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

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i)9 south central Wyoming. Elevation at the research site is 2,195 m. Long -term av- erage annual precipitation is 259 mm. The annual frost -free period averages 88 days. Topsoil used in reconstruction was a Borollic Haplargid of the fine -loamy mixed family (7). Topsoil was spread over regraded over- burden in a wedge shape, ranging in depth from 0 to 600 mm (Figure 1). Topsoil was direct - placed rather than stockpiled. Overburden was sloped so that placement of the topsoil wedge resulted in a level sur- face with similar aspect. Overburden was ripped after regrading, but before topsoil - ing. Table 1 presents selected chemical and physical characteristics of the topsoil and spoil. Overburden consisted of a 1 -m layer of White River geologic material covering Wind River formation material. The White River material consisted of ben - tonitic arkosic sands interbedded with fine silts and montmorillonitic clays, laid down during the Oligocene Epoch. The Wind River formation, laid down during the Eocene Epoch, is characterized by high silt and clay content with scattered lenses of arkosic sands in the upper portion of the formation. Topsoil was deep -ripped on 610 -mm centers, disked, then roller - harrowed. Be- fore disking, we broadcast ammonium ni- trate and treble superphosphate at 67 kg N ha - ' and 67 kg P ha - '. We established twenty 4.9- by 45.7 -m plots on the area. Ten randomly selected plots were seeded to barley (Hordeum vulgare L.) in April 1977 at 50 kg ha -'; the barley was allowed to mature, producing a stubble height of 20 to 25 cm. Because of the climate and grow- Figure 1 (below). Reconstructed soil and representative plot layout. Figure 2 (right). Effect of topsoil depth and mulch type on water in- filtration, 1979 -1982. Values with the same letter within a topsoil depth are not significantly different at the 5% level (Duncan's multiple range test). 4 45.7m 250 Journal of Soil and Water Conservation Table 1. Chemical and physical characteris- tics of topsoil and spoil used to construct variable soil -depth plot, Shirley Basin, Wy- oming. Characteristic Topsoil pH EC (mmhos cm C ( %) Kjeldahl -N (pg g -') NaHCO, -P (µg g -') Water soluble cations (meg liter -1 ) K Ca + + m + + Sand (/o) Silt ( %) Clay ( %) Saturation percentage ( %) 7.2 2.47 1.1 900 4.4 9.41 0.80 12.60 1.75 57 30 13 39 140 120 100 BO 60 40 20 0 Spoil 7.0 0.40 0.1 180 0.7 2.36 0.18 1.07 0.35 45 38 17 58 ing season, plants produced only minimum seed; therefore, competition from volun- teer plants was not a problem. In other geographic areas mowing is recommended to prevent seed development. The remain- ing 10 plots were fallowed during the 1977 growing season. In October 1977 we seed- ed all plots with a mixture of 3.9 kg ha - ' pure live seed each of western wheatgrass (Agropyron smithii Rybd.), thickspike wheatgrass [A dasystachyum (Hook.) Scribn. ], slender wheatgrass [A trachy- caulum (Link) Make] and green needle - grass (Stipa viridula Trin.). The 1977 bar- ley plots were direct - seeded; fallow plots were mulched with 5 t ha - ' of barley straw after seeding. We hand scattered and crimped the straw into the soil in two directions. In the spring of 1978 seedling emergence was evaluated (6), but limited growth dur- ing the establishment year prohibited col- lection of production data. Forage yields were obtained from 1979 through 1982 when the major species in the vegetative mixture matured. We established produc- tion sample sites on the plots at topsoil depths of 0, 200, 400, and 600 mm. Forage samples were clipped at ground level, and all vegetation within a 0.18 m= frame was air -dried and weighed. We sampled soil on all plots before plant growth initiation each spring at increments of 0 to 150, 150 to 300, 300 to 600, and 600 to 900 mm. Water content was determined by oven -drying at 105 °C. We used soil moisture and bulk density data to calculate stored water in the profile each spring. In September 1979 and 1982 we made field measurements of water infiltration using a double -ring infiltrometer (2). Soil moisture content at the time infiltration measurements were made ranged from 5 to 7% (w /w basis), which is below the mois- ture content at 15 -bar matric potential. We made five measurements at each top- soil depth for the crimped straw and barley stubble treatment. Cumulative water infil- tration over a 2 -hour period was deter- mined. We conducted an analysis of variance on all data using a factorial design, and used Duncan's multiple range test to test signifi- cant differences between treatment means. Results and discussion Forage production by the seeded species between 1979 and 1982 for the 400- and 600 -mm topsoil depth was significantly greater for grass established with barley stubble than for that established with crimped straw mulch (Table 2). This prob- M CRIMPED STRAW BARLEY STUBBLE 0 S2 200 400 TOPSOIL DEPTH tmm) 600 12 e