Dennis Robert Hoagland

Dennis Robert Hoagland
Born	April 2, 1884 Golden, Colorado, USA
Died	September 5, 1949 (1949-09-06) (aged 65) Oakland, California
Citizenship	American
Alma mater	Stanford University University of Wisconsin-Madison
Known for	Hoagland solution
Awards	Newcomb Cleveland Prize Stephen Hales Prize
Scientific career
Fields	Plant Scientist, Soil Chemist
Institutions	University of California, Berkeley Food and Drug Administration

Dennis Robert Hoagland (April 2, 1884 – September 5, 1949) was a chemist and plant scientist working in the fields of plant nutrition, agricultural chemistry, and physiology. He was Professor of Plant Nutrition at the University of California at Berkeley from 1927 until his death in 1949. He is commonly known for his pioneering work on water culture and the development of the Hoagland solution. His most important contributions are on the absorption of mineral nutrient elements by plants and their relations to physiological processes.^[1]

The Dennis R. Hoagland Award, first presented by the American Society of Plant Biologists in 1985,^[2] and Hoagland Hall, which is home to the Atmospheric Science program as well as the Environmental Health and Safety office at the UC Davis, are named in his honor.

Biography[]

Private life[]

Dennis Hoagland was the son of Charles Breckinridge and Lillian May Burch. He spent his first eight years in Golden and during his later childhood he lived in Denver. He attended the Denver public schools and in 1903 entered Stanford University. In 1920, Dennis R. Hoagland married Jessie A. Smiley. She died suddenly of pneumonia in 1933. He was left with the responsibility of bringing up three young boys named Robert Charles, Albert Smiley, and Charles Rightmire.^[3]

Career[]

Hoagland graduated from Stanford University (1907) with a major in chemistry. In 1908 he became an instructor and assistant in the Laboratory of Animal Nutrition at the University of California at Berkeley, an institution with which he would be associated for the remainder of his life. He worked in the fields of animal nutrition and biochemistry. In 1910 he was appointed assistant chemist in the Food and Drug Administration of the U.S. Department of Agriculture until 1912, when he entered the graduate school in the department of agricultural chemistry (McCollum lab) at the University of Wisconsin, receiving his master's degree in 1913. The following year he became Assistant Professor of agricultural chemistry and in 1922 Associate Professor of plant nutrition at Berkeley.^[4]

Work[]

During the World War I, Hoagland tried to substitute the lack of imports of potassium-based fertilizers from the German Empire to the United States with plant extracts from brown algae, inspired by the ability of kelps to absorb elements from seawater selectively and to accumulate potassium and iodide many times in excess of the concentrations found in seawater (Hoagland, 1915). Based on these findings he investigated the ability of plants to absorb salts against a concentration gradient and discovered the dependence of nutrient absorption and translocation on metabolic energy using innovative model systems under controlled conditions (Hoagland, Hibbard, and Davis, 1926). During his systematic research he developed the basic formula for the Hoagland solution between 1916 and 1919, whose composition was originally patterned after the displaced soil solution obtained from certain soils of high productivity, and established the essentiality of molybdenum for the growth of tomato plants. Hoagland was able to show that various plant diseases are caused by a lack of trace elements such as zinc, and that boron, manganese, zinc, and copper are indispensable for plant growth (Hoagland, 1937). He took special interest in soil-plant interrelationships addressing, for example, the physiological balance of soil solutions and the pH dependence of plant growth, in order to gain a better understanding on the availability of plant nutrients in soils (Hoagland, 1916, 1917, 1920, 1922; Hoagland and Arnon, 1941). Hoagland and his team of experts thus contributed to the understanding of fundamental cellular physiological processes in green plants that are driven by sunlight as the ultimate form of energy (Hoagland, 1944, 1946).^[5]

The macronutrient solution published by Hoagland in 1920 was applied to investigate plant growth parameters of barley in comparison with Shive's solution.^[6] The growth of Alfalfa in modified Hoagland's solution was investigated at various pH values in the mid-1920s.^[7] Around the 1930s Hoagland investigated diseases of certain plants, and thereby, observed symptoms related to existing soil conditions. In this context, he undertook water culture experiments with the hope of delivering similar symptoms under controlled conditions. For these experiments the Hoagland solution (0) including macronutrients, iron, and the "A-Z solutions a and b" or the trace element supplementary solution, respectively, was developed to investigate diseases of the strawberry in California. The Hoagland solution (0) described by Hoagland and Snyder (1933) has been modified several times over time, for example, by Hoagland and Arnon (1938, 1950).

