INTRODUCTION

Soil science rapidly evolved in the beginning of the 20th century, and there were developments in soil physics, pedology, soil microbiology and soil chemistry. Soil chemistry as a separate branch of agricultural chemistry focused on the development of plant nutrition, nutrient retention of soil, the application of mineral fertilizers and amelioration. The head of the Department of Soil Science of the Imperial Forestry Institute in Saint Petersburg, Piotr Kossovich (1862–1915), founded the chemical branch of soil science in Russia. Kossovich defined soil as the surface layers of rocks in which physicochemical processes take place under the influence of the atmosphere, flora and fauna. Soil forming factors, according to Kossovich, included: 1) rocks, 2) input of substances to the soil, 3) removing substances from the soil, 4) climate, 5) relief, 6) vegetation, and 7) animals. As a physiologist, he studied plant nutrition, using the vegetative method, which at that time had just begun to develop in Russia. His major contribution was in the study of physico-chemical processes — eluviation and illuviation of various substances in the soil. Konstantin Gedroiz was the most important follower of the school of Kossovich.

Gedroiz devoted his scientific work to soil chemical analysis, the study of soil absorption capacities and, based on this, the development of new practices to improve soils used for agriculture. In 1922, he introduced the idea of the “soil absorption complex”, which defined the ability of soil to absorb various substances. He showed that cations participate in the exchange between the soil solution and the soil absorption complex. “Following the research of K.K. Gedroiz, soil began speaking a living language to us, and our understanding of the main genetic types of soil acquired entirely new traits. In this lies its deathless merit”, wrote professor Aleksey Rode (1896–1979) (Rode, 1956). The American pedologist and director of the soil survey, Charles Kellogg, thought that the soil studies conducted by Konstantin Gedroiz were superior to all other work done elsewhere, and he considered most soil chemistry papers prior to the works of Konstantin Gedroiz useless (Kellogg, 1946).

THE JOURNEY TO SCIENCE

Konstantin Gedroiz was born on April 6, 1872 at the bank of the Dniester River in the town of Bendery in the Bessarabia region (currently Transnistria) (Fig. 1). His father was a field military surgeon, and spoke six languages in addition to Russian. Konstantin had five siblings and three of the children became medical doctors. Konstantin was the fourth child and when he was born his father was 58 and his mother was 36 years old. At 12 years old, Konstantin had typhus like most members of his family, which led to the development of a heart disease (mitral insufficiency), which later progressed.

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Bendery, the town where K.K. Gedroiz was born. (©https://nailizakon.com/fotogalereya_moldaviya/bendery/andreevskaya_ul.jpg.)

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From 1882 to 1884, Konstantin attended the gymnasium of the city of Bolgrad in the Bessarabia Governorate. After his father died, the financial situation forced his mother to enroll him in the Kyiv Cadet Corps, even though he was not healthy and was not interested in warfare. He graduated from the cadet corps in 1892, and was sent to St. Petersburg to continue his education at the Mikhailovsky Military Artillery Academy, from which he withdrew after a year due to a heart condition. In 1894 he enrolled at the Imperial Forest Institute in St. Petersburg, where he obtained a natural-historical education (Fig. 2).

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K. Gedroiz, a student of the Imperial Forestry Institute. 1896. (©ACSMD Fund 2. List 33. Case 2. Sheet 22.)

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After four years of study at the Imperial Forestry Institute, Gedroiz needed to acquire the title of a first-class forester scientist and had to defend a scientific thesis. Piotr Kossovich was the head of the Department of Soil Science and the Agricultural Chemistry Laboratory of the Ministry of Agriculture at the Imperial Forestry Institute, and he assigned Gedroiz to test the electrical method of determining soil salinity, which had been developed in the USA (Whitney and Briggs, 1897; Whitney and Means, 1897). This was his first scientific study, for which he received the title of a forester in 1899. It was published it in the first volume of the Journal of Experimental Agronomy (Gedroiz, 1900), which Kossovich had founded. This study laid the beginning of several studies on the chemical composition and physico-chemical properties of soils.

