and beast. But that which came from earth there is nothing more beneficial than to turn up a Early Roots of the must return to earth and that which came crop of lupines, before they have podded, eitherwith Organic Movement: from air to air. Death, however, does not the plough or the fork, or else to cut them and bury destroy matter but only breaks up the union them them in heaps at the roots of trees and vines.” A Plant Nutrition of its elements which are then recombined Though Pliny and subsequent writers over into other forms. (Browne, 1943) the centuries extolled the benefits of manuring Perspective from a scientific viewpoint, little advance was This atomic, cyclic, and nonconvertible chain made on the reasons for these benefits. Generally, ofelements through thesoil-plant-animal system the Aristotelian concept of the four elements held Ronald F. Korcak was opposed by Aristotle’s (384-322 BC) mutual sway into the Middle Ages. The Middle Ages, convertibility of the four elements: earth, water, generally, represent a quiescent period devoid of fire, and air. Since, according to Aristotle, the any advances in scienceand technology-no less material constituents of the world were formed in the understanding of plant mineral nutrition. from unions of these four elements, plants assimi- Some notable exceptions to this void would have Additional index words. humus theory, lated minute organic matter particles through their profound influences on the development of a theory Justus von Liebig, plant nutrition roots which were preformed miniatures (Browne, of plant nutrition near the end of the Middle Ages. 1943). This concept of “organic” nutrition of plants, evolving into the humus theory of plant nutrition, held for more than 2000 years, until the time of Post-Middle Ages ord Walter Northbourne first used the Justus von Liebig. Philippus Theophrastus Paracelus (1493- term “organic farming” in 1940 as a The course of experimentation and thinking 1541) gained fame as the first scientist to lecture in chapter heading in his book Look to the on the subject of plant nutrition, from the post-Greek German, in lieu of the traditional Latin, allowing for Land (Northbourne, 1940). That same philosopher period until the time of Liebig’s 1840 understanding and involvement in scienceamong year, coincidentally, was also the 100th monograph, is the concern of this review. Liebig’s lay persons, and recognition of the importance of Lanniversary of Justus von Liebig’s monograph monograph laid the foundation of a plant mineral experimentation in chemistry (Browne, 1943). More Organic Chemistry in its Application to Agriculture nutrient theory that was a precursor for the fertilizer germane to plant nutrition, he initiated a new and Physiology. The fundamental tenet of Liebig’s N-P-K mentality of crop fertility. The use and/or concept of plant nutrition, which was not aligned to doctrine was the development of the mineral nutri- abuse of synthetic mineral fertilizers subsequently the Aristotelian four elements. He stated: ent theory of plant nutrition. About 100 years later, became the bane of the organic farm movement. the primary American proponent of organic farm- . . . So also every vegetable of the earth ing, J.I. Rodale, cited Liebig as the founder of the Early investigations must give nutriment to the three things of fertilizer industry (Rodale, 1945) which he prob- which they consist. If they fail to do that the ably was, and the N-P-K mentality in agriculture. The beneficial responses observed from us- prima Condita (first substance) perish and The basis for these remarks was that “up to that ing green manures and animal manures and the use die in their three species. These nutri- time the humus theory had been the guiding basis of crop rotations on crop growth have directly influ- ments are earth and rain, that is the Liquor, for agriculture” (Rodale, 1945). What exactly was enced the development of plant nutrition theories. each of the three parts of which nourishes the humus theory? How did it evolve? Was it a The earliest record of the benefits of green manures its own kind-sulfur for sulfur, mercury viable theory? What was the role played by the dates back to the Chou dynasty (»1100 BC) in China for mercury, and salt for salt, for Nature pivotal player, Liebig? This review follows the (Pieters, 1927). Later (»500 BC), Tsi gave the contains these, one with the others. evolution of plant nutritional theories from the following advice: “They (green manures) are (Browne, 1943) early use of crop rotations in China, to the devel- broadcast in the fifth or sixth month, and plowed opment of the humus theory, and finally to the time under in the seventh or eighth month . . . Their A modern-day interpretation of this passage and work of Liebig and his influence on