2012-06-20_PERMIT FILE - C2010089 (60)

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Properties POWER ET AL,: EFFECTS OF TOPSOIL AND SUBSOIL THICKNESS ON SOIL WATER CONTENT 125 Table 1 -Some properties of the topsoil, subsoil, and mine spoil used. Organic C, % 1.5 Total N, % 0.13 Inorganic N, ppm 12 NaHCO,- soluble P, ppm 21 Sand, % 52.6 Silt, % 31.1 Clay, % 16.3 Water content (cm' /cm'): 1/3 bar 0.28 15 bars 0.13 Saturation percentage 41 p11 (saturated paste) 7.3 EC, mmho/cm' 1 Soluble Ca, meq/liter 6.7 Soluble Mg,meq /liter 4.1 Soluble Na, meglliter 1.4 Sodium adsorption ratio 1 Topsoil Subsoil Mine spoil 1.2 1.0 0.07 0.03 7 32 5 5 24.6 7.4 43.7 55.1 31.7 37.5 0.48 0.53 0.22 0.28 47 110 7.7 8.0 4 3 9.1 2.2 12.9 1.8 22.6 34.7 6 25 1.5 -m areas centered at intervals of 5.23 m up the slope, giving 10 sampling sites per subplot. Wheat was harvested in August, but the perennial crops did not grow enough in 1975 to warrant harvesting them, In September 1975, soil samples were collected from each subplot 1.25, 5.00, 15.0, and 45.0 m from the toe of the wedge. Each sample consisted of a composite of 3 cores 2.5 cm in diameter. Depth intervals of sampling varied with top- soil treatment and with distance from toe of the wedge, but in all cases they extended at least 30 cm into the mine spoils beneath the replaced soil material. These samples were air - dried and analyzed for NaHCO 1', organic C, and total and inorganic N. Saturation extract was analyzed for pH. elec- trical conductivity, saturation percentage, and soluble Ca, Mg, and Na. The Na adsorption ratio was then calculated. Extrac- tion and analytical methods were those suggested by Sandoval and Power (1978) for use on western mine spoils. In the spring of 1976, 1977, and 1978, spring wheat plots were again seeded, with 12 kg P /ha banded with the seed. All plots but those in alfalfa also received 55 kg N /ha broadcast (ammonium nitrate). Soil water content was measured in early spring and at 1 - to 2 -month intervals during the growing season. All crops were harvested at appropriate times, using the same sampling positions and procedures described above. After har- vest each fall, soil samples were collected from alfalfa plots only from 0- to 15- and 15- to 30 -cm depths and at 30 -cm depth intervals to 120 cm. Samples were taken at the same four slope positions indicated above and were analyzed as above. In 1976, a July hailstorm broke off an estimated 20 to 40% of the wheat heads, invalidating yield measurements for wheat that year. In both 1977 and 1979, severe spring drought and hot weather retarded wheat growth and development so much that the crop was destroyed in June, and the plots were summer fallowed thereafter. Consequently, usable wheat yields were obtained only in 1975 and 1978. RESULTS Soil chemistry data are presented only for 1975, the first year of the experiment (Table 1). The mine spoils were high in clay and in exchangeable Na, re- sulting in particle dispersion and very low perme- ability (< 15 cm /year). The Temvik silt loam topsoil materials, which developed primarily on loess with some glacial till at lower depths, were low in Na and in total soluble salts. Some year -to -year changes in concentration of soluble ions in the saturation extract occurred, but these were not large enough to influ- ence plant growth appreciably. There has been evi- dence of some upward migration of salt, but this phenomenon will be discussed more fully in later papers. Saturated paste pH of soils and mine spoils ranged from 7.3 to 8.0. Organic C content of 1.0% or more in spoils may have resulted partially from the inclu- sion of some wasted lignite in the spoils. In 1975, Table 2- Monthly precipitation during growing season at Stanton, North Dakota. Year April May June July Aug. Sept. Oct. 1975 1.1 1976 7.4 1977 0.3 1978 4.2 1979 3.2 t No record. 2.2 1.8 6.8 5.2 2.7 11.0 9.6 6.2 8.8 7.2 Precipitation cm 2.3 1.3 9.0 6.2 7.9 0.3 0.1 4.2 0.9 12.3 2.5 0.9 13.8 8.8 2.5 1.3 0.8 1- 1- 0.3 the mine spoils often contained over 30 ppm exchange- able Na and nitrate -N, and concentrations of this magnitude still occurred in some of the spoil material in 1978. The sources and transformations of the in- organic N in mine spoils were discussed in an earlier paper (Power et al., 1974). Monthly precipitation data are shown in Table 2 for the period of experimentation. In 1975, precipita- tion was near normal, particularly in June. In 1976, precipitation in all months except April was below normal, although some rains of 2 cm or more were again received in June. In both May and June of 1977, precipitation was far below normal, resulting in very poor early season growth of all crops; however, September 1977 precipitation established a record high. More normal precipitation was again received in 1978. In 1979, May and early June precipitation was low. Previous research has shown that crop yields under dryland conditions in the Northern Great Plains often depend upon May and June precipitation (Haas and Willis, 1962; Power and Alessi, 1970; Rogler and Haas, 1947). All crops established adequate stands with the first seeding attempt. Average annual yields of alfalfa are given in Table 3. Two crops of alfalfa were cut in all years except 1977, when extreme drought re- sulted in no regrowth after the first harvest. Highest yields were obtained in 1978. Maximum average yields were about 2 metric tons /ha. Except for 1977, alfalfa yields increased as subsoil thickness increased from 10 to about 90 cm. The severe drought in 1977 resulted in wetting of no more than the upper 30 cm of soil, and thus response to increased subsoil thick- ness was not evident that year. However, the 4 -year average yields increased with increasing subsoil thick- ness from 10 to at least 70 cm (differences were not always significant at P = 0.05). This trend was con- sistent for all topsoil treatments, but the magnitude of the yields varied. Greatest yields were measured where topsoil was spread over the subsoil. In the higher precipitation years sometimes yields exceeded 3 metric tons /ha -a good yield for dryland alfalfa on almost any soil in the Northern Great Plains. Thus, these results suggest that about 70 cm of subsoil and 20 cm of topsoil over sodic materials can restore al- falfa yields to a level equal to that expected from undisturbed Temvik silt loam under good manage- ment in this county (USDA, 1978). The 90 -cm thick- ness of topsoil and subsoil at which this yield level occurred is almost identical to the maximum depth to the calcium carbonate layer in undisturbed Temvik silt loam (USDA, 1978). Alfalfa yields decreased somewhat as soil thick- ness increased beyond 150 cm (Table 3). This trend