Hydroponics versus Organics



Author’s note: My apologies in advance. This is a long read (19, 500 words). Additionally, the following material discusses some complex information using, among other things, chemistry to demonstrate a few important points. While some of the information is relatively easy to follow, other parts, which are demonstrated through chemical equations, may prove extremely difficult to follow for some readers.  For what it is worth, don’t get caught up in the numbers – the message is the important thing. Of course, for those of you who are chemically minded feel free to crunch/check the sums. I’ve left the references out of this article and will place them on the last page.


This section is not so much about growing practices (although some important information will be addressed with regards to grow room design considerations, pesticide and fungicide issues, optimal plant nutrition for optimal yields etc) but organics versus hydroponics is covered in Integral Hydroponics in order to dispel some commonly held misconceptions and myths that are circulated by some about hydroponic growing methodologies.


For instance, some would have us believe that hydroponic fertilizers lead to toxic outcomes, that non-organic produce contains carcinogens that aren’t present in organic crops/foods, that high levels of pesticides are present in/on hydroponic produce, that inorganic fertilizers are radioactive and that inorganic fertilizers destroy/kill beneficial bacteria and fungi.


In some cases there is some basis to these claims while in other cases there is no basis at all. For instance, regarding claims that fertilisers kill beneficial bacteria and fungi, leading to dead/”sterilized” soils; firstly, it is important to note that from a scientific perspective, among other things, inorganic nutrients such as nitrogen, calcium, magnesium, phosphorous, potassium, iron, manganese, sulphur and traces of zinc, copper, and molybdenum are key elements in the beneficial microflora food chain. That is, these inorganic elements, when provided at the right levels, greatly promote beneficial bacteria and fungi numbers.


Besides these elements beneficial bacteria and fungi require oxygen, carbon and hydrogen. While the effects of inorganic agrichemical amendments (fertilisers and pesticides) on soil microorganisms that are reported in scientific literature are variable, inorganic fertilizers have in many cases been shown to increase soil microflora. This is because fertilizers increase plant production and therefore organic matter (e.g. carbon) levels in soil are increased. This is generally beneficial for bacteria and fungi numbers because their food sources are increased. (Graham, M.H. et al 2002 and others) Some direct toxic effects of fertilisers on microorganisms have been reported but generally effects are only in the band of application and very high levels of the chemical are required to cause damage.


One issue of concern, for instance, is the overuse of cheap chloride based fertilizers such as potassium chloride (commonly referred to as Muriate of Potash or MOP). Potassium chloride contains about 50-52.5% potassium and 45 – 47.5% chloride (e.g. a 99.5% purity MOP fertilizer contains 52.2% K and 47.3% Cl). In the soil the chloride combines with nitrates to form chlorine gas. If MOP is applied too heavily the relatively high levels of chlorine gas produced can impact on the soil biota.


A lot of other fertilisers can cause problems but most commonly from overuse of NPK fertilisers and not applying balanced nutrition of required nutrients like trace elements. A lot of farmers over the years tend to apply the same fertilizers every year without changing their practices or properly analysing soil tests if they had them done (not just a problem of farmers but also poor advice from agronomists). For instance, for many years it has become the habit on dryland pastures for cattle and sheep to fertilise once a year, usually around Autumn, to put out a yearly application single super phosphate (SSP) and nothing else. The outcomes of these practices can lead to highly imbalanced macro and micro nutrition in soils, which results in a reduction of soil microbes. For instance the dryland pasture relying on SSP over decadeshas slowly reduced responses to the application which has lead to higher rates of application which has only compounded problems. SSP contains more S than P with pasture needing about twice the amount of P as an ideal. In non-leaching soils S accumulates at a much higher rate than P and high levels of S in the soil can inhibit uptake of molybdenum and selenium by plants. Originally the SSP worked well as S deficiencies were high which meant that S was more desired than P. Also with the decline of nitrogen fixing legumes in pasture a lack of response to SSP applications has seen a need for higher application rates when the lack of response was due to a decline in nitrogen. Basically, what it comes down to is the inappropriate use of inorganic fertilizers on the part of some farmers has resulted in highly imbalanced soils and this can have some impact on soil biota.  Therefore, it is not so much the method of agriculture that is the problem but the practices that are employed by some.


Other than this, two important points need to be added. Firstly, statements to the effect, on the part of the organics movement, that inorganic fertilizer use leads to dead or “sterilized” soils are typically greatly overstated, overly simplified and/or completely misunderstood by those making such claims. For instance, other than chloride containing fertilizers, much hyperbole has been circulated about ammonia containing nitrogen fertilizers (e.g. ammonium sulphate, urea, ammonium nitrate) killing beneficial soil microflora. However, research by Biederbeck et al. (1996) in Canada showed minimal impact on soil microbial populations and soil quality after ten years of fertilization with urea and anhydrous ammonia.


