Phytometer or a "plant test" for sediment or liquid fertilizers

Tom Barr

Staff member
Jan 23, 2005
The phytometer is a method that uses an aquatic plant to test the ability of a sediment or nutrient solution to grow rooted plants.
This is a paper I did as part of class lab. It is essentially independent of any CO2 , light or water column effects as the plants are generally grown in a green house or terrarium and humidity levels can be adjusted to suit various aquatic plant species.
Most all aquatic plants are amphibious, they have an emergent stage. They possess the ability to live above the water's surface. Using this trait allows any aquarist to repeat similar methods to gauge and compare different sediments or nutrients without deal with having to maintain many aquaria, CO2, etc, water column nutrients, algae.

This provides much more reliable results for comparing.
It does tell differences between plants, treatments with respect to CO2 however.
There is no mixing or transfer of nutrients from each flask and these can be rather small and many replicates of each treatment may be done for better "statistical power", generally 6-8 is enough to see significant differences between treatments.
In any such "test", having a baseline for comparison is critical. Unfortunately, most aquarist have little idea how to provide a control.

In this test, we used DI water and hoalgand's modified solution for zero nutrient and the upper bound non limiting nutrient solutions.
We assumed that all other nutrient treatments tested would fall somewhere in between these two extremes. This assumption is reasonable and logical.
The measure of comparison is relative to these two measurements.

Hobbyists will not likely be able to easily do the N and P tissue content, however, the analysis could be sent to agriculture lab for such analysis for a fee.
However, most hobbyists can measure stem, leaf, dry weight biomass etc if they tried and used a good 0.001gram scale.

You could also just ask for one nutrient, say Fe for seeing what concentration or type of chelator is taken up best etc.
Then see what actually got into the plant.

Tom Barr


Lifetime Members
Lifetime Member
Aug 25, 2006
Inspiring and doable in the water column with enough small tanks (cups?) with matching top off schedules, no? Non-limiting and DI as extremes is a good idea. It's still always eye opening to see "Relative Growth Rates" when using the former vs anything else, even after all these non-limiting benchmarks with various nutrients you've posted over the years. If using solution instead of soil, am I silly to think it easier to let the plants dry up for a day then weigh instead of the paper towel thing, which I think most of us won't have the same enthusiasm for through all samples?

Tricky though is your Fe example for those of us who concur with your findings on "sheen" (I would go as far as leaf density and overall plant health and color, not necessarily red) without the cost for chemical analysis :( Maybe we could grind up the plant mass and titrate the Fe out :D
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