theories of fertilizing value is as good as silkworm excrement indicates that the nourishment of plants requires plant nutrition. and well-rotted farm manure” (Pieters, 1927). three principles: organicconstituents (sulfur), water King (1911) concluded from travels in the (mercury), and mineral matter (salt). There is even Introduction Orient, notably China, that the practice of deliber- a hint at the “law of the minimum” concept of plant ately adding organic matter to the soil dates back nutrition. Although the “three-principle” theory of Plant growth has been both a curiosity and a at least 4000 years and summarized his observa- Paracelus differs only slightly from that of Aristotle’s source of much documentation and experimenta- tions as: “This is a remarkable practice in that it is four elements, it represents, as Browne (1943) tion since the beginnings of agriculture. The “sub- very old, intensive application of an important points out, a “break with an outworn tradition.” stance” of plants has been explored and debated fundamental principle only recently understood The search for the true “substance” of plants since the time of the early Greek philosophers. The and added to the science of agriculture, namely, and a continuance of the break with the four current dichotomy over the source of plant nutri- the power of organic matter, decaying in contact elements of Aristotelian theory was furthered by ents between the organic vs. inorganic fertilizer with soil, to liberate from it plant food.” Bernard Palissy (1510-1589). Considered by some camps is not new. Democritus of Abdera (»460- Early Roman compilations of agricultural to be the founder of agricultural chemistry (Browne, 360 BC) proposed what would currently be consid- practices that enumerated the use of organic ma- 1943), Palissy relied on observation and experi- ered as an atomic philosophy of matter: nures and crop rotations were accumulated by the ence in making practical theories for manuring: prolific agricultural observer Cais Plinius Secundus “Manure is carried to the field for the purpose of Mother earth when fructified by rain gives (AD 23-79) better known as Pliny the Elder restoring to the latter a part of what had been birth to crops for the nourishment of man (Browne, 1943). He enumerated the advantages removed Proceeding thus you will restore to and disadvantages of most animal manures and the soil the same substances that have been re- U.S. Department of Agriculture, Agricultural Research recommended the use of green manures (Browne, moved by previous crops and which following Service, Fruit Laboratory, Beltsville, MD 20705, 1943). “It is universally agreed by all writers that crops will regain to their advantage.”

HortTechnology • Apr./June 1992 2(2) The idea that the same substances will be to Lime, and of other bodies putrefied by quantity, ‘twill grow and thrive there: otherwise reused by other crops would become central to the length of time. But the Chief of all these is ‘twill not grow” (Browne, 1943). development of the humus theory of plant nutrition Salt-petre, being the salt of Vegetables, According to Woodward, the soil could be 200 years later. Palissy also helped to overthrow Animalsand Minerals putrefied, especially regenerated only with a “new Fund of matter” by the concept of heat as important in the growth of because it is endowed with a certain occult fallowing, which enabled rain to supply a new stock, plants. Through the ages, the heat given off by a and sweet Fire. (Browne, 1943) or by manuring; particularly with vegetable manures, pile of composting manure probably drew the since they would serve “for the formation of other attention of many observers. This readily notice- Glauber did not realize that this organically like bodies” (Browne, 1943). Woodward’s concepts able trait coupled with the fire element of Aristotle based “fertilizer” added N-P-K as well as lime to of the importance of earth in the nutrition of plants was thought to be the “substance” from which soils. Saltpeter (potassium nitrate) was thought to were advanced by his contemporary, Jethro Tull plants benefited from manuring. Palissy had ob- be a constituent of plants, not a nitrate source; (1674-1740). Although best known for his ideas served that the benefits of marl (as a soil amend- therefore, by addition to the soil, one was adding concerning tillage, Tull believed that fine particles of ment) were long term and, therefore, not explicable an intrinsic part of the plant and thereby maintain- soil entered the root; therefore, the finer the soil in terms of heat. ing the “fatness” of the soil (Russell, 1926). The particles, via tillage, the better the growth. “And Earth No chronology of the early development of term “fatness” was coined by Plattes as the crop- is surely the Food of all