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HYDROPONIC NUTRIENT  FUNDAMENTALS

 

(Excerpt from Integral Hydroponics Evolution by G.Low. Coming soon!)

 

It is important to note that by the time you identify symptoms of nutrient deficiencies or excesses the problem has already impacted on yields (this is particularly true during the bloom cycle). I.e. a plant’s growth rates are reduced long before deficiencies or excesses become visually apparent. Scientists call this phenomenon “hidden hunger” (nutrient deficiency) or “incipient toxicity” (nutrient excess).

 

Because Hydroponic substrates are inert (devoid of food), the food is provided to the plant through a balanced diet of liquid nutrition (nutrient), which is added to water in the nutrient tank/reservoir. This is then fed to the plants, ensuring that they are getting adequate levels of food. This is why the pH of the water/nutrient is critical. For the plants to uptake the differing elements that make up the nutrient it is necessary to have the nutrient set at the correct pH. In addition to this, the EC is also critical. If the levels of food are too low the plant will be starved of nutrition. If the nutrient is too strong (EC is too high) other problems such as necrosis (burning/rusting) may be apparent.

 

Plant nutrition is a complex business. How each element affects the plant, whether the element is mobile or immobile within the plant and the interaction of each element with other elements along with their part in photosynthesis is always going to be a complex business to discuss.

 

Fortunately, it is something that the indoor grower doesn’t have to worry too much about today as there are many good nutrients on the market. They differ somewhat in their macro and microbalances; however, using a reputable brand should ensure that the plant is receiving the correct balance of micro and macro nutrition.

 

Often individuals will ask me to recommend a brand of nutrient over the other brands. I’m going to tell you the same thing as I tell them regarding this. “I really could not tell you. If I were to put 100 hydroponic gardeners in the same room there would be a raging debate about the best nutrient to use” (among other things).

 

What I’m saying here is that personal preference and your growing practices (recycling v. run-to-waste, nutrient tank/reservoir practices etc.) will determine the best nutrient for you. I would be extremely hesitant to recommend any one brand over another. There are many, many good nutrients on the market today.

 

Nutrients can be purchased as single part formulas, two part formulas and as triple pack formulas. Over the years I have played with all of these systems and achieved great results across the board. Again, personal preference (ease of use etc) will help you decide which is the most ideal for you.

 

My only recommendation…. the thing about nutrients that you ought to be aware of is the hype that goes with them. Be wary of paying too much for a product that probably isn’t going to perform any better than the product next to it that is 30 – 40% cheaper. You may be paying extra for an extravagant label, importation costs, and the manufacturer’s advertising campaign.

 

I’ve had some of the expensive brand names lab analyzed only to discover that they aren’t anything special compared to far cheaper brands. If you factor in the vast number of different growing methodologies practiced amongst indoor hydroponic gardeners, and if you understand what goes into a nutrient, the approximate cost of the constituents, the principles of plant nutrition and particularly the principles of the sufficiency and luxury nutrient ranges, which I discuss in detail on pages…. , you tend to be a bit sceptical about using higher priced products. For example, here is what a highly renowned PhD biochemist and plant nutrient expert had to say after analyzing perhaps the most expensive (given nutrient concentration and price) big name multinational brand on the market today.

 

(Quote)

 

“Interpretation:

 

There is nothing unusual or unexpected in the mixes. Veg is a fairly standard grow mix and Flower is a fairly standard bloom mix. Both are rather more acid­ic than optimal, due to the formulation used. Flower B contains much more ammonium than most other plant nutrients. This is because monoammonium phosphate is used to boost P to the high levels required. The following formulations will provide a solution which is close to those supplied. You can never be exact, because batch-to-batch variation between fertilizers means you will never get better than 98% reproducibility.”

 

(End Quote)

 

The store I worked in at that time was one of the top 10 Australian distributors of the line. After a falling out with its Australian distributor we had the products (nutrients and additives) lab analyzed and subsequently reverse engineered them.

