2012-06-20_PERMIT FILE - C2010089 (62)

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Introduction Re- vegetation of mined lands in west - central North Dakota is challenging because of the high clay and sodium content of the spoil material and the semi -arid climate. The clay and sodium content of the spoil limits infiltration and increases erosion during high intensity, short duration rain events, which are a common in semi -arid climates. An effective reclamation method used in this area is replacement of a suitable depth and type of soil material over sodic spoil to promote plant community and soil recovery on mined lands (Power et al., 1974). Several soil wedge studies were initiated to determine the suitable depth and type of soil needed to reclaim mined land in west - central North Dakota. Ries et al. (1978) conducted one of the first variable depth studies in Stanton, ND with 0, 5, 15 and 30 cm of topsoil placed over spoil with a Sodium Adsorption Ratio (SAR) of 25. Yields of crested wheatgrass (Agropyron cristatum) were consistently higher for the 30 cm plots compared to the other depths during a 9 year period. Other studies followed to test the addition of subsoil between topsoil and spoil material. Subsoil material was suspected to help minimize sodium movement towards the soil surface. Two soil wedges, the Zap Soil Wedge (ZSW) and the Stanton Soil Wedge (SSW), were established by the Agricultural Research Service (ARS) in 1975 and 1974, respectively. The soil wedges were constructed with motor scrapers and road graders to create large wedge- shaped areas of varying topsoil and subsoil depths over sodic spoil material. The ZSW and SSW study sites are located in Mercer County, North Dakota. The ZSW is located west of Beulah on the Indianhead Lignite Mine and the SSW is located south of Stanton on the Glenharold Mine. Both mining operations extracted lignite from the Tongue River and Sentinel Butte members of the Fort Union Reserves. The ZSW has since been released to a private landowner and the SSW is part of an extended reclamation area. The ZSW study, initiated by Merrill et al. (1998), was established with variable depths (0 to137 cm) and types (A, B, C) of subsoil and a uniform depth of a loam topsoil (20 cm). There were north and south facing slopes established on the wedge with 5% and 2% slopes, respectively (Figure 1). When established, subsoil material A, had an electrical conductivity (EC) of 7 mmhos cm -1 and 45% clay content (silty clay), subsoil B had an EC of 4 mmhos cm and clay content of 34% (clay loam) and subsoil C had an EC of 1 mmhos cm -1 and 13% clay (sandy loam). The soil wedge was seeded with crested wheatgrass, Russian wildrye (Psathyrostachys juncea), spring wheat (Triticum aestivum), and alfalfa (Medicago sativa) in separate subplots across the wedge. Smooth brome (Bomus inermis) was seeded on spring wheat plots after completion of the study. Optimum yields for crested wheatgrass were obtained on 51 to 81 cm of total soil, optimum spring wheat yields were obtained on 89 to 110 cm of total soil and optimum Russian wildrye yields were obtained on 51 to 81 cm of total soil. Crested wheatgrass and Russian wildrye yields were highest on sandy loam subsoil (C) and spring wheat yields were highest on clay loam subsoil (B). Rabbits consumed most of the vegetation on the alfalfa plots within the first two years oFhe study. As a result, alfalfa plots were not sampled. The SSW study was initiated by Power et al. (1981) in 1974. This soil wedge was established to determine plant productivity responses to various depths of silt loam subsoil (0 to 229 cm) and silt loam topsoil (mixed, 0, 20, 60 cm) over sodic spoil material (SAR = 25). Mixed topsoiLtrEatment� onsisted of half sn oil and half subsoil i 1 material. This site had a south facing slope only (Figure 2). Species of vegetation seeded in separate subplots across the soil wedge consisted of spring wheat, alfalfa, crested wheatgrass, and a native grass mixture of blue grama 1234