Plants, that with the proper plant nutrition would be complete without mention sustaining ingredient of soils (Browne, 1943). He share of the other elements, which each Species of of Jan Baptista van Helmont (1577-1644) and his considered both the air and soil as valuable in Plant requires, I do not find but that any common infamous potted tree experiment, which lasted 5 plant nutrition: “All fruits are compounded of a Earth will nourish any Plant” (Browne, 1943). years (Browne, 1943). The experiment, in brief, doublesubstance, the one terrestriall and the other In regards to the use and nutritional value of consisted of growing a 5-lb willow tree in a capped, aethereall, and for the most part, the want of the manures, Tull ascribes their benefit to the enhanced earthen vessel containing 200 lb of oven-dried terrestrial1 part causeth ill successe” (Browne, mechanical and physical properties of the soil: soil. After 5 years, with the addition of only water, 1943). the tree weighed »169 lb and the redried soil just The fatness of the soil, akin to its organic All sorts of Dung and Compost contain 2 oz less than 200 lb. The conclusion was that the component, could be removed either by crops or some Matter, which, when mixt with the 164-lb gain in tree weight was derived from water. carriedaway by erosion. Rudiments of this concept Soil, ferments therein; and by such Fer- Unfortunately, no mention is ever made if van of a soil’s fatness can still be found today in the ment dissolves, crumbles, and divides the Helmont weighed the water applied during the adage “living off the fat of the land.” Earth very much; This is the chief, and experiments 5 years. If he had, his conclusion, Coincident with the work of Glauber and almost only Use of Dung . . . This proves, obviously, would have been different. Van Helmont Plattes was a change in the English system of that its (manure) use is not to nourish, but had performed prior experiments with combusting agriculture from manorial to closed farms. Not to dissolve, i.e., Divide the Terrestrial charcoal and found 1 lb of ash from 62 lb of only was individual initiative greater, but newer Matter, which affords nourishment to the charcoal. The other 61 lb consisted of the “spirit of crops allowed for more farm animals and, thus, Mouths of vegetable roots. (Browne, 1943) the wood,” which he coined “gas” (Browne, 1943). more manure. New rotation systems, such as the Had he measured the water applied and applied his Norfolk rotation (Porteous, 1960) eliminated the The phlogiston period spirit of the wood concept, plant nutritional theory fallow year but included a legume crop for feed or may have been advanced by »100 years. for green manure. Green manuring with legumes The doctrine of the phlogiston school of Eighty years later, the classic water culture became the mainstay of rotation systems in con- early agricultural chemistry was that all substances experiment of John Woodward (1665-1728) dis- tinental Europe as well. By the end of the 17th that are changed by ignition contain a common pelled the concept of water as the sole substance century, much debate in Germany centered on combustible matter (Browne, 1943). The most of plants (Russell, 1926). Woodward, in 1699, whether or not the legume crop should be harvested important influence of this doctrine on plant nu- noted better spearmint growth in water containing or turned under (Pieters, 1927). trition was the general assumption that plants garden soil than when grown in rain water, or In the late 17th century, John Mayow(1643- generated alkalis (Russell, 1961). impure water (from the Thames River). 1679) and Nehemiah Grew (1641-1712) recog- Advances of a plant nutrition theory during Although van Helmont believed that the nized the importance of air in plant growth, and in this period resulted primarily from the work of growth substance of plants was water, it was the New World, John Winthrop (1606-1676) Francis Home (1719-1813). He not only recog- likewise known that salts were an important plant promoted the importance of salt and the manu- nized the importance of pot studies and plant constituent. This idea was generated from the facture of fertilizer saltpeter (Browne, 1943). Grew analysis (Russell, 1961) but also added fire and many early decomposition and distillation ex- conceptualized the root as a mouth into which oil to the list of important factors (air, water, earth, periments of plant materials. Two 17th century entered a watery nutriment solution from the soil, and salt) in plant nourishment: chemists, Johann Glauber (1604-1668) and along with air. The “principles” of plant growth Gabriel Plattes (ca. 1600-1655) exemplify the were preformed, carried into the plant, and then I join, in some measure, with all these; and early knowledge of the importance