On the other hand, mycorrhizal fungi (AM fungi) have been consistently reported to be decreased by inorganic phosphorous fertilizer applications, but the extent to which this occurs may be dependent of the species involved and the level of plant available P in the soil. One of the key functions of AM fungi is that they increase the uptake of poorly soluble organic P sources, such as iron and aluminium phosphate and rock phosphates by converting non bioavailable organic and inorganic forms of phosphates to inorganic readily bioavailable H2PO4 (Pi) and HPO42-. As a result, the benefits of AM fungi are greatest in systems where inputs of inorganic phosphorous are low. Put simply, organic phosphates which are not bioavailable to plants act as food for AM fungi and thereby promote their numbers.  Therefore, heavy usage of inorganic phosphorus fertilizers can inhibit AM fungi colonization.  For instance, a comprehensive literature review conducted by Kathleen K. Treseder (2004) concludes mycorrhizal abundance declines in response to adequate N (-15%) and P (-32%) fertilization by average across numerous studies.  AM fungi also increase the moisture available to plants and can increase drought tolerance and can directly or indirectly affect the diversity of soil microorganisms and nutrient cycling. But again the levels of AM fungi can be more attributed to farming practices being reduced by tillering of soil and damaging infective hyphae and the lack of rotation of crops that do not form a symbiotic relationship with AM fungi like brassicas.


Basically, to summarize, claims to the effect that inorganic fertilizers kill/sterilize soils are not scientifically supported. This, however, does not stop certain interest groups from making these claims.


Secondly, and more importantly where we are concerned, hydroponics differs significantly from all other forms of agriculture/farming. For instance, just one obvious point is that in hydroponic crop production plants are grown in systems that are separated from the ground/earth. For this reason, when discussing hydroponic growing methods, any arguments of inorganic fertilizers affecting soil biota are misplaced. Additionally, hydroponic nutrients do not contain chloride based fertilizers and therefore the chlorine issue does not present. Further, because hydroponic nutrients are precisely balanced, along with other key elements such as carbon and sugars, it is shown that microflora (beneficial bacteria and fungi) thrive in hydroponic growing systems.


However, what seems to happen, with the readership in mind, is that organic growers cherry pick often very misinformed literature that has been applied by some to outdoor agriculture  (typically grabbed from pro-organic internet blogs – hardly the source for credible, non-biased scientific information) and try to use it to demonise all inorganic methods of growing. Other growers then latch onto this information, facts unchecked, and mimic it (spam it) across the Net.  So, for instance, forums are alive with information to the effect that inorganic fertilizers kill beneficial microbes, that inorganic fertilizers are radioactive (yes they are, albeit that organic fertilizers are radioactive also – we’ll cover more on this later), that organic produce is invariably healthier, and that hydroponics equates to toxic, pesticide-laden produce.  We’ve just looked briefly at one of these claims and when the science is applied it is largely discredited (albeit, that in this instance there is at least some basis to the claim; however, greatly misunderstood and overstated).


So let’s delve deeper and investigate other claims…organics versus hydroponics… the science versus the hype…


Organic v. Hydroponic Nutrition


Soils, whether organic or inorganic naturally contain levels of the essential macro and microelements that are required for plant growth. Plants cannot absorb most organic elements because the molecules are too large, so these substances are broken down into simpler soluble inorganic elements by microflora (bacteria and fungi) and plants are then able to use them. Mycorrhizal fungi, for instance, increase the uptake of poorly soluble organic and inorganic sources of phosphorous (P) such as iron and aluminium phosphate and rock phosphates by converting non-bioavailable organic phosphates into bioavailable inorganic H2PO4 (Pi) and HPO4-2 phosphorous. Hence, organic phosphates must become inorganic soluble phosphorous before it can be uptaken by plants (once inorganic P is uptaken it is then synthesized within the plant into organic materials/molecules such as DNA).


Similarly, the nitrogen in organic matter is largely found in organic forms that plants, for the most part, cannot uptake. Bacteria found in soils convert organic forms of nitrogen to inorganic forms that the plant can then use. Nitrogen (N) is only available to plants as either inorganic ammonium (NH4+) or inorganic nitrate (NO3 ) or, to a lesser extent, as organic amino acids (e.g. Glycine, C2H5NO2) or the man made chemically organic urea.


Urea is an organic compound with the chemical formula of CO(NH2)2. The molecule has two NH2 groups joined by a carbonyl (C=O) functional group. Urea makes an interesting example because it was the first organic chemical that was produced entirely from inorganic starting materials and was an important conceptual milestone in chemistry, as it showed for the first time that a substance previously known only as a by product of life could be synthesized in the laboratory without any biological starting materials.


