Effects of combination of tillage with olive mill wastewater on soil organic carbon groups in arid soils

Soil fertility in arid areas is poor due to the climatic conditions, weak natural biomass and inappropriate agricultural practices. Soil fertility can be determined by asses the chemical composition of soil organic carbon (SOC) and soil organic matter (SOM) quantity in different systems of soil management. To identify efficient field management practices for enhanced soil fertility in arid regions, the impact of combination tillage with olive mill wastewater as compared to native vegetation were studied for more than 20 years of field experiment. Soil samples were collected from three field management treatments and three replicates for each treatment localized in Chaâl area in southern Tunisia. Field experiment includes uncultivated soil (NC) for more than 80 years (since 1936), with native vegetation, cultivated and tilled soil (CT1) and tilled soil with addition of 5 l.m−2 of olive mill wastewater (CT2). Soil properties were assessed and principal component analysis (PCA) was executed. In addition, structural functional carbon groups were investigated using MIR spectroscopy. The results showed that NC had the highest significant values of moisture content, soil organic matter, and exchangeable cations. This is likely to be due to the role of humified organic matter with colloidal properties. Significant reduction in pH and cation exchange capacity values were found in CT2 conversely to CT1. Olive mill wastewater mineralization provided soluble ions increasing electrical conductivity. MIR analyzes determined higher absorbance of aromatic/aliphatic C in NC and CT2 more than in CT1. Long-term using olive mill wastewater application improved soil carbon groups, which lead to the SOC stabilization for long-term sequestration in arid climates.