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SOIL PHYSICS NOTE

Chemical and Physical Treatment Effects on Aggregate Breakup in the 0- to 2-mm Size Range

^a Università di Torino, DIVAPRA–Chimica Agraria e Pedologia, Via L. da Vinci 44, 10095 Grugliasco (TO), Italy
^b Univ. of Tennessee, Dep. of Earth and Planetary Sciences, 1412 Circle Dr. Knoxville, TN 37996-1410

^* Corresponding author (silvia.stanchi{at}unito.it).

The <2-mm size range in soils may contain aggregates as well as primary particles. We investigated the breakup of aggregates <2 mm after applying different chemical and physical agents to 10 samples. Mass-size distributions were obtained by combining wet sieving and x-ray centrifugation after five treatments: water dispersion, chemical dispersion, organic matter removal, physical dispersion, and all of the above combined. The <2-mm range was subdivided into 20 size classes and the fragment production was evaluated with respect to water dispersion. Cluster analysis helped identify similar fragmentation patterns among samples for each determination method. The effectiveness of the single methods differed considerably among samples. Only their combination resulted in pronounced permanent dispersion. An empirical effectiveness index was developed to provide a quantitative assessment of the overall effectiveness of each method. This index indicated that both organic and inorganic binding agents contribute to topsoil aggregation in the <2-mm size range.

Abbreviations: ALL, complete treatment including organic matter oxidation and chemical and physical dispersion • CEC, cation exchange capacity • EDI, effective disruption index • NP, chemical dispersion • PER, pretreatment to oxidize organic matter • PHYS, physical dispersion • SOM, soil organic matter • W, water dispersion