Influence of Stability and Origin of Organic Amendments on Humification in Semiarid Soils

The application of soil organic amendments is a widely accepted strategy to maintain soil fertility by maintaining and increasing the levels of soil organic matter. The objective of this study was to evaluate the effect of land application of organic wastes of different sources and stabilization degrees on the soil organic matter humification, measured by changes in the chemical and structural characteristics of humic and fulvic acids by cross-polarization magic angle spinning C-13 nuclear magnetic resonance (CPMAS C-13-NMR) and Fourier-transform infrared (FT-IR) spectroscopy. A microcosm experiment lasting 360 d was performed with 500 g of a semiarid soil amended with different materials: sewage sludge from a wastewater treatment plant, composted sewage sludge, the organic fraction of municipal solid wastes, and composted municipal solid wastes. The addition of the organic amendments increased the amount of humic acids in the soil in all cases, whereas the amount of fulvic acids remained very similar to that of the control soil. The humic acids of the amended soils were characterized by an enrichment of N and aromatic C compounds, along with carboxylic groups, which increased their aromatic and hydrophobic characteristics. Aft er the 360-d incubation, some of the labile compounds added with the organic amendments had been incorporated into the soil humic pool and protected from degradation, contributing to the buildup of soil organic matter. Land application of organic wastes represents a key waste management option in semiarid regions where these materials can be used as an exogenous source of organic matter for soil rehabilitation.