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Part III, continued:

  Numerous observations and the results of accurate laboratory experiments have proved the positive effect of humus on the growth and metabolism of plants.

  Bottomley and his co-workers (1914) grew duckweed Lemna minor L., In the nutrient solution of Knopp supplemented with small doses of aqueous extracts of well-composed peat. He obtained the following results: after 35 days 30 individuals grew from the 10 originally in the solution, in the absence of humus; in the presence of humus 132 individuals grew in the same time. Those which grew in the presence of organic substances were much bigger and their green color was more intense. Their dry weight was 50.5 mg per 100 individuals, while the dry weight of the same number of control plants was only 29.4 mg. In his later experiments Bottomley (1920) showed that the peat extract has a positive effect also on some other plants such as Lemna minor L., Salvinia natans All., Limnobium stolonifer L. The yield of dry mass, when they were grown in the presence of peat extract, was higher than in the controls.

  Peat, after processing with microorganisms, stimulated the growth of plants more markedly than did the uncomposted natural peat. On this basis, Bottomley prepared a special fertilizer--humogen. This preparation gave positive results under laboratory conditions as well as under field conditions. It was patented and recommended for use in agriculture for various plants. According to the prescription in the patent, peptone was added to the peat to enhance the growth and metabolism of microorganisms. For a more rapid decomposition of the organic part of peat, Azotobacter, Rhizobium, and other bacteria were added. The inoculated peat was kept at a temperature of 25° C for 3-4 weeks. Afterward the preparation was ready for use.

  Mockeridge (1917, 1924) repeated the experiments of Bottomley and fully confirmed his data, She added extracts of composted and noncomposted peat to the nutrient solution and grew the duckweed. After 9 weeks, out of 10 individuals, 249 plants grew in the control, 3,134 in the presence of the processed peat, and 1,080 in the presence of nonprocessed peat. The dry weight of the duckweed was 6.5 mg in the control and 19.5 mg in the presence of peat humus.

  In our experiments we have employed well-processed composts prepared from various plant residues such as straw of Euagropyrum, wheat, oats, lucerne hay, and also from well-processed manure. The concentrated aqueous extracts from these composts and from manure were added to the nutrient mineral solution in quantities of 5-10 drops per 100 ml of the medium, which amounts to 0.005-0.01 mg of the dry substance. This nutrient solution was employed by us as a substrate for the growth of Lemna minor as well as for the fertilization of the sandy substrate in which we grew cereals and legumes.

  Lemna minor L. was grown under sterile conditions in glass vessels placed in the window of the laboratory. In the control vessels the medium did not contain the above-mentioned extracts. The crop was counted after 85 days. The number of individuals grown was counted and their dry weight was determined. Plants were chosen which were similar in their appearance. The results of these experiments are given in Table 30.

  As can be seen from these data, plants (Lemna minor) grow much better in containers with the organic substance. The plants were bigger, more intensely colored and their root system better developed.

  Different composts have different effect on the growth of Lemna minor. The greatest effect was obtained by the use of the compost of Euagropyrum and dungwash. The plants grown on them were the most developed. The extract of oatstraw compost favored the growth of the plants in numbers similar to those obtained with the extract of dungwash, but their size was smaller. The least effect was obtained when the compost of wheat straw was employed.

  Voelcker (1915) tested the effect of the Bottomley's preparation in vegetation containers and under field conditions, on peas, oats and on buckwheat. The greatest crop increment was obtained in the case of buckwheat, it amounted to 407%; the effect on oat was weaker, the crop increment of the latter was 131%. In the experiments with peas, increment in the green mass only was observed; this amounted to 231%. The yield of grain, on the contrary, was less (87%) than in the control (100%). Similar data were obtained by Clark and Roller (1924). This plant grew much less in a nutrient medium under sterile conditions than in the presence of humus. The most abundant growth of duckweed was observed in vessels containing manure and composted peat. The extract of lucerne compost had the smallest effect. These authors had found (1931) that composts are more effective when contaminated with bacteria than when sterile.

  Aschby (1929) points out that organic substances of the processed plant residues, though not indispensable for the growth of plants (Lemna minor L.), none the less have a considerable effect on their growth. Saeger (1925) introduced a mineral solution of alkaline extract of humus into the nutrient medium of growing duckweeds. The yield was twice as high as in the control. He found that the action of humus and yeast extract on the growth of plants was equal.

  Hillitzer (1932) on the grounds of his experiments and the analysis of the available data concluded that humus of the soil and composts stimulate the growth of plants. The components of humus act specifically on the root system enhancing its growth.