of salts and filtered among the various plant parts. John assert that plants are nourished by these their relation to both manures and plant nutrition Woodward, noted earlier for his classic experiment bodies, united with two others, oil and fire (Browne, 1943). In response to the lack of manures refuting van Helmont’s water-only theory of plant in a fixed state. These six principles to- brought about by the havoc of the Thirty Years War, nutrition, continued Grew’s argument for preformed gether, in my opinion, constitute the veg- Glauber invented what may be considered the first entry of nutriment into the plant. He further etable nourishment. (Browne, 1943) manure substitute, or chemical fertilizer, to fill the elaborated that different plants require different void. He called the material “philosophic dung” or “corpuscles” (the preformed substances of plants) Oil was considered one of the “natural prin- “fattening salt” and noted: and “... that every kind of vegetable requires a ciples” that was introduced to earth in rain, and fire peculiar and specifick matter for its formation and was found “in all bodies.” Home’s work marks one Of this salt, which we may use instead of nourishment . . . If therefore the soil, wherein any of the cornerstones in plant nutrition theory, i.e., a dung, there is great diversity, for it is vegetable or seed is planted contains all or most of multitude of factors are considered to explain the prepared of Wood-ashes, of Stones burnt these ingredients (‘corpuscles’), and those in due nourishment of plants.

HortTechnology • Apr./June 1992 2(2) Like Home, Johann Wallerius (1709-1785) believed to extract the humus from the soil exterior sources of these elements are eliminated? considered plant nutrition a multifaceted science. and to transform it into plant substance, by Are these inorganic elementary constituents so Regarding plant growth in general, Wallerius be- combining it with water. Plant nutrition essential that the vegetable organisms have con- lieved, “Plants derive no growth from any mineral was thus considered as similar to animal stant need of them for their complete development earths Thesubstances that promote plant growth nutrition, both plants and animals feeding (Browne, 1943)? The prize was awarded to A.F. must be (1) identical or analogous with substances upon complex organic bodies. As regards Wiegmann (1771-1853) and L. Polstroff for their preexisting in the plant, or (2) capable of being the function of minerals in plants, some of conclusions from an experiment comparing plant transmuted and combined into a nature that belongs the protagonists of the humus theory be- growth in a synthetic soil vs. sand alone. They to plants” (Browne, 1943). Therefore, humus was lieved that these were not essential for concluded, in part, “The inorganic constituents of the “nutritiva” or source of plant food while all other growth; they were believed to act as stimu- plants can in no respect be regarded as products of soil constituents were the “instrumentalia” that as- lants rather than as nutrients. Others looked their vital activity either as formations from un- sisted in making this food available (Russell, 1961). upon minerals as mere accidental plant known elements or as peculiar derivations of the Other notable discoveries during the phlo- constituents, or as the skeleton substances four elements known to make up organic sub- giston period would have profound influence on of plants similar to the bones of animals. stances” (Browne, 1943). the development of plant nutritional theories. These In regards to inorganic nutrition and ma- include the discovery of O by Joseph Priestly 2 The Modern Period nuring, Wiegmann noted that “...the soil has been (1733-1804) and his work on the purification of so robbed by the previously harvested crop of the air by plants and the discovery by Jan Ingen-Housz Theodore de Saussure, the eminent Swiss inorganic materials which are necessary for plant

(1730-1799) that plants give off CO2. Air, or more chemist, in his Chemical Researches on Plants development that another crop of the same kind properly “fixedair,” became the important principle (1804), overthrew many of the transmutation and (even when the ground is plowed and newly fer- of plant nutrition and, as Priestly stated, “the “principle” concepts of his predecessors. As tilized with an animal manure deficient in the principle is phlogiston” (Browne, 1943). Russell (1961) stated, de Saussure’s “conciseand necessary mineral element) is unable to find the logical arguments” are refreshing compared to the requisite amount of plant food that is necessary for THE HUMUS THEORY “lengthy and often wearisome works of earlier its complete development” (Browne, 1943). writers.” Among the accomplishments accorded Opposition to