Organic Matter for Plant Nutrition

It was the famous zoologist and geologist, Agassiz, who suggested that we “Study Nature not books.” Then, with similar suggestions that we put “Nature before man,” there was a poem in the ancient Latin, entitled (in translation) “For Nature Will be Conquered Only by Obeying.” That thought set up in rhyme was widely quoted several decades ago as “The Riddle of the Sphinx.” Science started as, and in truth still is, the organization of knowledge of natural phenomena. Unfortunately, we study technology, now, more than “natural” science.

The so-called “natural” gardeners and farmers are given to practices founded on empiricism or on the knowledge that those practices readily serve. Why their methods succeed is not yet interpreted by either science or sales literature. Natural gardeners use organic matter for the return of plant nutrients and the mobilization by decomposition and “chelation” ¹ of both the active and the reserve mineral elements as nutrients, to say nothing of newly synthesized organic compounds for higher qualities in the vegetable crops. Because by those gardening and farming practices, they try to duplicate the natural environment through which climax crops are grown in man’s absence rather than under a synthetic environment by this technological management, they have been derided by methods which in public debate are called “Argumentum ad hominem,” a personal attack on the opponent and not on the subject.

Adherence to the belief that soil organic compounds are essential in plant nutrition is claimed by pseudo-scientists and their sophisticated science to be a case of “clinging to a myth.” Those claims are often prompted by some bias for sales promotion. They forget that much that is “professional” in practice and of extensive service is no more than empiricism. It is by starting with empirical knowledge, however, that we are prompted to search for causes, and become scientific. Hence, we can still wisely use empiricism. We still do so extensively. The physiology of relief by taking aspirin, a drug consumed annually by the tons, is still a scientific unknown. Its use in medical practice may be also called a “myth” when it is founded on no more than the grinding of swamp-willow bark and using the extract of this as medicine.

Consequently, when the inorganic or mineral parts of plant nutrition are so widely emphasized and promoted, but the organic parts of the nutritional support are neglected, it might be well to tabulate some of the reasons for the undue emphasis of the inorganic and to present some of the unfamiliar “organic” facts of natural plant growth. It would be helpful to prevent some of the unfortunate tactics of useless debate about plant nutrition as commercially practiced. It might be more helpful to study crop growth in Nature without man’s management, but on fertile soils and according to particular climatic settings responsible for these.

The Dead Ash, Not the Living Organic Substance Is Emphasized

When some of the pioneer botanists² studied plant growth in the very dilute aqueous solutions of highly-ionized and chemically active salts, they were aiming at an accurate determination of the different elements required for plant growth. Research today is still using that method to determine the essentiality of various micro-nutrients or “trace” elements not yet so catalogued. But even that method is, seemingly, not refined enough to measure the small amounts of chemical substances to which the life processes of plants respond.

But nutrient solutions will supply plants over but a short period of time. Their use cannot enlighten us on the ratios of the amounts of elements taken in, or what amounts in combination of them would be considered a “balanced” plant diet. Such solutions require frequent changes or supplementations by a few elements. Unlike the soil growing plants naturally, they cannot supply, at the outset, the growing season’s total supply within the volume of root-reach.

As for the ratios of the dozen or more inorganic elements in any nutrient solution, those relations are determined by solubilities and the necessary prevention of their precipitation out of solution as insolubles and unavailables. Hence, solutions do not enable one to determine the effects on the plant’s chemical composition by variable ratios between two, three or more nutrient elements. Those effects by natural soil variations in such ratios are widely demonstrated by differences in the amounts or ratios of elements absorbed on, and exchanged to, the root by the soil’s clay or humus fractions. Those effects can now be readily demonstrated and measured by the colloidal technique which uses organic compounds both natural in the soil and synthesized in commerce, as well as by the finer fractions of colloidal clay.

The nutrient solution technique of the laboratory, or its commercial application as “hydroponics,” does not permit variation in ratios offered to meet the needs of different plants. Instead, it demands a dilution to the degree of expecting the inorganic ions to behave more nearly according to the laws of mixtures of gases (behaving independently of each other) rather than according to interchanges and reactions with precipitation out of solution complete enough to duplicate conditions accepted for quantitative chemical analyses. When the use of only the soluble inorganic salts for plant nutrition as a technology falls so far short of duplicating the growth of crops rooted in the soil as were Nature’s methods during the ages of plant evolution for their healthy survival–and when the major crops are grown where rainfall exceeds evaporation to wash soluble salt out of the soil–shall we chide the unsophisticated gardeners and farmers for trying to fit their soil and crop practices more nearly to what they call the “natural,” and what they have found successful during the centuries rather than what is only a recent technology? For them, the nutrients for all life coming from the soil are still “insoluble but available” to the crops by natural methods. They still speak of “A Living Soil” and according to their successes, “natural” farming is no myth.