 

What we immediately did was drop the price from a rather hefty $99.00 AUD for a 2 part 10ltr A&B set for the original, reducing it to $50 AUD for our product which was presented in unlabeled plain white bottles with A and B written on them in black or blue permanent marker (very high tech and truly a nutrient without the bells and whistles!). Not only this, but there was no impressive laboratory or white coats anywhere in sight – our product was knocked up by the biochemist in 200ltr plastic drums using a water pump to circulate the ingredients as he mixed.

 

We then told our customers that we were dropping their preferred line (largely preferred because we had recommended it in the first place) and that we had engaged a highly renowned PhD Biochemist to reverse engineer and “tweak” the original formulas and that the copy was as good as the original – if not better. We, however, added that if they didn’t find our nutrient to their liking we would order the original for them as they required.

 

As it turned out the product was a hit. Our PhD biochemist had weaved his magic and not only were our customers confirming the new products quality but also, in many cases, stating (insisting) that it was superior to the original, producing higher yields and a better quality end product. I myself, on trialing the product, was happy but didn’t see any differences in yields and/or quality, when compared to the original, and put my customers rave reviews down to a collective hysteria… a placebo effect based on savings. Nevertheless, the bottom line; not one single customer (not one) requested the original again and new customers began appearing at the store seeking our no thrills, cheaper product that they had heard so much about through their friends. Within weeks, the product was walking out the door and our customer base increased by approximately 20% within the year. No small feat given two new stores had opened within 10km of us in approximately the same period.

 

The moral of the story: The power of branding and marketing.

 

Were the original formulas any better than any other formula? Clearly many growers thought so. The company is multinational with a good reputation – one that it has worked hard to create – and certainly their nutrients are better than some formulas I have subsequently lab analyzed. On the other hand, as the biochemist noted, there was nothing “unusual or unexpected” about their mixes. Good formulas pretty much tend to look and perform about the same and the key difference – if any – comes down to marketing and consumer perception.

 

Why then did our store recommend the multinational product over others?

 

In truth, because it was a product I had used and liked (better than some – no better than others) and secondly, perhaps more importantly, due to its higher recommended retail price we made more profit from selling this product over cheaper brands. It is important to understand this factor and is true of all retail businesses, whether they be selling clothing or hydroponic specialty equipment. In short, hydroponic retailers by other retail standards have low profit margins on the goods that they sell; typically about 100% markup on wholesale price where consumables (e.g. nutrients and additives) are concerned and even lower margins in most cases on hardware. Think yourself lucky on this front. For instance, to generalize somewhat, clothing retailers typically markup 200- 400%. Basically though, if you purchase a $100 10L nutrient pack the retailer has made about $50.00. On the other hand, if you purchase a $50.00 10L nutrient pack the retailer has made $25.00. If you were him/her and had a business to run, with all of the associated costs (e.g. rent, insurance, wages), which product would you prefer to sell? It’s a case of simple business economics. Other than this, some nutrient manufacturers fully understand this principle as good business practice. I.e. create products that create higher profit margins for the retailer and they are likely to support it. For example, the company’s whose formulas we reverse engineered and sold to our customers was found guilty of price fixing in Australia in 2005 by an Australian Government corporate watchdog. The Australian distributor had sent an Australia wide letter to retailers demanding that they stop discounting their brand below the recommended retail price (RRP) or they wouldn’t supply them. This, as it turned out, was in breach in corporate law and as a result the company was called to task.

 

When discussing value for money, with regards to hydroponic nutrients, it is important to note that some nutrient brands are more mineral dense (concentrated) than others, meaning that some nutrients require a lower dilution rate than others to achieve the same EC in solution. Therefore, when considering the price/value of a nutrient be sure to factor in the product’s concentration. That is, if one product is 40% more concentrated than another and costs 25% more, this product is actually 15% cheaper than its less concentrated counterpart because it will go 40% further at only 25% more recommended retail price.

 

Okay, that was pretty simple wasn’t it? Now I’m going to get somewhat technical and explain what roles the different macro and microelements play in the plant.

