This article will show which plants can be cultivated in an aquaponic system. Before going into detail about the individual plants, however, it is important to understand which systems exist in the world of aquaponicsc, as some plants work better in system A than in system B, for example. Still others, on the other hand, have proven themselves in system B. This alone makes it clear that there is no such thing as the best system or the one system, and that when setting up or planning the design, you should pay close attention to which plants the system should be suitable for.

First of all, however, it can be said: theoretically, any plant can be cultivated in an aquaponic system. However, there are some exceptions where conventional methods work better. More on this later in the individual categories.  In this article you will find a list of experiences with individual plants.

Salads and herbs
Salads and herbs are probably the group of plants that work best in aquaponics. They are usually weak growers and are well taken care of in the aquaponic system. I have personally experienced lettuces that have grown strong, thick and robust with the help of aquaponics, so that biting into a single leaf felt like biting into a juicy piece of meat. Really crunchy.

What's more, lettuces and herbs will grow in any system, whether standing in gravel (Steady Flow / Flood & Drain), in planters both on polystyrene or similar (DWC) or in PVC pipe (NFT).

Recommended varieties:

Any lettuces such as chard, spinach, lettuce, iceberg lettuce, endive, rocket, purslane and so on have proved successful as have herbs such as basil, parsley, thyme and oregano.

Not recommended:

Mint should be avoided in the aquaponic system because it is rampant. It loves humid locations and is like paradise in an aquaponic system. Should it have its own system in isolation, there should be no problems, but together with other plants it will have overgrown them in no time.

Fruit vegetables
Fruiting vegetables belong to the group of highly nutritious plants and are also very popular in the aquaponic system. However, it should be borne in mind that some fruit vegetables can grow very large. Sufficient space above and below should be provided accordingly.

Tomato plants, for example, grow enormously. I have heard of cases where the tomato plant has grown over eight (8!) metres tall. For most people, this should represent a height that either does not fit into the desired space or makes any care of the plant an impossible task. Alternatively, cocktail tomatoes or vine tomatoes can be planted, which usually remain much smaller.

Cucumbers and other squash plants grow very wide and quickly overgrow the entire space. Here, too, thought should be given in advance to whether this space is available.

Furthermore, not every system is suitable for fruiting vegetables. Neither a DWC nor an NFT system is normally capable of supporting such large plants. Theoretically, this is also possible, but it would have to be readjusted regularly with supporting measures, for example with ropes or other suspensions.

Recommended varieties:

I would recommend smaller fruiting vegetables, such as chilli plants or peppers, for private households. Smaller tomato plants, such as cocktail tomatoes, are also possible.

Not recommended:

Any cucurbits, tomatoes and other plants that grow very large should only be cultivated with caution in an aquaponic system. Due to the high nutrient content in the water, enormous results can theoretically be achieved, but practically only if there is enough space.

Root and tuberous plants
Botanically not quite correct, but certainly acceptable for understanding: I count plants that develop edible parts underground as root and tuber plants, such as potatoes, carrots, beetroot, ginger, turmeric, parsnips and the like.

Theoretically, it is also possible to cultivate these plants in an aquaponic system, but some prerequisites are necessary here.

Soft tubers, like potatoes, should not be planted in the gravel bed (Steady Flow / Flood & Drain), as the tuber would form around the gravel. This could cause enormous toothache when eaten. Instead, for soft tubers, the Aeroponics method has proved successful.

With harder tubers, such as ginger and turmeric, the gravel bed is again possible, as their strength gradually pushes the gravel away.

Recommended varieties:

Ginger and turmeric I can recommend at this point, but only if there is enough space.

Not recommended:

Potatoes, carrots and other plants with relatively soft tubers I can only recommend if the necessary conditions have been created - see Aeroponic.

Leek plants
Leeks include the edible onion, the winter onion, the spring onion, chives, garlic, leeks and many more. All of these grow excellently in the aquaponic system.

Recommended varieties:

Depending on personal taste, pick one or two from the list of leeks that can grow alongside. They are easy to care for and the upper parts of the plants can be harvested several times during the year.

Not recommended:

Although onions and other leeks go well with almost any dish, care should be taken not to grow too many.

Exotics
As described above, theoretically any plant can be cultivated in an aquaponic system, as long as the necessary conditions are met. There are cases where even the cultivation of a banana and papaya plant has been successful in a specially constructed aquaponic system.

Summary:
Theoretically, any plant can be cultivated
Salads, herbs and allium plants grow particularly well and are easy to care for.
In the case of fruiting vegetables, it should be considered in advance whether there is enough space and room for them to develop.
Root and tuberous plants are only recommended under certain conditions.
Give free rein to creativity and inventiveness

ID: 130

The heart of an aquaponics system is its biofilter. The heterotrophic and autotrophic Bacterial communities in the biofilter naturally process organic waste and deliver biologically stable water that can be recycled for months. When choosing a biofiltration system for commercial aquaculture production, the efficiency of the technology and the substrate are very important because they determine the size, cost and energy consumption of the most expensive treatment components in circulatory systems.

Figure: Aquaculture engineers have to make a number of decisions when choosing the best biofilter for a particular application. Successive decisions at each node of the "decision tree" lead to the most reliable and cost-effective filter.

FBBs ( Floating Bead Bioclarifiers ) offer better solids separation ( 100% up to 30 µm ) as micro sieves and sedimentation tanks and at the same time avoid the problem of baking, which is typically associated with sand filters under high organic loads.

Under water or over water ?

Aerobic filters require oxygen. If the biofilm in the water that is transported to the filter can be adequately supplied with oxygen, choose an underwater filter. Otherwise, you should choose an ascending filter. Emergent (ascending) filters (EGSB) use a cascade-shaped mixture of water and air to ensure that a high oxygen content is maintained on the surface of the biofilm. Drip bodies distribute the water via a column filled with biofilter media. Rotating biological contactors - sometimes called wet / dry filters - use a more mechanical approach. They slowly turn into a water tank and out again, whereby the medium always stays wet, but is additionally aerated.

