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Part III, continued: 

  It can be seen from the above data that small doses of organic substances, present in processed compost or manure, are needed for the improvement of the growth of plants.

  The question arises which of these organic substances are the activators of plant growth.

  It was said above that the organic part of the soil consists of a multitude of complex compounds with specific and nonspecific proportion. The majority of these compounds are related to humic acids.

  Beside the humic acids many other substances were found in the organic part of the soil. They include substances with biocatalytic properties, Among these are enzymes, vitamins, auxins, certain amino acids and other biotic substances.

  Bottomley (1914-1920), Mockeridge (1924), Voelcker (1915), Clark (1935), Saeger (1925), and others, have assumed that the activating effect of humus fertilizers, processing manure and different composts with and without bacteria, in conditioned by special substances present in them, the so-called "auximones."

  Their action is similar to that of the yeast bios. The analysis of peat infected with bacteria showed the presence of purine bases. The latter were also found in the cells of Azotobacter. This was the reason for Mockeridge's conclusion that the activating compound of composts and Azotobacter to one and the same substance.

  It wax shown in later studies that the action of humus is caused by special substances produced by microbes (Nath, 1932, McCarrison, 1924, And others).

  Anstead (1935) proposed that these substances be called phytamins. According to him the phytamins are formed by microorganisms only. Upon entering the plants they are transformed into vitamins. The latter entering with food into the body of animals and human beings are subjected to certain transformations and are converted into hormones. Hormones and vitamins are excreted from the animal body with urine or excrements, find their way into the soil or manure, And are there transformed by microorganisms into phytamins.

  In such a way, according to Anstead, phytamins, vitamins and hormones are products of one and the same substance.

  Analogous views were hold by Daineko (1939). He assumed that there is no difference between the animal hormones and vitamins, and that they are interlinked.

  The link between plant and animal biocatalysts is stressed by many inventigators. However, there are no grounds for speaking of any cycle of these substances in nature.

  Lochhead and Chase (1943) attempted to elucidate the nature of the activating substance of humus. They prepared extracts from soil humus and subjected it to various procedures, such as extraction with organic solvents, absorption with carbon, and other absorbents followed by elution. The experiments showed that the ash of humus and composts had no effect whatsoever on the growth of plants and microorganism, Of 63 microbial cultures, only one grew in the presence of ash obtained from composts. The extracts obtained from composts and humus of the soil, however, had a positive effect on their growth. The acetone extract was the one most effective, In its presence 26 cultures grew well, 26 cultures adequately, and only 11 cultures did not grow. Alcohol and ether extracts also gave good results, Filtrates and eluates from charcoal, each gave a small effect, their effect was larger if they were combined.

  Allison and Hoover (1936) noted a positive effect of humic acids on the growth and activity of root-nodule bacteria. They have discovered the presence in humin of a special substance which they called "Factor R" or "Coenzyme."

  Robinson and Endington (1946) found a biotic substance in soils "fluorin." This substance, according to them, is absorbed in considerable amounts by plants.

  Parker-Rodes (1940) found auxins in the soil. The quantity of auxins varied according to the soil properties. In manure-fertilized soils the amount of auxins was 0. 200 µ g/ kg and in poor, nonfertilized soils only 0.06 g/ kg of soil. These substances are found in lesser amounts (0.09-0.106 µ g/ kg) in soils under mineral fertilizers. The soil is enriched in auxins in the course of composting. Sterilized soil contained 0.042 µ g auxins per kg of soil and after 6 days incubation in a glass house, under favorable temperature and humidity conditions, they increased to 0.146 µ g/ kg of soil.

  Williams, Stewart, Kejes and Anderson (1942) found larger quantities of auxins in soils than did Parker-Rodes. According to their data, the A-horizon of fertile soils contains up to 175 µ g auxins per kg of soil, Nonfertile soils contain 40-60 µ g auxins per kg of soil. In horizon B auxins were not detected.

  Hamense (1946) by the use of improved methods of analysis found 100 times more auxins in soils than did previous workers. According to his data the auxin content was 160-450 µ g per kg of soil (Schmidt, 1951, and Hamense, 1946).

  Stewart and Anderson (1942) had shown that the amount of auxins in fertile soils is entirely sufficient for the stimulation of plant growth. Hamense (1946) found in different soils 0.16-0.045 µ g equivalents of ß-indoleacetic acid in 1 g of dry soil. The auxin content increases after the application of organic fertilizers and then falls below the initial level and afterward rises again to the normal level, characteristic of the given soil. According to the author's observations, chemically pure preparations of auxins are not preserved in the soil for long periods.

  According to Matskov (1954), chemical preparations of 2. 4-dichlorophenoxyacetic acid are preserved in the soil for the duration of a whole winter (5-6 months). Another growth stimulant--heteroauxin (ß-indoleacetic acid) is not preserved in the soil that long.

  Auxins were also detected in the soil by Roberts I. and Roberts E. (1939) and some other investigators.