In 1899, Kossovich invited Gedroiz to join him as a junior laboratory assistant and work in the Laboratory of Agricultural Chemistry. By 1903, Gedroiz became a Senior Specialist in the Department of Agriculture and a fellow of the laboratory. The laboratory had a greenhouse in which his studies took place from 1897 to 1916 (Figs. 3, 4). The greenhouse in the park of the Imperial Forestry Institute was the largest in Russia at the time, and the work was based on the methods of the Swiss professor E. Schultz (1840–1912) (Bosch, 1934a). His laboratory work focused on critical testing of existing methods of soil chemical analysis and interpretation, and on soils that needed fertilization.

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Greenhouse at the Imperial Forestry Institute. (©https://novostipmr.com/sites/default/files/IMAGES/2020/03/ Ann/20200317-img_7565.jpg.)

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K.K. Gedroiz (the first from the right in the first row) – Senior Specialist of the Agricultural Bureau in a group of visitors to the greenhouse station in the Imperial Forestry Institute’s park. The second person left of him is Prof. PS. Kossovich. 1912. (©ACSMD Fund 2. List 33. Case 6. Sheet 15.)

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His active participation in issues of the “Journal of Experimental Agronomy”, shaped the scientific skills of Gedroiz. As he worked in journal’s abstract department, he became aware of the problems and achievements of agricultural science in other parts the world. After the death of Kossovich, Gedroiz became the journal editor from 1915 to 1931. The journal was published bi-monthly in Russian and consisted of two sections: 1) original works and 2) abstracts of Russian and foreign works. Gedroiz published over 2000 essays between 1900 to 1922 of which 700 were dedicated to methodological problems, 200 to general problems in soil science, and around 200 to the problems of soil fertility.

In the first period of his scientific career, Gedroiz studied phosphate plant nutrition and methods of determining phosphoric acid. Numerous experiments in the field led him to research the soil solution, as he assumed that the soil solution controlled plant nutrition. In 1906, he published a detailed paper about the ability of the soil solution to control the concentration and composition of soluble compounds (Gedroiz, 1906). He concluded that studying the soil solution required studying cations which were weakly bound to the colloid portion of the soil. This led to his research into soil colloids and the absorption capacity of soil.

His first study “Colloid Chemistry and Soil Science” was published in 1908 (Gedroiz, 1908): a new period of K.K. Gedroiz’s scientific career begins from the moment of publishing of this article. The Dutch chemist J.M. van Bemmelen (1830–1911) conducted research in the same field, but his work on soil colloids was published two years later (Bemmelen, 1910). He concluded that soil organic substances, like amorphous and colloid particles, have a large absorption capacity and do not enter into a chemical reaction with mineral compounds, but rather absorb the ions of the soil solution. He found that the structure of colloids and the concentration of ions in the solution affected the amount of absorbed substances. Van Bemmelen noted that organic substances formed absorption compounds most easily with bases, which he named humic acids.

Shortly thereafter, Gedroiz published two papers in which he formulated a definition of soils that are saturated and unsaturated by bases, noting that the saturation can be by organic and mineral compounds, and he provided a method for determining unsaturation, or the exchange of soil acidity. He found that the exchange acidity of the soil is due to the presence in the solid phase of hydrogen ions that are not displaced by neutral salts from the absorption complex, but are capable of being substituted by other cations when solutions of alkalis or hydrolytically alkaline salts are added to the soil.

Based on the results on the study of absorption capacity of soils, he provided recommendations when to use phosphorus fertilizers. Soil acidity must be taken into account when choosing mineral fertilizers (Gedroiz, 1911a,b) and he published 26 papers on this subject between 1900 and 1917. Other scientists (Aarnio, 1914) did not readily accept Gedroiz’s theory on soil acidity. For example, the Finnish soil chemist, Bernhard Aarnio (1876–1951) wrote that it was impossible to obtain correct determinations determining acidity by titration with hydrate as was published by Gedroiz in 1909 (Gedroiz, 1909). In a response Gedroiz (1909) noted, that there are no universal methods for chemical analysis that could be applied to all soils.