 

Before I do this, I had better point out that there are some nutrient deficiency symptoms outlined. However, it is important to note that while visual nutrient deficiency symptoms can be a very powerful diagnostic tool for evaluating the nutrient status of plants, one should keep in mind that an individual visual symptom is seldomly sufficient to make a definitive diagnosis of a plant’s nutrient status. Many of the classic deficiency symptoms such as tip burn, chlorosis and necrosis are characteristically associated with more than one mineral deficiency. Additionally, what appears to be a nutrient deficiency can be due stresses such as high ambient air temperatures, pathogens, high levels of sodium chloride in the substrate, oxygen starvation in the root zone (due to too high temperatures in the nutrient and/or substrate) and air pollution. Often, symptoms of these stresses closely resemble those of a nutrient deficiency. That is….

 

Some possible reasons for nutrient deficiency and excess symptoms beyond actual nutrient deficiencies and excesses:

 

1) The mains (municipal) water supply that you use may be high in microelements such as iron, copper and zinc. When these combine with the microelements in the nutrient solution toxicity is expressed due to too high levels of micro-nutrition in the nutrient working solution (I.e. the solution that is being fed to the plants).

2) Your mains water supply may contain high levels of both sodium and chloride. When combined this equates to high levels of common table salt (i.e. sodium chloride or NaCl) in solution. High levels of NaCl is toxic (phytotoxic) to plants and is expressed in what looks like nutrient deficiencies and/or excesses.

3) If growing in coco coir substrate, did you purchase a quality flushed and buffered coir substrate or a cheap compressed brick product? Similar to some mains water supplies, cheap coco coir products can come loaded in sodium chloride. The end result is phytotoxicty and what looks like nutrient deficiencies and/or excesses.

4) Plant Pathogens often produce an interveinal chlorosis in the leaves (yellowing or whitening of the leaf veins) that can be easily mistaken for a nutrient deficiency. Put simply, when a pathogen infects a plant, it alters the plant’s physiology, particularly with regard to mineral nutrient uptake, assimilation, translocation, and utilization. Plant pathogens/diseases can also infect the plant’s vascular system and impair nutrient or water translocation. Such infections can cause root starvation, wilting, and plant decline or death. Plant pathogen/disease symptoms can often be separated from nutritional symptoms by the rate in which they affect a population of plants. If the plants are under nutrient stress, all plants tend to develop similar symptoms at the same time. However, if the stress is the result of pathogens, the development of symptoms will have a tendency to vary between plants.

5) Too high ambient air temperatures (heat stress) severely limits utilization of absorbed light energy in photosynthesis which leads to exposure of the chloroplasts to excess energy and thus generation of reactive oxygen species (ROS) such as superoxide radical, hydrogen peroxide, hydroxyl radical and single oxygen. Therefore, oxidative cell damage is a common phenomenon in heat stressed plants.[1] The end result is what looks like nutrient deficiencies and/or excesses.

6) Excessive humidity slows transpiration in plants which results in slowing the distribution of nutrients throughout the plant. The end result is nutrient deficiencies.

7) Oxygen starvation in the root zone results in an unhealthy root system and thereby can greatly impact on nutrient uptake, resulting in deficiencies. In hydroponics, oxygen starvation in the root zone due to overly warm nutrient and/or media temperatures is probably the leading cause of root death and reduced growth rates. I.e. unhealthy roots = unhealthy nutrient uptake and, as result, nutrient deficiencies occur.

8) Salt buildup in the media and root zone can cause damage to the plants both through direct contact with the salt crystals around the plant stem, particularly in young plants, and by increasing the osmotic pressure around the roots. The end result is nutrient deficiencies.

9) pH problems are often the cause of nutrient deficiencies because pH determines the availability of mineral elements to plants. Too high or too low pH can, therefore, reduce nutrient availability resulting in deficiencies.

 

As you can perhaps see, nutrient deficiency or excess symptoms can be caused by numerous biotic and abiotic stresses. Therefore, any deficiencies and/or excesses need to be addressed holistically because often what appears to be deficiencies or excesses are caused by unfavorable environmental conditions, pathogens and/or root disease. As such, it is too simplistic to label the problem as a nutrient deficiency and/or excess before covering all of the bases. That is, if you plants show signs of nutrient deficiencies or excesses check that the roots are healthy and white (not turning brown).

