Trace Elements and Agricultural Production

We are slowly realizing that the essential chemical elements contributed by the soil in only “trace” amounts for support of microbes, plants, animals, and man are no less essential than those taken from the soil in larger amounts. Now that biological responses, such like the black wool on sheep turning gray under deficiency of copper and cobalt; fungi failing to sporulate in trace element absence; cobalt salts functioning via the intestinal microbial flora and not via the blood stream; and others; we are pushing the measuring means of the laboratory to greater refinement. Bioassay for trace elements and farmer reports of observations which were once questioned, are gradually coming into the academic categories. They are being slowly accepted by the critics.

Mass of Plant Ash and Magnitude of Growth Response Are Not Necessarily Correlated

But as yet, the varied biological responses and manifestations, associated with trace element treatments, do not let the magnitude of these phenomena relate themselves so directly to the amounts of trace elements recognized. When correlations between size of cause and magnitude of effects by major nutrient elements have become such a firm belief to make correlation statistics so widely accepted, it is difficult for the correlating mind to accept so small an amount of molybdenum as one-sixteenth of an ounce per acre as the cause for difference between clover abundance and absolute clover failure. In such gross biological manifestations it is difficult to assign to the “trace” element any specific function or physiological service responsible. Fractions of a milligram of cobalt per day (and of copper) are difficult to be mathematically correlated, or functionally connected with the wool of the black sheep staying black, or slowly turning to gray as they tell us that all black-born sheep in Missouri must do. Because such biological manifestations do not fit into academic patterns of past teachings and habitual laboratory manipulations, the minds are apt to be closed to “trace” elements as significant. But to say “I don’t believe it” may not be denial of the facts. It may be merely a confession of the ignorance of them. 

Fig. I. White wool, center, from sheep with “long waves” in wool, until given copper and cobalt, which changed the wave or crimp to shorter normals as shown by wool on right. Black wool, left, shows color change on shift to different area of grazing by black sheep.

 

Also when increased plant bulk is our major criterion of the effects by the soil fertility on plant growth, and when cheap gains in weight of the animal body resulting largely from additions of fat and water, are the measure of feed values, such physiological processes are all so far removed from the more refined or more complete nutrition for the production of seed and semen that certainly more plant bulk and more animal weight cannot be taken as responses manifesting the effects of trace elements. Some more refined criterion must be used to observe and measure the influence of trace elements in nutrition of crops and animals.

New Criterion Suggested

It seems most logical, then, to view the “trace” elements, not as parts or constituents of the masses grown, but rather as tools in the processes of growing them. “Trace” elements are possibly rendering repeated or recurring services. They are very probably entering into a reaction to bring it about, then coming out to repeat the reaction on another mass, just as we envision the helps by catalysts modifying immense masses but themselves never consumed by or retained in them.

Such functions of copper, for example, in the body will not be measured by an ash analysis of the young and then the older life form. Nor is quantity a variable when a contribution of this element relieves a symptom and then that symptom cannot be reestablished for a long time by withholding copper. The contributed copper does not escape from the organism. Instead it protects that body for a long time without extra copper being required.

Our use of copper in Bordeau mixture, and in its most insoluble form as a fungicid spray, should raise the question how much an insoluble form of this element can destroy a fungus by contact. It would seem more fitting to postulate the possibility that the close and lasting contact with the plant leaf of the insoluble copper hydroxide results in its conversion to the more soluble copper bicarbonate. This form may well enter the leaf then, and by serving in nutrition as a “trace” element may help in the plant’s synthesis of its own antibiotic and protective compounds simulating the proteins. Only extensive research can determine the propriety of such an hypothesis.

In the plant’s production of carbohydrates or the animal’s laying on of fat and other equally gross and common manifestations, then, one would scarcely expect “trace” elements like boron, manganese, copper, zinc, molybdenum, iodine, and others to demonstrate much effect. Rather the proteins, so generally manipulated by enzymes, would suggest themselves as the realm of physiological processes within which the influences by essential elements of trace amounts might be recognized. Enzymes are combinations of protein-like molecules, vitamin-like molecules, and inorganic ions (often the “trace” elements). If enzymes by the hundreds are responsible for the creation of proteins, composed as the latter are of their score or more of amino acids, then it would seem well to postulate that the variation in the supplies of a trace element coming from the soil might cause variation in the proteins, or in the array and amounts of the amino acids synthesized only by plants and microbes.

If one hammer and one saw are the essential tools for constructing a dog kennel, the conclusion does not follow logically that there will be a correlated increase in the number of hammers and saws in constructing a hundred kennels or dog houses a hundred times as large. Nor would an inventory of these kennels and dog houses find a single hammer or a single saw necessarily within them at the close of the constructing performances. “Trace” elements must be viewed as tools, or as enzymes which do not conform to common correlation thinking where large masses are concerned, and are connected with large causes controlling their behaviors.

Experimental Evidence is Accumulating

In our research, therefore, we have looked to the high protein-producing crops, namely, the legumes and more especially those of highest feed value in growing young animals and in aiding their reproduction. In the field trials, several trace elements (and also the neglected elements, magnesium, sulfur, sodium, etc.) were used as a multiple rather than single application. After such multiple treatments register their effects, then trials with the separate elements can well be undertaken.

