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Part III, continued:

The effect of humus on the growth of plants

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

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

  Peat, after processing with microorganisms, stimulated the growthof plants more markedly than did the uncomposted natural peat. On this basis, Bottomleyprepared a special fertilizer--humogen. This preparation gave positive results underlaboratory conditions as well as under field conditions. It was patented and recommendedfor 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 andfully confirmed his data, She added extracts of composted and noncomposted peat tothe 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, and1,080 in the presence of nonprocessed peat. The dry weight of the duckweed was 6.5mg in the control and 19.5 mg in the presence of peat humus.

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

  Lemna minor L. was grown under sterile conditions in glassvessels placed in the window of the laboratory. In the control vessels the mediumdid 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 experimentsare given in Table 30.

Table 30
The effect of plant composts on the growth of
(after 85 days)

Composts

Number of specimens in the vessel

Dry weight (mg) total

Dry weight (mg) of 100 plants

Control (without humus)

180

29

16

Compost of Euagropyrum

2,500

800

32

Compost of wheat

1,200

324

27

Compost of oats

1,800

540

30

Compost of clover

2,200

726

33

Dungwash

1,800

540

30

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

  Different composts have different effect on the growth of Lemnaminor. The greatest effect was obtained by the use of the compost of Euagropyrumand dungwash. The plants grown on them were the most developed. The extract of oatstrawcompost favored the growth of the plants in numbers similar to those obtained withthe extract of dungwash, but their size was smaller. The least effect was obtainedwhen the compost of wheat straw was employed.

  Voelcker (1915) tested the effect of the Bottomley's preparation invegetation containers and under field conditions, on peas, oats and on buckwheat.The greatest crop increment was obtained in the case of buckwheat, it amounted to407%; the effect on oat was weaker, the crop increment of the latter was 131%. Inthe experiments with peas, increment in the green mass only was observed; this amountedto 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 muchless 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 andcomposted peat. The extract of lucerne compost had the smallest effect. These authorshad found (1931) that composts are more effective when contaminated with bacteriathan when sterile.

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

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

  Olsen (1930) performed a whole series of experiments on the growthof duckweed and sunflower in the presence and absence of composts in the nutrientmedium. By his experiments he confirmed the results of Bottomley and Voelker. Inthe presence of small amounts of humus (aqueous extracts of processed peat) the duckweedas well as the sunflower grew considerably better than in their absence. The nutrientmedium employed by him was the solution of Dettmer. The dry weight of the duckweedgrown in the presence of humus was 482 mg and in the control vessel 189 mg; the weightof the sunflower in the presence of humus--1.33 g and in the control vessel--0.80g. 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 actingprinciple in humus and in composts are some forms of iron compounds.

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

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

Table 31
The effect of humus an the growth of plants
(dry weight in g)

Composts

Wheat: height of plant in cm

Wheat: weight of plant in gm

Rye grass: height of plant in cm

Rye grass: weight of plant in gm.

Control (without organic compounds)

14.9

0.95

10.2

0.64

Euagropyrum compost

18.5

1.63

12.6

0.98

Manure

17.1

1.52

12.1

0.71

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

  In the second series of experiments we tested the effect of well-processedmanure and fresh straw. One and a half g of the manure and 20 g of straw togetherwith the nutrient solution of Knopp were applied per kg of sand substratum, The experimentswere performed under sterile conditions. Wheat, oats and peas were grown. The resultsobtained 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 wassimilar to that in the control vessels.

  In one series of experiments we compared the effect of aqueous extractsof fresh straw of Euagropyrum and an extract of composted straw of the same planton the growth of rye grass. The dry weight of the plants in the control vessels (withoutthe organic fertilizer) was 0.5 g and in the presence of the extract from fresh straw0.7 g, and in the presence of composted Euagropyrum 1.1 g.

  In experiments with pine-tree saplings it was found that small amountsof Euagropyrum compost markedly stimulated the growth of the experimental plants.The latter grow higher than the controls, their stems were thicker, their needleslonger 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 nutrientsolution with and without the addition of organic substances, Extracts of soil humus,aqueous extracts of casein, and yeast hydrolysates were tested. All solutions contained6.05 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 theyield of legumes grown in the presence of organic compounds, but he noted the stimulatingeffect of microbes when the experiments were carried out under nonsterile conditions.

