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pected to be more responsive to stored soil moisture <br />in early spring. On the other hand, wheat plots were <br />cultivated and the surface soil was loose and friable; <br />growing season rainfall could ,be less subject to <br />runoff because it would infiltrate into the soil more <br />rapidly. The established root system of the cool - <br />season perennial wheatgrass could utilize moisture <br />at the lower depths early in the season, while utiliza- <br />tion of stored moisture by wheat would be limited by <br />the rate of development of the root system. These <br />factors may partially explain the differential <br />response of these two plants to topographic loca- <br />tion. It should also be noted (Figure 5) that higher <br />yields of both crops were obtained on the steeper, <br />moister north slope than on the gentler, dryer south <br />slope. <br />Wheat yields were always higher over the more <br />saline and more sodic fine - textured subsoils than <br />over the nonsaline, nonsodic coarse - textured sub- <br />soil, while crested wheatgrass yields, except in 1978 <br />on the summit position, were always higher over the <br />nonsaline, nonsodic coarse - textured subsoil. Even <br />though both crops are classified as moderately salt <br />tolerant (Merrill et al., 1980b), this differential <br />response between the two species may be due to dif- <br />ferences in salt tolerance, but it may also be due to <br />both seasonal growth differences and to seasonal <br />differences in root growth. <br />Falkirk Trench Experiment: <br />An experiment simulating reclamation was in- <br />itiated in the fall of 1978 near the Falkirk mine at <br />Underwood (Halvorson et al., 1980 and 1982) in which <br />various thicknesses of soil materials were replaced <br />over nonsaline, nonsodic overburden materials dif- <br />fering in texture. Two series of four trenches were <br />excavated to a depth of 15 feet, and three trenches in <br />each series were refilled with an overburden material <br />to within 9, 18, or 27 inches of the original soil sur- <br />face. The fourth trench in each series was refilled <br />with gravelly loamy sand overburden to within 5 feet <br />of the surface, and then with the original clay loam <br />subsoil (second lift) to within 9, 18, and 27 inches <br />from the surface. Topsoil was then replaced in such <br />a way as to refill each trench to the level of the <br />original soil surface; parallel strips of topsoil, at <br />depths of 9, 18, and 27 inches then extended the full <br />length of each trench (Figure 6). Thus, each of the <br />following four overburden and subsoil treatments <br />were overlain with topsoil depths of 9, 18, and 27 <br />inches: <br />1. Gravelly loamy sand overburden <br />2. Gravelly loamy sand overburden overlain by <br />clay loam subsoil, giving a total replaced soil <br />depth of 5 feet <br />3. Clay loam overburden <br />4. Silty clay loam overburden <br />12 <br />Properties of the soil and overburden materials are <br />given in Table 15. Crops were grown each year on ad- <br />jacent undisturbed plots for comparison with yields <br />on the "reclaimed" trench plots. Wheat was grown in <br />1979 and 1982, barley in 1980, and silage corn in 1981 <br />and 1983. Since the plots were cropped continuous- <br />ly, moisture levels at planting were generally low. <br />Rainfall during the growing season was limited each <br />year, especially during parts of the growing season <br />in 1980 and 1983. <br />Figure 6. Cross-section of a trench in the Falkirk experi- <br />ment showing the placement of topsoil, subsoil, and over- <br />burden materials. Subsoil was replaced in only one treat- <br />ment (gls + subsoil); in the other three treatments, topsoil <br />was replaced directly over the overburden at depths of 9, <br />18, and 27 inches. <br />Table 15. Chemical and physical properties of soil and <br />overburden materials used in the Falkirk trench plots. <br />Properties Soll' Overburden <br />Topsoil Subsoil Gravelly Clay Silty clay <br />loamy loam loam <br />sand <br />Clay ( %) <br />Water content <br />at 15 bars (% <br />vol.)' <br />pH <br />EC (mmho /cm) <br />SAR <br />26 32 <br />17 19 <br />7.4 7.5 <br />0.9 0.7 <br />0.8 1.1 <br />9 29 30 <br />8 19 22 <br />7.7 7.5 7.6 <br />1.0 2.7 2.3 <br />1.3 1.4 1.0 <br />Topsoil texture was loam, subsoil was clay loam. <br />Permanent wilting percentage, expressed as volumetric <br />moisture. <br />Throughout the experiment, yields at similar top- <br />soil depths tended to be lower on treatments with <br />gravelly loamy sand without subsoil than on other <br />treatments, except for wheat yields in 1979 at the <br />27 -inch depth (Table 16). Yields at similar topsoil <br />