Overwater filter

Emergent filters are able to achieve an extremely high area conversion of TAN (converted TAN in grams per square meter surface), are limited by a small specific surface area (square meters of biofilm per cubic meter of unit volume). As a result, emerging filters can be 5 to 10 times larger than the submerged alternatives, and caution should be exercised with some media types to prevent possible constipation. These filters offer secondary benefits in the form of ventilation and carbon dioxide stripping. They are best suited for heavily loaded systems, where their ability to supply oxygen to the biofilm can bring some benefits.

TAN: Total ammonia nitrogen / total ammonia nitrogen

Underwater filter

Proponents of immersion filters point out that the fish live in circulatory systems on the inlet side of the filters and that the TAN values have to be kept very low. They argue that it is not oxygen diffusion, but TAN diffusion in biofilms that limits the performance of biofiltration. Proponents of underwater filters usually focus first on maximizing the specific surface and then on biofilms and solids management to improve TAN diffusion rates.

Underwater pouring bed

The oldest biofilters consist only of a bed of submerged media through which the water is circulated. These filters generally have no biofilm or solid management functions, and little attention is paid to the specific surface. These filters are used with great success in husbandry systems for seafood, lightly polluted aquaculture, show aquariums and the like. The large, inexpensive filters do a good job until they are overloaded and get into a zone with positive bacterial growth that makes them unusable because no more water can penetrate the filter. These shortcomings in dipped bulk beds have been remedied by filters that can deal with the problem of solids accumulation.

Expandable granulate filters

Expandable granulate filters differ from other filter types by a backwash mechanism. Expandable granulate filters, which include fine sand filters, gravel filters and bead filters, have a similar backwash strategy that enables them to work in a wide range of functions. This choice controls water loss and has a major impact on how easily the filters' biofilms can be manipulated. Expandable granulate filters have the unique ability to work as mechanical filters, biofilters or bioclars. However, their effectiveness in these three areas is very different.

Fine sand filter

Fine sand filters are mainly used as mechanical filters in most applications, but contribute to a certain nitrification in circulatory systems. These filters are poorly suited as biofilters in most commercial applications because the development of a biofilm quickly overrides the washing mechanism. All sand and gravel filters require high flow rates to start their expansion, which also leads to high water losses during backwashing. These water losses can hinder biofilm management strategies that improve the performance of biofilters. Sand filters are often used as sewage treatment tanks for show aquariums, as mechanical inlet filters in aquaculture systems and as biofilters in very weakly loaded circulatory systems.Coarse sand and gravel media are used with some success because they have sufficient abrasion capacities to cut off organic flakes and to avoid the problems of baking that plague finer sandbeds.

Floating bead filter

Floating-bead filters have practically all the properties of sand and gravel filters, but reduce or eliminate the problems of biofouling and water loss. Depending on the application, bead filters can be used effectively as mechanical filters, biofilters or bioclars, at the same time intercepting solids and acting as biofilters. The backwash mechanism and the frequency of backwash of the plants are used as an instrument for managing the biofilm. Well-managed plants are therefore able to achieve volumetric TAN conversion rates that are highly competitive with other biofiltration formats. In addition, the water loss for these filters is between just over 1 percent and 10 percent of the backwash requirement for equivalent gravel filters.

Expanded biofilters

Expanded biofilters, in which sand or pearls are continuously expanded, do not catch any solids, but are used as highly effective biofilters. Biofilter with fluidized sand bed keep the sand particles in suspension evenly so that the medium behaves like a liquid. The extremely high specific surface of the fine sand medium enables the filters to operate effectively at low ammonia values of less than 0.1 mg-N per liter, even if they are exposed to unfavorable conditions such as low pH. Fine sand particles are best suited for lightly stressed systems in which very low TAN concentrations are required. For example, they are used with great success in the ornamental fish industry. However, the units tend to lose sand when the substrate content increases,and are only able to remove biofilm to a limited extent.

Coarse sand

Coarse sand filters still have an excellent specific surface, are very abrasive and are well suited for higher loading capacities. Coarse sand vertebral layers support very high TAN conversions, but usually only with increased ammonia values of more than 1.5 mg-N per liter. The biofilm is overused at low substrate concentrations.

The filter... which is not one

This is not a filter in the strict sense, since the main purpose is to separate gaseous or dissolved substances and not solid particles. In contrast to the biodiesel bed reactor, on the one hand, in which a so-called biological lawn forms on installations in the reactor, which is continuously flushed, and the bio-washer on the other hand, in which the microorganisms are predominantly suspended in a washing liquid, the microorganisms in the biofilter are fixed on a matrix that partially provides the nutrient supply.

The idea of cleaning exhaust air and waste water biologically already existed in the 1920s, and technical use took place in the 1960s at the latest. Over the years, biofilters have been optimized for a variety of applications.

Function

On the one hand, a biofilter filters physically undesirable solids and, on the other hand, it transforms with the help of microorganisms, among other things. the ammonia from the fish excretions into nitrate, which can therefore be used by the plants as fertilizer.

Mechanical filtering

In addition to water, solid excretions of the fish, feed residues or algae are pumped into the plant beds from the fish tank. So that the substrate of the filters does not clog, worms must either ensure that these solids are converted or the solids must be removed mechanically beforehand.

Depending on the system design, there is also a sedimentation basin (also called a sedimentation system). This is an almost flow-free basin, in which water constituents are sedimented by gravity and thus a separation of removable substances from a liquid can be achieved. Here the water speed is reduced to such an extent that suspended matter can settle at the bottom. From there they can be removed with a mulm vacuum cleaner or a mechanical rake.

Recycling of suspended matter by worms

Since nutrients are also contained in the suspended matter, it is of course better (and easier) to use them. That is why worms are placed in the plant beds. Not all worms are equally suitable for this purpose. The typical „ earthworms “ from the garden need different soil depths than we can provide in aquaponics. Redworms (Eisenia foetida, Eisenia andrei, Dendrobena veneta), which are sold for worm compost or as fishing bait, are well suited.

