espoker19
Active Member
For those of you who are into the science behind nutrient control, found an interesting article on nutrient solutions and the different groups of nutrients. Apparently high mobility nutes (group 1) are removed from the solution within hours, and therefore higher concentrations can be toxic. Turns out all higher plants can store nutrients to some degree in their cell vacuoles, and once they reach a critical threshold begin wasting energy attempting to "flush" out the excess nutrients back to solution. Problem is if the solution is already high in that nutrient it just results in futile cycling across the cell membrane, burning ATP (adenosine tri phosphate) each time, wasting energy. Well, here are the groups:
Table 1. Approximate uptake rates of the essential plant nutrients.
Group 1 Active uptake, fast removal NO3, NH4, P, K, Mn <= Removed with about one day, excess are cycled (wasting energy).
Group 2 . Intermediate uptake Mg, S, Fe, Zn, Cu, Mo, Cl <= Removed over the course of several days, generally higher concentrations fine.
Group 3 Passive uptake, slow removal Ca, B <= Tend to accumulate in nutrient solution, can become toxic if replaced too often.
Additionally, one must consider the transpiration rates when calculating nutrient strengths. Often you will see people who say "I run 1800 PPM's no problem" and others who say "I get burn at 500 ppm." A large reason for this disparity is possibly due to varying rates of transpiration. The more a plant "sweats" (low humidity/ high wind across leaves/ high heat) the more "free" movement of nutrient into the tissues because they get sucked in with the water as well. So if you have a hot grow room with low humidity, you must take that into account and keep concentrations lower.
Also, based on the groups of high mobility nutrients, starting a solution with say, 250 ppm phosphate will lead to problems down the road if not properly managed. The higher the group 1 nute strength, the higher you will need of group 2 and 3 to compensate since the plant much more easily takes up group 1 nutes. Excess K for example- will result in a calcium deficiency not because you don't have enough calcium, but because K is over taking calcium uptake. To exacerbate this problem, the plant opens up additional cell pathways in an attempt to let more calcium in, but because of the HIGH availability/ uniformity of the nutrient solution, it just ends up sucking in more K.
Anywho, interesting read. There's alot more about calculation of ppms and pH in here.
http://cpl.usu.edu/files/publications/publication/pub__9984184.pdf
Table 1. Approximate uptake rates of the essential plant nutrients.
Group 1 Active uptake, fast removal NO3, NH4, P, K, Mn <= Removed with about one day, excess are cycled (wasting energy).
Group 2 . Intermediate uptake Mg, S, Fe, Zn, Cu, Mo, Cl <= Removed over the course of several days, generally higher concentrations fine.
Group 3 Passive uptake, slow removal Ca, B <= Tend to accumulate in nutrient solution, can become toxic if replaced too often.
Additionally, one must consider the transpiration rates when calculating nutrient strengths. Often you will see people who say "I run 1800 PPM's no problem" and others who say "I get burn at 500 ppm." A large reason for this disparity is possibly due to varying rates of transpiration. The more a plant "sweats" (low humidity/ high wind across leaves/ high heat) the more "free" movement of nutrient into the tissues because they get sucked in with the water as well. So if you have a hot grow room with low humidity, you must take that into account and keep concentrations lower.
Also, based on the groups of high mobility nutrients, starting a solution with say, 250 ppm phosphate will lead to problems down the road if not properly managed. The higher the group 1 nute strength, the higher you will need of group 2 and 3 to compensate since the plant much more easily takes up group 1 nutes. Excess K for example- will result in a calcium deficiency not because you don't have enough calcium, but because K is over taking calcium uptake. To exacerbate this problem, the plant opens up additional cell pathways in an attempt to let more calcium in, but because of the HIGH availability/ uniformity of the nutrient solution, it just ends up sucking in more K.
Anywho, interesting read. There's alot more about calculation of ppms and pH in here.
http://cpl.usu.edu/files/publications/publication/pub__9984184.pdf
