Latest / Hydroponics Daily / Why Liebig's Barrel Falls Apart: Rethinking Nutrient Limits in Hydroponics

Transcript

Why Liebig's Barrel Falls Apart: Rethinking Nutrient Limits in Hydroponics · Hydroponics Daily

• 0:00
  Hello there and welcome back to
• 0:01
  Hydroponics Daily, your go-to podcast for everything soilless cultivation.
• 0:06
  I'm your host, Dr. Russell Sharp, the founder of Eutreema Limited.
• 0:10
  We make fertilizers, biostimulants and interesting biopesticides.
• 0:14
  Today I wanted to talk about something that is often cited and referenced in
• 0:19
  hydroponic literature and that is Liebig's Law of the Minimum.
• 0:24
  And this states that growth is controlled not
• 0:27
  by the total amount of fertilizer available
• 0:31
  or nutrition available but the scarcest one
• 0:34
  so if a plant has plenty of nitrogen and
• 0:37
  sunlight but very little phosphorus its growth will
• 0:40
  be limited by phosphorus no matter how much
• 0:43
  of the other resources you add and this is
• 0:46
  visualized by a barrel and the slats of the barrel is each one a different plant
• 0:53
  nutrient and if say phosphorus is really short then you can only fill the barrel
• 1:00
  with yield as far as the phosphorus slat goes.
• 1:05
  Obviously, if it was liquid, it would just fall out wherever the phosphorus
• 1:08
  was, even if the slat for nitrogen and boron and potassium were really high.
• 1:14
  Now, this is a really good way for students to visualize Liebig's law of the
• 1:20
  minimum and the idea that if you've got one limiting factor,
• 1:24
  that will be your cap on yield
• 1:28
  and your quality of your crop in hydroponics
• 1:31
  or any type of growing now that is
• 1:34
  true to some extent and it's a really good way of learning
• 1:38
  about fertilizers and thinking about how you fertilize it but it doesn't mean
• 1:42
  it's the absolute truth and that's where i've got an issue with it and how it's
• 1:47
  used sometimes in hydroponics it's given as it's the law or even worse it's
• 1:53
  if you say oh we we comply with liebig's lower than minimum.
• 1:57
  So we are at the forefront of science. This is like Victorian 19th century scientific principles. And.
• 2:08
  The world of nutrition and plant physiology and crop nutrition has moved on a lot since then so.
• 2:15
  Banging on that you you comply with Liebig's
• 2:18
  law of the minimum is a bit silly it's a bit like you
• 2:21
  know saying well our our motor
• 2:24
  vehicles are really good because we comply with how
• 2:28
  you know Daimler built their cars back in
• 2:31
  the turn of the century or whenever the Daimler was hanging around so it's
• 2:36
  i mean even some brands even have liebig on their label
• 2:39
  and then shout about it i just
• 2:42
  want to go on some of the limitations about liebig's law of the
• 2:44
  minimum it assumes that only one there's
• 2:48
  only one limiting factor at a time whereas in real
• 2:51
  systems often you have multiple interacting constraints
• 2:55
  water temperature and nutrients and these can compound or
• 2:58
  interact in a non-linear way so it's
• 3:01
  not always a single bottleneck and probably the
• 3:05
  most crucial one is they ignore factors that interact
• 3:08
  now especially nitrogen if you apply
• 3:12
  loads and loads of nitrogen plants will.
• 3:15
  Over consume that nitrogen to the point
• 3:18
  where they then require more phosphorus and potassium than would
• 3:21
  otherwise be required so if you
• 3:24
  increase the size of the slat for nitrogen
• 3:27
  suddenly the phosphorus and the potassium ones go
• 3:31
  down and that break the whole barrel analogy just falls apart literally the
• 3:36
  barrel just falls apart so and that and the converse can be the true if one
• 3:41
  another nutrients can inhibit the uptake of others so calcium can inhibit magnesium
• 3:48
  uptake and things like this so.
• 3:51
  Did the slats interact? And so yeah, the barrel analogy falls down there.
• 3:56
  And growth response curves are non-additive. So one resource can modify how others work.
• 4:03
  And then it's also a static view of what is essentially a dynamic system when you grow plants.
• 4:09
  So it's treating it as fixed, but in reality, things change every time.
• 4:14
  So in the morning, light might be limited.
• 4:17
  In the afternoon if you're growing in a greenhouse water stress
• 4:20
  might become more of a limiting factor and in
• 4:23
  the autumn excuse me pests might
• 4:26
  dominate as you get further on through the growing season it
• 4:30