  Olsen (1930) performed a whole series of experiments on the growth of duckweed and sunflower in the presence and absence of composts in the nutrient medium. By his experiments he confirmed the results of Bottomley and Voelker. In the presence of small amounts of humus (aqueous extracts of processed peat) the duckweed as well as the sunflower grew considerably better than in their absence. The nutrient medium employed by him was the solution of Dettmer. The dry weight of the duckweed grown in the presence of humus was 482 mg and in the control vessel 189 mg; the weight of the sunflower in the presence of humus--1.33 g and in the control vessel--0.80 g. In the presence of iron citrate the positive action of humus was smaller or nonexistent (according to the author). On the basis of this observation he assumes that the acting principle in humus and in composts are some forms of iron compounds.

  Our experiments in raising agricultural crops with the above-mentioned composts yielded similar positive results. We have grown wheat, rye, rye grams and clover on pure quartz sand, wetted with the mineral nutrient solution in the presence and absence of aqueous extracts from composts. The amounts of compost added were the same as in the experiments with duckweed,

  The experiments were carried out under sterile conditions. The plants were grown for 20-40 days, plucked out together with their roots and analyzed. Their total weight, height and general appearance were noted. The most spectacular results were obtained with wheat and rye grass (Table 31 ).

  As can be seen from the table the positive effect of Eumgropyrum compost and of manure an the growth of rye grams and wheat was of the same magnitude. All the plants have greater mass when grown in the presence of organic substances than in control vessels. The greatest mass increment was obtained in cereals, clover reacted less to the introduction of organic compounds,

  In the second series of experiments we tested the effect of well-processed manure and fresh straw. One and a half g of the manure and 20 g of straw together with the nutrient solution of Knopp were applied per kg of sand substratum, The experiments were performed under sterile conditions. Wheat, oats and peas were grown. The results obtained in the presence of manure were similar to those in the previous experiment. In the presence of humus the yield of oats was 35% higher, wheat 25% higher and peas (fresh weight) 42% higher. In the presence of extracts of fresh straw the crop was similar to that in the control vessels.

  In one series of experiments we compared the effect of aqueous extracts of fresh straw of Euagropyrum and an extract of composted straw of the same plant on the growth of rye grass. The dry weight of the plants in the control vessels (without the organic fertilizer) was 0.5 g and in the presence of the extract from fresh straw 0.7 g, and in the presence of composted Euagropyrum 1.1 g.

  In experiments with pine-tree saplings it was found that small amounts of Euagropyrum compost markedly stimulated the growth of the experimental plants. The latter grow higher than the controls, their stems were thicker, their needles longer and of a brighter color (Figure 61) Krasil'nikov and Raznitsyna, 1946, Raznitsyna, 1942).

  Chester and Street (1948) grew lettuce in sand in a full nutrient solution with and without the addition of organic substances, Extracts of soil humus, aqueous extracts of casein, and yeast hydrolysates were tested. All solutions contained 6.05 mg N per 10 m3 of the medium. The plant yields were as follows:

  Control (in the absence of organic compounts); dry weight (in gm) 0.157
  With the admixture of soil humus; dry weight (in gm) 0.199
  With the admixture of casein hydrolsate; dry weight (in gm) 0.158
  With the admixture of yeast extract; dry weight (in gm) 0.172

Figure 61. The stimulating effect of Euagropyrum compost on the growth of pine-tree seedlings

 

  Swaby (1942) did not obtain in his experiments an increment in the yield of legumes grown in the presence of organic compounds, but he noted the stimulating effect of microbes when the experiments were carried out under nonsterile conditions.

  According to Schaffnit and Neumann (1953), composted peat had a stimulating effect on the growth of potatoes and one the germination of lucerne seeds. They have ascribed the stimulating effect to the action of microorganism which grew abundantly in those composts.

  Andreyuk (1954) studied the effect of specially prepared composts of peat on the growth of grain cultures. The composts were prepared from peat, 25-50 % (by weight) manure and 1.5-2.0% phosphate flour. Then they were incubated under laboratory conditions or in the field for 4-7 months and longer. In some experiments Azotobacter, cellulose bacteria and other bacteria were introduced. The yield of winter rye in the presence of these composts was 2-2.5 times higher, and the crop of oats was 1.7-3 centners per hectare greater than in the control (5.3 centners).