Knowledge Comes Slowly

The development of our scientific information about plant nutrition and crop production naturally depended on the advances of chemical science. That consisted of only inorganic chemistry for many years. That early science was given to “ash” analyses. By combustion, those procedures eliminated, at the very outset, what is organic and what makes up about twenty times as much of the crop bulk as the inorganic parts do.

Then, also, we learn chemistry by beginning with the inorganic aspects including now about one hundred elements. Even that beginning phase of chemical science proves highly lethal to any further interest of a high percentage of students of that science. All too many of them fail to arrive at the organic phase of it. They do not learn of its many synthetic processes representing at this date about a half million different known compounds resulting mainly in connection with the life processes dependent initially on the organic synthetic processes of plants.

The study of soil as plant nutrition began by matching plant ash with its list of inorganic elements against the similar list of the ignited soil’s composition. When organic chemistry came along so late to become a synthetic science in place of mainly an analytical one in only recent decades, it should not be surprising that agricultural practices have not become concerned about organic compounds taken from soils by plants for their nutrition.

But it should be surprising (to say nothing of poor faith to his students) to see the reported claim of a chemist-agronomist of an experiment station that “Before the plant foods contained in compost, manure and other organic matter can be used by plants, they must be broken down by bacteria into simple mineral compounds which the plants assimilate, and there is no difference between these minerals and those processed in fertilizer factories.”³

For one content with such a naive concept of plant nutrition which limits “plant foods”⁴ to the inorganic substances of mineral (rock) origin even in the use of composts, the sight of a mushroom crop and its rapid growth would not be impressive, even when it grows by feeding on the organic compounds released by decomposing manure at only a certain stage in that natural process. Perhaps the teachings of the above type and the neglect to teach so many other basic and natural truths are reasons why the crop’s growth on soil by means of many organic compounds, as well as of the inorganic elements–both assimilated by the roots–remains a myth in the classroom where it might better be interpreted as Nature’s contribution through which man attempts to manage plant nutrition.

Seemingly, our teachings are limited to thinking only of inorganic salts and their plant service, or only as the very beginnings of chemical science envisioned them. Apparently the botanical science of plant physiology also is not studied extensively in agricultural production to learn the natural plant processes of organic compounds involved, when the tests of the use of only inorganic elements in plant nutrition on most any soil are undergirded by commercial grants to subsidize them.

Fertilizer Inspection Uses Dual Criteria

Inspection of commercial fertilizers by states also abets our ignorance of the role of soil organic matter in plant nutrition, while it helps the manufacturers see the chemical compositions of their competitors’ goods determined by the state inspection. That is a special service to the fertilizer manufacturers, even though it is claimed to be such to the farmers who pay the costs of it. That inspection uses water solubilities as the criteria for the amounts of nitrogen and the potassium in the erroneous belief that such a quantity outside of the soil is an index of their availability to, or absorption by, the plant roots for fertilizers within the soil.

But for inspecting the phosphorus guaranteed in the fertilizer, which element is taken by plants from mineral compounds too insoluble for solution in water to approach their availability to plants from soil, the criterion is solubility in an organic solution. viz. ammonium citrate. This suggests that it is a chelating solution of the phosphorus by means of an organic substance and, unwittingly, makes a close approach to the methods by which we now know plants mobilize the inorganic nutrients both from the soil and within themselves. By accident, not by science, one-third of the service, namely the test for one of the three inspected elements, is unknowingly using what is natural and has only recently been recognized within that aspect by our thinking.

Chelation, Nature’s Mobilization of the Inorganic Elements by the Organic Molecules

Within the last decade or two the significance of the soluble salt aspect and the ionization of its inorganic elements in plant nutrition has been reduced decidedly. Instead, their role in nonionized union within larger organic molecules has become magnified and extensive in Nature. Now the chemistry of plant growth (and of other life forms) is spoken of as “molecular biochemistry.”

Reactions are between large molecules, as illustrated by magnesium in chlorophyll during the past ages. That inorganic element within the immense chlorophyll molecule is not rendering service in photosynthesis by ionic behaviors of the magnesium as we have been comprehending most inorganic behaviors. We do not know just how the magnesium serves.