Permanent flooded plant beds with a simple overflow are not suitable for the use of compost worms. Regular flooding in pumped systems, on the other hand, does not harm the worms.

Chemical filtering

The substrate also forms the habitat for the bacteria, which convert ammonia excreted by the fish into nitrate in a two-stage process. The first step of this so-called nitrification takes place aerobically ( in an oxygen-containing environment ) as oxidation of the ammonia to nitrite by nitrite bacteria. 

In the second process step, nitrate bacteria convert nitrite into nitrate by oxidation. These bacteria also live aerobic, so they need oxygen. If the filters clog through suspended matter, anaerobic zones arise in which the bacteria in the nitrification process die and use anaerobic putrefaction processes. The water receives the oxygen by pumping into the substrate and with compressed air that is added.

Effect of nitrate

Nitrate is an important plant fertilizer that mainly produces leaf growth. For salads, this is desirable to a certain extent. Amounts of nitrate that are too high are deposited in the leaves and are absorbed in the body when consumed. Nitrate and nitrite are suspected by converting them into the stomach and intestines, among others. Nitrosamines to be carcinogenic.
In addition, an oversupply of nitrate in fruit-forming plants (e.g. tomatoes) leads to excessive leaf growth and atrophy of the fruit sets. It is therefore important to ensure a balanced ratio of biofilters to biomass fish.

Environmental conditions

A product of nitrification is acid, so water in the cycle can increasingly acidify. However, the bacteria in the biofilter need a basic to neutral environment, which is why countermeasures to stabilize the pH value must be taken as part of regular maintenance.

Depending on the season and latitude, attention must be paid to the temperature. Depending on the microorganisms used, temperatures of 40 should be minimal⁰ Celsius should never be exceeded. Even under 10° Celsius some bacteria slow down their work to such an extent that they are no longer useful. From 0 ° Celsius, the bacteria in the biofilter die. Such a system must always be "run in !

One more word about TAN (Total ammonia nitrogen / total ammonia nitrogen)

Quantification of nitrification

In the past, studies have shown nitrification rates based on the specific surface of the media, with higher SSA values being preferred. Theoretically, the larger the SSA, the more habitat for bacteria. In an ideal world, this would lead to higher nitrification rates.

In the real world of commercial aquaculture, however, the bacteria form a biofilm that can effectively cover the medium, possibly in a way that clogs the topographical or porous features of the medium, which are intended to enlarge the specific surface. This covering of the medium essentially creates a new media topography and reduces the surface actually used by the bacteria.

Volumetric TAN conversion rate

Therefore, the theoretical nitrification capacity of a certain filter medium based on the SSA does not always reflect the nitrification actually achieved in the real world. It was recently suggested, that the nitrification rates of biofilters should be based on the TAN conversion per unit volume of the non-expanded filter medium. Designated as the volumetric TAN conversion rate ( VTR ), typical units for this standard measure of nitrification are grams of TAN removed per cubic meter of biofilter medium per day.

The composition of hydroponic fertilizers is completely different compared to the fertilizers for earth cultures. Plants that are cultivated in soils require completely different fertilizer mixtures than hydroponics. As a guide: Organic fertilizers often need microorganisms (depending on their composition) to break down the nutrients for the plants. Inorganic fertilizers do not need microorganisms to be able to supply the plant with all nutrients. Of course, the following also applies here: the exception confirms the rule.

Hydroponic fertilizers must be accountable for the special conditions of a hydroponics. These result on the one hand from the lack of microorganisms, which are required for the chemical splitting of the fertilizer substances in the soil - and can only be found there, on the other hand from the lack of buffering of the hydroponic system and from the fact that it is a closed system.

Important boundary conditions include: Hydroponic fertilizers should not contain too many ballast salts (sodium, chloride, etc.). The ammonium and nitrogen content should not account for more than about 50% of the total nitrogen (N) supply in order to avoid acidification of the nutrient solution.

However, this in turn does not apply to very hard (lime-rich) irrigation water. The phosphate content should also be significantly lower - compared to fertilizers for earth culture.

Fertilizer with buffer effect / reservoir or so-called long-term fertilizer

There are ion exchange fertilizers on the market for hydroponics. For decades, the ion exchange fertilizer “ Lewatit HD5 ” has been the only ion exchange fertilizer on the market. It was developed by Bayer AG in the 1970s and marketed under various trade names. The same company later developed the “ Lewatit HD5 plus ” for low-salt irrigation water (soft water).

In the meantime, only the well-known Lewatit HD50 is manufactured. This should be optimized for every degree of hardness of the water. However, the manufacturer still recommends adding lime to soft water to ensure supply. 

Which liquid fertilizer can you use?

The range of liquid fertilizers and nutrient solutions has now become unmistakable (1). In addition to liquid fertilizers for the professional in larger containers, products are offered in smaller quantities for the hobby area. Mostly they are so-called universal fertilizers. However, some manufacturers also offer special fertilizers for hydroponics.

Striking here: almost all manufacturers hold back with specific information about the plants for which the fertilizer should be "optimal. Likewise in dosing depending on the growth development. Even if certain plants are named by name, apparently not detailed here. If you think of tomatoes, you will probably not think of all 3,200 varieties that are currently being grown (source). To believe that one and the same fertilizer delivers consistently good results here also seems completely unbelievable to the layperson.

1) You can find a (always) incomplete list of commercially available fertilizers here. We only keep this list as a list of ingredients for homemade nutrient solutions. You can find out how to do this here in detail using a sample mix. The series of articles begins here: Mix the hydroponic fertilizer yourself: introduction

There are several ways to fertilize plants in hydroponics:

• With liquid inorganic solid fertilizer, this is automatically added in large plants due to the conductivity measurement of the water.

• By fertilizer salt release from solid ion exchanger granules.

• Sludge up organic fertilizer or add such nutrient solutions.

• A humus or compost layer that is applied to the top substrate layer in low-fiber systems and is only watered from above when fertilizer is required.

