Citrus species associated with the coffee agroecosystem, as a potential source of humic biostimulants

Abstract

Humic fractions were obtained from residues of three citrus species used as shade trees in coffee-growing agroecosystems in the municipality of El Salvador, Guantánamo. The starting material was a mixture of fruit residues composed of albedos and pulp waste material. The materials were ground and subjected to a solid-state fermentation process for 90 days, using a passive aeration technique with periodic turning. Humic substances were extracted from the resulting composts through a sequential extraction process with solutions of sodium hydroxide, sodium pyrophosphate, and sodium fluoride. Carbon and nitrogen contents, the carbon-nitrogen ratio, and the total content of functional groups were determined. The results showed that the fractions obtained have potential for use as biostimulants for plant growth, as evidenced by their functional group content.