 

Check that your environmental conditions are within ideal parameters (temp, airflow, humidity etc).

 

Check that your pH and EC meters are calibrated and working properly (a trip to the hydro store to have your retailer look them over may be in order).

 

Check for signs of salt buildup in the media (if in doubt flush the media with pH adjusted water). And, treat your plants for potential pathogens (speak to your retailer for more information about product options). Last, but by no means least, dump your nutrient tank and mix a fresh batch of nutrient to cover all bases. Other than this, a foliar feed will greatly help the plants recover from a deficiency. After you have implemented all of these measures, watch the plants closely to make sure that the problem starts to clear up over a few days. Old growth may not recover, but new growth should appear healthy.

 

Steps to follow where a nutrient deficiency is apparent

 

  • Check the roots of the plants. Are they white (healthy) or brown (unhealthy)? If the roots are brown check your nutrient tank/reservoir solution temperature – it should be below 23oC (73.4oF)
  • Dump the nutrient tank/reservoir and mix a fresh batch
  • Flush the media with pH adjusted water (salt build up and or a nutrient excess may be locking out crucial nutrients)
  • Treat the plants for potential pathogens
  • Check that all of your grow room environmental factors (air tamp, water temp, relative humidity) are within ideal parameters
  • Foliar feed the plants as a quick fix to correct a deficiency (avoid in mid to late flower due to the potential for botrytis/grey mould)
  • Ensure that your pH and EC are within ideal ranges after you have made a fresh batch of nutrients
  • If in doubt about the reliability of your pH and/or EC readings take your meters to your hydroponic retailer to have them looked at (this is recommended either way)

 

 

It is important to note that by the time you identify symptoms of nutrient deficiencies or excesses the problem has already impacted on yields (this is particularly true during the bloom cycle). I.e. a plant’s growth rates are reduced long before deficiencies or excesses become visually apparent. Scientists call this phenomenon “hidden hunger” (nutrient deficiency) or “incipient toxicity” (nutrient excess).

 

We’ll be covering a great deal of material in the following chapter on nutrient science that helps you to understand the principles of hidden hunger and incipient toxicity. However, briefly for now, let’s begin with incipient toxicity, where a nutrient excess is present. As the name implies, incipient toxicity describes being in an initial stage; beginning to happen or develop. Therefore, incipient toxicity is where excess nutrients slowly begin to accumulate in the plant tissue to such a degree that they start to become toxic. Signs of excess won’t necessarily become apparent for some time. However, growth will be impaired long before nutrient excess signs become apparent. Therefore, while growers are providing too much nutrient (enough nutrients to impair growth) they can be completely unaware of this because the visual symptoms that growers attribute to excess aren’t apparent. Nevertheless they are losing yield because this excess is hidden and is impacting on growth.

 

Where “hidden hunger” (nutrient deficiency) is concerned, as the name implies, the plant is hungry but we cannot see it (i.e. symptoms of hunger are “hidden”). Because the exact concentration of a nutrient below which yields decline is difficult to determine precisely, some experts define the critical level as the nutrient concentration at 90 or 95% of maximum yield. However, hidden hunger can be present well before this without visible signs of a deficiency. For example, a grower may only be achieving 80-85% of the maximum possible growth before visual symptoms of a deficiency present.

 

In fact, scientifically speaking, the expression of nutrient deficiency symptoms varies for acute or chronic deficiency conditions. Acute deficiency occurs when a nutrient is suddenly no longer available to a rapidly growing plant. Chronic deficiency occurs when there is a limited but continuous supply of a nutrient, at a rate that is insufficient to meet the growth demands of the plant.

 

Most of the classic deficiency symptoms described in textbooks or online are characteristic of acute deficiencies. However, the most common symptoms of low-grade, chronic deficiencies are a tendency towards darker green leaves and stunted or slow growth. So basically, where a chronic deficiency is present, the plants leaves are dark green. As such, the plant looks healthy to novice growers (if its dark green its healthy right?). The problem is that dependent on the degree of a chronic deficiency many novice growers are unlikely to be able to spot that growth rates are less than optimal. From a scientific perspective, the only way of knowing that hidden hunger or a chronic deficiency is present is through lab analyzing the plant tissue or through having another plant that is being fed with more ideal nutrition to measure growth rates against.

