2002-07-08_GENERAL DOCUMENTS - M2002004 (3)

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In desert ecosystems of North America, soil salinity, sodicity and cation relationships have been shown to affect plant distributions and species diversity, especially at the landscape scale (Wallace et al., 1973; Franco - Vizcaino et al., 1993). Gates and others (1956) found significant edaphic differences between soils occupied by various shrub species in Utah, though no one species was completely restricted by a narrow range of a specific soil factor. Sagebrush and winterfat distribution were restricted by relatively high levels of salinity and sodium. Shadscale typically occupied soils with more intermediate levels of salt and sodium in the subsurface. Soils under greasewood were often, though not exclusively, high in salt throughout and alkaline below 6 in. (Gates et al., 1956). Examination of the soil physical and chemical properties in the northwest NM premine toposequence (Figure 2) shows similar plant -soil relationships as described by Gates et al. (1956). For EC and SAR, variability increases both within and between soils as one moves downslope. While Greasewood - sagebrush communities may not be desirable in a reclaimed landscape, they are found on soils that are saline- alkali, especially at depth. This suggests that it may be necessary to have higher EC and sodicity in the lower portions of the reconstructed soil for certain post -mine plant communities. Clay at depth is typical of well developed Aridisols with argillic horizons. In this landscape, argillic clay often occurs under Sagebrush grasslands (Figure 2). Current suitability standards restrict material >45% clay, presumably for agronomic and permeability reasons. Rejection of certain spoil materials could be a consequence of sample collection and preparation techniques (i.e. over - grinding) that may mask the positive effects of coarse fragments and minimal weathering that alleviate compaction and permeability problems. Soil reactivity appears to be uniformly alkaline across the landscape. Opportunities to introduce some habitat diversity based on acidic soil pH exist when one considers the expected variability of the spoil materials (Figure 2). Fortunately the spoils also have low acid generation potential. But with a truck- shovel operation, it is expected that only small areas of lower pH areas will occur sporadically in the regrade. The use of spoil pH as a gradient seems unlikely. 70 Pinyon - Juniper Sage Grassland Oreasewood /Saga i P -J Chained 80-4 50— s■ei.oihtji. 1t • -.- - V • 30— I t # . 20 - 10- E R. 15 W 25 20 95 —75 . 4 } I I I I I R IL} Ir ■ 1 ■ 75_r 165— 55 sriteo�iay l�mrcs 45 • 35 8044 70 80 50 re < 40 30 20 5wta540y limit 10— * Ort honts i $ 1 Orthias A Araie• Fl rents Spoil Figure 2: Physio - chemical variability of selected soils along a premine toposequence. Weighted average for salvageable topsoil indicated by marker; lines show variability within soil profile. Expected spoil variability on far right from nremine