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# [APD] Re: N budget

```Steve P. wrote:

> 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.

Do you have Diana Walstad's book, Steve?  She used published data
listing the critical concentrations of 12 elements in Eleodea
occidentalis to guesstimate her plants needs for 20 grams (dry wt.)
of growth each month (see pp. 78, 104-105).  Perhaps you could adapt
her method to your experiment.

For example, she used the critical concentration of 16000mg/kg N in
E. occidentalis to compute that her plants need 320mg N to sustain
20g of dry wt. growth each month (note that 20g = 1/50kg).

(16000mg/ 1kg) * (1kg / 50) = 320mg

The result can be converted to a 6 month supply of NO3;

320mg * 4.4 * 6 = 8448mg

You could do the same replacing N with P, K, or any of the other
elements listed.  And, of course, the figures can be tweaked as
deemed necessary.  If you don't have Walstad's book, I can give you
the rest of the data regarding the Elodea and the source she cited.

Going this route would still be something of a wild-a** guess, but I
think it'd at least get you near the ballpark.
--
Chuck Huffine
Knoxville, Tennessee

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