Characterization of Humic and Fulvic Acid under Long-Term Integrated Nutrient Management of Soybean-Wheat Cropping System in Vertisol

Abstract

The nature, content, composition and behavior of organic matter in soil are fundamentally important for growth of crops under diverse climatic conditions. Humic substances, present in soil, act as highly reactive natural polymers. The quality of soil organic matter according to functional groups governs the rate of sequestration of organic carbon. In the present investigation, effect of five years application of different integrated nutrient management (INM) interventions was assessed to note the changes in the fulvic acid and humic acid composition using fourier transform infrared (FTIR) technique. Humic acid and fulvic acid from selected treatments viz., control, inorganic NPK fertilizer (25, 30, 20 in soybean and 70, 30, 30 in wheat) and organic manure (8 t FYM ha-1 in soybean and 16 t FYM ha-1 in wheat) were fractionated from soil, separated and prepared for FTIR spectroscopy by following standard procedure. The obtained fractions were analyzed using FTIR spectroscopy. In control plot N-H stretching of amines, amides, aliphatic C-H stretching, C=O stretching of carboxylic acids, amides, ketones salt of carboxylic acid, C2H4 – in plane deformation (-CCH), aromatic C-H out of plane bend were found in humic acids, whereas aliphatic C-H stretching asymmetric COO- stretching, C-O stretching of polysaccharides, -C-C- stretching were observed in fulvic acid. Due to long-term humification in treated plots humic acid contained more number of functional groups than fulvic acid. Results indicated that application of 8 t FYM ha-1 in soybean and 16 t FYM ha-1 in wheat in soil helped in the formation of long chain humic acid which can sequester more organic carbon and subsequently improve soil quality and health. Experimental results were discussed with respect to the utility of FTIR spectroscopy in the assessment of organic matter quality in long term fertilizer experiment.