the humus theorywas to come OF PLANT NUTRITION de Saussure are theelucidation of plant respiration; from manysides. Experimentswith humusextracts The beginning of the 19th century coincided the recognition that soil, not air, was the supplier led Wiegmann and Polstrof to conclude that humus with the chemical revolution in agricultural science. of N; the realization of the active role of the root as plays an insignificant role in plant nutrition (Browne, However, remnants remained of those who believed an absorber of water and salts, not as a mere filter; 1943). Carl Sprengel (1787-1859) also ascribed in the Aristotelian four principles, phlogiston ad- the realization that ash constituents of plants all little nutritive value to organic matter: herents, and transmutation power of plants. Before occur in humus; and debunking the idea that advancing through this period of achievement in plants generate potash (the salt principle of his The conviction should have been reached agricultural chemistry and plant nutrition to the predecessors) (Russell, 1961). About 36 years long ago that humus is not such an impor- time of Liebig, it is worth exploring what the humus later, Liebig erroneously argued that air was the tant substance as we have been led to believe theory of plant nutrition was and how the pre- source of plant N (ammonia) and that this supply and that the current doctrine of humus (the Liebig scientific community accepted or rejected limited growth. humustheory) is exceedingly full of contra- this theory. De Saussure, however, was a defender of the dictions I have come more and more to The idea that increasing soil organic matter, humus theory. His general conclusions of plant the conviction that plants can entirely dis- either by plant residues or animal manures, in- nutrition included: pense with it (humus). (Browne, 1943) creased soil fertility and hence crop yields had been realized, as we have seen, for centuries. This That fertile soil contains a mixture of soluble Sprengel supported de Saussure’s opposi- readily verifiable role of organic matter, or humus, and insoluble organic substances and that tion to the old theory of transmutation of mineral combined with the later question concerning the the entrance of the former into the plant elements by plants and suggested that the mineral source of C for plant growth, led to the humus through the roots is a most important aid elements of plants are derived from without. The theory of plant nutrition. As noted earlier, Wallerius for the nourishment which they derive from supply of mineral elements depends on the in 1761 was the first to allude to the idea that air and water. chemical composition of the soil. Much work by humus was the food of plants (Kononova, 1961). Sprengel involved classifying fertilizing materials A half century later, Albrecht Thaer (1752-1828) is That plants obtain their nitrogen almost (Browne, 1943). He separated organic fertilizers credited with formulating the theory of the humus wholly by absorption of the soluble or- from mineral materials such as lime, clay, and a nutrition of plants (Waksman, 1942). ganic substances: direct experiment shows host of salts. These and other details of Sprengel’s Humus was considered the sole and direct that they do not assimilate it to an appre- writings, such as those on the effects of minimum source of plant nutrients. Waksman (1942) sum- ciable extent in the gaseous condition and maximum factors on the growth of crops, led marizes the humus theory, which had gained the (Browne, 1943) Browne (1943) to conclude that “...Sprengel support of early chemists, including Theodore de should always be remembered as the one who Saussure (1767-1845) and Sir Humphrey Davy Contradictory evidence for and against the paved the way for Liebig...” (1778-1829): concept that plants had the power of transmutation Among the last eminent pre-Liebig scientists to produce the principle of growth, and contro- was Jean-Baptiste Boussingault (1802-1887). According to this theory, plants feed upon versy over the importance of organic vs. inorganic Boussingault’s most significant impact on plant substances which are similar to them in nutrition of plants, reached an interesting stage by nutrition was his initiation of the first series of field nature. The organic matter of the soil, or 1838. A prize was offered in Germany for the most experiments (Russell, 1961). Boussingault and the soil humus, was regarded as the chief satisfactory answers to the questions: Do the so- his contemporary Gerardus Mulder (1802-1880) nutrient for plants and the major source of called inorganic elements, which are found in the were both proponents of the humus theory of plant soil fertility. The roots of the plants were ashes of plants, occur in these plants when the nutrition.