Hoagland's research was influenced by the plant pathologists H. E. Thomas and W. C. Snyder, and another pioneer of plant nutrition and hydroculture, .^[8] Gericke's groundbreaking results in this field inspired him to expand his research on the subject finally resulting in the Hoagland solutions (1) and (2).^[9] The composition of macronutrients of the Hoagland solutions (0) and (1) can be traced back to Wilhelm Knop's four-salt mixture (cf. Table (1))^[10] and the respective salt and element concentrations to Dennis Hoagland (cf. Table (2)). Knop's solution, in contrast to Hoagland's solution, was not supplemented with trace elements (micronutrients), with the exception of iron, because the chemicals were not particularly pure in Wilhelm Knop's day. Micronutrients were, without knowing it, already present as impurities in the macronutrient salts. More highly purified chemicals and more sensitive methods for analysing trace concentrations were developed from 1930 and onwards.^[11]

Table (1) Knop's four-salt mixture (1865):

Macronutrient salts
KNO3	0.25 g/L
Ca(NO3)2	1.00 g/L
MgSO4•7H2O	0.25 g/L
KH2PO4	0.25 g/L

Table (2) Concentration of macronutrients in Hoagland's solution (0, 1) and in Knop's solution:

Macronutrients	Hoagland's solution	Knop's solution
K+	6,000 µmol/L	4,310 µmol/L
Ca2+	5,000 µmol/L	6,094 µmol/L
Mg2+	2,000 µmol/L	1,014 µmol/L
NO− 3	15,000 µmol/L	14,661 µmol/L
SO2− 4	2,000 µmol/L	1,014 µmol/L
PO3− 4	1,000 µmol/L	1,837 µmol/L

Hoagland's students included Daniel Israel Arnon who modified the composition of macronutrients of the Hoagland solution (2) and the concentration of micronutrients (B, Mn, Zn, Cu, and Mo) of the Hoagland solutions (1) and (2) (cf. Table (3)) as a result of joint efforts,^[12] and Folke Karl Skoog.^[13] In contrast to the Murashige and Skoog medium, neither vitamins nor other organic compounds are provided as additives for the Hoagland solution, but only essential minerals as ingredients. It is concluded that the promotion of growth of tobacco callus cultured on White's modified medium is due mainly to inorganic rather than organic constituents in aqueous tobacco leaf extracts added.^[14]

Table (3) Concentration of micronutrients in Hoagland's solution (1, 2):

Micronutrients	Hoagland's solution
B(OH)4−	46.25 µmol/L
Mn2+	9.15 µmol/L
Zn2+	0.77 µmol/L
Cu2+	0.32 µmol/L
MoO2− 4	0.11 µmol/L or 0.50 µmol/L

In addition, 9 µM ferric tartrate is added to the Hoagland solution formulations (0, 1, 2), corresponding to a concentration of 18 µmol/L Fe³⁺. Solution (2) contains ammonium and nitrate salts and may sometimes be preferred to solution (1) because the ammonium ion delays the development of undesirable alkalinity (Hoagland and Arnon, 1950).

Awards and honors[]

Hoagland became a Fellow of the American Association for the Advancement of Science (AAAS) in 1916 and member of the National Academy of Sciences in 1934.^[15] In recognition of his many discoveries, the American Society of Plant Physiologists elected Dennis Hoagland as president in 1932 and awarded him the first Stephen Hales Prize in 1929.^[16] In 1940, together with Daniel I. Arnon, he received the AAAS Newcomb Cleveland Prize for the work "Availability of Nutrients with Special Reference to Physiological Aspects".^[17] In 1944 he published his Lectures on the Inorganic Nutrition of Plants subtitled "Prather Lectures at Harvard University" which he was invited in 1942 to give at Harvard University. In 1945 he was elected member of the American Academy of Arts and Sciences.^[18]

Perception[]

Nowadays the most common solutions for plant nutrition and plant tissue cultivation are the formulations from Hoagland and Arnon (1938, 1950),^[19] and Murashige and Skoog (1962).^[20] Their basic formulas are being replicated by modern manufacturers to commercially produce liquid concentrated fertilizers for plant breeders and average consumers. Even the names of Hoagland and Murashige and Skoog are used as a brand for innovative products, e.g., Hoagland's No. 2 Basal Salt Mixture or Murashige and Skoog Basal Salt Mixture, which are commonly used as chemicals in plant science.

Several nutrient recipes refer to a standard name although they have little to do with the original formula. As described by Hewitt (1966) several recipes have been published under the name of Hoagland, and confusion may arise from a loss of memory about the original composition.^[21][22]

Dennis Hoagland was considered a leading scientist in his field and his research merit was to initiate the solution named after him,^[23] thereby, creating the basis for a modern balanced plant nutrition that is still valid today. His findings are relevant to the sustainable use of natural resources such as soil, water and air, water and nutrient use efficiency in crop production and the production of healthy plant foods.^[24] His fundamental contributions are of historical relevance for plant nutrition research, which is reflected in the following bibliography.^[25]

Bibliography[]

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A Comparison of Sand and Solution Cultures with Soils as Media for Plant Growth. With J. C. Martin. Soil Sci., 16(5) :367-388.

