NPK ratio for aquatic vs terrestrial plants - The Planted Tank Forum
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post #1 of 11 (permalink) Old 04-26-2020, 01:00 PM Thread Starter
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NPK ratio for aquatic vs terrestrial plants

I have a question for aquatic and terrestrial gardeners.

In researching fertilizers for my lawn and garden, I came up with the following recommended NPK ratios.

For terrestrial plants
Scott turf starter 24,25,4
Scott turf builder 22,0,4
Vigoro vegetable/tomato garden 12,10,5
Vigoro flower garden 15,30,15

versus

For aquatic plants
EI recommends 19.6, 0.6, 25
ADA recommends 0.7, 0.6, 25

https://www.advancedplantedtank.com/...a-approach-101

The recommended NPK ratios for terrestrial plants are all over the map and much different from those recommended for aquatic plants.

EI and ADA recommendations are actually close as the latter assumed rich soil to furnish most N.

Why is there such a huge difference in recommended ratio and what are the basis of the variation.

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post #2 of 11 (permalink) Old 04-26-2020, 01:48 PM
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When fertilizing terrestrial plants, the ratios depend on the goal of the plant and stage of growth. Think of the uses for the nutrients in this way NPK: up, down, all around. Nitrogen helps the plant grow up with stem and leaf growth. Phosphorus helps the plant grow down with root development. Potassium helps growth all around in all tissues of the plant. A starter fertilizer should be balanced with nearly equal amounts of NPK.

Once the plant is established, the fertilizer you choose depends on the plants purpose. Grass and some ornamental plants are grown for foliage, so a fertilizer high in nitrogen and potassium is beneficial. Most soils have plenty of phosphorus for typical foliage growth so that is normally not needed for established plants.

Some plants are grown for flowers or fruits, in which case a fertilizer lower in nitrogen and higher in phosphorus helps encourage flower/fruit development and discourages the plant putting too much energy into leaf and stem development.

Some plants are grown for their roots (think carrots, potatoes, beets, etc). While you would think they need less nitrogen and more phosphorus, they actually do need a certain amount of nitrogen for leaf development so they can then photosynthesize enough sugars to store in the roots.

I am still learning about aquatic plant needs, but I would say since most of our ornamental aquarium plants are grown for foliage, the ratios are determined based on that use, and also account for nutrient loss in the substrate since water is great at leaching away nutrients. I don't know if any are specifically grown for flowers or roots. I'm sure an advanced hobbyist could adjust the ratios to encourage flowering if conditions are right.

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post #3 of 11 (permalink) Old 04-26-2020, 02:02 PM
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First; 1) I am not a biologist and 2) as you know, the structure of terrestrial plants is usually different from aquatic plants, and soil interactions, from my understanding, in both their importance and complexity, bear little in common with aquatic plants (CEC issues included in this). We have the benefit of viewing our aquatic plants as though they were one large root and can feed them from top to bottom. With terrestrial plants, for the most part, it’s all about the roots.

In both our lawn and gardens, phosphorus is important for root development, which is why we see it as being high for seedlings (Scott’s Starter fertilizer), but it is not necessary, to a large degree, in established lawns and can be problematic (waterway contamination of phosphates). Fruits and vegetables need large quantities because of flowering and fruit production. So, with established lawns, it is often best not to use it at all or very little. In general, for lawns, it is a good idea to get an inexpensive soil analysis to see what you need (similar to our aquariums).

Potassium is usually needed consistently at levels that are about one-half that of nitrogen, but soil often has decent quantities to start. Additionally, potassium is expensive, so fertilizer companies will use as little as possible to prevent sticker shock and most consumers have no idea what they are buying other than knowing that the bag is fertilizer. I occasionally have to add 0-0-60 to my lawn. Actually, in our aquariums, I think we use far more K than is needed but, since overdosing it is harmless, up to a point, we don't need to be concerned.

The missing dynamic is nitrogen. It can be consumed rapidly by lawns and the delivery methods are different (slow vs. quick release). Fertilizer companies have convinced consumers to buy quick-release nitrogen and slop it down at the beginning of spring. This sudden surge of nitrogen creates an explosion of leaf growth and greening just as the birds start singing. Then, we can all go outside and smile, with pride, about how ‘good’ our lawns look. However, this sacrifices good root development, which makes grass less able to survive summer heat and drought. It is better to put N down just before winter, around Memorial day and Labor day and to use slow-release N. We probably use more N on our lawns than necessary and the frequency of burned lawns can attest to this.