 

This is something that hydro nutrient manufacturers and others typically forget to mention – perhaps many of them don’t understand this themselves. That is, ‘hydro’ growers have been led to believe that if a nutrient deficiency or excess is present then the plant will tell them this through displaying symptoms of excess or deficiency.

 

Nothing could be further from the truth!

 

The fact is that yield losses can occur long before signs of excess or deficiency become apparent. The only way of knowing that these deficiencies or excesses are impacting on growth is through running tissue analysis or having a control plant which is being fed with more ideal nutrition to compare growth rates to.

 

Now that you have this important scientific fact under your belt, let’s move on

 

The Role of Nutrients in Plants – Overview of Pant Nutrients

 

Plants require 18 essential elements. Of these, 15 essential elements need to be provided to the rootzone. These are the macronutrients (needed in relatively large quantities) of nitrogen, phosphorus, potassium, sulfur, calcium and magnesium; and the micronutrients (needed in relatively small quantities) of iron, manganese, zinc, boron, copper, molybdenum, cobalt, chloride and nickel. All of these nutrients must be supplied by the hydroponic nutrient solution, although chloride, cobalt and nickel aren’t included in most recipes, as they’re typically found in sufficient quantities as impurities in fertilizers or provided through the water supply (e.g. mains water will provide chloride).

 

An element is considered to be essential if the plant cannot complete its lifecycle without it or if it forms part of an essential molecule or constituent.

 

A deficiency of one essential element causes primary metabolic defects leading to stunting or deformity of roots, stems, or leaves, chlorosis or necrosis of various organs and even plant death.

 

The essential elements that are provided to plants through fertilizers are called macro and micronutrients. The macronutrients are used in large quantities and can be categorized into two groups:

 

    1. Primary nutrients: nitrogen (N), phosphorus (P), potassium (K)
    2. Secondary nutrients: calcium (Ca), magnesium (Mg), sulphur (S)

 

The remaining essential elements are used in small quantities by the plant, but nevertheless are necessary for plant survival. These are called micronutrients and include iron (Fe), boron (B), copper (Cu), chloride (Cl), manganese (Mn), molybdenum (Mo), zinc (Zn), cobalt (Co) and nickel (Ni).

 

The following table lists the essential elements, their status as macro or micronutrients, their uptake forms, and their mobility (‘nutrient mobility’) in the plant.

 

Nutrient Mobility

 

The mobility of a nutrient relates to the ability of a nutrient to move within the plant tissue. In general, when certain nutrients are deficient in the plant tissue, that nutrient is able translocate (move) from older leaves to younger leaves where that nutrient is needed for growth. Nutrients with this ability are labelled ‘mobile nutrients’, and include nitrogen, phosphorus, potassium, magnesium, and molybdenum. Conversely, ‘immobile nutrients’ do not have the ability to translocate from old to new growth. ‘Immobile nutrients’ include calcium, sulfur, boron, copper, iron, manganese and zinc.

 

 

 

Macroelements

Element Symbol Available as Symbol Mobile in the plant
Carbon C Carbon dioxide

Carbonic acid

CO2,

H2CO3

Hydrogen H Hydron/hydrogen

Hydroxide

Water

H+

OH

H2O

Oxygen O Oxygen O2
Nitrogen N Nitrate ion

Ammonium ion

Urea

N03

NH4+

CO(NH2)2

Yes
Phosphorous P Monovalent phosphate ion

Divalent phosphate ion

H2PO4

 

HPO4-2

 

Yes
Potassium K Potassium ion K+ Yes
Calcium Ca Calcium ion Ca+2 No
Magnesium Mg Magnesium ion Mg+2 Yes
Sulphur S Divalent sulfate ion SO4-2 No

 

Microelements

 

