?

Some nutrients do the opposite and their presence has a positive effect on the uptake of other nutrients. These are called Stimulant Nutrients and an example of this is would be when increasing the nitrogen (N) availability to the plant, it will allow the plant to take in more magnesium (Mg) and up the demand for it. To show this we have the Mulder Chart.

(Copied from Bariya et al. 2014)

Put simply, high levels of a particular nutrient can interfere with the availability and uptake of other nutrients. The nutrients which interfere with one another are referred to as antagonistic. For example, high nitrogen levels can reduce the availability of boron, potassium, and copper; high phosphorous levels can reduce the availability of iron, calcium, potassium, copper, and zinc, and high potassium levels can reduce the availability of magnesium and calcium. For this reason, unless care is taken to ensure an adequate and balanced supply of all nutrients too much nitrogen, phosphorus, and potassium (and others) in fertilizers/nutrients can induce plant deficiencies of other essential elements.

Stimulation occurs when the high level of a particular nutrient increases the demand by the plant for another nutrient. For example, increased nitrogen levels create a demand for more magnesium. If more potassium is used then more manganese is required etc. Although the cause of stimulation is different from antagonism, the result is the same; induced deficiencies in the plant if it is not supplied with balanced nutrition.

Law of minimum:

Liebig’s Law of the Minimum is a principle developed in agriculture that states that if one of the nutritive elements is deficient or lacking, plant growth will be restricted and not in its full potential even when all the other elements are abundant. Any deficiency of a single nutrient, no matter how small the amount needed, will hold back plant development. If the deficient element is supplied, growth will increase. Excess supply however will not be helpful, due to the laws of nutrient antagonism discussed above.

For instance, excessive phosphorus will reduce the availability of iron, calcium, potassium, nitrogen, copper, and zinc. This is particularly true of the microelements iron, copper, and zinc. What this means is that the overuse of phosphorous in solution will potentially starve out other important nutrients/elements that are required for healthy growth/optimal yields.

Low nutrient levels will result in deficiencies, while high concentrated nutrient solutions lead to the potential for excessive nutrient uptake and, therefore, toxic effects may result. Many people think that more is better when supplying nutrients and additives and that it is better to have excess nutrients in the solution than levels that are only adequate. This is not necessarily true and this thinking can potentially lead to serious imbalances in nutrient uptake.

Mobility of nutrients:

All nutrients move relatively easily from the root to the growing portion of the plant through the xylem. Interestingly, some nutrients can also move from older leaves to newer leaves if there is a deficiency of that nutrient. Knowing which nutrients are ‘mobile’ (i.e., able to move) is particularly useful in diagnosing plant nutrient deficiencies because if only the lower leaves are affected, then a mobile nutrient is most likely deficient. Conversely, if only the upper leaves show the deficiency, then the plant is likely deficient in an immobile nutrient because that nutrient cannot move from older to newer leaves. The below table lists the six mobile and eight immobile mineral nutrients. Sulfur is one element that lies between mobile and immobile elements depending on the degree of deficiency.

Mobile Nutrients	Immobile Nutrients
Chloride	Boron
Magnesium	Calcium
Molybdenum	Copper
Nitrogen	Iron
Phosphorus	Manganese
Potassium	Nickel
	Zinc
Sulfur (intermediate between mobile and immobile)

 

Finally, Please note that Proper nutrient manage­ment should include the “Four R’s” of fertilizer use: apply the right nutrient, at the right rate, at the right time, and in the right place for the selected crop (Mikkelsen 2011).

References

Bariya H, Bagtharia S, Patel A. 2014. Boron: A Promising Nutrient for Increasing Growth and Yield of Plants In: Nutrient Use Efficiency in Plants.153–170. DOI: 10.1007/978-3-319-10635-9_6

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 micro nutrients 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.

Plants are similar to us humans and animals in that when under stress from poor nutrition, our bodies suffer in growth, development, and general health. Animals show these disorders in the form of weak bones, skin discolouration, and poor weight. Plants show nutritional defects in their vigour, strength of the stems, colour of the leaves and poor yields.

Whenever plants undergo any type of stress from environmental conditions to lack or excess of nutrients, they will express signs of disorders. Pest and diseases also cause stress and disorders within the plant.

Symptoms of disorders within the plant may be expressed as leaf yellowing (chlorosis), browning (necrosis), burning (white colouration due to loss of chlorophyll in leaves), deformation of leaves and growing tips, and stunting of overall growth. The first thing to observe with a nutrient disorder is the location of the affected tissue.

 

 

 

 

 

 

Leaves will, in general, show the symptoms first. If it is a root problem due to disease or lack of oxygen, examination of the roots will reveal that they are not turgid and white, but limy and brown. The plant will wilt during high light periods as the water loss by transpiration is greater than the roots ability to take up sufficient water.

The location of symptoms on the plant is the first clue as to the cause of the disorder. Focusing on leaf symptoms, if the lower leaves are expressing yellowing, browning, or spots first, then the group of nutrients responsible for the disorder would be those of mobile elements. Mobile elements can be re translated within the plant from the lower order tissue to the younger tissues in the top of the plant. These elements include N, P, K, Mg, Zn and Mo. Initial symptoms will be a yellowing (chlorosis) followed by browning or drying (necrosis) of leaf tissue. If the symptoms appear in the young leaves at the tip of the plant, this disorder is a result of a lack of immobile elements that cannot move from the older plant parts to the growing tip. These immobile elements are Ca, B, Cu, Mn, S and Fe. To determine which of these is the cause of the disorder there are some visual keys listed below allowing you to make a number of alternative choices. Each selection narrows the possible causes in the final step, there is a single element identified.