Urea is widely used in agricultural fertilizers as a convenient and cheap source of nitrogen.


Urea also serves an important role in the metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals. It is a colourless, odorless solid, highly soluble in water and practically non-toxic (LD50 is 15 g/kg for rat). The body uses it in many processes, the most notable being nitrogen excretion. However, the use of man-made “organic” urea fertilizers is not approved for use in organic agriculture while the use of urine (a combination of urea and inorganic ions such as sodium (Na+), potassium (K+), chloride (Cl), magnesium (Mg2+), calcium (Ca2+), ammonium (NH4+), sulfates (SO42-), and phosphates (e.g., PO43-) is. Therefore, technically, if I were to urinate on a plant and provide it with inorganic ions along with organic urea this would be deemed organic, while if I were to provide chemically pure organic urea to the same plant somehow this makes it inorganic. Of course, urea, whether as urine or as a ‘man made’ fertilizer, for the most part, must then be converted into inorganic ammonia (NH4+) before the plant can uptake it.


To a plant inorganic nutrition is life. There is, in fact, strictly speaking, no such thing as organically grown produce because, in reality, all plants require and uptake inorganic minerals. Therefore, in soil as in hydroponics, plants receive their food in the same form – inorganic ions dissolved in water. From a scientific/biochemical perspective an atom of nitrogen, whether it is derived from chicken manure or synthetically derived from air (as is the case in the manufacture of most nitrogen fertilisers), is exactly the same thing to the plant. That is, potassium is potassium, nitrogen is nitrogen, phosphorous is phosphorous etc, etc, etc. As far as a plant is concerned there can be no distinction made between two atoms of the same chemical element. As such, synthetic (man made) fertilisers and organic fertilisers to a plant result in the exact same thing and they are converted within the plant to the exact same thing (i.e. sugars and carbohydrates that are used in photosynthesis, and for protein synthesis, nucleaic acids for RNA and DNA synthesis to name a few).


Unfortunately, what many organic enthusiasts have done is deny the science of mineral nutrition and plants, believing all that is natural is good and, therefore, all that is “unnatural” is bad – a scientifically flawed reasoning that seems to, among other things, deny that many toxins are organic.


Addressing Claims that Organic Produce is Healthier and More Nutritious than Conventional Produce


There is widespread public belief, promoted by the organic food industry that organic food is safer, more nutritious, and tastes better than conventional food. These beliefs have fueled increased demand for organic food despite higher prices and much scientific evidence that disproves these claims.


That is, given the science of mineral nutrition and plants it is perhaps not surprising that claims, on the part of organic marketing groups, that organic foods are healthier and more nutritious than conventional foods have been discredited in recent years.


For example, scientists in England in 2006 surveyed 162 articles of scientific literature and they found, “no evidence that organic and conventional foods differ significantly in their nutrient content.”


As a result, the UK Standards Agency has stated: “In our view the current scientific evidence does not show that organic food is any safer or more nutritious than conventionally produced food”.


Similar conclusions have been drawn by the French Food Safety Agency (AFSSA) and the Swedish National Food Administration.


In research by the Stanford University’s Center for Health Policy, a team led by Dena Bravata conducted the most comprehensive meta-analysis to date of 237 existing studies comparing organic and conventional foods. They did not find strong evidence that organic foods are more nutritious or carry fewer health risks than conventional alternatives, although, the researchers noting that the consumption of organic foods may reduce the risk of pesticide exposure.


No consistent differences were seen in the vitamin content of organic products, and only one nutrient  (phosphorus) was significantly higher (while nitrogen was lower) in organic versus conventionally grown produce; however, the researchers also stated that because very few people have phosphorous deficiency, this has little clinical significance. There was also no difference in protein or fat content between organic and conventional milk, though evidence from a few studies indicated that organic milk might contain higher levels of omega-3 fatty acids.


The researchers were also unable to identify specific fruits and vegetables for which organic appeared to be the healthier choice, despite running what Bravata called “tons of analyses.”


As a result of these types of findings in scientific research, organic marketing groups in the UK are now banned from making claims that organic produce is more nutritious and healthier with the UK Advertising Standards Agency (ASA) fining two supermarket chains for false advertising in 2000.  According to ASA, Tesco Markets made numerous false and unfounded claims for the health, taste and price of organic foods, stating that the misleading advertising led to “unacceptable appeals to people’s fears”. Similarly, ASA also found another UK supermarket chain, Iceland Foods, guilty of making false and misleading claims that foods derived from conventional crops were dangerous to encourage customers to purchase higher priced organic foods.