Now that some organic compounds, produced in the laboratory, take from solutions and hold the inorganic elements by what seems much of a duplication of their adsorption (and exchange) by the inorganic clay minerals, we speak of that organic behavior toward the inorganic as “chelation” of the latter by the former. The commercial organic compound ethylene diamine tetraacetic acid (EDTA) is an illustration used extensively in recent experimental work. It adsorbs, or chelates, many different inorganic parts with improved nutritional services by the latter as a consequence of the uptake by the root and activities within the plant of that combination of the inorganic as an integral and non-ionizing part of the larger organic molecule. This is a service by the soil organic matter, or humus, in ways even more complex than those corresponding helps rendered by the clay fraction of the soil when it adsorbs and exchanges to the roots, the calcium, magnesium and other ions which are insoluble yet available because of that natural phenomenon.

One of the significant demonstrations of this natural phenomena was made by one of the naturalists among scientists, Professor Midgeley of Vermont, years ago. He studied the effects on the crop by phosphates and barnyard manure applied separately to the soil in contrast to mixing them before their application. The latter gave much better plant growth and made so much more phosphorus available as shown by plant composition, than the former method.

Drs. Hopkins and Whiting of Illinois, gave similar demonstration of the higher availability of phosphorus from rock phosphate when that was plowed under along with red clover as a leguminous green manure in a kind of sheet composting performance within the soil.

But more recently Vernon E. Renner of the Missouri Experiment Station, introduced radioactive phosphorus into the soil for use by young barley. That crop was harvested, carefully analyzed and used as an organic manure for a soybean crop on a soil high in its inorganic phosphorus, according to soil test. The application of the organic manure at the rate of a ton per acre mobilized its phosphorus into the soybean crop with an efficiency just a hundred times that of the movement of the inorganic soil phosphorus along the same biochemical course for crop production.

Methods of Teaching May Need Modification

The separation of inorganic chemistry from organic chemistry, in our methods of learning that science, has magnified unwittingly that former phase as if it were more important than the organic one in crop production. This has been unfortunate, when in Nature there is no such separation. The research into the biochemistry of photosynthesis by Melvin Calvin,⁵ which won the Nobel prize recently, emphasizes phosphorus active in the first carbon compound in the production of sugar by photosynthesis. That first compound is not a six-carbon sugar. Instead, it is a three-carbon compound containing phosphorus. Then, two of those unite by splitting out the phosphorus to result in the six carbon sugar–formerly considered the first stage in photosynthetic action–and releasing the phosphorus to repeat its service in synthesizing the three-carbon compounds into six-carbon ones.

Thus, there are natural exhibitions in which the so-called anionic phosphorus coming from the soil is chelated and combined into most improved molecular biochemistry of growth. We are gradually appreciating the similar services by cationic elements such as magnesium in chlorophyll, iron in hemoglobin of blood and copper in the similar life fluid of the crustaceans, like the lobster. We are viewing similarly many other enzyme-like performances in which the extensive list of inorganic macro- and micro-elements of the soil as either cations or anions are doing wonders within large molecules with a ratio of their ash to organic part that duplicates the ratios of those in living tissues. The arts of the pioneer practitioners of empiricism, i.e. the trial and error methods aiming to duplicate Nature’s behaviors, have long preceded what is now technology and the science supporting it. The latter is, unfortunately, coming along all too slowly when potential commercialization rather than curiosity about the natural is the major stimulus for research.

Agronomic Science Becoming More Organic-Minded

Textbooks of botany and bulletins of some years ago reported the uptake of organic compounds for their nutritional service.⁶ Amongst those reported as improvers of plant growth were such complex ones as coumarin, vanillin, pyridine, quinoline, aspargin, nucleic acids, and, in fact, some in each group of carbohydrates, organic acids and nitrogenous compounds. In entomological work, commercial research by the Boyce-Thompson Institute of near two decades ago reported that some three hundred and more organic compounds–aimed to be “systemic” insect poisons within the plants–were taken into the plant roots from the soil.⁷ Apparently such reports have not registered as cases of soil organic matter serving as large organic molecules moving into the plants from the soil. Research at the Missouri Experiment Station by Dr. George Wagner, working with seedlings under sterile conditions, has been demonstrating sugars and proteinaceous substances taken as nutritional values for them.

