Mean-weight diameter of aggregation as affected by initial screen size of two fine-textured soils

Authors: Franzluebbers, Alan; TANAKA, KATIUCA - Sao Paulo State University (UNESP); MOMESSO, LETUSA - Sao Paulo State University (UNESP); CALONEGO, JULIANO - Sao Paulo State University (UNESP); CRUSCIOL, CARLOS A. C. - Sao Paulo State University (UNESP)

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/2023
Publication Date: 3/23/2023
Citation: Franzluebbers, A.J., Tanaka, K.S., Momesso, L., Calonego, J.C., Crusciol, C. 2023. Mean-weight diameter of aggregation as affected by initial screen size of two fine-textured soils. Soil Science Society of America Journal. 87:644-655. https://doi.org/10.1002/saj2.20517.
DOI: https://doi.org/10.1002/saj2.20517

Interpretive Summary: Soil aggregation is an important characteristic of agricultural soils. However, methodology for determining soil aggregation is variable, so comparison of approaches is needed. An ARS scientist in Raleigh North Carolina collaborated with investigators from São Paulo State University to compare results of dry-stable and water-stable aggregate determination from two fine-textured soils under differential long-term crop management as affected by initial soil sieving, i.e. passing a screen with 8-mm openings or with 4.75-mm openings. Sieving soil through 4.75 mm had only minor differences in relative aggregation characteristics compared with a more traditional approach of sieving soil initially through 8 mm prior to water-stable aggregation determination. However, relative variation was lower when sieved to pass 4.75 mm than when passing 8 mm, giving this procedure a potential advantage in identifying small changes with management. Large soil depth effects on dry-stable and water-stable aggregation were equally discerned with both sieving approaches. Soil sieved to pass 4.75 mm also allows a bulk sample to be used for multiple analytical tests in the laboratory, including importantly for soil-test biological activity and other C and N mineralization assays. These results will be useful to scientists and soil-testing laboratories to evaluate conservation management impacts on soil biophysical properties.

Technical Abstract: Soil aggregation is considered a key indicator of soil health to protect soil against erosion, enhance organic C storage, and offer habitat for soil organisms. Various methods to assess aggregation may change interpretations of management, and therefore should be cross-calibrated. We assessed the impact of initial sieve opening size (8 mm or 4.75 mm) prior to determination of dry-stable and water-stable mean-weight diameter (MWD) from two fine-textured soils – a Rhodic Hapludox from São Paulo, Brazil and a Rhodic Kanhapludult from North Carolina, United States. Both soils were subjected to management expected to alter surface soil conditions. As expected, initial sieving through 8 mm led to greater dry-stable MWD (3.37 +/- 0.60 mm) than initial sieving through 4.75 mm (1.94 +/- 0.28 mm). However, soil stability index (water-stable MWD / dry-stable MWD) was not affected by initial sieve size opening (0.56 +/- 0.13 mm/mm under both initial sieve openings). Management interpretations were consistent with both approaches as well, and in particular to detect the strong depth effect on water-stable MWD (i.e. declining with depth). Water-stable macroaggregates had 32 +/- 25% greater C concentration than microaggregates; similarly under both initial sieving conditions. Soil stability index when initially sieved through 4.75 mm was highly associated with aggregate stability of 1-2-mm sized dry aggregates, which is a more common procedure. We conclude that passing soil through a screen with 4.75-mm openings to conduct a diversity of soil analyses can be appropriate for obtaining reasonable estimates of and interpretations about surface soil aggregation.