DISTRIBUTION AND FRACTIONATION OF ORGANIC CARBON IN ORGANOMINERAL FERTILIZERS PRODUCED WITH INDUSTRIAL SUGARCANE WA.STE IN COLOMBIA

Humic substances (HS) are important fraction of soil organic matter (SOM) this role in improving the soil's physical-chemical, and biological properties. Addition of HS through organo-mineral fertilizers (OMF) contributes to stability of these substances in soils. This study aims to evaluate the quality and quantity of HS in different composted substrates.

Three OMF products of fine, medium, and coarse particle sizes were evaluated. These products were obtained from industrial composting of sugarcane production waste, mixed with SOM-degrading organisms under cover conditions, material was composted by 150 days. HS were obtained through sequential extraction: Na₂B₄O₇.10H₂O, Na₄P₂O₇, and NaOH 0.1N, agitation (30 min, 170±5 rpm) and centrifugation (10 min., 4000 rpm) to separate HS from non-humified materials. The efficiency of the extractant and the %CO in solution and solid material of each extraction were determined by Walkey & Black.

The %CO in the OMF was 5.26%, 6.46%, and 4.74% for fine, coarse, and medium grain sizes respectively. In soluble, %CO average extractions in SH were 12.73% with Na₂B₄O₇·10H₂O, 11.69%, and 4.75% with Na₄P₂O₇ and NaOH, indicating differences in extraction values. In solid substrate, values ​​of 7.60%, 6.35%, and 2.17% were determined, respectively, suggesting different affinities of HS present in the OMF and more soluble and less stabilized materials. %CO content in alkali-insoluble fraction was 11.04%, 13.02%, and 10.01% for fine, coarse, and medium grain sizes. The production process of OMF increase the release of rapidly solubilizing HS, which allows for better fertility conditions for the soils.