Somewhat predictably, these studies and their outcomes regarding marketing restrictions were immediately slated by organic bodies and groups, in some cases with somewhat credible (albeit not, to date, scientifically supported) counter arguments while in a few cases with highly flawed and bordering on fringe lunatic conspiracy theories. For instance, one British tabloid led out with the headline, “A cancerous conspiracy to poison your faith in organic food”

Of course, this misses the point that cancer rates are falling and have been for the past 50 years. Proponents of organic food say there is a ‘cocktail effect’ of pesticides. Some proponents of organic food point to an epidemic of cancer. In fact, there is no epidemic of cancer, nor is there any evidence that agrichemicals contribute to cancer.


In fact, false advertising and fear mongering aside, as more research is done into the comparative cancer risk of those eating conventional versus organic foods what seems apparent is that consumers of conventional foods are at no higher risk of getting cancer than consumers of organic foods. For instance, Oxford University researchers (2014) looked at data on 600,000 middle-aged women who were being tracked by an earlier study (the Million Women Study). They compared 180,000 women who said that they never ate organic food with 45,000 who said they always or usually did, looking at how many got cancer over a nine-year period.


The researchers could find no difference in overall cancer risk when they compared the groups.


When they looked in more detail at each of the 16 different cancers, the researchers found a slightly higher risk for breast cancer and a lower risk for non-Hodgkin lymphoma in women who said they mostly ate organic food; however, adding that these findings maybe related to chance and other factors.


The bottom line – scientific evidence does not support claims that organic food is more nutritious and healthier than conventional foods and while links are made by organic lobby groups between cancer and agrichemicals these claims, like many other claims made by the organics movement, are not supported by science.


Organics and Heavy Metals


Another issue frequently overlooked by organic enthusiasts is the prevalence of excess heavy metals such as arsenic, lead, cadmium, nickel, mercury, copper, and zinc in organic soil, with cadmium being the most notable of these heavy metals where plant uptake is concerned.


Cadmium is a widespread, naturally occurring, element that is present in soils, rocks, waters, plants and animals. The chemical symbol for cadmium is Cd. It occurs naturally with deposits of zinc and phosphorus but, unlike these nutrients, it is not considered essential for life.


According to current knowledge, renal tubular damage is probably the critical health effect of cadmium exposure. Cadmium is first transported to the liver through the blood. It then bonds to proteins to form complexes that are transported to the kidneys. Cadmium accumulates in kidneys, where it damages filtering mechanisms. This causes the excretion of essential proteins and sugars from the body and causes further kidney damage. It takes a very long time before cadmium that has accumulated in kidneys is excreted from a human body. Where immunosuppressed individuals are concerned excessive cadmium levels can further suppress the immune system.


Jarup, L (1998) notes that the population group at the highest risk of cadmium exposure is tobacco smokers. The absorption of cadmium in the lungs is 10-50%, while the absorption in the gastrointestinal tract is only a few percent. Smokers have about 4-5 times higher blood cadmium concentrations (about 1.5 micrograms/l), and twice as high kidney cadmium concentrations as nonsmokers.3 The national geometric mean blood cadmium level for adults is 0.47 μg/L. A geometric mean blood cadmium level of 1.58 μg/L for New York City smokers has been reported. The amount of cadmium absorbed from smoking one pack of cigarettes per day is about 1–3 μg/day. Direct measurement of cadmium levels in body tissues confirms that smoking roughly doubles cadmium body burden in comparison to not smoking.  This information has telling implications for consumers of combustible crops.


Soil ecologists and environmentalists and, to some extent, the concerned public have known for more than a century that the synthetic pesticides of conventional farming leave heavy metals in the ground. But the fact that you can find the same toxins in organic soil and composts has been largely hidden from the public.


Scientists have known since the 1920s that organic fertilizers (composted animal manure, rock phosphates, fish emulsions, guano, and wood ashes etc.) contaminate topsoil with varying concentrations of heavy metals (HM). Organic advocates, who rely exclusively on these fertilizers, are well aware of the problem although they rarely publicise the point.


Some evidence indicates that organic soil can be more HM contaminated than inorganic soils. This is largely because cadmium binds strongly to organic matter (e.g. humus and manure) where it will be immobile in soil and be taken up by plants, eventually entering the food chain.


George Kuepper, an agriculture specialist with the National Centre for Appropriate Technology, observed in 2003 that composting manure actually concentrates the fertiliser’s heavy metal content, which could lead to greater levels of the contaminants in organic soil.


