This document summarizes the key points from a presentation on soil structure and stability. It discusses how organic materials like compost affect aggregate formation and stability through their carbon content, including polysaccharides, microbial biomass, and humic substances. The presentation describes a study that found municipal solid waste compost stabilized soil aggregates the most due to its high humic acid content. This improved hydraulic conductivity and yields. In conclusion, soil structural stability depends on the composition of applied organic materials, particularly their humic acid content.