In 1912, Gedroiz reviewed all papers on colloid chemistry (Gedroiz, 1912) including the methods more than 20 scientists, among them A. Bamann and E. Gullyна, B. Tache and H. Süchting, S. Odenyf, E. Mitscherlich, Th. Svedberg, H. Bechhold. He showed that research methods of the absorption capacity of soil were not fully developed and that different studies had reached different conclusions. Gedroiz shows that some of the authors’ conclusions are not based on experiments, but are borrowed from general provisions of colloid chemistry. This concerns the understanding of the processes occurring during the freezing of soil organic colloids, questions related to the nature of compounds of soil organic matter with metal ions. The arguments given by some authors, trying to determine the nature of soil organic matter, are often based on assumptions, the validity of which may be disputed.

In 1913, Gedroiz moved his field research from the greenhouse of the Forestry University to the field of the Nosovo Agricultural Experimental Station in the Chernigov Region of the northern Ukraine. Here he participated in the development of the agrochemical department, conducted soil-geographical research of the Dniepr Lowlands, and evaluated the soils of the station for its agronomic potential. In 1923, he became the Head of the Department of Agrochemistry and studied soil processes, which determine soil fertility under natural conditions and under agriculture (Fig. 5) and developed amelioration methods for sodium rich (sodic) soils by applying lime. Gedroiz studied sodic soils and in 1916–1917 he published articles about soil absorption capacity and zeolite bases, which started the study of the composition of exchange cations in soils and several exchange experiments. The main conclusion was that the classification and methods of amelioration for saline soils depends on the cation and anion composition. It allowed him to connect Solonetz to other saline soils, determine the origin of Solonetz, and explain the benefits of gypsum applications (Gedroiz, 1916a; Gedroiz, 1917).

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K.K. Gedroiz among the staff of the Nosov Agricultural Experimental Station. (©ACSMD Fund 2. List 33. Case 2. Sheet 8.)

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In 1915, Gedroiz became the head of the Dokuchaev Soil Committee laboratory (Figs. 6, 7) and the experimental laboratory of the Forest Institute. In 1922, he published “A study of soil absorbing capacity” (Gedroiz, 1922) in which he showed that there were five types of absorption capacity: mechanical, physical (adsorption), physical-chemical or exchangeable, chemical, and biological. The main focus of the book was on physical-chemical absorption capacity. A definition of the soil absorption complex was formulated: totality of the smallest colloidal and closely related in size soil particles of organic, mineral or organic-mineral composition, insoluble in water and capable of absorbing and exchanging absorbed ions. Cations (or bases) of soil, capable to exchange to cations of salts solutions have been named as absorbed or exchangeable. Gedroiz determined the composition and amount of cations in different soil types. Other topics that were covered in this seminal book included: exchange reactions; the role of the colloid and sub-colloid fraction in absorption and exchange reactions; the soil absorption complex and cation exchange capacity were introduced; the grouping of all soils into base saturated and unsaturated; the nature of soil acidity as explained by the presence of hydrogen ions in the soil solution and exchangeable hydrogen and aluminum ions in the soil absorption complex; and lastly the physical-chemical properties of Solonetz and Albic Gleyic Planosols were reviewed.

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First on the left–K.V. Malyarevskiy, fourth–K.K. Gedroiz, fifth–N.I. Sokolov. 1912. (©ACSMD Fund 2. List 33. Case 2. Sheet 15.)

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Results of chemical analyses conducted by K.K. Gedroiz. (©ACSMD Fund 2. List 33. Case 6. Sheet 37.)

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Gedroiz demonstrated that hydrogen is an exchange cation, following the same patterns as metal cations, and is responsible for the low base saturation of soils. He noted that the colloid part of soil can develop in two ways: via the formation of secondary minerals during the process of weathering of primary minerals, or by precipitation of colloidal hydrates of silicon oxide, aluminum and iron. The presence of exchangeable hydrogen in unsaturated soils explained the benefits of phosphorus meal, and served as the theoretical foundation for the liming of soils.