But it remained for P. C. deKock of Scotland to combine science and empiricism for attention by both the agronomists and the so-called “Natural” practitioners, when in 1955 he reported his exhibition of the curative effects on chlorotic plants offered and taking up the commercial organic compound, ethylene diamine tetraacetic acid (EDTA, molecular weight 380.20) and thereby mobilizing iron from the soil; and when he duplicated the same beneficial effects by substituting for the EDTA the organic matter extracted from the soil. Thus natural organic matter demonstrated its activities in moving the essential mineral nutrient for plants, namely, iron in chelation possibilities just as was demonstrated for the commercial organic EDTA.⁸

Only very recently was it demonstrated that an inorganic element fed to plants through the roots in chelated union with EDTA is no longer under control of that organic chelating agent by the time it is moving up through the stem. When samples of the exudate from the cut stem were examined, the organic element initially controlled by EDTA was chelated with other compounds, mainly the simpler malic (apple) acid (molecular weight 158.11) and malonic acid (molecular weight 104.06).⁹ This indicates the possibility that many organic compounds within the plant are operating to reduce the ionic activities of inorganic elements and are moving them about within the plants as parts of larger organic molecules. It is the latter, then, that dominates the former. The “ash” contributions from the soil come under control of molecular biochemistry.

Now that we find the natural behavior duplicating what we have done by laboratory techniques, we as agronomists are more ready to accept possible functions in plant nutrition by soil organic matter with more credence. The way is now open for many forthcoming research projects on soil organic matter for plant nutrition. This highly neglected half or more of past plant nutrition bids fair to be elucidated in the near future. But when the essentiality of inorganic elements is still an unfinished task that involves a list of no more than a hundred in total, then by what names might he not be called who will suggest a research project even under federal funds to determine the essentiality of the many organic compounds, of which but a half million are characterized or catalogued to date?

Discriminating Animals May Aid Research in Organic Compounds

The use of animals as bioassayers of feeds demonstrates that they recognize the dangerous, or beneficial, effects within what they will consume because of organic compounds taken directly by the plants from the soil. Animals respond to effects also from organic compounds in the soil as manures or organic fertilizers of the crops fed. Livestock has not taken readily to pasturing green sweet clover. If confined to a field of such, the various animals will first clean up the fence rows, water courses and areas of vegetation other than the sweet clover. Their reluctant taking of any sweet clover suggests such as only an act of desperation. They apparently recognize in the dicumerol, synthesized by that crop, its anti-coagulating effects on the blood and its cause of bleeding to death on injury or surgical treatment of the animals.

Hogs, given choice of corn grain grown with sweet clover as the preceding crop turned under for leguminous organic manure on plots given increasing combination treatments of calcium in lime, phosphorus and potassium, discriminated sharply amongst four simultaneous offerings of the grains. Those choices differed according to whether the sweet clover was turned under green in spring, or merely as the residue of a crop grown for seed the preceding year. In case of the organic manure of sweet clover residues from its use as seed crop on the four plots, the hogs chose to eat more of the grain according as more inorganic fertilizers were applied, or as more yield of corn per acre resulted. However, when sweet clover was turned under green ahead of the corn planting, the hogs decided to choose exactly in the reverse order. For them the less green, sweet clover used to fertilize the corn, the better. They preferred no green sweet clover as organic fertilizer for the production of their corn (maize) as feed.

No chemical data were taken to tell us whether dicumerol, or organic compounds suggesting it, were in the corn grain. The hogs merely reported that organic matter from green sweet clover, used to fertilize corn, carried organic effects in the grain which they refused. On the contrary, sweet clover used as dried, matured residue carried organic effects into the grain of their highest choice. While many folks may be deriding organic farming, the hogs vote for it. But they are not speaking of it in general. Even they report that judgment must be exercised as to the kinds of organic farming one is talking about, and that associated with attention to the inorganic essentials.

It is not common knowledge that the organic compounds of well known, specific, chemical structure giving the fecal odor, namely, indole and skatole, will be taken up by a plant like the white dwarf bean of Michigan fame. But it was demonstrated by Dr. F. M. Pottenger, Jr., of California, that those odorous organics as taken may be either stored in the seeds with the scent emanating from them, or may be converted into the well known growth hormone, indole acetic acid. That was suggested when fertilization of the soil by cat dung from raw milk fed the cats converted the dwarf beans to pole beans in two cat pens but corresponding dung or manure from cooked milk fed the cats in six pens did not violate their growth behavior claimed by their pedigree as dwarf plants.

Composting Pulverized Minerals is Natural

Nature’s management of soil for extended maintenance of its high productivity of crops as nutrition for all other life forms consists of two major practices. The first is the regular applications by wind (loess, dusts, etc.) and by water (alluvium, inwash, etc.) of deposits of unweathered, finely pulverized rock-mixtures on the surface of the soil. The second is the regular covering of the soil surface by organic matter as crop residues.

