Soil aggregation and stability is an important soil attribute influencing erodibility and hydraulic characteristics of arable lands and is linked to quantity (and quality) of soil organic matter (SOM). Objectives were to 1) determine effect of management on components of SOM and 2) elucidate relationships between components of SOM and aggregate stability. Components of SOM include glomalin, humic acid, carbon (C), and particulate soil organic matter (POM). Glomalin was measured on soil aggregates and on POM from aggregates that resisted slaking and aggregates that slaked. Aggregate wettability was measured as rate of water uptake under tension and was used to elucidate the degree of water repellency (property related to SOM). Water stability of aggregates was used to identify effect of management on soil slaking. Measurements were made on soil from four sites where each site provided a comparison of either the effect of tillage or crop management on soil quality. Management contrasts included: 1) no tillage (NT) versus tillage of a corn-soybean rotation; 2) level of corn stover removal under NT; 3) crop rotation under NT; and 4) native pasture versus corn-soybean. About 10 kg of soil from the top 5 cm was collected from 3 to 4 plots at each site. A rotary sieve was used to separate soil into six aggregate size groups. We found: 1) SOM was not uniformly distributed among aggregate groups; 2) aggregate wettability was less (improved stability) under NT than under tillage; 3) greater concentration of glomalin under NT compared with tillage (suggesting a link between glomalin and wettability); 4) greater soil C under NT compared with tillage; and 5) POM to be a sensitive indicator of soil condition and water stable aggregation. Results show improved soil aggregation within a short time following a shift to no tillage.
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