Context: 

ID: 419

Kontext: 

ID: 422 

Fertiliser programmes

Mixing hydroponic fertiliser yourself ?

The commercially available fertilisers consist of a complete fertiliser supplemented with macronutrients. They are offered by some hydroponics and/or fertiliser companies and vary depending on the hydroponic plant. An example of a fertiliser programme is the hydroponic tomato programme offered by Hydro-Gardens.

In this programme, growers purchase Hydro-Gardens Chem-Gro tomato formula. It has a composition of 4-18-38 and also contains magnesium and micronutrients. To make a nutrient solution, it is supplemented with calcium nitrate and magnesium sulphate, depending on the variety and/or growth stage of the plant.

Advantages of fertiliser programmes

Disadvantages of fertiliser programmes

Modified Sonneveld recipe / herbs

It is at the discretion of the breeder which fertilizers he uses to produce a nutrient solution according to a recipe. The fertilizers commonly used include:

Advantages of nutrient solution recipes

Nutritional solutions allow fertilizers to be adjusted based on the nutrients contained in water sources. An example: A gardener uses a water source with 30 ppm potassium and produces the modified Sonneveld solution for herbs that requires 210 ppm potassium. It would have to add 180 ppm potassium ( 210 ppm - 30 ppm = 180 ppm ) to the water in order to obtain the amount of potassium required in this recipe.
With recipes, nutrients can be easily adjusted. When a leaf analysis report indicates that a plant has iron deficiency. It is easy to add more iron to the nutrient solution.
Since recipes make it easy to adapt, fertilizers can be used more efficiently than in fertilizer programs. Using recipes can be less expensive than using fertilizer programs.

Disadvantages of nutrient solution recipes

It has to be calculated how much fertilizer has to be added to the nutrient solution. (Link to performing calculations). Some people may feel intimidated by the calculations involved. However, the calculations only require uncomplicated mathematical skills based on multiplication and division.
A high-precision scale is also required for the measurement of micronutrients, since the required quantities are very small. Such a scale can be found on Amazon from 30.- €: e.g .: KUBEI 100g / 0.001g.

This is about the calculation of nutrient solutions for your own needs

Picture: Boston Public Library is licensed under CC BY 2.0

Kontext: 

ID: 415

Calculation of the concentrations of nutrient solutions using the following two equations

The calculation of the amount of fertilizer that has to be added to the nutrient solutions is part of a successful hydroponic production. Only multiplication, division and subtraction are used for the calculations; no advanced mathematical knowledge is required.

If you want to know more about the compositions and concentration information, the article series can be too Stoichiometry and a look at the conversion of Mol and grams When specifying the concentration of the individual elements and connections, it is helpful to better understand the complexity of the topic.

If you master the general process, producing nutrient solutions and adjusting the amount of nutrients is child's play.

Fertilizer recipes for hydroponics are almost always given in ppm (in the long form: parts per million). This may differ from the fertilizer recommendations for growing vegetables and fruits outdoors, which are generally given in lb / acre (pounds per acre).

First you have to convert ppm to mg / l (milligrams per liter) using this conversion factor: 1 ppm = 1 mg / l (1 part per million corresponds to 1 milligram per liter). For example, if 150 ppm nitrogen is required in a recipe, 150 mg / l or 150 milligrams of nitrogen in 1 liter of irrigation water are actually required.

Ppm P (phosphorus) and ppm K (potassium) are also used in recipes for nutrient solutions. This also differs from the fertilizer recommendations for growing vegetables and fruits in the field, which use P2O5 (phosphate) and K2O (potash). The fertilizers are also given as phosphate and potash. Phosphate and potash contain oxygen, which must be taken into account in hydroponic calculations. P2O5 contains 43% P and K2O contains 83% K.

Let us check the previous circumstances:

1 ppm = 1 mg / l
P2O5 = 43% P
K2O = 83% K

Nutrient solution tanks are usually measured in gal ( gallons ) in the United States. When we convert ppm to mg / l, we work with liters. To convert liters into gallons, use the conversion factor of 3.78 l = 1 gal ( 3.78 liters corresponds to 1 gallon ). The invoice is also given below for continental interested parties.

Depending on the scale you use to weigh fertilizers, it may be useful to convert milligrams into grams: 1,000 mg = 1 g ( 1,000 milligrams correspond to 1 gram ). If your scale measures in pounds, you should use this conversion: 1 lb = 454 g ( 1 pound = 454 grams ).

Let us summarize these circumstances:

3.78 l = 1 gallon
1000 mg = 1 g
454 g = 1 lb

Now we have all the necessary circumstances. Let's look at an example.

How do you determine how much 20-10-20 fertilizer is needed to deliver 150 ppm N with a 5 gallon tank and a fertilizer injector that is at a concentration of 100:1 is set?

First, write down the concentration you know you want to reach. In this case it is 150 ppm N or 150 mg N / l.

Note that we multiply by 1. This allows you to cancel the units that are the same in the numerator and denominator. Now we can paint "mg N" and get the unit g N / l water.

Continue this process by converting liters into gallons. Most containers are still traded in gallons ( 3.78 liters ). Entertaining here: the metric system was invented by the Britten. If you want a metric result, omit this calculation step.

Now there are only grams of nitrogen left per gallon of water.
We'll get closer to it. Now we want to convert grams of nitrogen into grams of fertilizer. Remember that our fertilizer is a 20-10-20, which means that it contains 20% nitrogen. It can be imagined that 100 grams of fertilizer contain 20 grams of nitrogen. 

So where do we stand now? We calculated how many grams of fertilizer are needed in each gallon of irrigation water. At the moment we have a normally strong solution. Our example prompts us to calculate a concentrated solution of 100: 1. This means that for every 100 gallons of water that are applied, 1 gallon of stock solution is also applied via a fertilizer injector. We also know that our storage tank holds 5 gallons. Below see calculation for metric system (liters).

