Int.J.Curr.Microbiol.App.Sci (2018) 7(4): 3322-3328 3322 Original Research Article https://doi.org/10.20546/ijcmas.2018.704.376 Characterization of Metal Ion Complexes with Humic Fractions of Farmyard Manure by Potentiometric Titrations D. Rajashekhar*, M. Srilatha, P. Chandrasekhar Rao, S. Harish Kumar Sharma and K. Bhanu Rekha Department of soil science and Agricultural chemistry, College of Agriculture, PJTSAU, Rajendranagar, Hyderabad - 500 030, Telangana, India *Corresponding author ABSTRACT Introduction The humus formation is a composite of the individual processes like, mineralization, decomposition, humification and putrefaction (Choudhuri et al., 2010). The quantitative changes in soil humus are determined by the relation between the processes of synthesis and decomposition of the organic matter. They are dynamic and are expressed specifically under particular soil, climatic conditions and systems of agriculture (Koteva and Kostadinova, 2014). Investigations into humus focus not only on direct management, but also into sustainable management practices that define the dynamic of humus in the soil. It is known that many factors have an impact on the humification and mineralization of humus in soil, of which precipitation is one of the most important. Humification and mineralization takes place slowly under conditions in which the amount of precipitation is high and the temperature is low (Tajnsek et al., 2013). Humic substances (HS) are the major source of energy and nutrients for soil biota. They are also charge carriers and play vital role in complexing organic compounds and adsorbents in controlling the toxicity, transport and fate of a International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 04 (2018) Journal homepage: http://www.ijcmas.com The present study was carried out at the laboratory, Department of Soil Science and Agricultural Chemistry, College of Agriculture, Rajendranagar to characterize the complex formation of humic fractions with metal ions. The results observed that increase in pH of humic and fulvic acid when titrated with 0.1 N NaOH indicates higher buffering capacity of these fractions. Potentiometric titration curves obtained for both humic and fulvic acids are sigmoidal in shape indicating their weak acid nature. Absence of inflection indicates the formation of metal complexes. Among all the metal ions does not show any inflection with both humic and fulvic acid indicating metal ion forms more stable complexes with these humic fractions. In case of Zn shows greater stability at pH 8.0 and above. Thus these humic fractions can be used as carrier materials especially supply of micronutrients to in crop nutrition as these also prevents the loss of nutrients from leaching by forming complex with metal ions like cationic micro nutrients. Keywords Farmyard manure (FYM), Humic acid (HA), Fulvic acid (FA), Metal ions and Potentiometric titration Accepted: 26 March 2018 Available Online: 10 April 2018 Article Info