Research conducted in 2004 on the influence of organic matter (OM) on the uptake of cadmium (Cd), zinc, copper and iron by Sorgham plants found that OM promoted the translocation of Cd to shoots, “an effect that may pose a risk to public health because plant-animal transfer of Cd could be enhanced.” (Pinto A.P. et al 2004)

Under specific situations, metals supplied to soils by applying composts and manures (bio solids) can be percolated downwards through the soil and may have the ability to pollute groundwater (McLaren et al., 2005).


Research with greenhouse grown soybean has shown that 80–100% of the cadmium and 46–60% of the zinc in soils were bioavailable for uptake. Concentrations of both metals were highest in root tissues (10-fold higher for cadmium, and up to 2-fold higher for zinc). Although relatively little cadmium was translocated to pods and seeds, the seeds of all plants had concentrations of cadmium 3–4 times above the limit of 0.2 mg/kg set by the Codex Alimentarius Commission. This surprised the researchers given that cadmium in the soil was only 1 mg/kg – well below the maximum allowable limits for agricultural soil.
In 2007, research conducted on wheat crops grown on various farms in Belgium showed that consumers of organically grown wheat take in more than twice as much lead, slightly more cadmium, and nearly equivalent levels of mercury as consumers of wheat grown on conventional farms.

This situation may become even more pronounced when comparing organic growing methods to hydroponics.


This is because as an absolute rule, the higher the heavy metal levels in media and fertilizers, the higher the heavy metal uptake by plants. I.e. heavy metal concentration in soils, substrates and fertilizers (compost etc) is the dominant factor in heavy metal plant tissue contamination.


Where inorganic fertilizers are concerned, phosphorus containing fertilizers can contain high levels of cadmium depending upon the source of rock phosphate used in manufacturing. For this reason, many countries (e.g. Australia, USA, UK, EU/EC members) have adopted regulations that determine acceptable levels of cadmium in phosphate fertilizers.


For instance, the ‘Fertilizer Industry Federation of Australia’ (FIFA) initiated a program in the 1990s to reduce the levels of cadmium in phosphate fertilizers. This was achieved by using low cadmium phosphate rock in the manufacturing of superphosphate and importing low cadmium, high phosphorus analysis fertilizers. This said, when comparing inorganic phosphate fertilizers to their organic equivalents much higher levels of Cd are present in organic phosphate fertilizers than are present in inorganic fertilizers.


Let’s, for example, take a look at how much cadmium is found in inorganic phosphate fertilizers; firstly, a horticultural grade product from Australia. As a warning, I’ll be wading through a bit of chemistry  – don’t get hung up on the numbers. Grasping the calculations isn’t necessary. The important thing is the message. Of course, for those of you who are chemically minded go for your life.


Certificate of Analysis Monopotassium Phosphate (MKP) 0- 52- 34, Horticultural Grade


Phosphor (P205)                   min 51.5%

Potassium (K2O)                  min 34%

Cl                                       max 60ppm

Na                                      max100ppm

Heavy Metals                       max 10ppm

Insolubles                            max 0.1%

Moisture                               max 0.5%


In this case, the manufacturer doesn’t list heavy metals separately. However, looking at this analysis we can see that there is a maximum of 10ppm (10mg/kg or 0.001%) of total heavy metals in our MKP product.  When you consider that there is 1000mg in 1gram and 1000grams in one kilogram, and that a liquid concentrate, two-part fertilizer may contain approximately 30g/L of MKP and/or MAP this number doesn’t seem unreasonable. I.e. With this information we have 0.000030ppm/L of total heavy metals in a fertilizer concentrate (max value) derived from phosphate fertilizers. Next, let’s say that in a worst-case scenario we have a maximum of 10mg/kg of heavy metals present in the MKP product and that 1/3 of this is cadmium. This would leave us with 3.333mg/kg of Cd in the phosphate fertilizer product or 0.000010 mg/L of Cd in a hydro concentrate solution. Keep in mind that I’ve used conservative numbers and Cd levels are likely to be lower.


I’ve oversimplified this for now just to demonstrate HM contaminants drawn from a phosphorous fertilizer and in the case of a full spectrum hydroponic nutrient we would also need to account for cadmium drawn from other base fertilizers used in formulation  (e.g. potassium nitrate, calcium nitrate etc).


Here is a few more examples of phosphate fertilizers. In these examples, the heavy metal contaminants are listed separately.