Iron Fe Ferrous ion

Ferric ion

Fe-2

Fe-3

No
Manganese Mn Manganous ion Mn+2 No
Boron B Boric acid H3BO4 No
Copper Cu Cupric ion chelate

Cuprous ion chelate

Cu+2

Cu+

No
Zinc Zn Zinc ion Zn+2 No
Molybdenum Mo Molybdate ion MoO4 Yes
Chloride Cl Chloride ion Cl Yes
Nickel Ni Nickel ion Ni2+ Yes
Cobalt Co Divalent cobalt Co2+ Yes

 

 

The Essential Elements

 

The Major Nutrient Elements (Macroelements)

 

Nitrogen (N)

 

Of all the essential nutrients, nitrogen, along with potassium, is required by plants in the largest quantity and is most frequently the limiting factor in crop productivity. This element is part of all amino acids (hence proteins), of chlorophyll and of enzymes. It is very mobile in plants, and has a dominant effect on other nutrient use and uptake. Plants typically absorb nitrogen in the form of nitrates or ammonium, and the plant converts this ammonia to create proteins. Plants are also shown in more recent research to uptake the chemically organic, albeit synthetic, urea (another form of nitrogen fertilizer) and organic N containing amino acids (e.g. glycine).

 

Nitrogen is critical to fast, lush plant development. Photosynthesis occurs at high rates when there is sufficient nitrogen. A plant receiving sufficient nitrogen will typically exhibit vigorous plant growth. Leaves will also develop a dark green colour.

 

A deficiency in nitrogen is recognisable through yellowing of the leaves (particularly older, larger leaves), stunted leaf growth, older leaves falling off the plant, and in extreme cases a small spindly plant.

 

Phosphorus (P)

 

 

Phosphorus, in the form of inorganic phosphate (Pi), is one of the most important macronutrients for all organisms. It is not only used in the biosynthesis of cellular components, such as ATP, nucleic acids, phospholipids, and proteins, but it is also involved in many metabolic pathways, including energy transfer, protein activation, and carbon and amino acid metabolic processes. Large amounts of phosphate are required for cell survival. In plants, Pi is essential for growth and development.

 

A deficiency will appear as:

 

  • In the early stages the plant will appear a dark blue/green shade.
  • Plant growth and shoot development may be retarded.
  • Might result in delayed crop maturity and small fruit set
  • Purpling in older leaves
  • Leaves may curl and die

 

Generally, inadequate P slows the processes of carbohydrate utilization, while carbohydrate production through photosynthesis continues. This results in a buildup of carbohydrates and the development of a dark green leaf color. In some plants, P-deficient leaves develop a purple color. Since P is readily mobilized in the plant, when a deficiency occurs the P is translocated from older tissues to active meristematic tissues, resulting in foliar deficiency symptoms appearing on the older (lower) portion of the plant. Other effects of P deficiency on plant growth include delayed maturity and decreased disease resistance.

 

Note: phosphorus uptake is influenced by temperature and a deficiency may be induced by cool nutrient solution and/or ambient air temperatures.

 

Potassium (K)

 

Potassium is not an integral part of any major plant component, but it does play a key role in a vast array of physiological processes vital for plant growth. Potassium is used in large quantities by plants to maintain ion balances within the cells, maintain osmotic pressure throughout the plant and activate enzymes. It is also required for protein synthesis.

 

A deficiency will appear as:

  • The edges of the leaves turning rusty brown.
  • Leaf yellowing.
  • Leaf curling.
  • Plant growth being retarded
  • Flowers fail to develop
  • Older leaves develop marginal browning which can extend into the leaves, and forward curling of leaves

 

Since potassium is mobile in the plant, the symptoms appear on the older leaves first

 

Magnesium (Mg)

 

Magnesium is the essential element that forms the central atom in the chlorophyll molecule. Low magnesium levels reduce the plant’s ability to produce sugars from air and sunlight. Magnesium also helps regulate cellular pH and cation-anion balance within the plant. It is quite mobile in plants.

 

A deficiency will appear as:

  • Rusty spots may appear on leaves.
  • White stripes between the leaf veins may appear
  • Yellowing in veins of older leaves
  • The edges of the leaves may become yellow or bright green and may start feeling brittle to the touch
  • Older leaves are more affected than younger leaves.

