Billy Liar
Well-Known Member
While I'll not tell you that you're wrong I'll present some evidence for why I believe plants do not simply pick what they need from a recirculating hydroponic solution. For this I'll reference a paper from an 18 year study into nutrient management in recirculating hydroponics. For the record the paper and article you reference both talk about uptake from a soil solution. As I can't be exactly sure uptake is different between hydroponics and soil, I have though been in these discussions with an old friend with a PhD in plant physiology, and we've found contradicting findings in studies regarding uptake from soil solutions and studies regarding uptake from hydroponic solutions, so I continue to base my knowledge on the studies concerning hydroponics only.
First I'll derectly quote the paper from the study I mentioned, conducted by Professor Bruce Bugbee at the university of Utah.
From this I conclude that for an indoor grower providing a good environment for optimal growth and transpiration; it is imperative to make available in the recirculating solution only the amounts of nutrients needed for optimum growth, and not more, therefore avoiding excess within the plant.
I'm not saying the science is wrong that you've referenced, or that there's no upper limit, but nutrient excess within hydroponically grown plants is real, and is a result of uptake past the point of there being optimal amounts already in the plant. With Nitrogen being our example here, small root systems, stretchy weak stems and branches and possibly delayed flowering are all things a grower might want to avoid.
Therefore I would say plants don't just "pick what they need".
It may be semantics to a point, but a lot of learner growers, especially now home mixing nutrients is gaining popularity, will glean information in it's most simple form.
Peace
BL
First I'll derectly quote the paper from the study I mentioned, conducted by Professor Bruce Bugbee at the university of Utah.
So from his experiments and testing of leaf, stem and tissue he found that should there be available more of certain elements than required, the plant can continue to remove it from the hydroponic solution to the point it will reach excessive amounts in the plant which can cause imbalances with other nutrients.Managing nutrients by mass balance.
During the past 18 years, we have managed nutrients in closed hydroponic systems
according to the principle of "mass balance," which means that the mass of nutrients is
either in solution or in the plants. We add nutrients to the solution depending on what we want the plant to take up.
Plants quickly remove their daily ration of some nutrients while other nutrients
accumulate in the solution. This means that the concentrations of nitrogen, phosphorous,
and potassium can be at low levels in the solution (0.1 mM or a few ppm) because these
nutrients are in the plant, where we want them. Maintaining a high concentrations of
nutrients in the solution can result in excessive uptake that can lead to nutrient imbalances.
For example, the water removed from solution through transpiration must be
replaced and it is necessary to have about 0.5 mM phosphorous in the refill solution. If the
refill solution was added once each day, the phosphorous would be absorbed by the plant
in a few hours and the solution phosphorous concentration would be close to zero. This
does not indicate a deficiency; rather it indicates a healthy plant with rapid nutrient uptake.
If phosphorous was maintained at 0.5 mM in the recirculating solution, the phosphorous
concentration in the plant could increase to 1% of the dry mass, which is 3 times higher
than the optimum in most plants. This high phosphorous level can induce iron and zinc
deficiency (Chaney and Coulombe, 1982).
Feeding plants in this way is like the daily feeding of a pet dog, some dogs would be
seriously overweight if their food bowls were kept continuously full.
From this I conclude that for an indoor grower providing a good environment for optimal growth and transpiration; it is imperative to make available in the recirculating solution only the amounts of nutrients needed for optimum growth, and not more, therefore avoiding excess within the plant.
I'm not saying the science is wrong that you've referenced, or that there's no upper limit, but nutrient excess within hydroponically grown plants is real, and is a result of uptake past the point of there being optimal amounts already in the plant. With Nitrogen being our example here, small root systems, stretchy weak stems and branches and possibly delayed flowering are all things a grower might want to avoid.
Therefore I would say plants don't just "pick what they need".
It may be semantics to a point, but a lot of learner growers, especially now home mixing nutrients is gaining popularity, will glean information in it's most simple form.
Peace
BL