Monopotassium Phosphate (MKP 0- 52- 34)

Main content, min 99.0 %

P2O5 ≥51.3 %

K2O ≥34.0%

Water insoluble, max 0.1 %

Moisture, max 0.2%

PH 4.4-4.8

As ≤0.0025%

Heavy metal (Pb) ≤0.0003%

Hg None

Cd ≤0.0002% (2mg/kg or 2ppm/kg)

Cr ≤0.0002%

F ≤0.002%

CL ≤0.01%


Monoammonium Phosphate (MAP 12- 61- 0)


Main content, min 99.0 %

P2O5 ≥61.0 %

N, ≥12.0%

Water insoluble, ≤0.1 %

Moisture, ≤0.2%

PH 4.4-4.8

As ≤0.0025%

Heavy metal (Pb) ≤0.0003%

Hg None

Cd ≤0.0002% (2mg/kg or 2ppm/kg)

Cr ≤0.0002%

F ≤0.002%

CL ≤0.01%


Di-Ammonium Phosphate (DAP 21-53-0)


(NH4)2HPO4 99%

P2O5 ≥53.0 %

N ≥20.8%

Water in soluble ≤0.1% 0

Moisture ≤0.2%

PH 7.8-8.2

As ≤0.0025%

Heavy metal (Pb) ≤0.0003%

Hg None

Cd ≤0.0002% (2mg/kg or 2ppm/kg)

Cr ≤0.0002%

F ≤0.002%

CL ≤0.01%

In all cases 2mg/kg of Cd.

Let’s now have a look at an organic phosphate (phosphorous) fertilizer and compare the Cd numbers against inorganic phosphate fertilizers.


Bat Guano



Civa mg/kg                                              4, 8

Lead mg/kg                                             39, 6

Chromium mg/kg                                     29, 1

Zinc mg/kg                                             255, 1

Nickel mg/kg                                           26, 2

Cadmium mg/kg                                     3

Copper mg/kg                                        979, 8

Total phosphorus g/kg                             50

Total nitrogen %                                     8, 1

Total organic Matter %                            64, 7

Salinity %                                              0, 35

Electrical conductivity mS/cm                   13, 8

Humidity % 8, 7

pH – 2, 09


Looking at this analysis we have 3mg/kg of Cd (vey low cadmium levels by guano standards) which puts us on track with non-organic sources of phosphate fertilizers, or at least at first glance. However, our inorganic phosphate fertilizer has 51.5% (515g/kg) elemental P while our organic phosphate fertilizer has 5% (50g/kg) of elemental P, so to achieve the same levels of P in NPK %w/v we are adding much higher levels of cadmium to an organic liquid fertilizer. For instance, to achieve a 1%w/v phosphorous target in a fertilizer concentrate we would use 19.4g/L of our Australian MKP product or 200g/L of bat guano giving us approximately 10.3 times the amount of Cd in an organic phosphate solution at 1%w/v P than an inorganic phosphate solution at 1%w/v P. When you compare the numbers (the chemistry of organic v. inorganic) things become much clearer.


A couple more guano products that are sold in North America. You’ll note both products contain even more Cd than our first guano example.




Arsenic                       11.7000

Cadmium                    7.6000mg/kg

Cobalt                        12.6000

Lead                           1.200

Mercury                      0.0500




Arsenic                      13.3000

Cadmium                   10.0000mg/kg

Lead                          1.2000

Selenium                    5.5000

Mercury                     0.0500


Heavy metal contaminants in organic fertilizers become more problematic when you consider that kelp and other organic components used in formulation (e.g. fish by-product, blood and bone products, worm casting, molasses) often contain moderate to high levels of heavy metal contaminants. For instance, Burger J et al, studied Alaria nana kelp in Alaskan waters and found it contained high levels of cadmium, lead and selenium. Additionally, research investigating heavy metals in aquatic food chains has yielded similar findings….

Independent Lab Analysis of Heavy Metal Contaminants in Commercially Available Inorganic Hydroponic Fertilizers


We tested numerous fertilizers in European, North American and Australian laboratories. In most instances we tested only for elemental N, P, K, Ca, S, Mg and microelement values in order to analyse popular, internationally available formulas. However, in some cases, we conducted more thorough analysis where we tested for heavy metal contaminants.   I’ll now paste in an extract from one of these analyses (5 liquid samples from a European based multinational) so that we can evaluate Cd levels in an off the shelf inorganic hydroponic nutrient. (C following analysis)




In this analysis CA and CB (highlighted at top in red) represents Coco A and Coco B so we’ll look at this company’s two part Coco product.


Keep in mind that 1000 μg (μg = microgram) equals 1mg, so where we have <500 μg of Cd there is less than (< = less than) 0.5mg/L cadmium contaminant.


These formulas are reasonably concentrated (high mineral to water ratio) and therefore require a lower dilution rate, comparatively to many other brands. For this reason the contaminant numbers listed at μg/L need to be considered with this in mind (i.e. a less concentrated product – higher water to mineral ratio – would perhaps reflect lower contaminant/L numbers). Let’s hypothetically say that you were using one of these products at 2.5ml/L at an EC of 1.2 (in solution). What this would mean is that we would have, worst-case scenario, 1 μg/L (0.001mg/L) of Cd in solution derived from CA (Coco A) and the same again derived from CB (Coco B). I.e. 1 μg/L (part A) + 1 μg/L (part B) = 2 μg/L or 0.002mg/L Cd in solution. Keep in mind that we are dealing with a worst-case scenario and <500 μg/L Cd could mean 20 μg/L, 100 μg/L, or 300 μg/L.  Put simply, Cd in solution is minimal in this instance.