Maybe a biologist will step in and better explain the differences.
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post #4 of 11 (permalink) Old 04-26-2020, 02:45 PM
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I can weigh in here (it's my day job to fertilize terrestrial plants and by nightly hobby to fertilize aquatic ones)


Many, many factors are taken into account when we come up with ratios for terrestrial plants, some of them will include:

Soil type and soil texture - Differences in soil will have different nutrient interactions, different CEC amounts, different government laws associated to fertilizing them etc. etc.

Weather / climate - Different climates (micro or macro) will have a huge impact on fertilizing. Humidity, sunlight, moisture etc. will all determine which kind of fertilizer can or should be used.

Fertilizer ingredients - It's easy to come up with a blend that has desirable levels in terms of NPK %, but we are limited to what fertilizer ingredients we have access to. For example, a 16-16-16 NPK is very easy blend to make, we use Urea, Mono-ammonium Phosphate and Muriate of Potash plus some inert filler to reach that 16% of all N P and K. But, sometimes I have customers asking for blends that are physically not possible to make with the ingredients I have access to. Lets say a customer asked for a 38-38-38 (this would never happen but I'm using it as an example). With Urea being 46-0-0, MAP being 11-52-0 and Potash being 0-0-60, I cannot make up a 38-38-38, I would have to divide 38 by 2, and make a 19-19-19 and have the customer spread double the rate to achieve the same amount of nutrients as a 38-38-38 would. Basically, we are stuck within the bound of the products we have available (and cost).


Plant species - All plants are not the same, and all plants aren't going to uptake nutrients in the same amounts / ratios. Using legumes as an example, why would I invest in a Nitrogen fertilizer for a legume when they form symbiotic relationships with soil bacteria who fix atmospheric nitrogen into plant available forms of nitrogen in exchange for sugars from the plant. Next time you have some beans growing, pull one out of the ground and cut open the nodules found on their roots, it should be pink, because of the oxygen carrying proteins found within the nodules / bacteria.

Loss potential - Different soils / climates / plant species when combined will allow for various loss potential, that we need to take into account. A sandy soil, with very little biomass will have a huge nitrogen loss potential, so we either have to apply way too much nitrogen to anticipate loss (waste of money and not very environmentally conscious) or we have to use different products with different NPK values to allow for slower release / protected nitrogen. The same can be said about a heavy clay soil, too much water will allow for anaerobic conditions leading to de-nitrification, or wet warm soil will cause massive amounts of volatilization.



Heck, each and every one of my customers have completely different fertilizer blends, even the same customer will have massively different blends for use on the same species of plant on the neighboring field.


I could go on and on, and get way more in depth, I'm just throwing things at the keyboard and trying to keep it simple, but there are just so many factors at play for terrestrial plants, and so many factors for aquatic plants (let alone the ones we grow in our tanks) so trying to compare fertilizing guaranteed analysis is a massively steep uphill battle.

Not to mention, terrestrial guaranteed analysis are in terms of % by weight Nitrogen (we do not use this in our tanks) % by weight P2O5 (we do not use this in our tanks) and % by weight K2O (we do not use this in our tanks) --> we typically display our numbers as NO3 ppm, PO4 ppm and K ppm.



If you want more info, or want to see what kind of blends are possible PM me or just let me know, I'm happy to help.

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post #5 of 11 (permalink) Old 04-26-2020, 05:41 PM Thread Starter
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Loss potential - Different soils / climates / plant species when combined will allow for various loss potential, that we need to take into account. A sandy soil, with very little biomass will have a huge nitrogen loss potential, so we either have to apply way too much nitrogen to anticipate loss (waste of money and not very environmentally conscious) or we have to use different products with different NPK values to allow for slower release / protected nitrogen. The same can be said about a heavy clay soil, too much water will allow for anaerobic conditions leading to de-nitrification, or wet warm soil will cause massive amounts of volatilizations.
.
Very insightful information from all of the above responses. I have follow up questions on loss potential.

In fish tanks, we do regular water change and pruning to remove plant mass, so I assume EI recommends NPK 19.6, 0.6, 25 because it is roughly proportional to chemical constituents of plant mass.

Our lawn is not crop land. There is no net removal of plant mass as we typically mulch mow lawn and donít keep goat to graze our lawn today. I can smell strong ammonia from grass clipping compost, so much N is expected to return to soil by micros. Yes, some N can leach out of soil, but so can K which is even more mobile than N. So why is lawn fertilizer, 22,0,4 or 25,24,4, is disproportionally high in N and low in K?
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post #6 of 11 (permalink) Old 04-26-2020, 09:47 PM
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Our lawn is not crop land. There is no net removal of plant mass as we typically mulch mow lawn and donít keep goat to graze our lawn today. I can smell strong ammonia from grass clipping compost, so much N is expected to return to soil by micros. Yes, some N can leach out of soil, but so can K which is even more mobile than N. So why is lawn fertilizer, 22,0,4 or 25,24,4, is disproportionally high in N and low in K?

