, the mark of an acidic reaction, the amino acids of carbon chains of varied length and structure.Nodulation Modifies Nutrient Intake from Colloidal Clay by Soybeans
THE TERM, “the living soil”, is an age-old expression, but just what it connotes in the minds of different soil scientists or in our own thinking we are not sure. The legume bacteria represent an introduction of life into the soil. On my coming to the University of Missouri (1916) there was plenty of tight clay soil from northeast to southwest Missouri, so that about a fourth of the land was “dead” soil. My purpose was to make it a “living soil” and to take nitrogen from the air to accomplish that. Now, what is a “living soil?”
It was the Missouri soils’ shortage of nitrogen for more crop production that brought me to Missouri. It was for crops richer in nitrogen, the symbol of foods rich in proteins, that concerned us with nitrogen—even if we had to try to take elemental nitrogen out of the air by means of symbiotic bacteria producing nodules on legume roots, feeding by those roots the extra nitrogen into the plant proteins, and thus giving protein-rich feeds for animal growth and reproduction rather than carbohydrate-rich feeds serving mainly for gain in weight as fattening.
Speaking of protein, nitrogen is a symbol of it, composed as it is of what is called “amino” acids. Amino is a chemical symbol of N plus two hydrogens tied to one carbon, in a chain close to a so-called “carboxyl” group, , the mark of an acidic reaction, the amino acids of carbon chains of varied length and structure.
It is a protein that can be living, growing, protecting itself from attack and destruction by lower forms of life. In recent years we have learned, for plants, that if we balance their nutrition for what may be called a “balanced plant diet” in terms of about a dozen and a half natural elements, the plants protect themselves against fungus diseases and against leaf-eating insects. There is no need for poisonous sprays when the plants make their own necessary protective chemicals, or proteins, within their own body to give themselves immunity to microbial and fungus diseases and to attacks by many kinds of insects destroying the plants themselves.
When man manages the growing of crops for his foods and feeds for livestock, but diseases and insects destroy the crops, we do not ask ourselves, “Before man came on the scene, how did the Creator manage the crops to have them protect themselves to survive and be here for man’s adoption and modification as his own food for survival?” Isn’t it possible that continued cropping and fertility exhaustion from the soil have weakened the plant’s nutrition for good health, correspondingly growing less protein but more carbohydrate so that plants are too poorly nourished to defend themselves? Are not such poorly nourished plants less nutrition for us as food and for ourselves to be healthy in self-defense but more subject to human ailments? If our own feeds are grown on soils sadly exhausted of their own once prime fertility, primitive man may have been initially much healthier than we moderns are.
When we consider the elements which plants use in building themselves by growth carried out by proteins, we listed initially 10, later about a dozen and a half of the earth’s initial elements. Those were, namely; carbon and nitrogen from the atmosphere; oxygen and hydrogen from the water. Then, we have the soil-borne mineral elements, or the cations as alkaline earth elements: calcium and magnesium from limestone; potassium and sodium, the alkalis; then anions nitrogen, phosphorus, sulphur, and carbon; then trace elements manganese, copper, zinc, boron, molybdenum, chlorine and possibly others. The “trace” elements, as a soil deficiency, have become decisively essential since they have become connected with human deficiencies as elements in body processes and certain deficiency diseases like “brucellosis.”
Plan and Methods of Study
Using the colloidal clay technique with the colloidal clay carrying the nutrient cations and some anions, adsorbed on the colloid in specific amounts, soybean seeds were the only source of nitrogen to test the ability of the plants, innoculated with legume bacteria, to fix atmospheric nitrogen. By utilizing a series of graduate students, during several years, working with the colloidal clay technique, we had finally arrived at enough experience to use the colloidal clay, with acid-washed quartz sand, as plant diets to vary calcium, magnesium, potassium, as hydroxides, and phosphorus as calcium hydrogen phosphate, all titrated on the acid clay (pH 3.6) in suitably varied quantities as plant diets for this study.