• It is critical to recognize any symptoms occurring at an early stage of the plants, expression of these stress clues because as the disorder goes on without correction, the symptoms expand progressing from simple yellowing spots to complete yellowing and necrosis. At that stage, it is very difficult to know the first form of symptoms as they spread throughout the plant giving it an overall chlorosis, necrosis, and deformation of tissues. In addition, as the stress becomes more severe, it will be difficult, taking a lot of time to correct it once identified. The loss of the plant's health may become permanent or event result in its death. Yields will be greatly reduced as the stress is not corrected. The stress may begin as a cause from a single element and then as it progresses, another element uptake is slowed or blocked and the plant suffers from multiple disorders. A very useful procedure when a symptom first appears is to immediately change the nutrient solution. That is, make up a new batch. At the same time, to determine the exact cause send a nutrient or tissue sample to a laboratory for analysis. Similar to soil analysis, the laboratory will give you guidelines as to what the normal leaves of each nutrient should be in the solution or in the plant and direct you to make adjustments in the nutrient solution formulation.

Mobile Elements Deficiencies: -

Nitrogen: -

• Lower leaves become yellowish green and growth is stunted

Remedies: -

• Add calcium nitrate or potassium nitrate to the nutrient solution.

Phosphorous: -

• Stunted growth of the plant, a purple colour of the undersides of the leaves is very distinct and leaves fall off prematurely.

Remedies: -

• Add mono potassium phosphate to the nutrient solution.

Potassium: -

• The leaflets on older leaves of tomatoes become scorched, curled margins, chlorosis between veins in the leaf tissue with small dry spots. Plant growth is restricted and stunted. Tomato fruits become blotchy and unevenly ripen.

Remedies: -

• Apply a foliar spray of 2% potassium sulfate and add potassium sulfate to the nutrient solution.

 Magnesium: -

• The older leaves have interveinal (between veins) chlorosis from the leaf margins inward, necrotic spots appear.

Remedies: -

• Apply a foliar spray of 2% magnesium sulfate, add magnesium sulfate to the nutrient solution.

Note: - When applying foliar sprays, if in a greenhouse, avoid doing during high sunlight conditions as that can cause burning of the leaves. Apply in the early morning while the sun and temperatures are low.

 Zinc: -

• Older and terminal leaves are abnormally small. The plant may get a bushy appearance due to the slowing of growth at the top.

Remedies: -

• Use a foliar spray with1%-0.5% solution of zinc sulfate. Add zinc sulfate to the nutrient solution.

Immobile elements: -

• First, the symptoms appear on the younger leaves at the top of the plant.

Calcium: -

• The upper leaves show marginal yellowing progressing to leaf tips, margins wither, and petioles curl and die back. The growing point stops growing and the smaller leaves turn purple-brown colour on the margins, the leaflets remain tiny and deformed. Fruit of tomatoes shows blossom-end rot.

Remedies: -

• Apply a foliar spray of 1.0% calcium nitrate solution. Add calcium nitrate to the nutrient solution.

Sulfur: -

• Upper leaves become stiff and curl down, leaves turn yellow. The stems, veins and petioles turn purple and plant growth is restricted.

Remedies: -

• Add potassium sulfate or other sulfate compounds to the nutrient solution. A sulfur deficiency is usually rare because it is added to the nutrient solution by use of potassium, magnesium, and other sulfate salts.

 Iron: -

• The terminal leaves start turning yellow at the margins and progress through the entire leaf leading eventually to necrosis. Initially, the smallest veins remain green giving a reticulate pattern. Flowers abort and fall off, growth is stunted and spindly in appearance.

Remedies: -

• Apply a foliar spray with 0.02%-0.05% solution of iron chelates every 3-4 days. Add iron chelate to the nutrient solution.

Boron: -

• The growing point withers and dies. Upper leaves curl inward and are deformed having interveinal mottling (blotchy pattern of yellowing). The upper smaller leaves become very brittle and break easily.

Remedies: -

• Apply a foliar spray of 0.1%-0.25% borax solution. Add borax or boric acid to the nutrient solution.

 Copper: -

• Young leaves remain small, margins turn into a tube toward the midribs in tomatoes, petioles bend downward, and growth is stunned to get a bushy appearance of the plant at the top.

Remedies: -

• Use a foliar spray of 0.1% - 0.2% solution of copper sulfate. Add copper sulfate to the nutrient solution.

Note: - whenever applying a foliar nutrient spray, apply it first to a few plants and wait to apply it to all plants for about a day to be sure that no burn occurs from the spray.

Manganese: -

• Middle and younger leaves turn pale and develop a characteristic checkered pattern of green veins with yellowish interveinal areas. Later small necrotic spots form in the pale areas. Shoots will become stunted.

Remedies: -

• Apply a foliar spray of 0.1% manganese sulfate solution. Add manganese sulfate to the nutrient solution.

Molybdenum: -

• All leaves show a pale green to yellowish interveinal mottling. Usually progresses from the older to the younger leaves.

Remedies: -

• Apply a foliar spray of 0.07%-0.1% solution of ammonium or sodium molybdate. Add ammonium or sodium molybdate to the nutrient solution.

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.