When comparing organic to inorganic fertilisers our inorganic coco formulation contains 1.7 %w/v phosphorous (P). To achieve this %w/v of P with our earlier Bat Guano example we would require 340grams/L of guano, which would equate to 0.9 mg/L of Cd contaminant from the guano P source alone. This equates to roughly double the Cd contamination of our inorganic full spectrum hydroponic nutrient. Keep in mind that on top of an organic source of phosphorous, numerous other potentially HM contaminated organic fertilizers would also be required for nitrogen, potassium, calcium etc.


Given this, we would be looking at perhaps 4 – 5 times, or more, the Cd contamination in a full spectrum organic nutrient than is found in an equivalent %w/v NPK, Ca, Mg etc inorganic formulation.


As heavy metal concentration in soils, substrates and fertilizers is the dominant factor in heavy metal plant tissue contamination it is very probable that, at least where HM contaminants are concerned, hydroponics fertilizers produce a cleaner, healthier end product than organic fertilizers.


Heavy Metals in Organic Hydroponic Substrates


It’s perhaps worth noting here that having pointed out that organic fertilizers and soils can contain high degrees of HM contaminants, and as I promote organic substrate growing in Integral Hydroponics, the organic substrates (peat and coco coir) covered in the book are lowin heavy metal contaminants, albeit that inorganic media such as expanded clay and perlite would be lower in HM than both peat and coir.


Following are some lab tests that demonstrate HM contaminant levels in peat and coir.



ug/kg to mg/kg conversion

Cadmium                                    0.012

Chromium                                   19.656

Cobalt                                         1.364

Lead                                           1.216

Molybdenum                                0.204

Selenium                                     0.1108


The analysis shows very low levels of cadmium. It was conducted on a 50L bagged Canna Coco product. Canna Coco is buffered with calcium nitrate and magnesium nitrate (Cal Mag) prior to sale. It is, therefore, probable that some of the heavy metal content in the analysis may derive from the use of these fertilizers in buffering. I.e. Heavy metals in coco substrate + heavy metals in fertilizers (via CalMag buffer) = total.


Analysis of a Peat Substrate

ug/kg to mg/kg conversion


Arsenic             0.476

Cadmium             0.092

Chromium             1.308

Cobalt                         0.384

Lead                         2.104

Molybdenum             0.104

Selenium             0.54


Again, we have very low levels of HM contaminants present – with cadmium being slightly higher in Peat than in Coir.


So, let’s compare these numbers to some organic rating standards (soils and composts).


New Zealand Organic Regulations


Heavy metals in manures and composts must not exceed:


Metal                                    mg/kg

Zinc                                      1000

Copper                                  400

Nickel                                   100

Cadmium                              10

Lead                                    250

Mercury                                2


Heavy Metal Limits for Organic Composts (European standards)


Cd                   0.7

Cr                   70

Hg                  0.4

Ni                   25

Pb                  45


US Standard (Organic Composts)


Cd                   4

Cr                  100

Hg                  0.5

Ni                  50

Pb                  150


Comparatively speaking, when comparing peat and coir to organic compost standards hydroponics is looking extremely good.


Addressing Claims that Organics is Environmentally Friendly and Sustainable – A comparison of organic and hydroponic methodologies

Due to the benefits of higher yields with lower inputs (e.g. hydroponics significantly reduces water requirements by up to 90% by controlling and recycling the water used within the hydroponic system), improved soil and water quality and food safety, hydroponics in a world with an ever increasing population and diminishing water and land resources is without question the future of food production. Quite simply, there is no method of agriculture that even comes close to hydroponics where environmental friendliness and sustainability is concerned.


Today, the majority of greenhouse crops worldwide are grown in the soil using agricultural dry fertilizers or organic amendments such as composts, or a combination of both, but in developed countries, such as in Europe, North America and Australasia, hydroponic systems are far more common. In developed countries there was a move away from soil-grown greenhouse crops in the early 1960s, which, combined with improvements in the control of the greenhouse environments (temperature, CO2 enrichment etc), has resulted in considerable increases in yields compared with traditional soil-based systems. Professor Lim Ho (2004) has demonstrated that over the past 50 years productivity in environmentally controlled heated greenhouses has increased at 6.4% per year compared with only 1.7% for unheated greenhouses. In fact, 60 years ago the best greenhouse tomato growers were achieving 20kg/sqm/year. Today the best growers harvest 80kg/sqm/year, or four times more.