  Many other authors have noted the positive effect of small doses of humus (Nikishkina, 1948; Logvinova, 1939; Street, 1950, and others). The detailed studies of Khristeva (1948) had shown that solutions of humic acids exert a direct effect on higher plants. In negligibly small concentrations (0.001 % and 0.0001%) they enhanced growth and increased the yield of wheat, oats, barley, sugar beet, tomatoes and other plants. Of the tested plants, potatoes, tomatoes, and sugar beet gave the best reaction to the application of humus. Good reaction of wheat, barley, oats, millet, corn, rice, buckwheat, Euagropyrum, and lucerne was noted. Humus had a small effect on peas, mung bean,, beans, lentiles, peanut, cotton, and sesame and hardly any effect on sunflower, castor-oil plant, pumpkin, hibiscus, etc. The greatest increment in plant crops under the influence of humus substances exceeds that obtained by application of equivalent amounts of mineral fertilizers by about 10-50 %. The action of humic fertilizers was tested by the author in different soils such as podsols, serozems, chernozems, chestnut soils, and others, In all cases the effect was positive.

  According to Khristeva, humic substances find their way, in small amounts, into plants, there stimulate the phenol-oxidase system, and participate in the general metabolism of the plant. The physiological function of humic substances, is in the promotion of plant respiration. As a result. an increased influx of nutrients, activation of synthetic processes, and better growth of the root and aerial parts takes place.

  The strongest reaction to the humic substances is observed in young plants. The root weight and, consequently, the growth of the whole plant is increased.

  Kock (1955), stressing the positive effect of humus substances on plants, explains it by the action of iron which is present in humus, This, however, was not confirmed by the studies of other investigators.

  Tovarnitskii and Rivking (1937), Tovarnitskii and Statkovskaya (1938), Thiman, Lane and others (1933, 1939) employed urine and yeast extracts for presowing processing of oats, wheat, and other plants in order to stimulate their growth.

  In southern Italy urine of cattle is widely used for presowing processing of the seeds of cereals (Zeding, 1955). Virtanen and Hausen (1933-1934) added yeast extract to aqueous and sandy cultures of peas. Flowering occurred 5-10 days earlier and the crop was 50 % higher than in the control plants. These authors also observed that such effect could not be obtained by growing the plants in soil rich in humus. This could be explained by the fact that in soils rich in humus there is a large amount of biotic substances.

  A large amount of material on bacterial fertilizers should be added to the data given in this chapter. The practice of employing bacteria-containing fertilizers gives, in many cases, certain positive results. The addition of peat "azotogen" brings about a 10-25 % increment in crops, this increment may in some cases be even higher.

  The bacterial preparations used as fertilizers under the name of "azotogen" are extensively employed in our country. They are prepared from cultures of Azotobacter on crumbs of peat. The selected peat must be of an appropriate quality. It must not be acidic and should be well processed. During the production of the preparation, easily assimilated sources of nutrition are added. These are sugars, alcohol, beet juice, etc. The Azotobacter--inoculated peat is incubated at optimal temperature and humidity; it is frequently mixed to ensure better aeration.

  The incubation lasts 10- 20 days. During this time the peat is well composted. Not only Azotobacter, but also many other bacteria, fungi and actinomycetes, grow abundantly in the peat mass.

  The number of nonsporeforming bacteria at the time of their maximal growth in a good preparation reaches several billion cells per gram. The number of Azotobacter amounts to 100-200 million per gram (Table 32).

  As can be seen from the table, peat composted whether in the presence or in the absence of Azotobacter contains the same number of microbes. Their total number considerably exceeds that of the initial peat.

  The group composition of the compost microflora varies with the increase of the maturity of the compost. In the first days of incubation the nonsporeforming bacteria of the genera Bacterium and Pseudomonas, and fungi, grow abundantly. The fungi grow only on the surface. Mycobacteria can be detected in large numbers in the composted peat. At the end of the incubation (maturation) of the preparation, the bacteria and fungi decrease in number, their place being taken by actinomycetes. The latter attain such vast numbers that the peat lumps are covered with them. This covering is of a white flour color and is visible with the naked eye. The maturing of the compost can be judged by the intensity of growth of the actinomycetes.

  Analyses show that this consecutive development and change of microflora is observed in approximately the same quantitative relations in peat composted without Azotobacter. The introduction of the latter, however, may cause a change in the composition of the species of the nonsporeforming bacteria, but it can be marked only in certain species. The general group composition is not changed.

  Trials of peat (noncomposted, or composted in the presence or in the absence of bacteria) were carried out by us in pots and in fields during a number of years. Different plants--grains and cultivated crops were involved. The general character of the efficacy of these preparations under field conditions is given in Table 33.

