2002-07-08_GENERAL DOCUMENTS - M2002004 (4)

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Effects of soluble salt: Soluble salts, including sodium salts, are mobile in the soil and tend to become redistributed in the root zone of disturbed soils and may move upward from spoil materials into replaced soil materials (Sandoval and Gould, 1978). When soluble salts are present, an understanding of salt transport within and below the root zone is needed for planning for the permanent restoration of productivity. When the soil is sufficiently permeable to the 4 or 5 -foot depths, soluble salts in the upper root zone can leach downward. Sandoval et al. (1972) increased the soluble salt level in the surface layer of a sodic clay soil in western North Dakota by deep plowing, but after five years, soluble salt concentrations in the top 12 inches had decreased from 5.8 to about 2.1 mmho/cm, with slight decreases in the 12 to 36 -inch depths. Merrill et al. (1980a) reported that soluble salts had leached out of the top 12 inches and ac- cumulated in the 12 to 36 -inch zone after the first year from a respread moderately saline subsoil over which no topsoil had been applied. In an experiment reported by Schroeder and Doll (1984), soluble salt level of the topsoil of a reclaimed soil decreased from 6.1 to 2.7 mmho/cm in three years. Moderate levels of soluble salts (EC 7) in the fine - textured sub- soil at Zap (Table 14) did not affect yields as much as the coarse texture of the nonsaline subsoil. In general, soluble salts do not appear to be a serious problem in reclaimed soils in North Dakota, although research data are limited. When spoil characteristics and the topographic configuration are conducive to the formation of perched water tables, the possibility exists for the eventual development of saline seeps due to lateral salt movement at some locations. Effects of sodicity levels: When the sodium content of a soil or spoil material is high and the soluble salt content is low, clays become dispersed, water movement is restricted, and conditions become unfavorable for root growth. When soil materials are placed over highly sodic spoil, sodium may tend to move upward and the lower portions of the replaced soil may become unsuitable for root growth. Sufficient soil material must be replaced so that the effective root zone will be deep enough for optimum production after upward sodium movement has ceased. Merrill et al. (1983a) have discussed the factors involved in sodium movement in reclaimed soils in North Dakota; their data show that upward movement of sodium was usually about 4 to 6 inches when 12 inches of soil was replaced over highly sodic spoil. They stated that as the depth of replaced soil was in- creased, the upward movement of sodium would also increase. Upward sodium movement will de- pend upon the sodium content and permeability (hydraulic conductivity) of the underlying spoil. 18 When the underlying spoil was sodic, the early ex- periments (Tables 1 to 3 and Figures 1 and 2) have shown that 12 inches of soil Is not sufficient for op- timum yields. In the Knife River experiment, 12 inches of topsoil over moderately sodic spoil (SAR 12) appeared to be sufficient for optimum yields after two or three years (Tables 4 and 5). On the Stan. ton wedge experiment, the underlying spoil was sodic (SAR 25), and total soil depths for optimum yields varied from 30 inches for perennial grasses to 45 inches for wheat (Tables 7 through 10). On the Zap double wedge experiment, the underlying spoil was moderately sodic, and highest yields of crested wheatgrass were obtained at soil depths of 20 to 28 inches and wheat at depths of 45 Inches.These results indicate that crops are able to utilize some moisture from sodic materials; Merrill et al. (1982 a and b) reported that while some water was extracted from sodic spoil in the Stanton wedge experiment, water uptake from spoil was severely restricted due to low hydraulic conductivity. In areas where the spoil materials are sodic, the productivity of the soils before mining is often low. The amount of soil materials suitable for replace- ment is frequently inadequate, and Tess desirable materials must be used. Reclamation of such areas poses special problems, and research data are limited. Water movement and downward leaching of salts (including sodium) are restricted. In some situations, application of gypsum or a source of soluble calcium will be beneficial. The authors feel that additional research is warranted to study the use and amelioration of poor quality soil and spoil materials in reclaiming stripmined soils. Suggested guidelines for soil depth replacement: Replacement of topsoil is required for restoration of productivity on all reclaimed soils, but the amount of subsoil that will be needed Is dependent upon the chemical and physical characteristics of the undedy ing spoil. Although the productivity Indira of the reclaimed soil will be related to the topographic location and shape, gradient, and &spigot of the slope, sufficient data are not available to lustily variation in the depth of soil replacemenl bawd on topography. The suggested guidelines g*vsn below are related to the depth and propertlikal Of the 1001 zone needed for optimum production= When Mow. perties of the spoil and the amount trod *NNW of available soil materials are not suffiGiifli for roe** tion to this productive level, the po*i1f111ne IOW use must be adjusted accordingly, Pot et hoof t1t tion of Tess than "Ideal" ea ind f1�1iii1Mls� consideration must be given t0 Mutton of vitious properties of topsoil and subioff thehtflithl and* in. teractions between rheas When available, at feast 1 fo0$ t 1$ t) should always be respteed When the underlying WS