 

Calcium (Ca)

 

Plants require a large amount of calcium as it is an essential part of cell walls, enzymes and chromosome structure. Calcium is also involved in the cation-anion balance and maintenance of osmotic pressure, allowing the plant to pump required nutrients around.

 

A deficiency will appear as:

  • Yellow/brown spots on leaves – the spots generally start small and slowly increase in size. The older larger leaves will show the symptoms first.
  • Plant growth is retarded.
  • Leaves fail to fully expand.

 

Sulfur (S)

 

Some plants require as much sulphur as phosphorus. In the plant sulphur is necessary for chlorophyll formation and is a component of methionine, cysteine and cystine, three of the 21 amino acids which are the essential building blocks of proteins.

 

A sulfur deficiency is characterised by:

 

  • Retarded plant growth.
  • Plants may appear very spindly
  • Purpling of leaf stems.
  • Yellowing of leaves.
  • In extreme cases the plant will have yellow leaves and purple stems.

 

Minor Elements (Micro or Trace Elements)

 

Boron (B)

 

Boron is essential to the transport of sugars in the plant, to pollen formation (fertility) and to cell wall structure (like calcium). The main functions of boron relate to cell wall strength and development, cell division, fruit and seed development, sugar transport, and hormone development. It is necessary for normal cell division, nitrogen metabolism, and protein formation. Boron is also essential for proper cell wall formation. It plays an important role in the proper function of cell membranes and the transport of potassium (K) to guard cells for the proper control of internal water balance

 

As boron is required to build plant cell walls, when not enough B is available the areas of the plant with rapidly growing new cells (i.e. the growing point and new leaves) are affected first. The growing tip often aborts (effectively “pinching/tipping” the plant). This leads to proliferation of lateral branches. The branches and new growth are distorted, thick and brittle. Also, the upper foliage can exhibit a mottled chlorosis (i.e. scattered yellowing of leaves). When the roots are examined they are often short and stubby. Boron deficiency is somewhat unique in that unlike most other nutrient deficiencies B deficiency may not appear uniform across the crop.

 

Copper (Cu)

 

Copper is an important component of proteins found in the enzymes that regulate the rate of many biochemical reactions in plants. Copper is an enzyme activator in plants and is concentrated in the chloroplasts of leaves, assisting the process of photosynthesis. Thus, copper plays an essential role in chlorophyll formation and is essential for proper enzyme activity.

 

A copper deficiency can be identified through leaves curling downwards, the tips and margins of the leaves may exhibit coppery gray or slightly blue discolorations with a metallic sort of look. In between the veins, the leaves may yellow, new growth may have a hard time opening and leaves may appear small.

 

Iron (Fe)

 

Iron has special importance in biological redox systems involved with chlorophyll formation/synthesis and protein synthesis.

 

Because of iron’s involvement in chlorophyll synthesis a deficiency will appaear as chlorosis (yellowing) of the leaves. Often the symptoms appear near the top of the plant on newer leaves.

 

Manganese (Mn)

 

Manganese is an important enzyme activator involved in the assimilation of nitrates to form proteins and is also important for photosynthesis.

 

A deficiency will show as intervenal chlorosis. i.e. Leaves may become yellow in the veins, with mottled brown spots on the affected leaves. These brown dead patches may spread. Growth rates may slow.

 

Zinc (Zn)

 

An integral component of many enzymes. Zinc plays a major role in protein synthesis and is involved with the carbohydrate metabolic processes. Zinc is also required for maintaining integrity of biomembranes and protecting membranes from oxidative damage from toxic oxygen radicals.

 

A deficiency will show symptoms of yellowing between the veins of leaves, plant growth will slow and there will be less growth/distance between the internodes of the plant.

 

Molybdenum (Mo)

 

Molybdenum plays an important role in the enzyme system which is involved in nitrate to ammonium conversion.

 

Deficiency symptoms include failure of leaves to develop a healthy dark green colour. The leaves of affected plants show a pale green or yellowish green colour between the veins and along the edges. In advanced stages, the leaf tissue at the margins of the leaves die. The older leaves are the more severely affected.