The Hungarian scientist Alex de Sigmond (1873–1939) and the German scientist Georg Wiegner (1883–1935) studied the nature and structure of soil colloids, their charge, amphotericity, and the mechanism of absorption and exchange of cations and anions. Their research mainly was focused on physical-chemical absorption, and they were interested in the practical aspects: the connection between soil absorption capacity, their acidity, alkalinity, and the application of various forms of mineral fertilizers, lime and gypsum (Wiegner, 1926; de Sigmond, 1935). The publication of a theoretical system on the absorption capacity of soil, based on analytical material, was an extraordinary event in the emerging field of soil science. In 1924, the book “A study of soil absorbing capacity” was translated and published in the USA for distribution at experimental stations and universities. As a result, Gedroiz became widely known, his previous publications were studied, and he was invited to attend the First International Congress of Soil Science in Washington DC in 1927. But he avoided participating and said such congress was too tiring for him (Bosch, 1934b).

In 1924, begins the third period of Konstantin Gedroiz’s scientific career – the period of theoretical generalizations. If in 1916 Giedroiz wrote that “scientists still do not know the basic positions of absorptive capacity of soil, qualitative side of the phenomena of absorption and exchange, and there are not even developed methods for them” (Giedroiz, 1916b), now he presented his work on absorptive capacity of soil and developed methods of its study. An extended version of the book “A study of soil absorbing capacity” was published in 1929, 1932, and 1933. In the book “Soil absorbing complex and the absorbed soil cations as a basis of genetic soil classification” the study of soil colloids was extended with a geographical interpretation. Gedroiz showed that the composition of exchangeable cations was related to the origin of soil and affected by soil properties and processes (Gedroiz, 1925). Data on the composition of absorbed cations in soils were given for Chernozems, Solonetz, Albic Gleyic Planosols, and Ferralsols (WRB, 2022). Like his mentor, P.S. Kossovich, Gedroiz attributed soils to climatic conditions, specifically the physico-chemical reactions during leaching. In his monograph, “Solods” (Albic Gleyic Planosols) Gedroiz concluded from analytical and experimental data that Solods were a product from the evolution of Solonetz (Gedroiz, 1926).

Gedroiz not only studied absorption, but also the development of an analytical method for the determination of exchangeable cations, which was subsequently introduced into numerous soil laboratories of the world. The work “Chemical analysis of soils” published in 1923 was re-published several times and is a classic text on cation-exchange properties of soils, determination of exchangeable sodium, gypsum and soil alkalinity, and extraction of readily soluble salts (Gedroiz, 1923; Vorobyova, 1998). It provided methods of analysis including those for: exchange calcium, magnesium, potassium; qualitative identification of exchangeable hydrogen; qualitative identification of sodium; identification of the total absorption volume; method of highlighting the organic matter part of the absorption complex and the method of soil ultramechanical analysis; the method of identification of amorphic silicic acid in soil as was used in the study of Albic Gleyic Planosols formation.

EDUCATIONAL CAREER

From 1917 to 1930, he was a professor, and from 1919 the head of the Department of Soil Science at the Petrograd Forest Institute where he succeeded S.A. Zakharov (Fig. 8). From 1920, Gedroiz was a professor at the Stebut Agricultural, Polytechnical and Agronomical institutes in Petrograd. He prepared demonstrations for experiments and in his teaching, he introduced students to facts, demonstrated a large number of tables with chemical data and analyzing them. He lectured slowly, and thoroughly. In laboratory lessons he tried to use questions to push the student toward the correct conclusion and encouraged students to carefully think through the steps of the experiments, and showed examples of work himself (Fig. 9). Although he did not enjoy teaching, Gedroiz was a wonderful lecturer.

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Soil science office of the Forestry Institute. K.K. Gedroiz among his students. From left to right: Ya.V. Vasiliev, A.G. Gael, K.K. Gedroiz, V.V. Alyokhin and V.I. Kogrin, 1926. (©ACSMD Fund 2. List 33. Case 2. Sheet 13.)

