The artificial solution described by Dennis Hoagland in 1933,[1] known as Hoagland solution (0), has been modified several times, mainly to add ferric chelates to keep iron effectively in solution,[6] and to optimize the composition and concentration of trace elements other than iron, some of which are not generally credited with a function in plant nutrition.[7] In Hoagland's nutrient recipes of 1938, referred to as Hoagland solution (1, 2), the number of trace elements was subsequently reduced to the generally accepted essential elements (B, Mn, Zn, Cu, Mo, Fe, and Cl).[2] Later research confirmed that their concentrations had been adjusted for optimal plant growth.[8]
In Arnon's revision of 1950, only one concentration (Mo 0.011 ppm) was changed compared to 1938 (Mo 0.048 ppm), while the concentration of macronutrients of the Hoagland solutions (0), (1), and (2) remained the same since 1933, with the exception of calcium (Ca 160 ppm) in solution (2).[3] The main difference between solution (1) and solution (2) is the different use of nitrate-nitrogen and ammonium-nitrogen based stock solutions to prepare the respective Hoagland solution of interest. Accordingly, the original 1933 and the modified concentrations of 1938 and 1950 for each essential element and sodium are shown below,[9] the calculation of the latter values being derived from Tables 1 and 2:
Sprint 138 iron chelate is produced as Na-Fe-EDDHA (C18H16FeN2NaO6), while Hoagland's original solution formulations contain ferric tartrate (C12H12Fe2O18), but no sodium ions.[1][2][3] Synthesizing a sodium-free ferric EDTA complex (C10H12FeN2O8−) in a laboratory is sometimes preferred to buying ready-made products.[6][9] Variable micronutrients (e.g., Co, Ni) and rather non-essential elements (e.g., Pb, Hg) mentioned in Hoagland's 1933 publication[1] (known as "A-Z solutions a and b"[16]) are no longer included in his later circulars.[2][3] Most of these metallic elements, as well as organic compounds, are not necessary for normal plant nutrition.[17] As an exception, there is evidence that, for example, some algae require cobalt for the synthesis of vitamin B12.[18]
^ abcdHoagland, D.R.; Snyder, W.C. (1933). "Nutrition of strawberry plant under controlled conditions. (a) Effects of deficiencies of boron and certain other elements, (b) susceptibility to injury from sodium salts". Proceedings of the American Society for Horticultural Science. 30: 288–294.
^ abcdeHoagland & Arnon (1938). The water-culture method for growing plants without soil (Circular (California Agricultural Experiment Station), 347. ed.). Berkeley, Calif. : University of California, College of Agriculture, Agricultural Experiment Station. OCLC12406778.
^ abcdeHoagland & Arnon (1950). The water-culture method for growing plants without soil. (Circular (California Agricultural Experiment Station), 347. ed.). Berkeley, Calif. : University of California, College of Agriculture, Agricultural Experiment Station. (Revision). Retrieved 1 October 2014.
^Arnon, D.I. (1938). "Microelements in culture-solution experiments with higher plants". American Journal of Botany. 25 (5): 322–325. doi:10.2307/2436754. JSTOR2436754.
^Schropp, W.; Arenz, B. (1942). "Über die Wirkung der A-Z-Lösungen nach Hoagland und einiger ihrer Bestandteile auf das Pflanzenwachstum". Journal of Plant Nutrition and Soil Science. 26 (4–5): 198–246. doi:10.1002/jpln.19420260403.
^Murashige, T; Skoog, F (1962). "A revised medium for rapid growth and bio assays with tobacco tissue cultures". Physiologia Plantarum. 15 (3): 473–497. doi:10.1111/j.1399-3054.1962.tb08052.x. S2CID84645704.
^Kumudha, A.; Selvakumar, S.; Dilshad, P.; Vaidyanathan, G.; Thakur, M.S.; Sarada, R. (2015). "Methylcobalamin – a form of vitamin B12 identified and characterised in Chlorella vulgaris". Food Chemistry. 170: 316–320. doi:10.1016/j.foodchem.2014.08.035. PMID25306351.
