Beyond Homogenized Soil Samples: The Importance of Soil Aggregates in Biological Soil Analyses as Demonstrated by Aggregate‐Scale Enzyme Activities

ABSTRACT

Conventional soil analysis is typically based on the < 2 mm soil fraction, assuming structural and functional homogeneity within this size range. However, soils are inherently heterogeneous systems composed of aggregates with diverse physical, chemical, and biological properties. This study rethinks conventional soil analysis by evaluating the role of aggregate size in determining soil enzyme activities under different tillage systems. Soil samples were collected from wheat fields managed under conventional tillage and minimum tillage for 4 years in Iğdır, Turkey. Aggregates were separated into distinct size classes using a dry sieving method, and catalase, urease, and alkaline phosphatase activities were measured in each fraction. Whole‐soil enzyme activities were then calculated using a weighted average approach based on aggregate size distribution and compared with values obtained from the conventional < 2 mm method. Results showed that aggregate size distribution differed significantly between tillage systems, with minimum tillage promoting a higher proportion of smaller aggregates. Enzyme activities varied significantly among aggregate size classes in both tillage systems ( p  < 0.05), indicating strong aggregate‐size‐dependent biological heterogeneity. The weighted average method consistently produced higher and statistically different enzyme activity values compared to the < 2 mm approach, particularly for urease and phosphatase activities. These findings indicate that focusing solely on the < 2 mm fraction may lead to an underestimation of actual soil enzyme activity and may mask important biological variability within the soil. It means that including information about the distribution of different soil aggregate sizes in soil analyses allows for a more precise, realistic, and representative evaluation of how soil biological processes function. This study highlights the need to reconsider conventional soil analysis protocols and emphasizes aggregate size as a critical dimension in soil health evaluation.