Plant Nutrient Comparison

Soil-grown, Hydroponics, and Aquaponics

Plant Nutrient Comparison – soil-grown, hydroponics, and aquaponics

I have been involved in a bit of discussion lately about plant nutrient comparison grown in different types of production methods. To date, as far as I can find, there is very little comparative research on the nutritional value or density of foods grown in soil, aquaponics systems, and hydroponic systems.  I suspect that there are several reasons for this.  Such a comparison would take a top tier research facility and a multi-disciplinary approach to the research.  Doing such comparative research would be expensive and time-consuming. 

As someone who gardens in both soil and aquaponics, I have some grounding in both subjects.  The third, hydroponics, is rather well researched and documented on the methods and theories of vegetable production.   Using what I know and what research is available, I think I can make offer some reasonable information on these questions.

pH vs. nutrient availability

Nutrient Delivery

First, we need to have some understanding of the mechanics of nutrient delivery to the plants in each production method.  Plants will require the same balance of nutrients no matter what production method is chosen.  We know that there are about several macro-nutrients that plants require, carbon, oxygen, nitrogen, potassium, and phosphorus.  Carbon and oxygen the plants get from the air in the form of carbon dioxide.  The other three, usually referenced as N-P-K, are sourced through the roots. A host of other micro-nutrients are also required.  These include magnesium, calcium, copper, zinc, and several others.  These are also sourced by the plant roots.   To complicate things even more, although the nutrients may be available in quantities large enough to sustain the plants, several factors can affect the availability of the nutrient to the plant.

First, the nutrient has to be in the right form for the plant to have access.  The nutrient may be locked into a form that makes it unusable by the plant.  Second, many nutrients are only available to the plant when a secondary nutrient is available.  For example, nitrogen uptake by plants may be inhibited where calcium is not present in sufficient quantity or type.

pH may also affect the ability of the plant to uptake and use nutrients and can affect the availability of nutrients to plant roots. A  pH too high or too low may lockdown available nutrients in forms the plant roots cannot access.

The Mystery of the Biome

soil biome and plant nutrition

In soil production, there is one factor about which our knowledge is still far from complete.  That is the functions of the soil biome, that universe of life from the microscopic to the visible that exists in healthy soil.  Vast amounts of research have been done on this, and we still do not completely understand the intricacies and complexities of this world beneath our feet.

With that bit of quasi-science under our belt lets look at the three forms of production. 

Obviously, in my mind at least, the nutrient value of the food grown in soil is directly related to the quality of the soil in which it is grown and the methods used in the production.  Post World War II, the focus of agriculture has been to increase production and decrease costs.  That is the bottom line approach.  The chemical industry was seen as the knight in shining armor in this quest as they provided chemical after chemical to aid the farmer’s production goals.  Fertilizers, pesticides, herbicides, and pre-emergents all became tools in the farmer’s box of tricks.   Only now are we beginning, in a broad sense, to understand the effects of these chemicals on the soil. 

What is Organic

spray application of herbicides

This has led to the growth of the “Organic” markets to the extent that the United States Department of Agriculture now owns the trademark on the labeling of “Organic” products and has a certification process that must be adhered to in order to attain the right to use the term “Organic” on a product label.  The problem many see is the USDA and its administration of the program, which has allowed questionable practices to remain in large scale production operations growing food now labeled as “Organic.”

DA Organic

Studies have concluded that since the advent of industrial farming practices, the nutrient values in most commercially farmed soil and the nutrient values in the crops grown in that soil has declined. Research has also shown that the same plants grown in healthy soil which has been cared for properly, can produce plants with extremely dense nutritional value without the application of synthetic materials, an approach that most people would term organic.  Note that there is a difference here between Organic (big O) and organic (little o).  This gets confusing.  Let me try to explain in my own style.

Big O vs. little o

The difference, as I see it, between big O Organic and little o organic is where the focus of the producers lies.  Big O Organic is, by and large, still focused on end result production.  How much is produced, how much is marketable, and how much is it worth.  Little o organics tend to focus first on producing healthy, nutrient-dense vegetables in a sustainable biologically based system. This is not to say that producing in a little o organic method is not economically feasible.  It just means that the priorities are re-arranged and production methods are crafted based on those re-arranged priorities.

Healthy Soil

healthy soil

What has been lost is the concept of “healthy soil.”  Application of synthetic chemicals to the soil degrades the life in the soil, sometimes to the point that the soil is virtually sterile.  Those little understood interactions between the soil biome and plants is lost and, as research has proven, over time, the nutrient value of food has decreased as well.  Obviously, the dependence on synthetic chemicals, especially fertilizers, is not bringing all the right answers to the table.

Feed the Soil vs. Feed the Bottom Line

Big O “Organic” is a marketing method that depends on getting a certification from the USDA that the producer is meeting certain minimum standards of production.  Yes, there are some restraints on the use of chemicals but not as much as you might think.  What is lacking is any consideration of managing soil health.  

Little o organics is much more concerned with managing soil health.  Anyone who produces organically (little o) will abstain from the use of any synthetic chemical-based product on their plants or their soil.  The focus in little o organic production is usually on the soil.  The great concern is the overall health of the soil biome based on the concept that feeding the soil is more important than feeding the plant.  Healthy soil will provide everything the plant needs in the right proportions and at the right time.

