VARIATION IN SOIL ORGANIC CARBON AND MANURE TRANSFORMATION WITH APPLICATION OF MICROORGANISMS IN WARM CLIMATE ANDISOLS OF COLOMBIA

Soil organic carbon (SOC) is fundamental for maintaining soil fertility, structure, and biological activity. Manures can influence physicochemical and biological properties, affecting SOC decomposition rate and their contribution of stable material. Objective was to evaluate changes over time in contribution of SOC from different manures under field conditions.

At Monteilindo Farm (Caldas University, 1050 m.a.s.l., 2150 mm*year^-1), applications of fresh manure with and without addition of lactic-acid bacteria were evaluated from: horses (EE, EE-b), cattle (EB, EB-b), and poultry (EC, EC-b), to compare mineralization rate. Grids measuring 1.0x1.0x0.10m were used for application of each material. Eleven sampling events, distributed every three weeks, were carried out to evaluate residual manure and soil. OC was determined using Walkley-Black in each treatment and sampling, in the coarse (FG), medium (FM) and fine (FF) fractions.

From initial application, 15.5±0.5K (EE) and 9.0±1.0K (EB and EC), mineralization rates of 55.17%, 53.61%, and 40.22%, respectively; these indicate differences compared to the EC treatment, but no differences due to addition of bacteria. This suggests that the transformation process under tropical conditions is not enhanced by these microorganisms. OC increased from 2.65% to 4.56% and 4.01% (EB, EB-b), 4.44% and 3.53% (EE, EE-b), and 2.96% and 3.16% (EC, EC-b). Average OC of manure decreased from 21.89%-7.83% in FG, 17.78%-8.90% in FM, and 13.35%-9.39% in FF, indicating higher transformations of larger particle sizes. Analysis of OC from manure sources provides important information for the proper management of these materials in agricultural systems and their appropriate use in crops.