  Beside auxins, soils also contain many other biotic substances such as vitamins, biotin, nicotinic acid, pantothenic acid, folic acid, amino acids, various growth factors R, Z, X, and others, These substances have been found in the following quantities:

  Apart from complete vitamin molecules, molecule fractions are encountered in nature which have the same effect on some organisms as the whole molecules, for example, the pyrimidine, thiazole and others (Lilly and Leonian, 1939).

  We have found vitamins in different soils; as a rule, they were in larger quantities in places where the microbiological processes were more intense. Thus, they appear in chernozems in larger amounts than in podsol soils (Table 37).

  Cultivated soils contain more vitamins than virgin soils.

  The vitamin content of the soil is qualified not only by the extent of cultivation but also by the nature of the vegetative cover. Plants which favor abundant growth of microorganisms, as a rule, assimilate more biotic substances in the soil. In the serozems of Central Asia the highest concentrations of biotic substances were found under 2-3-year-old lucerne, their concentration was lower under cotton and very little was found in virgin soils (Table 38).

  According to Shavlovskii (1954, 1955), soil under potatoes contains 0.5 µ g/kg biotin, and soil under clover--l.3 µ g/kg. In the Lvov Oblast' in serozem forest soils and podsol chernozem the author obtained the data shown in Table 39.

  In soil adjoining the root system there are more biotic substances than outside the rhizosphere. In one kg of soil from the rhizosphere of wheat grown in fertilized fields of the Experimental Station of Dolgoprudnoe (Moscow Oblast') we found per 100 g soil 10 µ g of thiamine, 150 µ g riboflavin, 35 µ g biotin; outside the rhizosphere, 1.2 µ g thiamine, 25 µ g riboflavin, 3 µ g biotin; in the rhizosphere of tobacco, 10-15 µ g thiamine, and outside the root zone 1.5-4.0 µ g per 100 g of soil.

  According to Shavlovskii, the amount of vitamins in the rhizosphere of buckwheat is twice as high as that outside the root zone. On the 20th day of growth he found:

  Higher concentrations of vitamins in the rhizosphere were noted by Roulet (1954). The amount of biotic substances in the upper layer of the soil is higher than in the lower layers. The highest concentrations are found in the upper layer (0-20 cm) (Table 40).

  In some soils a small increase in the concentration of biotic substances is noted at a depth of 60-70 cm.

  Some other investigators have noted the decrease in concentration of vitamins in deep layers of the soil. Roulet and Schopfer (1950) give the following data on the distribution of vitamins according to, layers (per 100 g of soil):

  These authors found thiamine and biotin even at a depth of 2.0 to 8.5 m.

  Lilly and Leonian (1939) found considerable quantities of thiamine and biotin, as well as vitamin B₁ and its components thiazole and pyrimidine, in the soil. They were concentrated in the upper layer of the soil. At a depth of 60 cm they were not detected. West and Wilson (1938, 1939) found thiamine and biotin in the root zone of tobacco and flax.

  According to Schmidt and Starkey (1951), riboflavin can be found in the soil in varying amounts, according to soil fertility, vegetative cover, etc. In soils under forests the authors found 500 µ g of riboflavin and in soils under plow and in fertile soils about 10 µ g per 100 g of soil.

  After the application to the soil of organic fertilizers such as straw, grass or sugar, the amount of riboflavin increased. The more organic substances applied, the higher was the concentration of riboflavin in the soil. For example, after application of grass 15%*, about200 µ g riboflavin were found; if the amount of grass added was 10% 120 µ g riboflavin were found, in the presence of grass of 5% only 60 µ g riboflavin was found. The amounts of riboflavin are given per 100 g of soil (Figure 62). *[The 15% refers to the grass, It is not clear what the percentage refers to.]

Figure 62. The formation of riboflavin in the soil, in the presence of various quantities of organic substances (lucerne grass):

1--15%; 3--5%

 

  By the end of the growth period, in August-October, more vitamins are found in the soil than in the spring. The amount of riboflavin found in spring was 80-300 µ g, in autumn it reached 600-980 µ g per 100 g of soil.

  Roulet (1954) found that the amount of biotin in the upper layer of a botanical garden increases in the autumn and decreases in winter and in spring.

  According to this author, forest and marshy soils contain even more vitamins than garden or meadow soils.

  The amount of biotic substances in the soil constantly changes, according to external conditions such as temperature, humidity, season, etc.

  The vitamins are preserved in the soil for various periods of time, the length of which also depends upon soil and climatic conditions. According to Stewart and Anderson (1942), growth-stimulating substances can persist in dry soil for 3-4 years, According to Schmidt and Starkey, 50% riboflavin can be detected in fresh soil after 3 days, pantothenic acid is completely decomposed in one day.

  Some amino acids can be listed among the growth factors of lower and higher plants. Plants synthesize these amino acids in the same way they synthesize vitamins, but, nevertheless, the addition of small doses of amino acids has a positive effect on the growth of plants.

