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

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and 2) soluble salt and /or sodicity levels. Modifica- tions of these properties can result from changes in topography and parent material (underlying spoil) and will be discussd in more detail in a following section. The properties of agricultural soils in the stripmin- ing area of western North Dakota have been discuss- ed by Omodt et al. (1975 pages 34 -37). They state that the most productive soils in western North Dakota are located on concave slopes and concave land- scape positions, are medium or finer in texture, con- tain less than 10 percent free lime, the topsoil con- tains 2 percent or more organic matter and is no more than slightly saline or sodic, and the subsoil is no more than slightly saline or somewhat sodic. A discussion of the relation of soil and overburden pro- perties to their use in reclamation is given by Patter- son and Schroer (1980, pages 19 -33). These criteria specify the desirable chemical and physical properties of the soil, but not the optimum depth of the rooting zone. Power et al. (1974) stated that in western North Dakota small grains exhibit root activity to the fourth foot, perennial grasses to the fifth or sixth foot, and alfalfa to the eighth foot. Schroeder and Bauer (1984) noted little change in soil water below 4 feet in revegetated spoil and un- disturbed grassland sites at four mines in western North Dakota over a seven -year period. Unpublished data from the Falkirk trench experiment show no changes in soil water below 5 feet during the four years of the experiment (moisture levels in the top 5 feet are given in Table 18). Bauer (1980) monitored soil water use by wheat in central North Dakota for five years on Heimdal silt loam , a nonsaline, non - sodic well- drained soil of medium texture. The results given in Table 20 are typical of those obtain- ed in this experiment. Moisture depletion was from the top 2 or 3 feet early in the season, and from the top 4 feet later in the season. Moisture depletion below 4 feet was minimal. Moisture was determined using a neutron scattering moisture meter, so small differences (0.20 inches or less) between sampling dates are probably not significant. Danielson (1967) stated that irrigated crops tend to remove water ap- proximately in the proportions 40:30:20:10 from suc- cessively deeper quarter fractions of the root zone. The data in Table 20 tend to subtantiate this pattern of water uptake by dryland crops. Unpublished NDSU data from both reclaimed and undisturbed sites in western North Dakota also support this pat- tern of water use. For maximum productive capacity, reclaimed soils should have the chemical and physical proper- ties listed by Omodt et al. (1975) with a minimum ef- fective root zone depth of 4 feet. These criteria can be used as a guide for determining the needed depth of soil replacement. The lower portion of the root zone may be either replaced subsoil or spoil materials which have satisfactory properties. When the supply of suitable soil and spoil materials is plentiful, replacement of more soil materials than 16 Table 20. Available soil water at various soil depths at Carr- ington in 1971 between wheat planting to harvest. Wheat yield was 39 bushels per acre. Adapted from Bauer (1980). Available soil water at various soil depths (feet) Date 0-1 1-2 2-3 3-4 4-5 5.6 inches 4/30 0.60 0.45 1.00 0.90 1.50 1.20 6/09 0.40 0.65 1.10 1.05 1.50 1.30 6/28 0.75 1.00 1.50 1.20 1.45 1.20 7/19 -0.50 0.00 0.80 0.75 1.30 0.95 8/17 -0.80 -0.45 0.20 0.75 1.30 1.15 'Rainfall received since preceding sampling date upper "B" horizon. Carter and Doll (0 that the productivity of a mixture Ol t "B" horizon materials was ages horizon materials. Topsoil must reclaimed soils for rapid resstabt tivity. Rainfall 2.63 4.65 1.65 1.02 needed to provide an adequate root zone depth will not increase postmine productivity. If the underlying spoil has undesirable properties, more than 4 feet of soil materials will usually need to be replaced to pro- vide a buffer between replaced soil material and the underlying spoil. Frequently, the amount and quality of soil materials available for replacement Is not ade- quate to meet these optimum criteria. In this case, available suitable materials must be effectively utilized, possibly in combination with other Tess suitable materials, to provide the best possible postmine land use. Relation of soil and spoil properties to depths of replacement: During soil development, the topsoil ( "A" horizon) evolves into the most favorable horizon for plant growth. An active microbial population becomes established, a dynamic organic matter content develops, stable aggregates form which facilitate en- trance and movement of air and water into the soils, and available nutrient elements accumulate. Replacement of the original topsoil materials pro- vides a medium for the relatively rapid reestablish- ment of favorable topsoil properties even though the structure and the chemical and microbiological pro• cesses are severely disrupted during rerhoval, stockpiling and respreading. Without the replace- ment of topsoil, the development of these favOI*bII properties would be extremely slow. Carlson it Ma (1961) reported that when topsoil was removed du ing land levelling in North Dakota, replaCOM41 It of a few inches of topsoil helped restore productivity, In the Stanton wedge experiment (TAO** 7, ti S highest yields were obtained only whafl to respread; yields were consistently $oWlt*hS soil and subsoil were mixed prior to Tasmanian" topsoil, or first lift, removed before NOV consists of all the "A" horizon and