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

  Andreyuk (1954) studied the effect of specially prepared compostsof 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 underlaboratory conditions or in the field for 4-7 months and longer. In some experimentsAzotobacter, cellulose bacteria and other bacteria were introduced. The yieldof winter rye in the presence of these composts was 2-2.5 times higher, and the cropof 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 ofhumus (Nikishkina, 1948; Logvinova, 1939; Street, 1950, and others). The detailedstudies of Khristeva (1948) had shown that solutions of humic acids exert a directeffect 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 beetgave the best reaction to the application of humus. Good reaction of wheat, barley,oats, millet, corn, rice, buckwheat, Euagropyrum, and lucerne was noted. Humus hada small effect on peas, mung bean,, beans, lentiles, peanut, cotton, and sesame andhardly any effect on sunflower, castor-oil plant, pumpkin, hibiscus, etc. The greatestincrement in plant crops under the influence of humus substances exceeds that obtainedby application of equivalent amounts of mineral fertilizers by about 10-50 %. Theaction 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 smallamounts, into plants, there stimulate the phenol-oxidase system, and participatein 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 partstakes place.

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

  Kock (1955), stressing the positive effect of humus substances onplants, 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 presowingprocessing of oats, wheat, and other plants in order to stimulate their growth.

  In southern Italy urine of cattle is widely used for presowing processingof the seeds of cereals (Zeding, 1955). Virtanen and Hausen (1933-1934) added yeastextract to aqueous and sandy cultures of peas. Flowering occurred 5-10 days earlierand the crop was 50 % higher than in the control plants. These authors also observedthat 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 largeamount of biotic substances.

  A large amount of material on bacterial fertilizers should be addedto the data given in this chapter. The practice of employing bacteria-containingfertilizers gives, in many cases, certain positive results. The addition of peat"azotogen" brings about a 10-25 % increment in crops, this increment mayin 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 Azotobacteron crumbs of peat. The selected peat must be of an appropriate quality. It must notbe acidic and should be well processed. During the production of the preparation,easily assimilated sources of nutrition are added. These are sugars, alcohol, beetjuice, etc. The Azotobacter--inoculated peat is incubated at optimal temperatureand humidity; it is frequently mixed to ensure better aeration.

  The incubation lasts 10- 20 days. During this time the peat is wellcomposted. 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 maximalgrowth in a good preparation reaches several billion cells per gram. The number ofAzotobacter amounts to 100-200 million per gram (Table 32).

Table 32
The quantitative composition of the microflora in peat azotogen
(number of cells, in thousands per g, in the period of maximal accumulation)

Preparation

Bacteria, sporeformers

Bacteria, non-sporeformers

Myco- bacteria

Actino-
mycetes

Fungi

Noncomposted peat

100

40,000

1,000

1,500

750

Peat composted without Azotobacter

1,500

5,500,000

1,000,000

3,500,000

150,000

Peat composted with Azotobacter

1,700

7,500,000

1,500,000

3,200,000

250,000

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

  The group composition of the compost microflora varies with the increaseof the maturity of the compost. In the first days of incubation the nonsporeformingbacteria of the genera Bacterium and Pseudomonas, and fungi, grow abundantly.The fungi grow only on the surface. Mycobacteria can be detected in large numbersin 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. Thiscovering is of a white flour color and is visible with the naked eye. The maturingof the compost can be judged by the intensity of growth of the actinomycetes.

  Analyses show that this consecutive development and change of microflorais observed in approximately the same quantitative relations in peat composted withoutAzotobacter. The introduction of the latter, however, may cause a change inthe composition of the species of the nonsporeforming bacteria, but it can be markedonly in certain species. The general group composition is not changed.

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

Table 33
Comparison of the action of fertilizing preparations on plant yields

Bacterial inocculation of the preparation

Corn: centner per hectare

Corn: %

Potatoes: center per hectare

Potatoes: %

Beets: centner per hectare

Beets: %

Wheat: centner per hectare

Wheat: %

Control

32.0

100.0

230

100

559

100

--

--

Azotobacter strain 54

33.9

106.0

255

110.8

610

109

--

--

Peat azotogen

37.1

116.0

261

113.7

649

116

--

--

Composted peat

36.7

114.7

263

114.3

639

114

--

--

Noncomposted peat

34.1

108.7

254

110.4

615

110

--

--

  As can be seen from the table the pure culture of Azotobacter(collection strain. No 54) is less effective than the peat azotogen. Peat compostedwithout Azotobacter produces approximately the same yield increment as theazotogen prepared from peat. An already mentioned, noncomposted peat is less effectivethan composted peat.

  We obtained similar data in experiments carried out under variousconditions in podsol soils of fields near Moscow and in the serozems of Kirgiz SSRand 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 thanthose prepared without bacteria (Table 34).

