|
Vut -t` • _ , l p1 ("ti (-".4-
<br />Reprinted from the Journal of Environmental Quality °/ I � ~
<br />Vol. 13, no. 3, July- September 1989, Copyright © 1989, ASA, CSSA, SSSA
<br />677 South Segoe Road, Madison, WI 53711 USA
<br />Soil Depth Requirements for Revegetation of Surface -Mined Areas in Wyoming, Montana,
<br />and North Dakota'
<br />ABSTRACT
<br />The objective of This study was to determine depth of soil that
<br />should he applied over spoil to ensure adequate production of cool -
<br />season grasses al surface mines in the Northern Great Plains. During a
<br />6 -yr period, data were collected from 15 wedge plots and the response
<br />of perennial grass production to increasing soil depth was measured.
<br />Production responses were dependent on spoil trails and four spoil
<br />types were recogni,ed: generic, sodic, acid, and soil -like. Soil depth
<br />required for maximum production was 50 cm for generic spoil, 71 cm
<br />for sodic spoil, indeterminate for acid spoil, and 0 cm for soil -like
<br />spoil. Root penetration into spoil appeared limited to s 10 cm, except
<br />for soil -like spoil where root penetration exceeded 110 cm. Native and
<br />introduced grasses responded in a similar manner to increasing soil
<br />depth, and precipitation had no significant effect on the depth of soil
<br />required for maximum grass production.
<br />Additional Index Words: spoil traits, rooting depth, reclamation,
<br />cool - season grasses.
<br />Barth, R. C., and B. K. Martin. 1984. Soil depth requirements for re-
<br />vegetation of surface -mined areas in Wyoming, Montana, and North
<br />Dakota. J. Environ. Qual. 13:399 -404.
<br />The vast deposits of subbituminous coal found in the
<br />Northern Great Plains (NGP) are being developed
<br />rapidly as a domestic energy source. Surface mining
<br />techniques used to extract this resource disturb large
<br />areas of land, and the return of these areas to an ac-
<br />ceptable post- mining land use is the goal of reclamation
<br />efforts. An important step in reclamation is the salvage
<br />and eventual return of soil to recontoured spoil sur-
<br />faces. Numerous studies have demonstrated the benefit
<br />of applying soil during reclamation, but this process
<br />represents the most costly single item in terrestrial
<br />reclamation. In 1983, the cost to salvage and return 30
<br />cm of soil was estimated at $7600 h '. From an ecologi-
<br />cal, economic, and energy use standpoint, it behooves
<br />us to quantify soil depth requirements necessary to meet
<br />post- mining land -use objectives.
<br />Soil depth research in the NGP was initiated in 1972
<br />when Ries et al. (1978) applied from 0 to 30 cm of soil
<br />to sodic spoil; grass production was greatest at the 30 -cm
<br />soil depth. Utilizing a wedge -type plot design that
<br />allowed soil (mixed topsoil and subsoil) depth to vary
<br />from 0 to 190 cm over sodic spoil, Power et al. (1981)
<br />found that vegetative production reached maximum
<br />levels at soil depths ranging from 70 to 130 cm, depend-
<br />ing on the species. Preliminary results from Halvorson
<br />et al. (1981) indicated that maximum yields of annual
<br />crops can be obtained by applying 30 cm of soil to
<br />moderately sodic spoil, but in some years, precipitation
<br />appeared more important to plant production than soil
<br />' Contribution of the Environ. Technol. Div., Colorado School of
<br />Mines Res. Inst., Golden, CO 80403. Research supported from funds
<br />provided by the Bureau of Mines, U.S. Dep. of Interior, under
<br />Contract no. J0265025. Received 4 Nov. 1983.
<br />'Senior Research Ecologist and former Research Biologist, respec-
<br />tively, Colorado School of Mines Res. Inst.
<br />RICHARD C. BARTH AND BROOKS K. MARTIN'
<br />depth. Merrill et al. (1982) suggested that 60 to 90 cm of
<br />soil depth was required for maximum production of
<br />forage grasses when revegetating moderately sodic.
<br />spoil. Schuman and Power (1981) stated that no
<br />increase in forage and crop yields was evident when
<br />> 76 to 102 cm of soil was applied to spoil in the NGP.
<br />The above -cited literature indicates that soil depth re-
<br />quirements for maximum yields in the NGP range from
<br />30 to 130 cm, depending on spoil characteristics, pre-
<br />cipitation, and species requirements.
<br />This wide range in soil depth requirements provides
<br />little guidance for those involved in reclamation, and
<br />more precise information is needed. This study was de-
<br />signed to provide some of this information by quantify-
<br />ing soil depth requirements to maximize cool- season
<br />grass production pursuant to revegetating spoil gener-
<br />a ted during surface coal mining in the NGP.
<br />MATERIALS AND METHODS
<br />Plot Construction
<br />Using spoil considered representative of that being produced at a
<br />given location, 15 wedge -type plots (Fig. 1) were constructed at sur-
<br />face coal mines in Wyoming, Montana, and North Dakota. The
<br />wedge design established a uniform soil depth gradient ranging from 0
<br />to 152 cm; plot dimensions were 6 by 15 m except for two larger plots
<br />having dimensions of 15 by 33 m. Most plots were located in recon-
<br />toured spoil being prepared for soil application; slope ranged from 1
<br />to 3 %. Soil was obtained from existing "topsoil" stockpiles at each
<br />plot location and these soils were considered typical of the soil avail-
<br />able for reclamation use. As used in this paper, soil is defined as those
<br />portions of the A, B, and C soil horizons which have chemical and
<br />physical traits conducive to plant establishment and growth and which
<br />are suitable for reclamation use according to state and federal regula-
<br />tions. Most plots were constructed using tracked machinery that mini-
<br />mized compaction; areas of suspected compaction were deep ripped
<br />during construction. A 1.5 - buffer area surrounded each plot and all
<br />plots were fenced and diked immediately after construction. Most
<br />plots were constructed in 1977, although some plots were constructed
<br />in subsequent years until 1980.
<br />Following seedbed preparation and fertilization (67 kg ha of P and
<br />56 to 112 kg ha of N), perennial grasses were drill seeded into the
<br />plots at a rate equivalent to 320 live seeds m and at a depth of 2 cm.
<br />Grass rows were oriented north -south and were spaced at 30 inter-
<br />vals. To establish a vegetative constant, seven rows of 'Nordan'
<br />crested wheatgrass [Agropyron desertorum (Fisch.) Schutt.) were
<br />planted in each plot. Depending on edaphic conditions, six rows each
<br />of two other species were planted in each plot; these species were
<br />selected from 'Luna' pubescent wheatgrass [A. trichophorum Link
<br />(Richt.)l, 'Rosanna' western wheatgrass (A. smithii Rydb.), 'Critana'
<br />thickspike wheatgrass (A. dasystachyum (Hook.) Scribn.), and
<br />`Lodorm' green needlegrass (Stipa viridula Trin.). Jute netting was
<br />applied to the plots immediately following seeding.
<br />Field Data Collection
<br />Perennial grasses were harvested during August of 1978 through
<br />1983 in 0.91 -m wide strips perpendicular to the soil depth gradient; the
<br />number of plots harvested in a given year ranged from 6 to 13. An in-
<br />dividual plot was not harvested until it had completed its second grow-
<br />ing season. Stubble height was designed to reflect general management
<br />practices for revegetated areas, and height was either 10 or 20 cm,
<br />depending on production. Harvesting at this height removed from 50
<br />J. Environ. Quaff., Vol. 13, no. 3, 1984 399
<br />
|