  As can be seen from the table the pure culture of Azotobacter (collection strain. No 54) is less effective than the peat azotogen. Peat composted without Azotobacter produces approximately the same yield increment as the azotogen prepared from peat. An already mentioned, noncomposted peat is less effective than composted peat.

  We obtained similar data in experiments carried out under various conditions in podsol soils of fields near Moscow and in the serozems of Kirgiz SSR and Tadzhik SSR (Vakhsh valley). In the majority of cases azotogen prepared on peat, and well-composted peat with Azotobacter gave similar plant-yield increments.

  In a number of cases bacterialized composts were, more effective than those prepared without bacteria (Table 34).

  Many investigators assume that the favorable effect of humus, manure and composts in caused by their ash content, of which nitrogen is the constituent of greatest importance. The latter, according to these investigators determines the efficacy of compost mass and humus of the soil. The higher the nitrogen content in the compost the more it is effective. According to the adherents of this point of view, after the mineralization of the organic compounds the nitrogenous substances are transformed into inorganic substances and so become available to plants.

  According to our observations and the available data in literature, the active principles of humus and composts are not the mineral nutrients present in them but the organic substances and the biologically active metabolites of microbes. Mineral substances applied in amounts equivalent to the composts do not have an effect comparable to the latter.

  Mineral elements obtained by burning manure, composted peat or soil humus do not produce an effect comparable to that obtained by the application of organic substances. We have carried out experiments with duckweed in nutrient solutions, supplemented with small quantities of extracts prepared from manure, compost and humus. In other experiments ash was added to the nutrient solution. The ash was obtained by burning equivalent amounts of these substances. The results are given in Table 35.

  Lochhead and Thexton (1952) obtained similar results. According to their data, the ash obtained from composts have a smaller effect on the growth of microbes than the composts themselves.

  All this speaks in favor of the assumption that the observed stimulation of plant growth by humus is caused, not by its mineral fraction, but by other substances. 

  Vegetative composts, manure, and humic substances not only activate plant growth and increase their yields but also improve their nutrient value which in a matter of great importance. Plants grown in fields fertilized with manure are richer in vitamins and other valuable substances than those grown in nonfertilized fields. McCarrison (1926) found that seeds of millet and wheat, harvested from fertilized fields, contain more vitamins than seeds from fields under mineral fertilizers. Animals, fed on fodder from fields fertilized with manure, were more resistent to infections. and their appearance was healthier than those fed on fodder from nonfertilized fields.

  Roulands and Wilkenson (1930) determined vitamins of the B-complex in the hay of clover grown in fertilized and nonfertilized fields. In the former case the clover contained more vitamins. Rats fed on clover from fertilized fields gained weight more rapidly than those fed on clover from nonfertilized fields. In the 30 days of the experiment the first gained 110 g and the latter 60 g.

  Clark (1935) found more vitamin B and C in cultures of duckweed grown in nutrient solution supplemented with humus, than in a similar culture grown without humus.

  Nath and co-workers (1927, 1932) have shown that organic substances of manure and composts, as well as cod-liver oil and some other substances, enhance the growth of plants and increase their vitamin content. Cereal seeds grown on fertilized fields have a greater viability and the percentage germination is higher than in seeds from fields fertilized with mineral fertilizers.

  According to Graff (1928) timothy grass, fescue and meadow grass (Phleum pratense L., Festuca rubra L., F. pratensis Huds. and Poa. pretensis L.) contained more vitamins of the B-group when grown in soil fertilized with urea than when grown in soil to which mineral fertilizers had been applied.

  Antoniani and Monzini (1950) analyzed plants which grew in fields irrigated with sewage waters, and plants which grew in fields irrigated with water supplemented with mineral nutrient salts. The vitamin B₁ content was greater in the former plants.

  Leong (1939) compared the effect of manure and mineral fertilizers on the vitamin B₁ content of wheat and barley tissues. The vitamin B₁ content of wheat was similar in both cases; barley, however, contained twice as much vitamins when grown in the presence of manure than in the presence of full mineral fertilizer (Table 36).

  Hurni (1944, 1945) grew plants in sand in the presence of a full mineral fertilizer and found that in these conditions the formation of thiamine was less than during growth in the presence of humus substrate.

  In Lebedev's experiments (1953), lucerne grown in fields fertilized with manure or composts, contained 81 mg/kg carotene during the period of bud formation, while plants from nonfertilized fields contained only 27 mg/kg.

  Ott (1937) noticed an increase in vitamin content of plants grown in fields fertilized with a mixture of organic and mineral fertilizers.