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Prof. K.K. Gedroiz in his laboratory. Forestry Institute. 1928. (©ACSMD Fund 2. List 33. Case 2. Sheet 11.)

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ADMINISTRATIVE CAREER

The First International Congress of Soil Science was held in Washington DC in 1927. Gedroiz was invited but did not attend. At the congress Konstantin Glinka was elected to become the next President of the International Association of Soil Science (ISSS), and organize the second congress in Russia. After sudden death of Academician Konstantin Glinka, the ISSS leadership decided that Russia should nominate candidates for the replacement on the post of the President, and Gedroiz was unanimously chosen as a candidate. At that time, he was well-known for his work on base exchange capacity and colloidal properties of soil (Waksman 1932). The ISSS accepted the Russian nomination and Konstantin Gedroiz was appointed as the President of the International Society of Soil Science and organizer of the Second International Congress of Soil Science (Fig. 10).

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Academic K.K. Gedroiz. (©ACSMD Fund 2. List 33. Case 2. Sheet 20.)

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The Second International Congress of Soil Science was held in Leningrad (St. Petersburg) and Moscow from the 20th until the 31st of July 1930. The President of the ISSS Konstantin Gedroiz, was to open the congress, but he was ill and unable to attend. Instead, the opening address was given by the geographer and polar explorer Rudolf Samoilovich, who read the opening speech of Konstantin Gedroiz who apologized for his absence: «…our country with great attention, as never before, listens to the voice of science, awaits and seeks its aid. And undoubtedly our country will get this aid from the International Congress. At the same time, it is quite certain that members of the Congress will also return home after the Congress and the excursion are over, enriched by the scientific achievements and the experience accumulated by five generations of soil scientists of our Union. They built up and are continuing to build a theoretical pedology and during recent years, have begun to work closely on its practical application to life». The proceedings of the Second Congress were published in seven volumes in 1932, covering over 2100 pages. Most of the papers were edited by Konstantin Gedroiz, Arseny Yarilov and Dmitrii Vilenskii, although each of the volumes had help from others and the commission chairs (Hartemink, 2021).

On 1929, Gedroiz earned the majority of votes to become a member of the USSR Academy of Sciences. Also, in 1929, he became the director of the V.V. Dokuchaev Soil Science Institute and had no longer time to teach. At this time, a geographical direction reigned at the Soil Science Institute and to broaden scientific work, Gedroiz opened a chemistry laboratory at the institute (Fig. 11), but the stress and overexertion began to take a toll. At the beginning of 1930, Gedroiz requested to be relieved of his role of director.

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Chemical laboratory at the Institute of Soil Science in Leningrad. 1930–1932. (©ACSMD Fund 4. List 1. Case 1. Sheet 102.)

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PERSONALITY

Gedroiz was modest and consistent in social interaction – he respected others’ opinions regardless to whom he spoke. He was kind, and conversations with him stood out for their warmth and benevolence, and he was always ready to help everyone and share his knowledge. He was just as kind and caring toward his loved ones. On September 10, 1900, he married Olga Viktorovna Bobrova, who became a friend for the rest of his life. She worked as a school dentist. Gedroiz gave every free minute to their children, of whom there were three in the family: a son who acquired a psychiatric disorder as a young man and two daughters, one of whom passed away at a young age, the second graduated from pedagogical college. The family’s financial resources were limited, and the only thing Konstantin Gedroiz allowed himself was books. Philosophy and social science books and scientific books in soil science and agronomy in different languages comprised a significant part of his library. After his death, his library became part of the library of the Moscow State University.

According to the recollections of the soil scientist and educator G.N. Boch (1871–1942), who worked for a long time at the Department of Soil Science of the Forest Institute with K.K. Gedroiz, and from 1918 to 1923 served as dean and rector of the Forest Institute, Gedroiz was a focused scientist. “He could dive deeply into his work in the same room where the children were playing and being loud, he could outwardly detach from his work, responding to other questions, and calmly continue to work. In the office at the laboratory, when he wrote his scientific thesis in his clear handwriting, he was constantly interrupted, and he would calmly set down his pen in the middle of a word, reply in a friendly manner, sometimes the conversation would become lengthy, but as soon as it ended, Gedroiz would immediately pick up his pen again, as if his thought was not interrupted even for a second,” recalled G.N. Boch (ACSMDc). Gedroiz disliked public speaking and they were burdensome to him. He only gave presentations on his work once or twice; in all other cases he would send them in writing and would not attend conferences. This even prompted a comment at one of the conferences about whether this “invisible scientist,” whose presentation raised discussion, might be a myth?