N is very mobile, P and K are much less mobile (K is way less mobile in soils than N, youíve got that backwards).

There is more that just one way to lose N, itís not just to leaching. Volatilization and denitrification are big contributors to the Nitrogen cycle (aquaria version of the N cycle is only part of the entire N cycle). Plant uptake is another large contributor to N removal from the soil.

When you can smell ammonia from the clippings, that smell is volatilization occurring. For a different example, spreading manure on top of a field, in warm weather, can induce 100% free nitrogen loss.

Iíve seen soil samples from lawns, and they are insanely high in N, P and K. But, the N is not at high in proportion to the P and K. If you spread a higher P and K fert for a few seasons, your soil levels will be very, very high because there is little loss (unless you are bagging clippings, then there is a lot of removal).

N is a different story, after a large snow melt each year, or the downpours of the rainy season in warmer climates, N loss can be very high, meaning we still need to fertilize N. Sulphur is the same, sulphate is prone to leaching much the same as nitrate, and we arenít getting the Sulphur deposits like we used to do to coal plants becoming a thing of the past, so we should be fertilizing sulphur at a 10:1 (ish) ratio of N:S.


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post #7 of 11 (permalink) Old 04-26-2020, 10:16 PM Thread Starter
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N is very mobile, P and K are much less mobile (K is way less mobile in soils than N, youíve got that backwards).

There is more that just one way to lose N, itís not just to leaching. Volatilization and denitrification are big contributors to the Nitrogen cycle (aquaria version of the N cycle is only part of the entire N cycle). Plant uptake is another large contributor to N removal from the soil.

When you can smell ammonia from the clippings, that smell is volatilization occurring. For a different example, spreading manure on top of a field, in warm weather, can induce 100% free nitrogen loss.
Thanks for correcting my misconception. I was confused with the fate and transport of NPK in aquatic environment versus terrestrial.

Plants uptake K predominantly from the water column in an aquarium, so I assume (incorrectly) K must be very mobile in soil and would leach out with rainfall and irrigation infiltration.

There is no volitalization loss of NH3 in an aquarium as it is more soluble than volatile, and denitrification is insignificant in aerobic environment of a fish tank. So without plants and water change, N will accumulate as nitrate indefinitely in an aquarium. So I assume (incorrectly) that N behaves the same in soil.

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First; 1)

The missing dynamic is nitrogen. It can be consumed rapidly by lawns and the delivery methods are different (slow vs. quick release). Fertilizer companies have convinced consumers to buy quick-release nitrogen and slop it down at the beginning of spring. This sudden surge of nitrogen creates an explosion of leaf growth and greening just as the birds start singing. Then, we can all go outside and smile, with pride, about how Ďgoodí our lawns look. However, this sacrifices good root development, which makes grass less able to survive summer heat and drought. It is better to put N down just before winter, around Memorial day and Labor day and to use slow-release N. We probably use more N on our lawns than necessary and the frequency of burned lawns can attest to this.
For years, I only fertilize my lawn in fall and skip spring fertilizing. I want my lawn to be lush, but not too fast growing. High N fertilizing in spring will guarantee quantum top growth, meaning more mowing chore. Fall fertilizing promotes healthier lawn without excessive growth.

Your are right that homeowners probably apply more N than necessary. EPA has done a study and found that average homeowner applies 4 times more fertilizer per acre than agricultural land.
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post #8 of 11 (permalink) Old 04-27-2020, 12:42 PM Thread Starter
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I have a couple more follow up questions.

Scott definition of starter turf fertilizer sounds like starting a new lawn in virgin land. If I am reseeding bare spots in my lawn, I do not need starter fertilizer as there is already plenty of P and K from previous fertilizing in existing lawn, right?

ADA dosing (0.7, 0.6, 25) is popular in Asia, but less known in US.
https://www.advancedplantedtank.com/...a-approach-101

The low N dosing in ADA is counting on high N supply from rich soil. But nutrients in soil will not last forever unless one replaces with new soil every now and then. Without regular soil replacement, dosing will be short on N over long term, right? ADA dosing is actually equivalent to API Leaf Zone, which contains only potassium and iron.
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post #9 of 11 (permalink) Old 04-27-2020, 12:54 PM
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I have a couple more follow up questions.

Scott definition of starter turf fertilizer sounds like starting a new lawn in virgin land. If I am reseeding bare spots in my lawn, I do not need starter fertilizer as there is already plenty of P and K from previous fertilizing in existing lawn, right?