Hydroponic crops have a lower carbon footprint than other methods of farming. Because of the greater yields that can be achieved in smaller spaces crops can be produced closer to cities or, indeed, as is occurring now, produced on the rooftops of buildings in cities etc. This means the carbon footprint of transportation (i.e. fossil fuel emissions) and the reduction of habitat intrusions are greatly reduced when compared to both organic and conventional agriculture.


Comparatively speaking, in the case or organic farming.


The increasing world population requires higher crop yields from the land available for agriculture. Lower crop yields from organic farming mean that much more land is needed to grow enough food organically. The output from organic agriculture is not sustainable or sufficient to feed the growing global population.


In South America, 140 million hectares (346 million acres) of land have become degraded and infertile due to traditional agricultural practices that use little or no external ‘chemical’ inputs. An additional 100 million hectares (247 million acres) of rainforest have been cleared mainly to compensate for the loss of agricultural land; the deforested area increases every year.


The decimation of the rain forests is only comparable to the impact it has on global warming. The Amazon rainforest is a critical influence on South American climate and one of the world’s most important carbon banks. Covering almost as much land as the United States, the Amazon is home to 20 per cent of the planet’s animal and plant species and stores the equivalent amount of carbon as a decade of global fossil fuel emissions in its trees.


Each year, thousands of square miles of rainforest are cut down, releasing global warming pollution in the form of carbon dioxide and methane from burning and decaying vegetation.

The Amazon is an important repository of carbon and water. Deforestation disrupts the water cycle by allowing water to runoff directly to rivers rather than being trapped in soil and vegetation and slowly released throughout the year. This makes the forest more vulnerable to drought and the further loss of trees and increase of global warming.


In contrast, 4 million hectares (10 million acres) of farmland has been returned to forest in North America over the last decade. This land has become available for forestry because modern agricultural methods, including agrichemicals, have allowed growers to achieve their production goals on less land. It has been estimated that if organic production were adopted throughout the USA, an additional 170 million hectares of forest would need to be cleared and planted to maintain today’s level of food production.


Organic farmers claim they can ultimately exceed the yields of conventional rivals through smarter soil management. But current practices tell us that organic farming, if it is to stay true to its principles, would require vastly more land and resources than is currently being used.


Developments in the past 25 years have shown how conventional agriculture can be much more sustainable and environmentally friendly than organic farming. A conventional farm can match organic yields using only 50–70% of the farmland. Hydroponic production methods produce even more yield per hectare and therefore places even less pressure on land requirements. As a result, excess food is being produced in Europe, so farmers are being encouraged by governments to set aside up to half of their land for fast-growing willow plantations which are then frequently trimmed and used as fuel. With this approach, now in operation throughout Europe, fossil-fuel use and carbon dioxide production are much lower than in organic farming, and because of carbon recycling this method of farming is much more sustainable. The plantation of willow trees, with its undercover of weeds, bird-nesting sites and mammal and insect refuge, outperforms organic farms on any biological measure of environmental diversity; however, this practice depends crucially on the most efficient use of land for food production and organics simply isn’t productive when compared to conventional and, particularly, hydroponic growing methods.


The Swiss Research Institute for Organic Agriculture reports yield reductions of 40% for potatoes, 30 – 40% for cereals and 20% for organic trials overall. One estimate for additional land requirement if organic farming were to be widely adopted is that lower yields would require between 25% and 82% more land to sustain food production.


The study of Life Cycle Assessments (LCAs) for the UK, sponsored by the Department for Environment, Food and Rural Affairs, should concern anyone who buys organic. It shows that milk and dairy production is a major source of greenhouse gas emissions (GHGs). A litre of organic milk requires 80 per cent more land than conventional milk to produce, has 20 per cent greater global warming potential, releases 60 per cent more nutrients to water sources, and contributes 70 per cent more to acid rain.


The organic movement disputes these claims, stating among other things that while more land may be needed in the Northern hemisphere better output in the Southern hemisphere would offset this situation. They claim many things, but are yet to provide any credible evidence to support such claims.


Author’s note: To be fair and cover the middle ground, the sustainability and eco friendliness of hydroponics well above and beyond organic agriculture does not extend to under lights growing (whether hydroponics, organics or otherwise) due to the energy intensive use of artificial lighting. That is, the carbon footprint associated to HID lighting (i.e. energy consumption) offsets any claim to sustainability and eco friendliness. On the other hand, greenhouse hydroponic methods, which utilize natural lighting, are shown to have a far lower carbon footprint than both conventional and organic agriculture.

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