In gallons

In the calculator: 150 x 1: 1000 x 3.78 x 100: 20 x 100 x 5 is 1417.5 grams on 5 gallons of water (in the storage tank)

After we have deducted everything, we have a gram of fertilizer left. This is the amount of fertilizer we need to put in our storage tank to apply 150 ppm N at a concentration of 100: 1. Multiply and divide and you get the answer 1417.5 grams of fertilizer.

In liters

In the calculator: 150 x 1: 1000 x 100: 20 x 100 x 10 is 1500 grams per 10 liters of water ( in the storage tank )

After we have deducted everything, we have a gram of fertilizer left. This is the amount of fertilizer we need to put in our storage tank to apply 150 ppm N at a concentration of 100: 1. Multiply and divide and you get the answer 750.0 grams of fertilizer.

This means that for every 100 liters of water that is applied, 1 liter of stock solution is also applied via a fertilizer injector. We also know that our storage tank holds 10 liters. 

If we measure in pounds, we have to put 0.75 kg / 1.15 lb fertilizer in our storage tank to apply 150 ppm N with a concentration of 100: 1.

You have just completed one of the two equations. Now let's look at the other one.

We just found that we need to add 750 grams of fertilizer to deliver 150 ppm nitrogen at a concentration of 100: 1. The fertilizer we used was a 20:10:20. In addition to nitrogen, we also add phosphorus and potassium. With the next equation we determine how much phosphorus we supply. This is basically the reversal of the first calculation.

We start with the amount of fertilizer that we put in our tank. The final units are ppm or mg / l. As with the previous calculation, we use our specifications until we receive these units.

Multiply with the concentration of the nutrient solution.

Multiply to convert to liters.

Next, convert milligrams of fertilizer into milligrams of phosphate.

Next we will convert grams of phosphate into grams of phosphorus, assuming that phosphate contains 43% phosphorus.

Finally, we convert grams of phosphorus into milligrams of phosphorus.

When we calculate this, we find that we have added 32.25 mg / l P or 32.25 ppm P. This is the second equation. We can also use them to determine how much potassium we have added. 

We added 124.5 mg / l K or 124.5 ppm K.

With these two basic calculations, you can use any nutrient solution recipe program. How they are used to calculate a recipe can be seen in this article:

Kontext: 

ID: 416

Here we have created a short introduction to the topic of fertilizer and nutrient solutions, with which you can learn the concept, the basics and also the calculation of self-created nutrient solutions. In the last article you will find a brief overview of deficiency symptoms and how you can recognize and correct them. 

Please also keep in mind that the perfect recipe for your own plant requires enormous knowledge, complex technology and a lot of experience. However, for many areas this is not necessary at all. If you, as an entrepreneur, are in competition and have to work to the optimum in order to be profitable, things look different. But this little guide is not aimed at entrepreneurs who need to make money with it. For commercial applications, please do not hesitate to take advantage of our experience, our knowledge and the technology required for this:  just ask us - email or phone call is enough.

A brief introduction to fertilisers & nutrients

Fertiliser: Calculation of nutrient solutions

Fertilizer: Calculate a nutrient recipe

Fertilizer: Essential Nutrients, Function, Deficiency and Exces

Common Concentrations in Nutrients

To ensure a highly optimised nutrient supply throughout the entire growth process, you need analytical equipment. Here a short overview and Selection.

Kontext: 

ID: 407

Now that you have the two basic equations for the production of nutrient solutions, we want to use them to calculate the amounts of fertilizer required for a nutrient solution recipe.

If you are not familiar with the two equations, read this first: Hydroponic systems: Calculating the concentrations of nutrient solutions using the two equations.

Here is our problem: We want to use a modified Sonneveld solution (Matson and Peters, Insidegrower) for herbs in an NFT system. We use two 5-gallon containers and injectors set to a concentration of 100: 1 and call them storage tank A and storage tank B. How much of each fertilizer do we have to put in each storage tank ?

You may be asking: why two storage tanks? This is due to the fact that certain chemicals in our fertilizer solution react with each other as soon as they come into contact with each other. In all nutrient solutions ( fertilizer mixtures ) you have calcium, phosphates and sulfates - among other things, these three chemicals for all plants vital are. The last two react with calcium and are no longer present in the form we need in our nutrient solution. They connect to each other and fall to the bottom of the container as white flakes ( precipitates ). Therefore, phosphates and sulfates must be kept separate from calcium and, when introduced into the nutrient solution of the ( system, saved from direct mixing by means of a dosing pump or measuring cup ).

Modified Sonneveld recipe for herbs

These are the fertilizers that we will use. Some fertilizers contain more than one nutrient in the recipe, while others contain only one. Here is a small overview Commercial fertilizer from which you can put together your recipe

The first thing you notice is that we have three sources of nitrogen (calcium nitrate, ammonium nitrate and potassium nitrate), have two sources of potassium (potassium nitrate and potassium phosphate monobasic) and one source of calcium (calcium nitrate) and phosphorus (single-base potassium phosphate). We can start calculating the calcium or phosphorus in the recipe because only one fertilizer provides each nutrient. Let's start with calcium.

The recipe provides 90 ppm calcium. We calculate how much calcium nitrate we need to use to achieve this by using the first of our two equations.

We need to add 895.3 g calcium nitrate to get 90 ppm calcium. However, calcium nitrate also contains nitrogen. We use the second equation to determine how much nitrogen should be added in ppm.

We add 73.4 mg N / l or 73.4 ppm nitrogen. Our recipe provides 150 ppm nitrogen. If we subtract 73.4 ppm nitrogen from it, we have to add 76.6 ppm nitrogen.

Let us now calculate how much single-base potassium phosphate we have to use to deliver 31 ppm phosphorus.

We need to add 262 g of potassium phosphate monobed to get 31 ppm phosphorus. However, potassium phosphate also contains single-base potassium. We use the second equation to determine how much potassium should be added in ppm.

We add 39 mg K / l or 39 ppm potassium. Our recipe provides 210 ppm potassium. If we subtract 39 ppm of potassium from it, we see that we still have to add 171 ppm of potassium.

We have only one other source of potassium, namely potassium nitrate. Let's calculate how much we have to use of it.