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Effect of Certain Alkali Salts on Growth of Plants. With J. S. Burd and A. R. Davis. (20) Abstract. Nature and Promise of Soil Solution. (21) Abstract of Papers Read Before Pan-Pacific Scientific Congress, Australia.

The Influence of Light, Temperature and Other Conditions on the Ability of Nitella Cells to Concentrate Halogens in the Cell Sap. With P. L. Hibbard and A. R. Davis. J. Gen. Phys., 10(1) :121-146.

The Investigation of the Soil from the Point of View of the Physiology of the Plant. 4th Int. Conf. Soil Sci. Rome, 1924, 3 :535-544.

The Synthesis of Vitamin E by Plants Grown in Culture Solutions. With H. M. Evans. Am. J. Phys., 80(3) :702-704.

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An Apparatus for the Growth of Plants in Controlled Environment. With A. R. Davis. Plant Phys., 3(3) :277-292.

Minimum Potassium Level Required by Tomato Plants Grown in Water Cultures. With E. S. Johnston. Soil Sci., 27(2) :89-109.

The Intake and Accumulation of Electrolytes by Plant Cells. With A. R. Davis. Protoplasma, 6(4) :610-626.

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The Water-Culture Method for Growing Plants without Soil. With D. I. Arnon. Calif. Agr. Exp. Sta. Cir., 347, pp.  1-39.

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A Comparison of Water Culture and Soil as Media for Crop Production. With D. I. Arnon. Science, 89 :512-514.

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Salt Absorption by Plants. With F. C. Steward. Nature, 145 :116-117.

Hydrogen-Ion Effects and the Accumulation of Salt by Barley Roots as Influenced by Metabolism. With T. C. Broyer. Am. J. Bot., 27 :173-185.

Upward Movement of Salt in the Plant. With T. C. Broyer and P. R. Stout. Nature, 146 :340-340.

Minute Amounts of Chemical Elements in Relation to Plant Growth. Science, 91 :557-560.

Methods of Sap Expression from Plant Tissues with Special Reference to Studies on Salt Accumulation by Excised Barley Roots. With T. C. Broyer. Am. J. Bot., 27(7) :501-511.

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General Aspects of the Study of Plant Nutrition. Sci. Univ. Calif., pp. 279–294.

The Investigation of Plant Nutrition by Artificial Culture Methods. With D. I. Arnon. Biol. Rev. Cambr. Phil. Soc., 19(2) :55-67.

Lectures on the Inorganic Nutrition of Plants. (Prather Lectures at Harvard University). Published by Chronica Botanica Co. Waltham, Mass.

Molybdenum in Relation to Plant Growth. Soil Sci., 60(2) :119-123.

Potassium Fixation in Soils in Replaceable and Non-Replaceable Forms in Relation to Chemical Reactions in the Soil. With J. C. Martin and R. Overstreet. Soil Sci. Soc. Am. Proc., 10 :94-101.

The Nutrition and Biochemistry of Plants, Currents in Biochemical Research. Interscience Publ. Inc. N. Y., pp.  61–77.

Little-Leaf or Rosette of Fruit Trees, VIII: Zinc and Copper Deficiency in Corral Soils. With W. H. Chandler and J. C. Martin. Proc. Am. Soc. Hort. Sci., 47 :15-19.

Trace Elements in Plants and Animals by Walter Stiles. Rev. Arch. Biochem., 13 :311-312.

Fertilizers, Soil Analysis, and Plant Nutrition. Calif. Agr. Exp. Sta. Cir., 367 :1-24.

Minute Amounts of "Minor" Elements Essential in Addition to "Regular" Fertilizer. Agr. Chem.

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Fertilizers, Soil Analysis, and Plant Nutrition. Calif. Agr. Exp. Sta. Cir., 367 :1-24 (Revision).

Absorption and Utilization of Inorganic Substances in Plants. With P. R. Stout. Chap. VIII of Agricultural Chemistry, ed. by Frear, Van Nostrand.

The Water-Culture Method for Growing Plants without Soil. With D. I. Arnon. Calif. Agr. Exp. Sta. Cir., 347, pp.  1-32 (Revision).

Availability of Potassium to Crops in Relation to Replaceable and Non-Replaceable Potassium and to Effects of Cropping and Organic Matter. With J. C. Martin. Soil Sci. Soc. Am. Proc., 15 :272-278.

Courtesy of The National Academy of Sciences Archives, and without these entries it would not have been possible.

References[]