Justus von Liebig's Law of the Minimum states that crop yields are limited by the nutrient in least supply, right? Nope. While often interpreted as such, this is not correct, and while Liebig is attributed as the "Father of the Fertilizer Industry" and he promoted mineral nutrition via salts, he was not "anti-humus" or against the biological side of agriculture.
The attached photo is a popular version of Liebig's Law of the Minimum, although he never presented his information as a barrel. The barrel is attributed to Hans Arnold von Dobeneck, and is also called Dobeneck's Tub in some countries.
On most versions of the nutrient barrel, each stave is shown to represent a nutrient. The lowest stave marks max capacity, interpreted as max yield capacity. But is this accurate?
Liebig first considered 3 nutrients for his Law: N, P, and K. At one point, Liebig thought all plant N came from the air, so air was added, as was moisture, temperature, soil conditions, humus, carbonic acid, ammonia, and more. Modern versions have added lots of additional staves, but understand that Liebig did not put all emphasis on nutrients.
In his Principle of Agricultural Chemistry, Liebig numerically listed 50 "propositions" he held to be true regarding nutrition and chemistry of soils and plants. He summarizes them this way:
"The nutrition, growth, and development of a plant depends on the assimilation of certain bodies, which act by virtue of their mass or substance. This action is within certain limits directly proportional to the mass or quantity of these substances, and inversely proportional to the obstacles or to the resistance which impede their action." This has been summarized into today's version of Liebig's Law of the Minimum.
In later works, particularly his "Organic Chemistry in its Application to Agriculture and Physiology" (which is available as a free book online), Liebig heavily researches/discusses humus, manures, molds, yeasts, coals, nitrification, and many "biodynamic" topics.
Liebig was far from the King of Fertilizer Salts. His work in that regard was that of a chemist, and he was attempting to solve food production concerns, as the quantities of available manure could not keep up with the needs of small farms and increasing populations. He repeatedly wrote of the fallow effect, where land can become unsuitable for one crop while being suitable for another, and by letting the land rest, it can again become suitable, especially with animal excrements (manures). In absence of manures, he speculated, then proved, that inorganic salts could satisfy the nutritional needs of plants.
Is the Law of the Minimum useful? Absolutely. "A chain is only as strong as the weakest link" is a perfect rephrase of Liebig's concept. "Law" may be a stronger-than-appropriate word, but the concept of identifying and strengthening areas of weakness is an excellent method for improvement. Where one must be cautious is how you identify the shortest staves. A quick search online reveals that Liebig never attempted to put order of importance into the factors of production. These will vary widely, and even change through a single growing season based on temps, rainfall, crop, crop stage, etc.
Liebig's Law should not be confused with ROI or Mitscherlich's Law of Diminishing Returns. Liebig was unable to quantify crop responses based on identified limitations, which is partly why B.E. Livingston wrote that the Law of the Minimum was "still quite incomplete logically." Liebig could not specify a quantity to overcome a deficiency, nor predict crop response. He was able to predict a LACK of response, though, which was impressive for his time. Don't apply what plants already have plenty of. Caveat here: Your soil test or tissue test may not reveal whether your plant has plenty of something or not.
In summary, Liebig is popularly idealized as the villain of sustainable agriculture due to his inorganic mineral nutrition theory. Interestingly, he was also one of the pioneering chemists of organic chemistry. Liebig understood both sides of the humus vs inorganic debates that we've had for 100 years. Like most things, they've been misconstrued and used for ideological purposes and/or product sales rather than as educational sources. The next time you see Liebig/Dobeneck's barrel on a sales flyer or in a presentation, I have this brief daytrip through ag history comes to mind, and helps put things into perspective.
Thanks for making it to the end.
@bandedagllc
@RyanPriest11974