FINAL YEARS

In the late 1920s Gedroiz health declined as the aortic sclerosis intensified, and he was advised to stop working. In the spring of 1930, he received an invitation from the director of the Science Institute of Fertilizers, E.V. Britske, to become the head of the agrochemical laboratory on the Dolgoprudny Experimental Field Station near Moscow. As Gedroiz wrote: “I did it because my long-term laboratory works in soil science and agrochemistry have come to such a stage that they demanded for their further development and application the close ties of laboratory work with agricultural experiments on plants” (ACSMDd). Gedroiz was transferred to the suburbs of Moscow and, not having an opportunity to regularly visit Academy of Sciences section meetings, addressed the Secretary of the Academy of Sciences with a request to allow him to offer consultations from time to time. As noted before, he did not attend the Second International Congress of Soil Science in Leningrad and Moscow, which disappointed several participants who had wanted to meet him in person. The absence of the President was annoying for most of the participants, and provided certain confusion among the attendees of the Congress.

In Dolgoprudnoye, Gedroiz was offered excellent conditions including a new primary and field laboratory, a greenhouse for 6000 containers and a residential house. He participated in designing the rooms and designing the laboratories. However, construction took more time than expected, and he had to live in two small rooms with his family and work in a scantly equipped and small laboratory, but he did not care about domestic inconveniences (Fig. 12). During the final period of his scientific career from 1930 to 1932 on the Dolgoprudny experimental field station, Gedroiz published eight works on the relationships between soil exchange cations and fertilizers. These were the seminal works to mention the importance of microelements and magnesium in plant nutrition.

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K.K. Gedroiz. Dolgoprudnoye experimental field. 1932. (©ACSMD Fund 2. List 33. Case 2. Sheet 7.)

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On October 5, 1932, having finished his greenhouse experiments, K.K. Gedroiz was supposed to go to Caucasus with his wife for medical treatment. Death caught up with him as he was boarding the train. Help was provided immediately, doctors fought for his life for almost an hour, but K.K. Gedroiz passed away in the train station’s clinic from an aortic dissection without having regained consciousness.

Obituaries about K.K. Gedroiz’s were published in all mainstream newspapers and special magazines both in the USSR and beyond. The funeral took place at the Vvedenskoye Cemetery in Moscow.

Documents from 1932, stored at the Archives of the Central Soil Museum of V.V. Dokuchaev (ACSMDa), serve as an evidence of the high regard of K. Gedroiz’s works in all the world: “Gedroiz triggered a revolution in our understanding of the absorption capacity of soil” S.A. Waksman (1888–1973), Rutgers University; “he high scientific value of this Russian scientist is indisputable for all of us. He will forever remain unforgettable to us, as a scientist and even more as a person who was capable of thinking honorably” F.W. Schucht (1878–1941), University of Cologne; “Gedroiz’s works have an enormous value as the foundations of soil science” D.J. Hissink (1874–1956), Soil Science Institute at Groningen; “We have all acknowledged the teacher in his works and followed his research with the utmost interest” E.J. Russell (1872–1965), Rothamsted Experimental Station. “Following the research of K.K. Gedroiz, soil began speaking a living language to us, and our understanding of the main genetic types of soil acquired entirely new traits. In this lies its deathless merit,” wrote professor A.A. Rode (1896–1979) (Rode, 1956).