HortTechnology - Apr./June 1992 2(2) In 1840, the Chemical Section of the British (Russell, 1926). These experiments showed the Association for the Advancement of Science re- value of phosphates and alkali salts, which Liebig quested a report on the state of organic chemistry had emphasized, but they also vividly showed (Bradfield, 1942). The invitee was Justus von Liebig’s mistake in relying solely on an atmospheric Liebig. The opening paragraph of his Organic source of N. The initial studies led Lawes to Chemistry in its Application to Agriculture and formulate a “patent manure” consisting of a mix- Physiology would define organic chemistry, and, ture of superphosphate, phosphate of ammonia, according to many, the rest of the text would have and silicate of potash (Russell, 1926). A similar dramatic implications on the practice of agriculture artificial manure was patented by Liebig (1845) and plant nutrition. The opening paragraph states, but since it was based on the ash composition of “The object of organic chemistry is to discover the plants, its use was short-lived. chemical conditions essential to the life and per- Besides these observationsand opinions on fect development of animals and vegetables, and the current controversies of his day, Liebig also generally to investigate all those processes of noted the relationship of plant ashes to crop re- organic nature which are due to the operations of quirements and that water extracts of humusyielded chemical laws” (Bradfield, 1942). little or no residue upon evaporation (Howard, 1940). He espoused the concept that ash analysis Justus von Liebig would foretell which salt would need to be applied Fig. 1. Justus von Liebig (1803-1873). to obtain a full crop. Acceptance of this concept led Justus von Liebig (1803-1873) was recog- to the downfall of the humus theory, since the two nized as one of the most distinguished chemists of Similar vacillations by Liebig can be found concepts could not coexist. However, the ash his day (Fig. 1). His combined activities as in- on the topic of the source of plant N. Liebig concept often is cited as one of Liebig’s false vestigator, editor, teacher, and writer were un- maintained that atmospheric ammonia, not hu- conclusions in relation to the value of organic equaled during his career (Browne, 1942). His mus-derived N, was the source of plant N. How- manures. theory of the mineral nutrition of plants has ever, Liebig’s stance on this important question is dominated the thinking of most students of soils of interest. In hisoriginal monograph, Liebig states, Conclusions and plant nutrition. Moore (1947) perhaps presents “Cultivated plants receive the same quantity of the best condensed interpretation of Liebig’s theory: nitrogen from the atmosphere as trees, shrubs, The evolution of plant nutrition theory has “The soil was a sort of reservoir from which man and other wild plants; but this is not sufficient for been outlined from the fundamental observations could take out no more than he put in.” the purposes of agriculture” (Browne, 1943). of ancient writers, who believed that manures Two important plant nutrition-related con- In subsequent editions, the last portion of produced better crops, to the time of Justus von troversies were broached by Liebig: thecontroversy Liebig’s statement was changed to read “... and Liebig, when visual observations were merged concerning the source of C and that concerning the this is quite sufficient for the purposes of agricul- with the chemistry of the day. The mysterious heat source of N in plant nutrition. ture . . .,” a change that was to have a profound given off from the composting of manures and The humus theory held that humus was the impact (Browne, 1943). What caused Liebig to the resulting brownish-black liquor provoked the source of C. Liebig argued, in a typical scathing alter this most important sentence is not known. curiosity of many through the ages. If we ascribe attack on his contemporaries and predecessors, Liebig was intrigued by the problem facing the this progression in plant nutrition theory to the that prior experiments on humus as the C supplier colonists in Virginia, who, after a century of wheat “scientific advancement” achieved in all fields, “... are considered by them as convincing proofs, and tobacco production without the addition of one also realizes that this progression was not whilst they are fitted only to awake pity” (Russell, manure, were now abandoning their lands. He independent of the society then in existence. 