Liebig's Law Of The Minimum, And Below "Shelford's Law of Tolerance"

From Wikipedia, the free encyclopedia: Liebig improved organic analysis with the Kaliapparat-- a five-bulb device that used a potassium hydroxide solution to remove the organic combustion product carbon dioxide. He downplayed the role of humus in plant nutrition and discovered that plants feed on nitrogen compounds and carbon dioxide derived from the air, as well as on minerals in the soil. One of his most recognized and far-reaching accomplishments was the invention of nitrogen-based fertilizer.

Liebig believed that nitrogen must be supplied to plant roots in the form of ammonia. Though a practical and commercial failure, his invention of fertilizer recognized the possibility of substituting chemical fertilizers for natural (animal dung, etc.) ones. He also formulated the Law of the Minimum, stating that a plant's development is limited by the one essential mineral that is in the relatively shortest supply, visualized as "Liebig's barrel". This concept is a qualitative version of the principles used to determine the application of fertilizer in modern agriculture.

Liebig's Law of the Minimum, often simply called Liebig's Law or the Law of the Minimum, is a principle developed in agricultural science by Justus von Liebig. It states that growth is controlled not by the total of resources available, but by the scarcest resource. This concept was originally applied to plant or crop growth, where it was found that increasing the amount of plentiful nutrients did not increase plant growth. Only by increasing the amount of the limiting nutrient (the one most scarce in relation to "need") was the growth of a plant or crop improved.

Liebig used the image of a barrel-now called Liebig's barrel-to explain his law. Just as the capacity of a barrel with staves of unequal length is limited by the shortest stave, so a plant's growth is limited by the nutrient in shortest supply.

Liebig's Law has been extended to biological populations. For example, the growth of a biological population may not be limited by the total amount of resources available throughout the year, but by the minimum amount of resources available to that population at the time of year of greatest scarcity. That is, the growth of a population of animals might depend not on how much food is available in summer, but on how much food is available in winter.

The University of Giessen today is officially named after him, "Justus-Liebig-Universität-Giessen". Organic Chemistry in its Application to Agriculture and Physiology (1840), Organic Chemistry in its Application to Physiology and Pathology (1842)

Shelford's Law of Tolerance

Shelford's Law of Tolerance is probably the more accurate reflection of natural complexity. It holds that first the presence and then the success of an organism depend on the completeness of a complex of conditions. The absence or failure of an organism, then, is a function of qualitative or quantitative deficiency or excess with respect to any one of several factors approaching that organism's limit of tolerance for it.

More precisely, each organism--whether the individual or the species population--is subject to an ecological minimum, maximum, and optimum for any specific environmental factor or complex of factors. The range from minimum to maximum represents the limits of tolerance for the factor or complex. Significantly, if all known factors are apparently within their respective ranges for the subject organism and yet it fails, it is necessary to consider additional factors or a more complete array of interrelationships, including interactions with other organisms.

When faced with any such situation, it is essential to remember yet another caveat, a biological reality to be taken seriously: Studies in the intact ecosystem must accompany experimental laboratory studies, which, of necessity, isolate individuals from their populations and communities. Put another way, it is essential for field biologists to consider the wisdom to be discovered in the laboratory and for biologists ordinarily bound to the laboratory to be aware of the ecological reality associated with the processes they are investigating.

There are significant corollaries to the Law of Tolerance. An organism may have a wide range of tolerance for one factor but a narrow range for another. Logic suggests that organisms with wide ranges of tolerance for many, if not all, factors will be the most widely distributed. Within an organism or species, when conditions are non-optimum for one factor, limits of tolerance for others may be narrowed. Tolerance is most likely to be limited during periods of reproduction.

Evolution of narrow limits constitutes one form of specialization and reflects greater efficiency, but it does so at the expense of adaptability. These are the kinds of factors that contribute to increased diversity in the community as a whole.

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