  Nielsen and Hartelius (1938) tested amino compounds, Six of them--ß-alanine, asparagine, aspartic acid, glutamic acid, lysine and arginine markedly enhanced the growth of lower organisms; ß--alanine had the greatest effect. Five µ g of ß-alanine per 50 ml of medium was sufficient to enhance the growth and increase the yield by 66% dry weight. The maximal stimulation was found at the concentration of 1:100,000. Arginine acts at a dilution of 1:20,000 and lysine at a dilution of 1:4,000. Glutamine exerts a positive effect on the growth of organisms in a dose of 1:1,000. Substances in such doses can be considered as sources of nutrition. Other amino acids such as asparagine and others act at even higher concentrations and cannot be regarded as growth factors but as nutrients.

  The amount of amino acids in soils varies; it depends upon the properties of the latter and upon climatic conditions. The more fertile the soil, the more amino acids it contains. The concentration of amino acids is determined by the rate of their influx into the soil and by the length of time of their preservation.

  This list does not include all the biotic substances of the soil. It should be assumed that the soil, the same as other natural substrates, contains many other substances unknown to us, which act as biocatalysts, enhancing the metabolism of organisms.

  Lochhead and Texton (1940, 1950, 1952) detected activating substances in the soil which were of an unknown nature and could not be replaced by any of the known growth factors. 

  All the diverse biotic substances have their origin in the metabolic activity of plants and microbes.

  Formation of biotic substances by the plants. It was mentioned above that, during their lifetime, the roots of many plants excrete substances which stimulate the growth of organisms, For example, the seeds of broomrape germinate, only in the vicinity of roots of sunflower, flax, corn, soy and some other plants, The root excrements of these plants activate the growth of broomrape sprouts. The activating factor is thermostable and is, not decomposed on boiling and prolonged drying (Bartsinakii, 1935; Beilin, 1941).

  According to Golubinskii (1950), morning glory stimulates the germination of melon seeds. Pollen grains of angiosperms mutually stimulate each other on germination by excreting activating substances (Golubinskii, 1946).

  Timonin (1941) found thiamine and biotin in the root secretions of flax. According to him, these vitamins secreted by the roots, considerably promote the growth and proliferation of microorganisms in the rhizosphere.

  West (1939) found thiamine and bios substances in root secretions of flax and tobacco.

  Meshkov (1952) found biotin and thiamine in root secretions of corn and peas. According to him, the more of these substances are secreted, the more intense is the growth of the plants. Corn secretes more biotin, and peas more thiamine. The root excretions contain vitamins in the following amounts per g dry weight of the plants: corn--0.5402 µ g of thiamine and 0.2308 µ g of biotin; peas--0.6634 µ g of thiamine and 0.2658 µ g biotin.

  According to our observations, peas, wheat, and corn secrete more biotic substances in their early growth period than in the period of fruiting (Table 41).

  Plants grown in aerated solutions secrete more biotic substances than those grown in poorly aerated solutions. For example, wheat grown with good aeration secreted 0.21 µ g thiamine, and wheat grown in the presence of small amounts of oxygen secreted 0.11 µ g thiamine. The respective amounts of biotin secreted were 0.8 and 0.6 µ g (per cm³ of medium).

  There are indications in the literature that germinating seeds of various plants secrete small amounts of vitamins into the medium (Meisel, 1950; Schopfer, 1943).

  Biotic compounds can find their way into the soil together with decomposing residues. It is known that plants contain considerable amounts of various compounds which can stimulate the growth and development of organisms. For example, according to Burcholder and others (1944), the following amounts of thiamine are present in the tissues of: soya 47-61 x 10^-7; barley 28-51.8 x 10^-7; corn 17.6-31.2 x 10^-7 (in mols per kg dry weight). The aerial parts contain more thiamine than the roots: in the leaves of corn were observed 17.6-30. 2 x 10^-7; and in the roots--4.06-9.78 x 10^-7 mols per 1 kg of dry mass.

  Auxins, vitamins of the B-group, bios, vitamins, D, K, C, H and P, pantothenic acid, paraaminobenzoic acid, nicotinic acid, purine derivatives and various hormones, etc, have been found in plants (Zeding, 1955; Ovcharov, 1955, and others.

  Many biotic substances are excreted in the feces of animals and human beings. For example, human beings excrete daily in urine 60 µ g of thiamine, 600 µ g riboflavin, 626 µ g inositol and large quantities of pantothenic acid, as well as other compounds (Meisel, 1950). Vitamins of the B-group, pantothenic acid, nicotinic acid, folic acid, and other substances are found in the faces of human beings and animals. The investigations show that these substances are synthesized by the microflora of the intestines (Perets, Gryazno and Agibalova, 1948; Nepomnyashchaya, 1950; Najjar and others, 1943-1950; Perets, 1955), The vitamins and other substances enter the soil with manure. According to Bonner and others (1938), 1kg of manure contains 130 µ g thiamine. Riboflavin, pantothenic acid, nicotinic acid, and other activating substances are present in manure. Sauerland (1948) found considerable amounts of substances of the bios type in manure, feces and urine of cattle, The quantities of these substances fluctuate with the seasons. The largest amounts being found in summer, less in winter. The amount of growth factors in manure and animal feces also varies according to the quality of the fodder.

  All these substances accidentally find their way into the soil, and on the whole they constitute only a small traction of the total amount of biotic substances in the soil. The microorganisms are the main factor in the enrichment of the soil with these substances. 

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