SCIENTIFIC RECOGNITION

It took a long time before the works of K.K. Gedroiz were recognized, both in Russia and abroad. The soil microbiologist Selman Waksman translated 11 of his papers into English, and the United State Department of Agriculture distributed copies of these translations. In 1927 a textbook on chemical analysis, “Die chemische Bodenanalyse,” was published; in 1930 the books “Der adsorbierende Bodenkomplex und die adsorbierten Bodenkationen als Grundlage der genetischen Bodenklassification” and “On the Problem of exchangeable Hydrogen and exchangeable Aluminium in acid soils”, в 1931 – “Die Lehre vom Adsorptionsvermögen der Böden.” In 1924, two volumes of K.K. Gedroiz’s works were published in English in the USA. The English scientist Harold Page presented a detailed report about Konstantin Gedroiz’s research in the field of soil absorption capacity at the Second Commission for the Study of Soil Chemistry in Groningen (Netherlands) in 1926. His presentation covered works published from 1912 to 1925. In 1927, a translation of his book, “Chemical analysis of soils,” was published in German; in 1930 a translation of the book “Soil absorbing complex and the absorbed soil cations as a basis of genetic soil classification”; in 1931 “A study of soil absorbing capacity.”

Konstantin Gedroiz’s works on agrochemistry and soil science were highly appreciated and in 1927 he received the Lenin Prize. Also, in 1927 he was elected a CorrespondingMmember of the USSR Academy of Sciences, and became an Academician in 1929. Also, in 1929, he became a Corresponding Member of the Czechoslovakian Agricultural Academy.

CONCLUSION

The first research on soil colloids appeared at the end of the 19th century (J.T. Way, J.M. van Bemmelen, E. Veitch and others), but Russian research on the colloid properties of soils by K.K. Gedroiz’s advanced basic knowledge. His contribution to the study of saline and sodic soils is very important, and even now it is basic for understanding of the evolution of salt-affected soils. Gedroiz suggested and justified simple methods of studying colloid phenomena, exposed their essence and introduced the science of soil colloids to the framework of Dokuchaev’s ideas on soil formation. He was a successful scientist with an original line of research. Being proficient in analytical methods of research, he carried out most of his practical work independently. All conclusions K.K. Gedroiz tested experimentally and developed them further only after confirming their correctness. It allowed him to establish the most important regularities of absorption and exchange of bases, as well as the behavior of soil colloids.

Studying soil structure, working on plant nutrition or melioration problems, Gedroiz always had agronomical implications in mind. The phenomena which he discovered and studied covered not only soil, but also played a role in the other Earth sciences, since the colloidal fraction and exchangeable cations are characteristic of all clays and silts. For example, the road and building properties of soils are affected by exchangeable cations. He found that soils whose soil-absorption complex is saturated with sodium have very low filtration. Following Gedroiz findings the Ukrainian soil scientist A.N. Sokolovsky (1884–1959) proposed artificially saturating the soil-absorption complex of the bed of canals and reservoirs with sodium salts in order to reduce filtration.

K.K. Gedroiz had few colleagues and direct students, but the value of his scientific works, his interactions with many young scientists and his authority in the field of the problems contributed to the creation of a school of his followers. In 2016, with the goal of preserving the memory of a remarkable scientist and organizer of Russian science, the presidium of the Russian Academy of Sciences (RAS) established to create a gold medal in the name of K.K. Gedroiz to be given for outstanding work in the field of soil science and agrochemistry. The first winner of the gold medal was given to Dr. Shafran S.A., from the D.N. Pryanishnikov Institute of Agrochemistry in Moscow, for a series of studies on optimizing the mineral nutrition of plants and regulating the agrochemical parameters of soil fertility. In 2002, a 100-ruble coin with K.K. Gedroiz portrait was released in his birthplace in Transnistria. In 2022, a stamp was published for his 150-th anniversary in Prednistrovie (Fig. 13) (https://commons.wikimedia.org/wiki/File:Konstantin_Gedroits_2022_stamp_of _Transnistria.jpg?uselang=ru).

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The stamp published for the 150 anniversary of the birth of K.K. Gedroiz. (©https://commons.wikimedia.org/wiki/File:Konstantin_Gedroits_2022_stamp_of_Transnistria.jpg?uselang=ru.)

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