 

Cobalt (Co)

 

Cobalt is a transition element, and is an essential component of several enzymes and co-enzymes. It has been shown to affect growth and metabolism of plants, in different degrees, depending on the concentration and status of cobalt in the rhizosphere.

 

A deficiency in cobalt is shown in reduced Vitamin B12 production and lower nitrogen fixation which is reflected by uniformly pale green to yellow leaves. .

 

Nickel (Ni)

 

Nickel, in low concentrations, fulfills a variety of essential roles in plants, bacteria, and fungi. Nickel naturally occurs in a few plants where it functions as an essential component of some enzymes (e.g., ureases) that are involved in nitrogen assimilation.

 

Ni deficiency produces an array of effects on growth and metabolism of plants, including reduced growth, and induction of early senescence (fruit ripening) and leaf tip chlorosis (paling/yellowing).

 

Chloride (Cl-)

 

Chloride (Cl-) is an essential element for plants. It is a component of common salt and found in seawater. It should not be confused with other forms of the element such as chlorine gas (highly toxic and unstable), chlorine in swimming pools, hypochlorite (a sterilant and bactericide), hydrochloric acid (corrosive and dangerous liquid) etc. Chloride (Cl) is the negatively charged anion of chlorine, which is the form it is found in naturally. It is non-toxic and readily adsorbed by plants.

 

Chloride regulates the function of several enzymes, it is essential (working in tandem with potassium) to the proper function of the plants stomatal openings, thus controlling internal water balance. It functions in cation balance and transport within the plant and is essential for transport of the nutrients calcium, magnesium and potassium. Studies have shown that Cl- diminishes the effects of fungal infections in an as yet to be understood way, although this might be related to Cl- reducing N accumulation in plant tissue. That is, it is speculated that Cl- competes with nitrate uptake. This may be a factor in its role in disease suppression, since high plant nitrates have been associated with disease severity.

 

Although chloride deficiency symptoms are rare, wilting is a common symptom of chloride deficiency and the leaves turn yellow to white.

 

 

Note: Overall stunting of the whole plant is a sign of all nutrient disorders, and the hardest to detect unless normal plants of the same kind and age are available for comparison.

 

Beneficial Elements

 

Other than the essential elements, there are beneficial elements for plant growth. Beneficial elements are elements that help optimize the growth and development of plants but they are not essential for growth.  When they are absent in the solution/substrate, plants can still live a normal life. Here are a few criteria that can distinguish between the essential elements and the beneficial ones. Beneficial elements can:

 

  • Compensate for the toxic effects of other elements.
  • May replace mineral nutrient in some other less specific function such as the maintenance of osmotic pressure.
  • May be essential to some but not to all plants
  • May enhance plant growth and benefit yields

 

 

Aluminum (Al), sodium (Na), selenium (Se), and silicon (Si) are considered beneficial elements for plants: they are not required by all plants but can promote plant growth and may be essential for particular plant species. These beneficial elements have been reported to enhance resistance to biotic stresses such as pathogens and pests, and to abiotic stresses such as drought, salinity, and nutrient toxicity or deficiency. While most of the beneficial elements can aid plant growth when present at very low levels they can also be toxic to plants at higher levels.

 

The exception here is silicon (Si) which is uptaken by plants at reasonably high levels, and is considered a ‘quasi essential’ element for plants because its deficiency can cause various problems with respect to plant growth, development and reproduction. The addition of Si to hydroponic solutions exerts a number of beneficial effects on growth and yield of several plant species, which include improvement of leaf exposure to light, resistance to lodging, decreased susceptibility to pathogens and root parasites, and amelioration of abiotic stresses. Silicon can also alleviate imbalances between zinc and phosphorus supply. In general, dicot plants (e.g. tomato, cucumber, peppers) show a tissue accumulation of Si at 0.5% or less. You can read more about silica in hydroponics here…

 

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Refs:

[1] Yamashita et al. 2008; Suzuki et al. 2012; Marutani et al 2012