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Re:NPK ratio's

> Subject: N-P-K
> A few months ago there was a thread about someone that had come up with
> research/theory supporting a fixed ratio of N-P-K that plants needed.

Plants species have a wide range of needs. You can get a "middle range" by
doing dry analysis and assuming what's in the dry weight, is what the plant

But(!!!) the dry weight analysis plants need to be in the health that you

A healthy optimally grown plant will have different ratios of many major
macro nutrients than say a weak plant. You need to know that your plants are
indeed healthy and what you want to test for first.

Then there are issues such as what light intensities you are interested in.
The nutrient ratios for a plant grown at 1.5w/gal vs 4-5w/gal will also be
quite different even if they are the same plant etc.

Then there are issues of luxury consumption, (e.g. plants take up more PO4
than they need for good growth).

Then is the issue of types of N, such as NH4 and NO3 and the ratios supplied
to the plants etc.

It can be done, but it's going to take a fair amount of work to get good

I've just eye balled and guessed and have come fairly close. There will
always be a few plants......in anyone's NPK ratio that won't do as well as
the rest. With plants, there's always exceptions.

> study is also mentioned in Walstad's book "The Ecology of the Planted
> Aquarium."  I am trying to find the thread in the archives, and I have
> looked all through Diana's book and cannot find it.  Does anyone remember
> what I am talking about?  Something about critical ratios maybe?

Well you can find this on page 105.
But, this is for only one single plant.

Be very careful in using a book such as this of generalizing and scaling up
to ALL aquatic plants. Most of these studies are for _one_ particular plant.
Many plants will be different. Many plants have other mechanisms and ways to
accomplish submersed growth.

This is why comparative studies and testing more than one single plant is
important in ecology. You find other trends, often ones you never expected:)

Tom Barr  
> Ben in SW Virginia
> (anyone else out here?)