By means of two soybean series, one sterile of legume bacteria, and the other innoculated with laboratory Rhizobia culture for soybeans, the changed plant physiology demonstrated what one microbial life form in the soil could accomplish in the phenomenon of ion exchange between the plant roots and the colloidal complex of the soil. The colloidal complex had initially been made the equivalent of sterile soil by electrodialysis during several days. By this means we were able to demonstrate that the root of a legume plant is a decidedly different force in exchanging ions with the soil than is the root of a non-legume plant.
We aimed to learn several facts about legume plants. We used as possible postulates for the research the following:
1. We already knew that a yield of larger crop mass is not necessarily proof of crops’ delivery of more food value in either protein or minerals.
2. Is what might be called a “living soil” in terms of more microbial life in root nodules a modification of the plant’s larger, possibly better balanced nutrition, especially relative to protein production by more mineral nutrient intake?
3. How effective is proteinaceousness of the plant’s roots as a help in its taking more inorganic nutrient elements from the exchangeable supply adsorbed on the colloidal complex?
4. Do different quantities of cations on the clay favor, or hinder, each other’s services in plant nutrition; e.g., is magnesium as an excess disturbing to calcium?
5. Does potassium, as an increased carbohydrate synthesizer by the plant, serve to supply it with more energy for its nitrogen fixation?
6. Do proteinaceous roots suggest plants of more nutritional value as food by intake of more inorganic fertility?
Other postulates might have been added.
Two levels of calcium, 10 and 20 M.E. per plant were used, and coupled with each of those were three levels of potassium, 5, 10, and 15 M.E. per plant, thus varying both calcium and potassium. For magnesium and phosphorus the constants of 10 M.E. for the former and 7.5 M.E. for the latter were used in both series. The M.E. of barium for the first potassium series of 5, 10, 15 M.E. and for the constant 10 M.E. series of calcium were 25, 20, and 15 M.E.; but were 15, 10, and 5 M.E. of barium for the second potassium series combined with 20 M.E. of calcium. Table 1 gives the details of the initial plan of the M.E. of nutrients titrated on the clay. The clay mixed with quartz sand was the growth medium in which one series (A) was non-nodulated and the other (B) was nodulated. Both crops were started in May, the (A) in 1941 and the (B) crop in 1942.
Results
Nitrogen in the Crops. The non-nodulated crop’s contents of nitrogen was only that offered initially to the seed. The percentages of nitrogen in the dry matter of the crop were 1.50 as a minimum and 2.66 as a maximum while the corresponding figures for the nodulated crop (B) were 3.24 and 4.00. The average figures for the six cultures in duplicate in each of these two series were 1.91 for the former and 3.50 percent of nitrogen for the latter. The average values for total nitrogen per 50 plants were 349.7 mgms for the non-nodulated (A) crop and 449.7 mgms for the plants with nodules. The ratios for the percentages are A:B::1:1.8 and for the totals of nitrogen their ratios were A:B::1:1.2 with the increases due to the use of the extra atmospheric nitrogen. This meant that the nodulated crop was 80% more proteinaceous. This test demonstrated that protein on the inside of the root as a colloid itself might be a factor modifying the exchange through the root membrane with the soil colloidal complex on the exterior of the root. The “living soil” via added living legume bacteria made a big difference. Weights of the Crop. Quite contrary to expectation, the weights of the non-nodulated soybean crop, which was behaving as a non-legume with reference to its nitrogen, were much larger than those of the nodulated crop (reported as Table 2). This occurred when both were growing on the same supply of available nutrients adsorbed on the colloidal clay. Here then, the mass of plant growth was almost 50% larger in total when the series was behaving as a non-legume.
More significant, however, is the fact that the nodulated crop had contact with the same amount of clay and total nutrients, a total root mass that was only half, and less, that of the non-nodulated crop. Nevertheless, its ratio of tops to roots of the latter was 2.31 while for the crop behaving as a legume, the tops had 3.53 times as much mass as the roots.