1961). Liebig claimed that plants had an inex- ascribed this development to the century-long Thus, Glauber’s salt, one of the early saltpeter haustible supply of carbonic acid in the air. Ac- drain on the mineral elements in the soil, not to mineral fertilizers, was not only the product of his cording to Liebig, humus was primarily a source of insufficient N or a reduction in soil humus. This scientific endeavor but also a reaction to the CO, from decomposition, but the role of this CO, conclusion was consistent with Liebig’s concept devastation of the Thirty Years War. Similarly, in was to aid in the solubility of inorganic soil con- of an atmospheric source of plant N. Liebig’s time, according to Sykes (1949) in En- stituents (Kononova, 1961). An additional benefit Liebig did recognize, however, that animal gland, the establishment of artificial manures of this humus-derived CO2 was the increased ab- manures were important sources of N (Bradfield, was not only due to Liebig’s theories but also sorption by leaves as it diffused from the soil 1961). He had experimented with cow manure (low helped “... by the decline in agricultural tech- (Waksman, 1938). in N) and human urine (high in N) and reported nique; by the necessity to reduce agricultural costs; Later, however, Liebig does attribute one role more favorable gluten production from wheat grown and by the influences, everywhere in evidence, of humus as a C supplier to plants, but in a nonhumus- from the latter amendment. Three pages later in his which were compelling the farmer to get more out theory form, e.g., humus in an altered state. “Humus monograph, Liebig notes the following, which of the land, to put less into it, and to diminish costs does not nourish plants, by being taken up and probably could be found among the pages of many at every turn.” assimilated in its unaltered state, but by presenting present-day organic magazines: “It should be the Nor does the progression of a theory nec- a slow and lasting source of carbonic acid which is care of the agriculturalist so to employ all the essarily produce a perfect correlation with truth. absorbed by the roots and is the principle nutriment substances containing a large proportion of ni- The abstract notion that plants contained a “force” of young plants at a time when, being destitute of trogen, which his farm affords in the form of animal or “creative power” to transmute substances was leaves, they are unable to extract food from the excrements, that they should serve as nutriment to finallytoppled by Liebig. However, although Liebig atmosphere” (Waksman, 1942). his own plants” (Bradfield, 1942). knew of the benefits of manures from a N standpoint, Liebig seems to waver as to the role of Liebig’s theories on the atmospheric source he opted, erroneously, for a purely atmospheric humus as the source of plant C. His opinion that of ammonia-nitrogen for plant growth led John origin for plant N. The fact that Liebig was a humus per se was not assimilated by plants was Lawes in 1843 to establish the now infamous “compiler and summarizer” of the importance of “proof” that the humus theory was not valid. Broadbalk Field wheat experiment at Rothamsted mineral nutrients placed hismineral elementtheory

HortTechnology • Apr./June 1992 2(2) on an unsound foundation (Marschner, 1986). future roads may be paved that lead to an enhanced However, this became the primary reason for the appreciation of the dynamics underlying the nu- work of Lawes and many other scientists to trition of plants. follow. Twenty years after the publication of Liebig’s monograph, the science of microbiology began to Literature Cited flourish (Waksman, 1938); after another 20 years, Balfour, E.B. 1927. The living soil. Faber & Faber, Lon- Darwin published his study on the effects of earth- don. worms (Darwin, 1976). Studies in soils and plant nutrition would no longer be considered in the Bradfield, R. 1942. Liebig and the chemistry of the soil, p. context of an abiotic system. The dynamic nature 46-55. In: F.R. Moulton (ed.). Liebig and after Liebig. of soil and the role of humus as a microbial media