Comparing tomatoes to tomatoes?

So, in our comparison question, the first stumbling block is whether the vegetables you are comparing were grown with industrial agriculture practices, big O Organic practices, or little o organic practices.  Even when a producer is growing using those little o organic practices, there may be soil health problems that are undiagnosed or undiscovered that may affect plant nutritive value.


hydropopnics. a sea of lettuce

Next, we have to consider hydroponics production.  Hydroponics is really a hybrid version of industrial agriculture systems.  Plants are grown in facilities that tightly control growing conditions.  Light, heat, temperature are all managed to provide “optimal” growing conditions.  Plants are grown in huge arrays of fixed systems that deliver a constant flow of nutrient water to the plant roots.  This nutrient mix is a blend of synthetic chemical fertilizers that are designed to deliver “optimal” nutrient rates. 

The entire system is created to give that “optimal” output.  What is optimal output?  The most production with the lowest cost.  These are, after all, mostly large commercial operations which are providing huge quantities of vegetables to wholesale markets.  Most of these production facilities are a monoculture.  They only produce one variety of crop, such as lettuce.   

What’s missing?

nydroponics vertical
Hydroponically grown Strawberry vines growing in a hothouse

The missing ingredient here is soil biology.  As good as science is, even soil biologists admit that no one fully understands the interactions and symbiotic relationships between the soil biome and plants.  In hydroponics, those soil-based relationships are missing completely.  The nutritional needs of plants change as they move through various phases of growth and fruit production.  No matter how well the hydroponics system is managed, these complex needs of the plants cannot be adequately met using a man-made formula.  In any large greenhouse operation, plants may be found in widely different phases of growth, each needing a subtly different nutrient mix.  Without the supporting biology of the soil, these needs cannot be adequately met.

Hydroponic systems are very successful at what they do.  They can produce large quantities of vegetables in relatively small spaces.  We are now seeing plant varieties that have been specially bred just for hydroponic production. 

The Priorities Matter

Another problem with both hydroponic and industrial soil farming is production practices itself.  Commercial growers are not paid for the nutritional value of their crop.  They are paid based on the amount of production that reaches the buyer in a fit state to be resold or processed.  A focus on these criteria means that consistent size, shape, color, and weight are of more importance than nutritional value. 

So, hydroponics by its very nature is suspect in its capability of delivering nutrient-dense foods.  The dependence on man-made chemical-based production removes the soil biome component from the equation.


home based aquaponics system

Which leads us to aquaponics.  Aquaponics is a hybrid production system of aquaculture and hydroponics.   There are many variations in the way aquaponics practices are applied.  To date, the number of commercial operations relying on aquaponics production practices are small.  There are many more small systems in operation than large commercial operations. 

In most aquaponics systems, fish are grown as a part of the production cycle to be harvested as part of the financial return from the system.  The fish are fed and naturally produce waste products, most of which is in the form of ammonia.  The operation of the system depends on the same biome structure as a soil system.  Exactly the same bacteria and other microscopic life are present in the water as in a healthy soil biome.  These organisms perform the same role in the aquaponics system as they do in the soil.  One of the functions they perform is to convert the available nutrients into forms that are available to the plant roots.  A properly maintained aquaponics system should have the same sort of biome as exists in healthy soil.  This includes visible life as well as the microscopic life.

The Essential Link between Aquaponics and the soil

Since the interaction between the plant and the biome is essentially the same, the aquaponics system should provide the same quality and quantity of nutrients as a soil biome.  Plants can signal the biome through root exudates to provide nutrients in the proper amount and at the proper rates, just as in a soil biome. 

Again, we must consider the health of the system in question.  Even an aquaponics system may grow plants that, in the end, are not as nutrient-dense as possible due to problems within the system itself.  Aquaponics systems are highly sensitive to pH balance.  The quality of the food provided to the fish is ultimately the controlling factor in the availability of nutrients to the plants.  This means that another set of variables is added to our equation.

commercial aquaponics system

In the end, I have my opinions, based on years of soil gardening and aquaponics growing.  I believe that industrial-based agriculture production, including hydroponics, delivers a substantially less nutrient-dense end product.   In many ways, the products labeled with the big O Organic label suffer from some of the same problems due to the priorities and focus of the producers.

Aquaponics and soil-grown products should, in theory, be capable of equally nutritious food production.  The interactions between the biomes of each, making them prone to the same sorts of problems. In soil, the use of little o organic systems to replenish the soil are critical.  It goes back to the concept of “feed the soil, not the plant.”  Care in creating a healthy, vibrant soil biome is the basis of producing healthy nutrient-dense vegetable.  In an aquaponics system, the same can be said of the biome that exists in the system.  A healthy and vibrant system biome will produce healthy, nutrient-dense vegetable.

My Conclusions

I grow the same vegetables, in many cases the exact same varieties, in both my soil garden and in my aquaponics system.  We have been practicing little o organic gardening for years now and our grow beds are dynamic with life.  Our aquaponics system has been running continuously for nine years and produces beautiful vegetables.  It is almost impossible to distinguish the difference in the vegetables taken from the soil garden or the aquaponics system.  I have not had any sort of nutritional testing down on either. However, I can tell the difference in my vegetables and the ones that we occasionally buy at the market.

For more information about soil health, aquaponic growing, the soil biome and other organic (little o) related topics, please visit our website at


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