Is uptake rate dependant on nutrient availability?

m lemay

Prolific Poster
Jan 23, 2005
The answer at first glance would seem to be "yes", but I suspect that it goes a lot deeper than that.

I'm gonna set a theoretical standard for a tank. 4.4WPG,75 gal tank, c02@30ppm, abundant micro nutrients. Abundant plant mass.

Scenario 1: 20ppm nitrate, 2ppm phosphate, 20ppm pottasium

Scenario2: 5ppm nitrate, 0.5 ppm phosphate, 10ppm pottasium.

Do the plants in scenario 2 have a more difficult time of extracting macro nutrients from the water column due to the relative scarcity of macro nutrients in the water column as compared to scenario 1? Does the rate of nutrient uptake slow down because of this relative scarcity?

Notice that I kept the ratio of N-P at the "mythical 10-1 ratio". My plants always seem to do better with more P. Would a higher percentage of P relative to N push nutrient uptake further? When is more macros too much, and when is less not enough? It seems logical that there must be a point of diminishing returns at both ends of the scale.


Tom Barr

Staff member
Jan 23, 2005
Re: Is uptake rate dependant on nutrient availability?

If you keep these both stable, I think you will see little difference. As long as nothing is allowed to become limiting, ratios do not apply unless you don't do any water changes and allow things to rise to toxic levels. I do not know what those levels might be for PO4, NO3, or K+.

Concentration will drive uptake but only to a point, see the Vmax graph in the article.This max uptake rate will not exceeded for that given organism.

In otherwords adding more does not increase uptake/growth.

If you look at my common rec's for folks I'm helping, the PO4 is often higher than 10:1 ratio.

Adding more than 10ppm of NO3 also seems to do well for many plants.


Tom Barr