This feature deserves emphasis, namely, that the root mass of the nodulated crop was 50% more efficient in producing mass of top as related to mass of roots. If we can assume that the larger root mass represented correspondingly larger total root surface for clay contact, and ionic exchange functions with it, then it is immediately evident that the nodulated root, which is also the more proteinaceous root, is more effective in producing mass of top per unit mass and surface of root. If the legume plant carries in addition more nutrients taken from the soil, as is common for it, then the root of the leguminous plant must also be a more efficient physio-chemical system for the movement of ions from the colloidal clay complex through its wall into the interior of the root.
Potassium, Calcium and Magnesium in the Crops. The fact that the roots of the nodulated soybean plants were more active in moving nutrient ions into themselves from the adsorption atmosphere of the colloidal clay is evident from the data for concentrations and totals of the three nutrients, potassium, calcium and magnesium, in the two crop series given in Table 3.
Perhaps the most interesting fact is the much higher concentration of potassium in the nodulated crop. As an average of the six treatments, this was 3.36% of the plant dry matter for the nodulated crop and only 1.92% for that not nodulated. The total potassium in the nodulated crop was also larger in every treatment in spite of the fact that the mass of the crop was smaller.
As for the calcium, the concentration of this element showed no regular variation in either the nodulated or non-nodulated crop, save as the soils offer increased. The total in the nodulated crop increased consistently as more potassium was offered and taken at either level of calcium supplied. In the non-nodulated crop at 10 M.E. of calcium, the totals were all very similar but at 20 M.E. of calcium they decreased as more potassium was taken. Nevertheless, at the 20 M.E. level of calcium this larger supply resulted in reduced concentration of potassium in the plants at all levels of the potassium supply. Here, then, the increasing intake of potassium by the non-legume suggests an excluding effect by potassium on the calcium, and the higher calcium similarly on the potassium when both were on the clay in exchangeable forms.
The concentrations of magnesium were higher in every case for the nodulated crop. At the 10 M.E. of calcium there was a decrease in concentration of magnesium with increased concentration of potassium in the crop whether behaving as a legume or non-legume. In the non-nodulated plants to which 20 M.E. of calcium were available, the decrease in magnesium concentration was not as regular.
The largest total amount of magnesium was in the nodulated crop given the maximum of calcium and minimum of potassium. The lowest total amount of magnesium was in the non-nodulated crop given the minimum of calcium and the maximum of potassium. The fuller significance of these facts must await later discussion.
Efficiency of Use by Nodulated and Non-Nodulated Plants of Potassium, Calcium, and Magnesium Adsorbed on the Clay. In order to enhance appreciation of the larger movements of plant nutrients into the roots in consequence of their proteinaceousness, the total amounts of the potassium, calcium, magnesium taken by the plants were calculated as percentages of the supplies offered on the clay. The data are assembled in Table 4.
Again the high efficiency with which the potassium moved into the crop, and the higher efficiency for the nodulated crop, are outstanding. This naturally raises the question whether this larger amount of potassium means more carbohydrate synthesis for its use in plant respiration and synthesis of protein. Certainly, the more proteinaceous roots were more efficient in encouraging potassium entrance, when as an average 78.5% of the total on the clay was taken in contrast to 67.0% taken by the non-nodulated, less proteinaceous roots.
The plant’s efficiency of consumption of calcium by the non-nodulated crop was not responsive to potassium differences. It was higher, in general, namely, 26.5%, as the mean, than for the nodulated crop (mean 23.0%). In the nodulated crop, increasing amounts of potassium meant higher efficiency in the movement of calcium into the plants, but mainly at the lower level of calcium.
In general, the efficiency of magnesium utilization declined as more potassium was offered and there was a suggestion of less efficient use by the non-nodulated crop.