ADA dosing (0.7, 0.6, 25) is popular in Asia, but less known in US.
https://www.advancedplantedtank.com/...a-approach-101

The low N dosing in ADA is counting on high N supply from rich soil. But nutrients in soil will not last forever unless one replaces with new soil every now and then. Without regular soil replacement, dosing will be short on N over long term, right?
Starter helps regardless of soil tests levels, because the more P (not so much K) you can drive into a seeding, the better off it will be. So supplying a high P fertilizer near the germinating seed (preferably a fertilizer with a low salt index to prevent burn) will give easy access to plant available P that isn't bound up in the CEC / adsorbed to soil particles.

Now, for a lawn that has been well fertilized for a few seasons, you don't really need it. Maybe a small amount.



Now, onto ADA. You are completely correct with relying on rich soil derived N. But, ADA tanks after they age, are usually run with the lights dimmed right down to suppress algae, and to keep growth speeds lower to allow for less trimming / easier scape maintenance. Thus, the N demand will be lower, and ADA scaped tanks are rarely jacked full of fast growing stem plants that like the higher N.

Also, a lot of the red's you see in those tanks are from species who turn red more so from an N deficiency not so much light intensity (not an easy task to perform efficiently).
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post #10 of 11 (permalink) Old 04-29-2020, 12:19 PM Thread Starter
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Now, onto ADA. You are completely correct with relying on rich soil derived N. But, ADA tanks after they age, are usually run with the lights dimmed right down to suppress algae, and to keep growth speeds lower to allow for less trimming / easier scape maintenance. Thus, the N demand will be lower, and ADA scaped tanks are rarely jacked full of fast growing stem plants that like the higher N.

Also, a lot of the red's you see in those tanks are from species who turn red more so from an N deficiency not so much light intensity (not an easy task to perform efficiently).
I re read Dennis Wong article on ADA approach, he did mention that aging soil need to be replenished with new soil or root tabs. The ADA approach is equivalent to hybrid Walstad and high tech, relying on rich soil, CO2, but limited water column dosing. Like Walstad, ADA tanks are rare on stem plants which demand rich water column dosing. It’s interesting that, according to Dennis, N and P are barely detectable in ADA water column testing. So Tom Barr’s EI approach is more appropriate for Dutch garden colored stems, but can be over killing for easy nature aquarium plants.

There is another big difference between aquatic and terrestrial fertilizer regarding micro and gH dosing. Aquascapers regularly dose micro, iron and GH, but homeowners rarely do. Most lawn and garden fertilizers don’t even include them in the formulation. I fertilized every year but haven’t lime my lawn for a decade until I struggled with grass not growing in certain areas, did a soil test, and found the pH at 4.5. After couple season liming, the bare areas disappeared.
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post #11 of 11 (permalink) Old 04-29-2020, 12:53 PM
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I re read Dennis Wong article on ADA approach, he did mention that aging soil need to be replenished with new soil or root tabs. The ADA approach is equivalent to hybrid Walstad and high tech, relying on rich soil, CO2, but limited water column dosing. Like Walstad, ADA tanks are rare on stem plants which demand rich water column dosing. Itís interesting that, according to Dennis, N and P are barely detectable in ADA water column testing. So Tom Barrís EI approach is more appropriate for Dutch garden colored stems, but can be over killing for easy nature aquarium plants.
In a nut shell yes. Aqua soils also have a high CEC in the 30ish meq/100 grams (if I remember correctly) which is very high, so it can uptake a lot of nutrients from the water column and supply the plants with these nutrients.



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There is another big difference between aquatic and terrestrial fertilizer regarding micro and gH dosing. Aquascapers regularly dose micro, iron and GH, but homeowners rarely do. Most lawn and garden fertilizers donít even include them in the formulation. I fertilized every year but havenít lime my lawn for a decade until I struggled with grass not growing in certain areas, did a soil test, and found the pH at 4.5. After couple season liming, the bare areas disappeared.
That's because most soils are already at adequate levels of micros, and micro toxicity in terrestrial plants is a very real thing. My software has warning on it when mixing up certain micro nutrient blends (Boron especially) as it can cause a complete crop failure if done incorrectly. I would bet people would over apply a lawn fert with micro's and fry off their lawn / cause long term damage by over applying a micro into toxic soil test territory. Last soil sample I seen from a lawn showed everything as high or very high, only Mg was low, which for me area is fairly normal - higher Ca, less Mg.

At a pH of 4.5, you're looking at a lot of nutrients tied up and unavailable to the plant. Just under 7 is the best compromise.

If you've fertilized every year, I'm willing to bet you can get away with only applying N and S for 2 seasons (unless you bag clippings / crop removal).

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