Table 34
The growth of duckweed in water culture in the presence of small amounts of peat compost inoculated with bacteria

Conditions of experiments

Total samples

Dry weight: 100 samples in mg

Control (without compost)

106

26

Compost not inoculated by bacteria

450

37

Compost inoculated by bacteria:

 

 

Az. chroococcum

510

39

Ps. flourescens No. 14

580

38

Ps. flourescens No. 15

85

27

  Many investigators assume that the favorable effect of humus, manureand composts in caused by their ash content, of which nitrogen is the constituentof greatest importance. The latter, according to these investigators determines theefficacy of compost mass and humus of the soil. The higher the nitrogen content inthe compost the more it is effective. According to the adherents of this point ofview, after the mineralization of the organic compounds the nitrogenous substancesare 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 presentin 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 effectcomparable to the latter.

  Mineral elements obtained by burning manure, composted peat or soilhumus do not produce an effect comparable to that obtained by the application oforganic substances. We have carried out experiments with duckweed in nutrient solutions,supplemented with small quantities of extracts prepared from manure, compost andhumus. In other experiments ash was added to the nutrient solution. The ash was obtainedby burning equivalent amounts of these substances. The results are given in Table35.

Table 35
Effect of humus ash on growth of Lemna minor L.
(on the 50th day of growth)

Experiment

The number of specimens in the vessel

Dry weight of 100 specimens, mg

Control

750

27

Manaure

1,800

39

Ash of the manure

850

33

Peat composted with bacteria

1,150

40

Ash

900

31

Soil humus

1,100

33

Burned soil

700

29

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

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

The effect of humus on the vitamin content of plants

  Vegetative composts, manure, and humic substances not only activateplant growth and increase their yields but also improve their nutrient value whichin a matter of great importance. Plants grown in fields fertilized with manure arericher in vitamins and other valuable substances than those grown in nonfertilizedfields. McCarrison (1926) found that seeds of millet and wheat, harvested from fertilizedfields, 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-complexin the hay of clover grown in fertilized and nonfertilized fields. In the formercase the clover contained more vitamins. Rats fed on clover from fertilized fieldsgained weight more rapidly than those fed on clover from nonfertilized fields. Inthe 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 grownin nutrient solution supplemented with humus, than in a similar culture grown withouthumus.

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

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

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

  Leong (1939) compared the effect of manure and mineral fertilizerson the vitamin B1 content of wheat and barley tissues. The vitamin B1content of wheat was similar in both cases; barley, however, contained twice as muchvitamins when grown in the presence of manure than in the presence of full mineralfertilizer (Table 36).

Table 36
The vitamin B1 content in plants in relation to fertilization
(µg per 1g of plant mass)

Fertilizer

Wheat

Barley

Without fertilizer (control)

1.0

1.1

Manure

1.2

2.0

Full mineral fertilizer P, K, Mg, NO3

1.2

1.1

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

  In Lebedev's experiments (1953), lucerne grown in fields fertilizedwith 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 grownin fields fertilized with a mixture of organic and mineral fertilizers.

  Hammer and Maynard (1942), summarizing the literature, noted thatthe 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 nutrientvalue of the soil and especially to the presence of humus and fertilizers in general.

  At the present time the majority of investigators concentrate theirattention on mineral sources of nutrition as the factors affecting the vitamin contentof plants. Vitamins A, C, B1 and B2 were determined in thetissues of many plants (leguminous and cereal) grown in fields fertilized with varioussalts of potassium, phosphorus, and nitrogen (Scheunert and Wagner, 1938; Scharerand Preissner, 1954, and others).

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

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

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

  Considerable increase in the vitamin B1 content of plantswas observed in the experiments in which granulated phosphorus was applied. In aweakly acidic loamy soil the following results were obtained: control--grain yield7.12 g, vitamin content--558.7 µ g /100 g; after the application of N, K andsuperphosphate 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 growingin the root tissue, form vitamins which find their way from the nodules into theplant.

  Schounert and Wagner (10939, 1940) studied the vitamin B1and B2 content in the seeds of barley and rye, grown in fields which werefertilized for many years as well as in fields with no fertilizer at all, Comparisonof the analyses did not show any marked difference in the vitamin content of plantsgrown in fertilized and nonfertilized fields.

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

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

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

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

  The material presented by us shows that animal and plant residuesand organic substances in general have a favorable effect only after their decompositionand 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 productsof microbial metabolism, the products of secondary synthesis.

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



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