Phosphorus, Silicon and Barium in the Crops. The concentration of phosphorus in the crops, whether nodulated or not, responded inversely to the concentrations of the potassium, more particularly when only 10 M.E. of calcium were available. This is shown in Table 5. The concentrations in the nodulated crop were always higher than those in the corresponding treatments of the non-nodulated crop. The total amounts of phosphorus in the crops given 10 M.E. of calcium and nodulated increased as more potassium was offered. Without nodulation at both calcium levels, and with nodulation at the higher calcium level, this relation did not suggest itself.
These facts suggest that for the nodulated legume root, the increasingly added potassium encourages increased intake of phosphorus from a constant supply in the soil where the calcium supply is moderate or low, but not when this is more liberal.
The concentration of silicon, even more pronouncedly than that of phosphorus, showed an inverse relation to the concentration of the potassium. Potassium, therefore, suggests itself as having an excluding effect on silicon. Calcium classifies in the same category since at 20 M.E. the concentrations of silicon were roughly only about one-half those at 10 M.E. of calcium. Increasing the potassium from 5 to 15 M.E. shifted the silicon concentration from 2.54 to 1.46% for the nodulated crop and from 2.28 to 1.10% for the non-nodulated, both grown with 10 M.E. of calcium. With 20 M.E. of calcium, the corresponding shifts were from 1.60 to 0.81 and from 1.13 to 0.91 respectively with increase in potassium offered. The nodulation permitted a higher concentration of silicon.
When the totals of silicon are considered, there was more of it in the non-nodulated or heavier crop. The increasing potassium and the increasing calcium both served to demonstrate their effects of excluding the silicon, or the equivalent of nourishing the plant so that a different physio-chemical situation in the root meant less movement of silicon into it.
The concentrations and totals of barium followed the amounts present in the soil and did not relate themselves in any recognized way to any physiological factors. The non-nodulated series originally given 5 M.E. more of barium to each culture had more total barium in the crop. Barium suggests itself as striking up a kind of an equilibrium between that within and that without the plant.
Efficiency of Use by the Nodulated and Non-nodulated Plants of Phosphorus and Barium Adsorbed on the Clay. The same supply of phosphorus on the clay was used more efficiently by the nodulated crop grown with 10 M.E. of calcium as more potassium was applied. This is shown in Table 6.
There is a suggestion of a similar condition for the non-nodulated crop. At the higher levels of calcium, namely 20 M.E. there were no distinct suggestions. It is interesting to note that from 40 to 55% of the offered phosphorus found its way into the crops, and that, in general, the figure was higher on the non-nodulated crop.
That the nodulated crop which was synthesizing more nitrogen into more protein should use less phosphorus from the soil supply suggests that the non-legume was building phosphorus into compounds other than proteins or was merely moving the phosphorus into the crop as a deposition in some inorganic or less complex organic form.
Summary
In summary, the soybean crops grown with different soil treatments pointed out that the nodulated crops with their more proteinaceous roots represent these as different physio-chemical systems when tested against the colloidal clay than are the roots of non-nodulated soybeans. When the concentrations and totals in the crops of the originally adsorbed ions on the clay are considered, the nodulated crop demonstrated more regularities and consistent relations between those within and those outside the crop roots.
Even though the non-nodulated crop masses were larger, the nodulated crops were higher in concentrations and totals of potassium, in concentrations of calcium, of magnesium, and of phosphorus; but lower in totals of the non-nutrient silicon. In terms of the ingo of exchangeable ions into the crop from the clay, higher percentages of the potassium and magnesium were taken in consequence of nodulation. Calcium and phosphorus in totals moved into the non-nodulated crop as readily as into the nodulated crop.
These results suggest that the composition of the legume forage, in terms of several of the mineral nutrient elements from the soil, is different because the protein nature of the root makes this part of the plant a different physio-chemical system in relation to the colloidal complex of the soil for its intake. Plant nutrition as a movement of adsorbed ions from the clay into the root is not only a matter of kinds and amounts of ions on the clay and the total clay in the soil, but also a matter of the physiology of the particular root as well.
