Abstract
<jats:p>Soil salinization is one of the critical environmental problems that negatively affects soil microbial activity and enzymatic processes. This study aimed to evaluate the enzymatic activity and humic acid composition of soils from two contrasting regions: non-saline soils of Chinaz district (Tashkent region) and the saline soils of Nishon district (Kashkadarya region). Soil samples (0–30 cm) were analyzed for enzymatic activity (polyphenol oxidase, peroxidase, and phosphatase), while humic acids isolated from the 0–10 cm layer were studied for amino acid and microelement composition. The results showed that saline soils had higher concentrations of soluble salts (Cl⁻, SO₄²⁻, Ca²⁺, Mg²⁺), reflecting increased alkalinity and salinity, whereas non-saline soils contained lower salt levels. Enzymatic activity was significantly higher in non-saline soils, with notable seasonal variations, while saline soils showed a pronounced decline in enzyme activity. Amino acid content in humic acids of non-saline soils (531.77 ± 1.75 mg g⁻¹ was about 1.5 times higher compared to saline soils (348.80 ± 2.04 mg g⁻¹ 1). In contrast, iron concentration in humic acids was higher in saline soils (853.37 ± 1.15 mg g⁻¹) than in non-saline soils (545.27 ± 1.19 mg g⁻¹ ). These findings suggest that both enzymatic activity and humic acid composition can serve as reliable biochemical indicators for assessing soil quality and the impact of salinization.</jats:p>