Impact of a synthetic zeolite mixed with soils of different pedological characteristics on soil physical quality indices

The addition of natural or synthetic zeolites induces changes in a soil's chemical, physical, and biological characteristics. Zeolites possess intricate internal frameworks that allow them to modify soil structure and texture, thereby impacting soil hydrological properties. This potential offers opportunities to control soil and groundwater pollution as well as optimize irrigation management practices. In this study, three sandy-loam soils and a silty-loam soil were collected and mixed with different amounts of synthetic zeolite derived from coal fly ash. Repacked soil samples were combined with four levels of zeolite ranging from 1% to 10% by weight and were then hydraulically characterized. This included measuring soil water retention curves (SWRCs) of soil-zeolite mixtures. The data revealed, in accordance with recent research findings, that zeolite influences the hydraulic behavior of soils. In general, we observed that, as the percentage of zeolite increases in the soil, the SWRCs are shifted upwards. This effect is fundamental for explaining the observed changes in the whole set of investigated soil hydraulic properties. The observed changes are also fundamental to evaluate selected soil physical quality (SPQ) indices of agronomic interest, which are investigated in depth in the present research. A specific focus was on the impact of zeolite on modifying the soil's capacity to retain water, hence on the energy required by plants to acquire a unit mass of soil water (referred to as integral energy, EI). Finally, the ANOVA test, linear regression, and multivariate analysis were performed on the entire dataset to support, from a statistical standpoint, the observed correlations between SPQ indices and zeolite amounts. These findings underscored the significance of soil texture in selecting the appropriate soil type for zeolite amendment, confirming that coarse-textured soils are more suitable for zeolite treatment compared to fine-textured soils.