By the latter, as energy and sustenance for the microbial flora, its life processes decomposing the finely pulverized minerals represent an active development of a new stratum of surface soil where the earth and the atmosphere with its meteorological forces meet. The surface phenomena there are the dynamics by which Nature’s composting processes are combining the organic matter with the rock mineral fertilizers to make those insoluble inorganic soil elements become available plant nutrition (not salts) through their union with the conserved organic nutrient compounds, or through Nature’s blending in support of microbes and plants. Unfortunately, our inorganic salt concepts, magnified by their commercial potential, have kept us blinded from Nature’s more efficient management of production to support all that lives.

The reported “Healthy Hunzas,” isolated in the high Himalayas have not been viewed as a case of a climax human crop dependent on their complete adoption of the practices by which the soil productivity is naturally maintained for climax crops (and livestock) of domestication with the Hunzas as a corresponding climax human crop included.

Nature’s Part is Still the Major Unknown Factor in Technological Agriculture

Of course, we talk about and teach only what we know. Hence, if we don’t know that crops are nourished by organic compounds taken from the soil–a fact demonstrated as early as the first climax crops in the course of their evolution before domestication–we are just naturally content to believe that crops are nourished only by what has been “broken down by bacteria into simple mineral compounds.” Then, too, “we are just naturally down on what we are not up on.” With limited information of nature’s performances, our discussions and debates about our managements of those in what we include in agriculture may miss the truth widely and become illustrations of “argumentum ad hominem.” We need to study Nature, not only books.

 

* * *

Nature Will Not Be Conquered Except By Obeying 

(“Natura enim non nisi parendo vincitur”) 

At first men try with magic charm 

To fertilize the earth, 

To keep their flocks and herds from harm, 

And bring new young to birth. 

Then to capricious gods they turn 

To save from fire or floods; 

Their smoking sacrifices burn 

On altars red with blood. 

Next bold philosopher and sage 

A settled plan decree, 

And prove by thought or sacred page 

What Natuxe ought to be. 

But Nature smiles–A Sphinx-like smile–

Watching their little day 

She waits in patience for a while 

Their plans to dissolve away. 

Then come those humbler men of heart

With no completed scheme,

Content to play a modest part,

To test, observe and dream.

 

Till out of chaos come in sight

Clear fragments of a Whole–

Man, learning Nature’s ways aright,

Obeying, can control.

 

The great Design now glows afar;

But yet its changing scenes

Reveal not what the pieces are

Nor what the Puzzle means

 

And Nature smiles–still unconfessed

The secret thou-ght she thinks–

Inscrutable she guards unguessed

The riddle of the Sphinx.

* * *

Natural chelation is suggested when phosphatic fertilizer and barnyard manure applied separately are not biochemically as effective (Pots 9 and 12) as when applied to the soil in a mixture (Pots 10 and 13, with three inches of soil treated in case of the first numbers and six inches, the second.)

The phosphate-manure mixture plowed under in the field grew clumps of roots in the buried clumps of manure, even though it was but a delicate root that searched out those root-growing fertility centers. Lower photo of three plants, A, B, C, carefully dug from the soil.

By courtesy of Prof. A. R. Midgley, Vermont Experiment Station.

 

References Cited:

1. A combining of the inorganic elements into a large non-ionized organic molecule.
2. Among the formulators of nutrient solutions were the early names of Sachs, 1860, and Knop, 1865, of Germany, and the later name of Hoagland, 1948, of California.
3. Reader’s Digest, July, 1962, p. 104.
4. The term “plant foods,” according to botanical usage, refers to substances synthesized particularly by the leaf processes and taken up as organic compounds by the cells. Those substances serve in the metabolic processes within the cells. The inorganic elements taken from the soil are considered as “nutrients,” since they do not supply energy in plant nutrition.
5. Melvin Calvin. “The Path of Carbon in Photosynthesis.” Science, 135:879-889, 1962.
6. Edwin C. Miller. Plant Physiology. McGraw-Hill, 1938.
7. Annual meeting Amer. Assn. Adv. of Science, St. Louis, Missouri.
8. P. C. deKock. “Influence of Humic Acids on Plant Growth.” Science, 121:474, 1955.
9. L. O. Tiffin and J. C. Brown. “Iron Chelates in Soybean Exudates.” Science, 135:311-313, 1962.