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SOIL BIOLOGY & BIOCHEMISTRY

Aggregate-Associated Carbon and Nitrogen in Reclaimed Sandy Loam Soils

^a Dep. of Crop and Soil Environmental Science, 246 Smyth Hall, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
^b Dep. of Renewable Resources, Univ. of Wyoming, 1000 E. University Ave., Laramie, WY 82071-3354

^* Corresponding author (afwick{at}vt.edu).

Minimal research has been conducted on aggregate, C, and N in coarse-textured soils used to reclaim surface coal mine lands. Furthermore, little is known about the contribution different plant communities make to the recovery of aggregation in these soils. Two chronosequences of semiarid reclaimed sites with sandy loam soils were sampled under shrub- and grass-dominated communities. Aggregation, aggregate fractions, and associated C and N were measured. No definitive trends of increasing macroaggregates between sites were observed under shrubs; however, macro- and microaggregation was greater in the 16-yr-old (0.20 and 0.23 kg aggregate kg^–1 soil, respectively) than in the 5-yr-old soils (0.02 and 0.08 kg aggregate kg^–1 soil, respectively) under grasses. Although C and N concentrations were drastically reduced (50–75%) with mining activity between the <1-yr-old and native soils, aggregate C and N concentrations under shrubs and grasses were similar to each other and to the native soils in the 5-yr-old site. Soils under grass in the 16-yr-old site had lower available and aggregate-occluded C and N concentrations than the 5-yr-old site, while C and N concentrations did not change between 5- and 16-yr-old soils under shrubs. Conversely, aggregate C and N pool sizes under shrubs and grasses both increased with site age to conditions similar to those observed in the native soil. Reclaimed shrub site soils had consistently higher C concentrations in the older reclaimed sites (10 and 16 yr old) than the soils under grasses, indicating greater accumulation and retention of C and N in organic material under shrub than grass communities in semiarid reclaimed sites.

Abbreviations: iPOM, aggregate-occluded particulate organic matter • LF, light fraction • OM, organic matter • POM, particulate organic matter • SPT, sodium polytungstate