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[APD] N budget

Hi Thomas,

I didn't notice a response on the APD so I'll send this to you again.

Let's suppose we have a healthy plant weighing 20 grams soaking wet. Is that
reasonable? What might be a typical dry weight for this? 2 grams?

Of the dry weight, what percentage is typical for N? 3% by dry weight?

So we might need 0.06 grams of elemental N to make a nice sized plant. Is
that a reasonable SWAG?

What I'm working towards is a target N budget for each plant for a 6 month
or 3 month period.

Let's give each plant 10 times the amount of N it might need for that period
and give each plant 4 square inches of turf. My two tanks are each 1' x 2'
which gives 288 sq in. or room for lets say 72 plants or so. My fertilizer
is 14-14-14 so at 14% N and 0.6 g N I need 4 grams of fertilizer. That's a
pretty massive fertilizer ball. If we make the budget only 2 X the expected
N content that would give us about 0.8 grams of fertilizer per ball per
plant per 4 square inches.

As for agar; what is the composition of this stuff? Isn't it going to turn
to mush underwater? Won't the bacteria start rotting it? I'd be nervous
about using it until somebody else had tried it. I've used clay balls lots &
so I'm not scared of using them. I usually use about a gram of fertilizer
per ball & recommend up to 3-4 balls for a large plant like a Sword or
Aponogeton. 1 ball is usually enough for a Crypt & I've been telling folks
to replace them at 6 months.


Thomas wrote:
>> How many grams of N (elemental) could a typical plant use?

> You need to pick a plant/biomass of plants/light value etc.
> Focus the question down to something much more specific.

>> Make & state whatever assumptions necessary.

Ok, late me supply some assumptions:

How much N is in an average sized Sword plant?
How many grams does an typical Sword weigh wet or dry?

Repeat question for:

Alternanthera reineckii  "Dragon flame"
Bacopa caroliniana
Hygrophila polysperma "Sunset" or "Rosanervig"
Lobelia cardinalis
Hemianthus micranthemoides

Anubias barteri
Anubias barteri nana
Anubias coffeeafolia
Anubias lanceolata

Spathiphyllum wallisii

Echinodorus horemanii
Echinodorus parviflorus
Echinodorus quadricostatus "Dwarf Sword"

Aponogeton crispus  "Ruffled Aponogeton"
Aponogeton madagascariensis  "Madagascar Lace Plant"

Cryptocoryne blassii
Cryptocoryne bullosa

Cryptocoryne lucens or Cryptocoryne x willisii
Cryptocoryne nurii
Cryptocoryne pontederiifolia
Cryptocoryne retrospiralis syn. C balansae, C crispatula
Cryptocoryne wendtii "green"
Cryptocoryne wendtii "brown"

Bolbitus heudelotii  "African Fern"
Vesicularia dubyana  "Java Moss"
Microsorium pteropus  "Java Fern"
Microsorium pteropus var Windelov "Java Fern"

Glossostigma elatinoides

Salvinia minima

The above is the list of plants which I have available to me in my current
tanks. I did say you could choose the plant & size to make the question
easier to answer. If you want a size, then the size will be the size of my
hand or a single 6" strand of stem plant.

The objective is to make a scientific wild-a** guess as to how many grams of
NPK to incorporate into clay balls for a given planting density & at what
point in time to add new balls. The guess need not be precise because the
plant is going to use a portion of whatever I give it. This is the first
iteration of a practical trial. Obviously, if a plant is growing too fast, I
will reduce its N budget; if its growing too slowly for my taste, I will
increase its budget.

I'm using the word budget because the plant has to work with what I give it.
If its not happy, it can't borrow N from other plants, it can only go into
deficit. Unlike the government, plants can't diddle the money supply or
synthesize N.

I'm looking for data of any kind to make guesses with.

Steve P

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