Tarbiat Modares University Journal of Agricultural Science and Technology 1680-7073 Articles in Press 2026 07 22 Influence of Conventional and Minimum Tillage on Soil Aggregate Size Distribution and Aggregate-Associated Enzyme Activities in a Semi-Arid Region of Türkiye 29023 EN Erhan Erdel Department of Soil Science and Plant Nutrition, Faculty of Agriculture, Igdır University, Igdır 76000, Türkiye. Journal Article 2025 05 12 Tillage practices influence soil structure and biological activity in semi-arid agroecosystems. This study aimed to determine how conventional tillage, minimum tillage for 5 years, and minimum tillage for 10 years affect soil aggregate size distribution and soil enzyme activities in a semi-arid region, and whether long-term reduction in tillage intensity improves soil structural and biological properties. Soil samples were collected from the 0–30 cm layer with three replicates under each tillage system. Soil texture, organic matter, pH, and electrical conductivity were determined, and aggregate size distribution was assessed using the dry-sieving method. Catalase, urease, and alkaline phosphatase activities were measured in different aggregate-size fractions. Results showed that tillage systems significantly affected both soil aggregate size distribution and enzyme activities (p < 0.05). Conventional tillage increased the proportion of macroaggregates (0.425–2.00 mm), whereas minimum tillage, particularly after 10 years, significantly increased the proportion of microaggregates (0.02–0.425 mm). Enzyme activities were significantly higher under minimum tillage than under conventional, with the highest catalase (69.62 ml O₂ 3 min⁻¹ g soil⁻¹), urease (5.81 μg N g soil⁻¹ h⁻¹), and alkaline phosphatase activities (53.94 μg p-nitrophenol g soil⁻¹ h⁻¹) recorded in the 10-year minimum tillage. Enzyme activities also varied significantly among aggregate-size classes. Findings demonstrate that long-term minimum tillage promotes the formation of microaggregates and enhances enzymatic activity, thereby improving soil structure, biological functioning, and overall soil quality. The study highlights reduced tillage as an effective and sustainable soil management strategy for semi-arid agricultural systems. https://jast.modares.ac.ir/article_29023_1fee5d8b6b5230e47fc933334d03ff5b.pdf