Effects of Land Form and Soil Characteristics On Plant Community Development and Productivity On 28-Year Old Reclaimed Mine Land.

Research in the 1970’s showed that topsoil and subsoil salvage and spreading would adequately reclaim sodic minespoils in the northern Great Plains, but long term assessments were needed. A 1.4 ha North Dakota coal stripmine site was reclaimed in 1975 with 0.2 m of topsoil over 0 to 1.2 m of subsoils, forming a double wedge with 5% north and 1.5% south slope. Subsoils A, B, and C had 43%, 23%, and 14% clay. Seeding treatments were crested wheatgrass (CWG, Agropyron cristatum), Russian wildrye (RWR, Psathyrostachys juncea), alfalfa (ALF, Medicago sativa), and smooth brome (BRN, Bromus inermus). In 2003, plant productivity, biomass diversity and soil properties were determined. Species persistence of treatments was: CWG, 50%; BRN, 49%; RWR, 19%; ALF, 5%. Areas seeded to ALF had highest diversity index value. The order of production of CWG & RWR treatments by subsoil in 1978-81 was C > B > A with 25% avg. C-A difference, which changed little in 2003: C ~ B > A with 28% C-A difference. Productivity of CWG & RWR treatments in 1978-81 was greatest on lower-midslope areas, and relationships between productivity and slope position were strong (P < 0.0001). In 2003, positions with greatest production in CWG & RWR treatments had moved upslope, to upper-midslope and shoulder, but not as much upslope for ALF & BRN. Productivity vs. position relationships in 2003 were weaker (P = 0.03 to 0.05). Strong relationships of productivity to position in 1978-81 obscured response to soil depth, but 2003 results showed productivity responding to 0.8 to 1.0 m soil depth. Increased diversity by 2003 implies more species were using water later in the season than during 1978-81, thereby increasing response to soil depth. Soil EC (0 – 0.6 m) in 2003 was lower than in 1978, indicating soil development, which should have improved response to soil depth.