  doesn't account for biological adaptation so plants
• 4:34
  and any sort of organism can adjust its physiology but
• 4:38
  to partially compensate for limitations if you
• 4:41
  don't give enough potassium plants can use
• 4:44
  sodium sometimes in the enzymes it's not
• 4:47
  perfect and it can cause issues but
• 4:50
  say a beet plant sugar beets or
• 4:53
  swiss chard can do that so they can swap
• 4:56
  out potassium for sodium and so they can do
• 4:59
  adaptations there it ignores
• 5:02
  thresholds and saturations so once a limiting
• 5:05
  nutrient reaches an optimal level adding more gives no
• 5:08
  benefit and can be toxic so you can't just
• 5:10
  keep on increasing the slats level for
• 5:13
  all nutrients and that's one of the problems that a lot
• 5:16
  of newbies noobs in hydroponics don't realize
• 5:19
  is you just can't adding more fertilizer and
• 5:22
  more additives and more bottles doesn't necessarily increase yield it can become
• 5:26
  toxic and you can have real problems and effects are non-linear so if you add
• 5:32
  more fertilizer you spend 10 pounds or twice as much on your fertilizer you
• 5:37
  won't get twice as much increase in yield so So.
• 5:41
  There's some other factors that don't really fit into this model.
• 5:44
  There have been a few attempts to extend the theories of Liebig's law of the minimum.
• 5:50
  So Shelford's law of tolerance has upper and lower limits, and that takes account
• 5:56
  of the fact that it can also limit growth, too much can limit growth.
• 6:01
  There's multiple limitation hypothesis that looks at interacting limits,
• 6:06
  so several resources can co-limit simultaneously.
• 6:10
  The dynamic systems model time-based
• 6:13
  and adaptive limitations change with feedback and
• 6:16
  adaptation and ecological stoichiometry with nutrient ratios the balance between
• 6:22
  carbon nitrogen phosphorus is key not just the absolute minimum the calcium
• 6:27
  to magnesium ratio for example will feed into ecological stoichiometry however
• 6:32
  shelfer's law of tolerance multiple limitation hypotheses.
• 6:36
  Dynamic system models, and ecological stoichiometry are a lot harder for beginners
• 6:42
  to get their head around.
• 6:44
  And so people still talk about Liebig's law of the minimum.
• 6:48
  And scientists who think that they're scientists, or certainly fertilizer manufacturers
• 6:54
  who think they're being clever, will still reference Liebig's law of the minimum
• 6:57
  and try and sound like they know what they're talking about scientifically.
• 7:01
  But I don't know of any soil scientists who you talk about Liebig's law of the
• 7:06
  minimum. It's a bit like in regenerative agriculture.
• 7:09
  You know you're talking to a guru
• 7:12
  or a con man if they start talking about Albrecht and Albrecht ratios.
• 7:18
  Yes, Albrecht was a scientist, but he was 60 years ago.
• 7:24
  A lot of the gurus and charlatans and con men still talk
• 7:27
  about albrecht because they can sell lots of products and advice
• 7:30
  based on the those sorts of principles so yeah
• 7:34
  that's been liebig's law of the minimum it's useful as a teaching aid
• 7:37
  but not essentially the trees and science has
• 7:40
  moved on and our understanding of crop nutrition has moved on a lot
• 7:43
  since then let me know what you think if you think i'm talking absolute
• 7:46
  nonsense and liebig's law of the minimum is still valid in your
• 7:49
  eyes even a high level hydroponic growing then
• 7:52
  let me know that's been hard products daily for today if you found this interesting
• 7:55
  if it's advanced your knowledge of crop nutrition then please
• 7:58
  follow the podcast give an apple podcast review if
• 8:01
  you listen on any platform or the platform don't leave us a review
• 8:04
  because it's pretty much useless just check out utreema.co.uk we
• 8:08
  have a fantastic periodic table of plant
• 8:11
  health i will put it in the show notes so you
• 8:14
  can click those and you can get yourselves a poster
• 8:17
  that describes every single plant nutrients every single
• 8:19
  well not every single toxin but some examples of toxins that are
• 8:22
  on the element periodic table and some beneficial elements and some elements
• 8:27
  that have no effect on plant growth and just there as an example it's a really
• 8:31
  interesting tool a really interesting resource and i think you'll love it so
• 8:34
  check that out too go and click the link now go on go on go and click it cheers
• 8:39
  see you tomorrow goodbye.