Hi all,
in the first link above you stated that the floaters had at least one deficiency. Maybe the knowledge level has advanced since, but I remember Zapins over at the APC saying that a plant can have only one deficiency at a time. Found that interesting so I made a mental note to myself.... Any thoughts on that?
Yes, there is a difference between which element is limiting, and which elements are stopping optimal growth.
Liebig's law of the minimum
At any one point only one element is limiting plant growth, this is described in <"
Liebig's law of the minimum">.
It states that growth is controlled not by the total amount of resources available, but by the scarcest resource (limiting factor).
You can think of it like an assembly line, the speed of the whole assembly line can't go quicker than the slowest process, if you speed up all the other parts of the assembly line you don't get any more production. However if you speed up the slowest process, more units will be assembled, but another process (the new slowest) will then govern the the productivity of the whole assembly line.
It is just the same with plant growth, it is an assembly line. What governs the potential productivity is the amount of light (PAR -
Photosynthetically Active Radiation), because light drives photosynthesis.
For that full potential to be utilised all other nutrients need to be non-limiting. If you have low levels of plant nutrients one will be limiting (usually one of carbon (C), nitrogen (N) or potassium (K), because they are the nutrients that plants need most of). If you add more CO2, the plants can only utilise it if they have access to non-limiting levels of N, P, K etc.
If you add more nitrogen, but potassium levels are limiting growth, you don't get any more growth. To get more growth you need to add more potassium etc.
Because my tanks have low levels of all nutrients, one nutrient will be the limiting factor, but nearly all the others will be deficient as well.
cheers Darrel