Long-term tillage practices effects on soil organic matter humification and Humic acids structural changes in soil profiles typical of an arid region

Abstract

Abstract Soil organic matter (SOM) humification and changes in molecular structures of humic acids (HAs) induced by long term practices management over soil profile have been scarcely investigated in arid climates. This study aims to assess SOM humification, HAs molecular structures changes over soil profiles induced by long- term tillage practices under arid climate in south-eastern Tunisia. Two experimental fields were studied: cultivated soil with olive tree and tilled for long term (CT); uncultivated without any practices with native vegetation (NT). Soil samples were collected at different depths from (CT) and (NT) profiles to determine chemical properties. Humic acids were isolated and studied by measuring UV-visible ratios (E465/665, E280/664 and E472/664) and fluorescence spectroscopy analysis. Results showed that long-term tillage practices reduced the SOM amount, aromatic condensation, molecular size and humification degree in surface layer of CT confirmed by the decrease in the emission fluorescence areas and UV- visible ratios. Inversely, in deep layers, results showed a greatly humified organic matter and aromatic structures condensation in CT. Long-term tillage leads to a significant decrease in aromatic condensation and OM humification degree in surface layers. Soil under no-tillage retains their aromatic chemical structures and increases OM humification degree. No-till System is the best alternative to maintain OM chemical structures and restore soil quality underlong- term practices management.