Compost derived from olive mill cake: Effects on isohumic soil quality based on humic acids characterization

Area of Science:

• Soil Science
• Environmental Chemistry
• Agronomy

Background:

• Soil organic matter (SOM) is crucial for soil health and stability.
• Compost amendments are used to improve soil properties, but their impact on SOM stability requires detailed investigation.
• Understanding the humification process is key to assessing the long-term benefits of soil amendments.

Purpose of the Study:

• To evaluate the effects of compost on soil organic matter (SOM) stability.
• To compare compost effects with manure application on humic substances.
• To characterize the humification process and the resulting humic acids (HA) under different amendment scenarios.

Main Methods:

• Greenhouse experiment with soil amended with manure (10%) and compost (10%, 20%, 40%) for 90 days.
• Extraction of humic acids (HA) and fulvic acids (FA) from soil layers (0-15 cm and 15-30 cm).
• Determination of C_HA/C_FA ratio, humification parameters, and spectroscopic characterization (E₄/E₆, FTIR) of HA.

Main Results:

• Amendment concentration influenced humification parameters over time.
• Compost applications (10% and 20%) resulted in higher humification levels and more oxidized HA structures compared to 10% manure and 40% compost.
• Spectroscopic analysis revealed increased aromaticity and O-containing groups in HA, indicating enhanced molecular associations and humification.
• The upper soil layer showed higher HA reactivity, while the lower layer was more humified.

Conclusions:

• Compost application, particularly at 10% and 20% rates, effectively enhances SOM stability through improved humification.
• The humification process leads to the formation of more stable, complex HA macromolecules with increased functionalization.
• Soil depth influences the humification process and SOM characteristics, with upper layers exhibiting greater reactivity.