We need to add 885 g of potassium nitrate to get 171 ppm of potassium. However, potassium nitrate also contains nitrogen. We use the second equation to determine how much nitrogen should be added in ppm.

We add 61 mg N / l or 61 ppm nitrogen. Our recipe provides 150 ppm nitrogen. We supplied 73.4 ppm nitrogen from calcium nitrate and had to add 76.6 ppm nitrogen. Now we can subtract 61 ppm nitrogen. We still have to add 15.6 ppm nitrogen. The only source of nitrogen that we have is ammonium nitrate.

Let us now calculate how much ammonium nitrate we have to use to deliver 15.6 ppm nitrogen.

We need to add 86.7 g of ammonium nitrate to get 15.6 ppm nitrogen.

At this point we have completed the nitrogen, phosphorus, potassium and calcium part of the recipe. For the other nutrients, we only need to use the first equation, since the fertilizers that we use for their supply contain only one nutrient in the recipe.

We need to add 498.5 grams of magnesium sulfate to get 24 ppm magnesium.

We need to add 18.9 grams of Sequestren 330 to get 1 ppm of iron.

We need to add 1.5 grams of manganese sulfate to get 0.25 ppm manganese.

It is easier to weigh small amounts of fertilizers in milligrams. The conversion from milligrams to grams is therefore carried out as follows

We need to add 692 milligrams of zinc sulfate to get 0.13 ppm zinc.

We need to add 0.17 milligrams of copper sulfate to get 0.023 ppm copper.

We need to add 2.8 milligrams of borax to get 0.16 ppm borax.

We need to add 0.12 milligrams of sodium molybdate to get 0.024 ppm molybdenum.

Summary:

Now all calculations have been completed. Now we have to decide in which storage tank, A or B, we give the individual fertilizers. In general, the calcium should be kept in a tank other than the sulfates and phosphates, as they can form precipitates that can clog the drip bodies of the irrigation system. Using this guideline, we can put the calcium nitrate in one tank and the monobasic potassium phosphate, magnesium sulfate, manganese sulfate, zinc sulfate and copper sulfate in the other tank. The rest of the fertilizers can be placed in both tanks.

You should also consider the amount of nutrients in irrigation water. For example, if we use irrigation water that contains 10 ppm magnesium, we only need to add 14 ppm more with our fertilizer (24 ppm Mg, which are required in the recipe, minus 10 ppm Mg in water). This is a great way to use nutrients more efficiently and fine-tune your fertilizer plan.

With some micronutrients, you have to decide for yourself what you want to add. You could do a small experiment to find out whether you need to add 0.12 milligrams of sodium molybdate to your stock solution, for example, or whether you are satisfied with the performance of your plants without this addition.

One last point to consider. Sometimes the calculations don't work as well as here for fertilizers that contain more than one required nutrient, and you may need to add more of a nutrient, than is provided in the recipe to provide the other nutrient.

For example, if you apply calcium nitrate to meet calcium needs, the solution may not contain enough nitrogen. In such cases, you have to decide which nutrient you want to give priority to. For example, you could apply calcium nitrate to meet the plants' nitrogen needs because the excess amount of calcium does not harm the plants. Or you choose to apply it based on the plant's calcium needs because the lack of nitrogen is just a few ppm.

Here you will find what problems there may be with a lack and excess of fertilizer

At this point we can give you recommendations for your plantations with modern analysis technology. Contact us...

Context: 

ID: 417

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

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

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

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

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

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

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

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

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

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

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

Detection: leaf analysis.

Correction :  increase the fertilizer dose. Correct the pH: keep it well above 4.0. 5.5 to 6.5 is a good average for many plants. Enrich the soil with Epsom salt / magnesium sulfate / MgSO ₄ : one teaspoon per 2 liters of water (approx. 1% concentration).

First we look at the nutrient solutions, some of which have been around for over a hundred years. This shows us in which concentrations the measurement must take place. 

This serves as an initial orientation as to what nutrients or elements must be contained in a solution. A further step is to closely observe plant growth in order to be able to identify deficits as such.

The next step is to get an idea of ​​which elements, and therefore which compounds, are in the end product. Unfortunately, such an analysis (the plant is put into a blender and additional chemicals are added depending on the compounds we are looking for) has the disadvantage that it doesn't really reveal everything that interests us. This is because the chemical compounds can rarely be found in the plant in the form in which they were originally added. This is where biology comes into play. The only example that we would like to mention here is the citric acid cycle, which we do not want to withhold from you. It illustrates the complexity of metabolism.

Nutrition of hydroponic plants

• moles to grams
• grams to moles

Here are some recipes for nutrient solutions...

Here you can view the plants that have similar pH and Ec values ​​and can therefore, at least in this respect, be planted together in an aqua or hydroponic system. Also pay attention to the temperature.

What are the nutrient requirements for certain plants? This list shows the nutrient concentration preferred by each plant. Note the differences within the subspecies/breeding . Please remember: there are 23,000 varieties of tomatoes - of course these vary in terms of preferred temperatures as well as Ec and pH values! The fine-tuning of the nutrient composition is not even mentioned here. More details about the list at the end of the same.

Nutrients that cannabis needs can be divided into three categories: Primary macro-nutrients, secondary macro-nutrients and micro-nutrients. This division is based on how much of each nutrient the plant needs.

Nitrogen, for example, is categorised as a primary nutrient because the plant needs more of it than calcium or sulphur, for example.  Cannabis has different nutrient requirements in different phases. Nitrogen, for example, is mainly needed in the growth phase, but much less in the flowering phase.

On the other hand, the need for other nutrients, such as phosphorus, increases. In the growth and flowering fertilisers from well-known manufacturers, the nutrients are already optimally adapted in each case. (You can find more about the correct fertilising depending on the phase of life further down in the text).

You can find a more comprehensive and filterable overview in the pH & Ec Finder here...