  Hammer and Maynard (1942), summarizing the literature, noted that the vitamin content of plants varies in accordance with the soil and climatic conditions, season, age of plants, etc. They ascribed the greatest importance to the nutrient value of the soil and especially to the presence of humus and fertilizers in general.

  At the present time the majority of investigators concentrate their attention on mineral sources of nutrition as the factors affecting the vitamin content of plants. Vitamins A, C, B₁ and B₂ were determined in the tissues of many plants (leguminous and cereal) grown in fields fertilized with various salts of potassium, phosphorus, and nitrogen (Scheunert and Wagner, 1938; Scharer and Preissner, 1954, and others).

  After the application to the soil of a full mineral fertilizer, black currant gave a berry yield of 5,158 kg/hectare (Stepanova, 1950). Their total vitamin C content was 1,827 mg/kg. The berry yield without fertilizers was 3,199 kg/hectare and the vitamin content was 1,599 mg/kg. According to Dyakova (1945), application of one portion of nitrogen increased the carotene content of oats from 10 to 28 mg and an application of triple nitrogen increased the carotene content from 10 to 53 mg (in the stalk-formation state). The application of calcium to the soil also increased the carotene content of plants. Lack of calcium in the soil decreases the synthesis of thiamine in tobacco plants (Ovcharov, 1955).

  Some authors studied the variation of vitamin content in plants in connection with the application of microelements to the soil. Mc Harque (1924) noted a positive effect of manganese on the accumulation of vitamin B1 in the seeds of wheat, rice, tomatoes, and citrus fruits. Hammer (1945) gives data on the effect of microelements on the formation and accumulation of ascorbic acid and carotene in plants.

  Scharer and Preissner (1954), on the basis of their experiments, reached the conclusion that the more complete the mixture of fertilizer employed, the higher the vitamin content of the plants. The amount of vitamins does not always correspond to the weight index of the crop yield. It is not infrequently observed that the vitamin content is high at relatively low crop yields. For example in an average barley crop of 4.3 g* the vitamin B₁ was 440 µ g and in a crop of 11.93g-39 0 µ g per 100 of the grain. *[The unit used is not clear in the Russian; it probably refers to an arbitrary yield index.]

  Considerable increase in the vitamin B₁ content of plants was observed in the experiments in which granulated phosphorus was applied. In a weakly acidic loamy soil the following results were obtained: control--grain yield 7.12 g, vitamin content--558.7 µ g /100 g; after the application of N, K and superphosphate the crop yield was 24.5 g and the vitamin content was 798 µ g /100 g of grain,

  The greatest accumulation of vitamins was noted in leguminous plants, This could be explained by the presence of root-nodule bacteria. The latter growing in the root tissue, form vitamins which find their way from the nodules into the plant.

  Schounert and Wagner (10939, 1940) studied the vitamin B₁ and B₂ content in the seeds of barley and rye, grown in fields which were fertilized for many years as well as in fields with no fertilizer at all, Comparison of the analyses did not show any marked difference in the vitamin content of plants grown in fertilized and nonfertilized fields.

  The lack of any effect of mineral or even organic fertilizers was also noted by several other investigators (Hornemann, 1925; Harris, 1934), These authors did not give an explanation. It should be assumed that their experiments were carried out under conditions unfavorable for the synthesis of vitamins.

  Data exist which show variations in amino-acid composition of plant tissues in the presence of different fertilizers. According to Sheldon, Blue and Albrecht (1948), lucerne and some other plants grown on fertilized fields, have a different quantitative and qualitative amino-acid composition than those plants grown in nonfertilized fields. The highest amino-acid content was found in plants grown with manure,

  It should be noted that the majority of investigators studying the effect of mineral fertilizers on the plant vitamin content did not take into account the microflora, and especially that which inhabits the rhizosphere.

  Mineral and organic fertilizers are known to have a great effect on the life of microbes in the soil. The latter grow and synthesize various biologically active substances including vitamins. For example, in many soils, phosphates and nitrates are known to considerably increase the growth and accumulation of bacteria, fungi and actinomycetes. Azotobacter, root-nodule bacteria, certain species of the genus Pseudomonas and other forms of microbes grow well around lumps of superphosphate.

  The material presented by us shows that animal and plant residues and organic substances in general have a favorable effect only after their decomposition and processing by microorganisms, i.e., after they have been transformed into humus. The active substances of humus are not the animal or plant residues but the products of microbial metabolism, the products of secondary synthesis.

  We assume that the active principles of composts, manure, and of humus in general are not the mineral elements of nutrition or more strictly, not so much they, as some special compounds of an organic character. These compounds vary in their nature and comprise a special group of the so-called biotic substances. 

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