Amer. Assn. Adv. Sci. Special Publ. 16, Washington, D.C. were not and could not be envisioned in Liebig’s Browne, C.A. 1942. Justus von Liebig-Man and day. teacher, p. 1-9. In: F.R. Moulton (ed.). Liebig and after Liebig. Amer. Assn. Adv. Sci. Special Publ: 16, Wash- Epilogue ington, DC. Browne, C.A. 1943. A source book of agricultural chem- Given the state of knowledge during Liebig’s istry. Chronica Botanica 8(1):1-290. career, one would be hard-pressed to accept his summations as the harbinger of doom for the Darwin, C. 1976. Darwin on earthworms. Bookworm Publ. world’s production of food and fiber via the route Co., Ontario. of the chemical fertilizer industry. Current plant Howard, A. 1940. An agricultural testament. Oxford Univ. nutrition theory recognizes the ionic uptake of Press, London. nutrients from the soil through the root. Selectivity King, F.H. 1971. Farmers of forty centuries. Harcourt, exists and varies between plant species as to which Brace Publ., New York. elements are taken up and to what extent. However, this occurs independent of the source of the nutri- Kononova, M.M. 1961. Soil organic matter. Its nature, its ents, either synthetic or organic fertilizers. role in soil formation and in soil fertility. Pergamon What then is the controversy between syn- Press, New York. thetic chemical fertilizer and organic fertilizer us- Liebig, J. 1845. An address to the agriculturalists of ers? Ultimately, if the plant uses N from dried Great Britain explaining the principles and use of his blood or ammonium nitrate in a similar fashion, artificial manures. Thomas Baines, Liverpool, England. why should one be a better approach? The argu- Liebig, J. 1964. Organic chemistry in its application to ments, pro or con, run the gamut from a concept of agriculture and physiology. Johnson Reprint Corp., New a “living earth” to economics and human health. York. (Facsimile Cambridge ed., 1842.) Many of the contentions between the organic and chemical fertilizer proponents are not germane to Marschner, H. 1986. Mineral nutrition of higher plants. Academic, New York. plant nutrition per se. However, there are several points that have direct bearing on plant nutrition. Moore, E.J. 1947. Men who went before, p. 1-16. In: Included among these are nutrient concentration Science in farming. The yearbook of agriculture 1943- and release rate, a dead vs. a living system, and 47. U.S. Govt. Printing Office, Washington, DC. economics. Numerouscitations on the abuses and Northbourne, W.E. 1940. Look to the land. Dent, London. the benefits (albeit short term) of chemical fertil- izers can be made. Research on slow-release fer- Pieters, A.J. 1927. Green manuring. Wiley, New York. tilizers, fertilizer placement, split applications, and Porteous, C. 1960. Pioneers of fertility. Clareville Press, the like are examples of a desire to maximize London. nutrient uptake with a concurrent increase in yield. Rodale, J.I. 1945. Pay dirt. Farming & gardening with However, concepts such as using fertilizer as composts. Devin-Adair Co., New York. “cheap crop insurance” on high-value crops are abusive. Russell, E.J. 1926. Plant nutrition and crop production. According to Balfour (1947) Liebig’s theory Univ. California Press, Berkeley. of mineral plant foods was a “rather naive theory” Russell, E.W. 1967. Soil conditions and plant growth. since it considered only mineral salts. As noted Wiley, New York. earlier, a concept of a dynamic, living soil was beyond the scope of Liebig or any of his contem- Sykes, F. 1949. Humus and the farmer. Rodale Press, Emmaus, Pa. poraries. It is, perhaps, more unfortunate that, even today, this view is still held by many. Waksman, S.A. 1938. Humus. Origin, chemical com- The driving force behind the acceptance or position, and importance in nature. 2nd ed. Williams & rejection of the mode of providing nutrients to the Williams Co., Baltimore. plant was, as with the advent of Glauber’s salt, and Waksman, S.A. 1942. Liebig-The humus theory and is economics. Turning the economic wheel in the role of humus in plant nutrition, p. 56-63. In: F.R. either direction may not be the role of those wear- Moulton (ed.). Liebig and after Liebig. Amer. Assn. Adv. ing the cap of plant nutritionist, but we can hope Sci. Special Publ. 16, Washington, DC.

HortTechnology • Apr./June 1992 2(2)