Context: 

ID: 145 

Basics In hydroponics and the associated aquaponics, there are different methods to supply the plants with nutrients. These can be divided into active and passive systems. Passive systems have the advantage of being independent of the power supply. Their efficiency is lower than that of active approaches.   Passive and Active Hydroponic Systems Passive hydroponic systems are systems that function without a power supply. Active hydroponics uses pumps, aerators, humidifiers or spray nebulisers. These require electricity. Active hydroponic systems are more complex in design, but many times more effective in terms of plant growth due to the oxygen input.	Overview Wick Irrigation Ebb - Flood Systems NFT - Nutrient Film Technique DWC - Deep Water Culture DFT - Deep Water Nutrient Film Technique (Deep Flow Technique) Drip Irrigation Aeroponics - Mist from nutrient solution Aquaponics - Plant cultivation and fish farming Aquaponics - CHOP ( Constant Height, One Pump)   Schematic of an aquaponics system
A brief overview of the most common systems in aqua- and hydroponics
Passive Hydroponics: Wick Watering
The wick system (Wick Watering) does not require any moving parts or electricity. The plants are cultivated in a substrate that is supplied with the nutrient solution through the capillary action of the "wick". Supplying the plants via this system is not very effective. In addition, the wick can largely lose its nutrient transport properties due to mineral deposits. Another disadvantage is that no extra oxygen is supplied to the roots. The system is technically simple but plant growth is slower than with other active hydroponic systems. Pros: cheap purchase without electricity without technology low nutrient consumption low control effort   Cons: very low yield slow growth
Active Hydroponics: Ebb and Flood Systems
Ebb and flood systems (Ebb and Flood or Flood and Drain) use pumps (4) that flood the plants with the nutrient solution in a time-controlled manner (2). The plants are embedded in a net pot. After the pump is turned off, the excess nutrient solution is returned to the reservoir (1) via an overflow (3). Often a residual amount is left to make the system less vulnerable in case the pumps should ever fail, enough water remains in the plant basin as the overflow ensures a minimum water supply. By raising and lowering the liquid level (2), oxygen is introduced in the root area, which leads to more intensive plant growth. An electronic control system must adapt the ebb and flow rhythm to the requirements of the plants. Pros: low nutrient consumption low water consumption high yield in case of power or pump failure: no crop loss   Cons: high purchase costs power supply necessary Control effort
Active Hydroponics: NFT - Nutrient Film Technic
NFT or Nutrient Film Technic (NFT) systems provide a permanent flow of nutrients that flow around the roots in a thin "film". A pump conveys the nutrient solution to an inclined plane on which the plant roots lie, thus providing them with a continuous supply. The constant flow prevents nutrient build-up. NFT systems also add oxygen to the nutrient solution, for example through downpipes or intermeshing systems. The plant substrate is usually dispensed with, so that the roots have direct access to nutrients and oxygen and can thus grow quickly. A disadvantage is the loss of all plants in case of defective pumps or power failure. Pros: low nutrient consumption low water consumption very high yield   Cons: high purchase costs power supply necessary Control effort in case of power or pump failure: loss of harvest
Active Hydroponics: DWC - Deep Water Culture.
In deep water culture systems, also known as DWC systems, already rooted plants are placed in a net pot on a floating plate in the liquid reservoir, like a raft. To stabilise the plant, the net pot can be filled with substrate, such as clay balls. The roots hang directly in the nutrient solution, which is enriched with oxygen. This is done by means of an air pump and aeration stones that introduce very fine air bubbles into the water. Since the roots are constantly supplied with oxygen-rich nutrient solution, the plants grow very quickly and vigorously. The system is simple and safe, even in the event of a power failure nothing will happen to the plants. Thanks to the large water reservoir, the system can be left alone for a few days without having to worry about it. With the DWV system, the plants can also sit on a kind of raft and float on the nutrient solution. Pros: low nutrient consumption low water consumption very high yield fast growth (oxygen) in case of power or pump failure: no crop loss Cons: high purchase costs power supply necessary Control effort
Active Hydroponics: DFT - Deep Flow Technique (Deep Water Nutrient Film)
Active Hydroponics: DFT - Deep Water Nutrient Film Technique (Deep Flow Technique) The Deep Flow Technique, better known as DFT, is a variation of the NFT technique, also known as the Nutrient Film Technique. Instead of the thin nutrient film, the plants are flowed around by a nutrient solution about 2-4 cm high. The principle procedure is the same and works recirculatory. The deep flow technique DWT makes this cultivation system safer, because in case of pump failure the roots are still supplied. However, the method has hardly become established in the industry, because especially with longer / larger systems, the supply of oxygen to the plants varies and the plants grow unevenly as a result. It counts as one of the active hydroponics systems. Pros: low nutrient consumption low water consumption very high yield   Cons: high purchase costs power supply necessary Control effort in case of power or pump failure: loss of harvest
Active hydroponics: drip irrigation
With drip irrigation (drip system), the nutrient solution is dripped onto the substrate around the plants via a drip line. The nutrient solution flows past the roots and supplies them directly. The excess liquid flows off, supplying oxygen to the root area. Non-recovery system: In industrial cultivation there are non-recovery systems to achieve a high yield without measuring technology. Here, the plants are always supplied with fresh and equally adjusted nutrient solution. The nutrient is not returned to the cycle to avoid the spread of pathogens. This method uses more water and unused nutrients are lost. This system does not require control of nutrients but relies on experience with nutrient use. One can run the system "blind". Pros: very high yield fast growth in case of power or pump failure: no crop loss little control effort Cons: high purchase costs power supply necessary high nutrient consumption High water consumption   Recirculating system: The nutrient solution is fed back into the system, which means that only the nutrients that the plant actually needs are consumed. The flow rate is adjusted to the needs of the plants. Due to the closed system, however, it is necessary to control the nutrients in order to adjust them to the growth phase-dependent consumption. This system needs a regular control of the nutrient concentration. Pros: very high yield fast growth in case of power or pump failure: no crop loss Cons: high initial costs power supply necessary Control effort	Ohne Kreislauf                       Mit geschlossenem Kreislauf
Active hydroponics: Aeroponics - fog of nutrient solution
In an aeroponic growing system, the roots of cuttings or plants are not suspended in a liquid but in a mist of nutrient solution. The plants are hung with net pots in a chamber where the roots are sprayed or fogged with nutrient solution through water nozzles / fog nozzles. Aeroponic systems offer the optimal supply of the roots with everything they need to grow, they work very effectively and deliver maximum plant growth and therefore belong to the active hydroponic systems. However, the technical effort is high because of the high water pressure for the nozzles or the nebulisers used. In addition, technical measures must be taken to prevent the nozzles from clogging. A disadvantage is that a failure of the nebulisers is not tolerated by the free-hanging roots for a long time. Pros: very high yield fast growth   Cons: high purchase costs power supply necessary high nutrient consumption high water consumption Control effort
Active hydroponics: aquaponics - plant cultivation and fish farming
Aquaponics (aquaponic) is made up of aquaculture (fish farming) and hydroponics (plant farming), so two farming systems are combined. The excreta of the fish are used to supply the plants with nutrients, they are recycled and serve as fertiliser. The excreta are converted into nutrients that can be used by plants with the help of microorganisms. At the same time, the water is cleaned so that it can be returned to the fish tank and the fish have good living conditions. This creates a win-win cycle. In addition to growing lettuce and vegetables, fish are bred for food or ponds are kept clean with ornamental fish.	Fish farming can be combined with all systems that allow separation and control of nutrients through a circuit.
Active hydroponics: aquaponics - sump tank (CHOP: Constant high, one pump)
The decisive advantage of introducing a sump tank is that the height of the water level - especially in the fish tank - always remains constant. Only when water enters the fish tank from above through the pump does water flow back through the overflow. On the one hand, this means less stress for the fish and, on the other hand, the tank is filled with water even if the system fails (e.g. due to a burst pipe), as the water level can never drop below the overflow.

