Abstract

GARCES, Nelson; HERNANDEZ, Alberto; CARO, Iosmel  and  ARTEAGA, Mayra. The humus of cuban soils in preserved tropical ecosystems and the energy. Terra Latinoam [online]. 2009, vol.27, n.2, pp.85-96. ISSN 2395-8030.

For the first time, the topic of humus of Cuban soils and the analysis of the energy involved in the formation or decomposition of the macromolecules of humic substances was studied. Studies conducted in other countries and employed methods were taken as a reference, but the approach and part of the mathematical calculations are original. The soils studied are those of greatest extension in Cuba and are representative of the characteristic types and subtypes. In order to show how data obtained and published by other authors may be used, energy calculations were done starting from molecular structures proposed in other countries. In this study basic thermodynamic concepts were used and an equation of the free energy of these systems is proposed. The elemental composition of humic and fulvic acids of Cuban soils and of humic substances obtained from vermicompost was determined. Kinetic parameters and heat of combustion-decomposition were determined using thermogravimetric techniques (TG), differential thermal analysis (DTA), and gravimetric thermal analysis (GTA). Data on combustion heat and on the formation of humic substances are offered and preliminary calculations of its free energy are presented. The possible sequence of organic substances that enter and leave the soil ecosystem is shown; these pass through the stationary status of degradation-reconstitution that takes place in the humus of the soil. Application of thermochemical valuation may contribute to enrich knowledge of soil organic matter.

Keywords : humic acids; fulvic acids; thermochemistry.