Monday, November 13, 2006 - 11:10 AM

Soil Structural Recovery in Relation to Carbon and Nitrogen Content in a Chronosequence of Reclaimed Sites.

Abbey Wick1, Peter D. Stahl1, Lachlan J. Ingram1, Gerald Schuman2, and George F. Vance1. (1) Univ of Wyoming, 1635 Spring Creek Dr, Dept 3354, Laramie, WY 82070, (2) USDA-ARS High Plains Grasslands, 8408 Hildreth Rd, Cheyenne, WY 82009

Recovery of belowground ecosystem components, such as soil structure and nutrient cycling, in reclaimed mine lands is crucial to successful reclamation of disturbed lands. Our objectives in this study were to observe soil structural recovery through time and examine organic carbon (C) and nitrogen (N) contents of:  (1) 250-2000 and 53-250 µm aggregate size fractions, (2) free light fraction (LF) for each size fraction, and (3) intra aggregate particulate organic matter (iPOM) for each size fraction on a chronosequence (0.3 year old topsoil stockpile, 14 and 26 year old reclamation, and a native site) of several mine sites. We determined water stable aggregate size distribution with wet sieving, LF and iPOM with high density liquid flotation and total C and N concentrations through dry combustion.   Total C data were corrected for inorganic C to enable evaluation of organic C.  There was a significant increase (P≤0.05) in macroaggregates (250-2000 µm) on a weight basis from recently stockpiled soil to reclaimed soils and free macroaggregates decreased through time on a trajectory towards the native soil structural condition. Free microaggregates (53-250 µm) decreased between the stockpile and reclaimed soils with time, indicating incorporation of free silt and clay and free microaggregates into macroaggregates. Organic C and N increased with time in the various aggregate size fractions, indicating recovery.  These preliminary results suggest that soil structural recovery occurs on a time scale of 10 to 20 years in reclaimed soils and is mechanistically related to organic C (soil organic matter) accumulation.