Overview of the most common systems

Passive hydroponics: wick irrigation
Active hydroponics: Ebb and flow systems
Active hydroponics: NFT - Nutrient Film Technology
Active Hydroponics: DWC - Deep Water Culture
Active Hydroponics: DFT - Deep Water Nutrient Film Technique (Deep Flow Technique)
Active hydroponics: Drip irrigation
Active hydroponics: Aeroponics - Fog from nutrient solution
Active hydroponics: Aquaponics - plant cultivation and fish farming
Active Hydroponics: Aquaponics - CHOP - Sump Container (Constant Height, One Pump)

Context: 

ID: 116

Historical background:

Aquaponics has ancient roots, although its first appearance is disputed:

The Aztecs cultivated agricultural islands known as chinampas in a system considered by some to be an early form of aquaponics for agricultural purposes,[4][5] in which plants were grown on stationary (or sometimes movable) islands in the shallows of lakes and waste materials dredged from the chinampa canals and surrounding cities were used to manually irrigate the plants.[4][6]

Southern China and all of Southeast Asia, where rice was grown and cultivated in rice paddies in combination with fish, are cited as examples of early aquaponics systems, although the technology was brought by Chinese settlers who had migrated from Yunnan around 5 AD. [7] These polycultural farming systems existed in many Far Eastern countries and raised fish such as the Oriental loach (泥鳅, ドジョウ), [8] swamp eel (黄鳝, 田鰻), carp (鯉魚, コイ) and crucian carp (鯽魚)[9] as well as pond snails (田螺) in the rice fields. [10][11]

The 13th century Chinese agricultural manual Wang Zhen's Book on Farming (王禎農書) describes floating wooden rafts heaped with mud and soil and used for growing rice, wild rice and fodder. Such floating planters were used in regions that form today's Jiangsu, Zhejiang and Fujian provinces. These floating planters are known as either jiatian (架田) or fengtian (葑田), meaning "framed rice" or "rice field" respectively. The agricultural work also refers to earlier Chinese texts, which indicate that rice cultivation on floating rafts was practised as early as the Tang Dynasty (6th century) and the Northern Song Dynasty (8th century) of Chinese history.[12]

4) Boutwelluc, Juanita (December 15, 2007). "Aztecs' aquaponics revamped". Napa Valley Register. Archived from the original on December 20, 2013. Retrieved April 24, 2013.
5) Rogosa, Eli. "How does aquaponics work?". Archived from the original on May 25, 2013. Retrieved April 24, 2013.
6) Crossley, Phil L. (2004). "Sub-irrigation in wetland agriculture" (PDF). Agriculture and Human Values. 21 (2/3): 191–205. doi:10.1023/B:AHUM.0000029395.84972.5e. S2CID 29150729. Archived (PDF) from the original on December 6, 2013. Retrieved April 24, 2013.
7) Integrated Agriculture-aquaculture: A Primer, Issue 407. FAO. 2001. ISBN 9251045992. Archived from the original on 2018-05-09.
8) Tomita-Yokotani, K.; Anilir, S.; Katayama, N.; Hashimoto, H.; Yamashita, M. (2009). "Space agriculture for habitation on mars and sustainable civilization on earth". Recent Advances in Space Technologies: 68–69.
9) "Carassius carassius". Food and Agriculture Organization of the United Nations. Fisheries and Aquaculture Department. Archived from the original on January 1, 2013. Retrieved April 24, 2013.
10) McMurtry, M. R.; Nelson, P. V.; Sanders, D. C. (1988). "Aqua-Vegeculture Systems". International Ag-Sieve. 1 (3). Archived from the original on June 19, 2012. Retrieved April 24, 2013.
11) Bocek, Alex. "Introduction to Fish Culture in Rice Paddies". Water Harvesting and Aquaculture for Rural Development. International Center for Aquaculture and Aquatic Environments. Archived from the original on March 17, 2010. Retrieved April 24, 2013.
12) "王禎農書::卷十一::架田 - 维基文库，自由的图书馆" (in Chinese). Archived from the original on 2018-05-09. Retrieved 2017-11-30 – via Wikisource.

Related article: Types of planting