In Figure II, there are photographs showing the differences in the stubble crops of sweet clover on separate plots as a result of the only variable, namely, the application of a mixture of the “trace” or minor elements. That the legume should have excluded the non-legume so completely in these trials suggests that the former is helped by the treatment of “trace” elements in synthesizing its own proteins more effectively for more cell multiplication and more growth to the exclusion of the non-legume which survives on much less synthesis of the proteins.

Fig. II. When a legume forage crop given “trace” elements as fertilizer treatments grows well enough to exclude the non-leguminous competitor plants, or weeds (upper photo), which come in prominently and regularly on the adjoining plot given no “trace” element fertilization (lower photo), there is the suggestion that “trace” element deficiencies will probably be associated first with the crop representing higher concentration of protein, like the legumes.

Fig. III. Better sporulation (darker color) by a fungus reflects the “trace” element (copper in this case) present in larger amounts. Sporulation, much as heavier seed production by a crop, reflects larger amounts of the major fertility elements. Spore production by the standards (0.0 – 2.0, upper two rows of plates) gives the standards as parts per million for the measure of the copper in some of the different Missouri soils. A, B, C, 4, 5, 6, are test results for different Missouri soils.)

Fig. IV. Magnesium–a neglected essential element in our fertilizer thinking–was added to the 25 soybean plants per pot in 0, 24, 48 and 96 parts per million (left to right respectively). The bigger growth and improved size and quality accordingly emphasize the significance of “trace” amounts of essentials for healthy growth.

 

Plants Function or Fail According as Their Required Suite of Amino Acids Is or Is Not Synthesized

That the synthesis of the separate components of the proteins, namely, the different amino acids might be related to the “trace” elements, was the hypothesis under test with alfalfa, for example, in Missouri. Grown in Colorado and imported into Missouri, alfalfa, as a dried feed, is an excellent protein supplement to corn. But grown on Missouri soils, even on those treated with the major nutrient elements, it is not of such high value in this respect. When corn protein is deficient, especially in the amino acids tryptophane, lysine, and even methionine, it seemed well to treat alfalfa growing in Missouri with the trace elements, some used separately and several in combination, to learn whether these protein components are shifted in their concentrations in the alfalfa by “trace” element fertilization.

It was interesting to note that boron was effective for increasing tryptophane decidedly and the lysine almost as much. It is significant to note also that the major influences by the “trace” element fertilization registered themselves in the increased concentrations of those amino acids most grossly deficient in corn and likewise of lowest concentration in the alfalfa grown on the Missouri soils without “trace” element fertilization. While boron alone containing no sulfur did not increase the concentration of methionine in the alfalfa, the other “trace” elements carrying sulfates did. This was verified by other work and demonstrates the suggestion that soil deficiency in the neglected element, sulfur, (and possibly other neglected elements) may be responsible for the proteins which are incomplete in methionine, the sulfur-containing amino acid.

 

Concentrations of Different Amino Acids in Alfalfa Hay According to Soil Treatments With “Trace” Elements (Percentage of Dry Leaves)

Treatment	Methionine	Tryptophane	Lycine	Threonine	Histidine	Arginine	Valine	Isoleucine	Leucine
Calcium Calcium and boron Calcium/manganese Calcium and mixture*	0.10  0.17  0.24  0.23	0.54 0.85  0.64  0.67	1.57  2.13  2.12  1.87	0.86  1.07  0.95  1.014	0.65  0.72  0.81  0.83	0.38  0.42  0.43 0.41	2.19  2.13  2.40 2.59	2.64  4.09  3.63  3.44	4.37 5.55 4.89 5.24

* Mixture of cobalt, copper, zinc, manganese, and boron.

 

In the bioassay of the effects on the plants by “trace” elements as soil treatment, it is highly probable that the animal has been registering the incompleteness vs the completeness in the required amino acids of the proteins. We have been too easily satisfied when we measure these as “crude” proteins by determining the total nitrogen of which almost half may be in chemical combination other than the amino or readily usable form. When by means of “trace” elements via the soil, the amino acid nitrogen in the plants can be increased without increasing the total nitrogen, there is the suggestion that the “trace” elements may be more fully understood only when we study the plant parts and processes in which the “trace” elements probably play their major roles, namely, the synthesis of the proteins, the enzymes, and the other phases in cell multiplication or cell reproduction.

 

References:

Acknowledgment is gladly made to the Tennessee Corporation, Atlanta, Georgia, for the interest and support of the research in the trace elements.

“Microbiological Assays of Hays for Their Amino Acids According to Soil Types and Treatments Including Trace Elements.” Wm. G. Blue, Victor L. Sheldon, and Wm. A. Albrecht. Soil Sci. Soc. of Amer. (SSSA) Proceedings, Vol. 13, 1948.

“Biosynthesis of Amino Acids According to Soil Fertility. I. Tryptophane in Forage Crops. II. Methionine content of plants and the sulfur applied.” V. L. Sheldon, Wm. G. Blue, and Wm. A. Albrecht. Plant and Soil III, No. 1, January 1951.

“Protein Deficiencies Via Soil Deficiencies. I. Ecological Indications. II. Experimental Evidence,” Wm. A. Albrecht. Read before the Eighth Annual Seminar for the Study and Practice of Dental Medicine, The Desert Inn, Palm Springs, Calif. Oct. 31, 1951.