Page 305 - Advances In Productive, Safe, and Responsible Coal Mining

Sustainable reclamation and water management practices 281

microorganisms in the native soil aid in creating channels for air and water movement
that is essential to productive vegetation.
Salvage and reuse of native soil is also important when conducting reclamation for
a postmining use such as cropland. For example, soil consists of visually and texturally
distinct layers that have been described by soil scientists as follows from top to
bottom:
Horizon A: The top layer is often referred to as topsoil. It consists primarily of darker
decomposing organic materials called humus. It is the horizon in which the most biological
activity occurs.
Horizon B: Commonly referred to as subsoil, this horizon consists primarily of concentrated
mineral layers, such as clay or oxides of iron or aluminum. It may contain some organic
matter. Both organic and mineral matter are typically moved to this horizon by leaching.
Horizon C: The bottom layer is weathered bedrock. It may contain large boulders or shelves
or parent rock that is still undergoing the weathering process.
These horizons are sometimes divided into subhorizons to account for certain special
characteristics. Occasionally, these subhorizons are identified separately. For exam-
ple, Horizon O (for organic) is used to identify a top layer of organic plant residue in
relatively undecomposed form; Horizon E (for eluviated) is used to identify top soil
that has had most of its mineral and/or organic material leached out. Research has
shown that the salvage and respreading of individual soil horizons to a depth of
1.3m (4ft) can greatly aid in restoring the agricultural productivity of prime farmland
(further details are provided later).
Soil compaction is necessary at mine sites that are being prepared for developed
postmining land uses such airports, shopping centers, and industrial parks. At most
mine sites, however, soil compaction is not desirable and should be avoided. Living
plants extend roots into the soil to obtain water and nutrients, but compacted soils will
hinder development and activity of functional rooting systems. Dense soils will phys-
ically impede root extension, water movement, and movement of air between the
rooting zone and the surface. Minimizing compaction during soil spreading operations
is always desirable when the postmining land use is dependent on the productivity of
living plants.
Hay land, pasture, and other agricultural postmining land uses often require
smooth surfaces. Experience has shown that pasture grasses and legumes are able
to survive and grow on mine-soil surfaces that have been graded smoothly if soils
are graded when dry, are not excessively compacted, and have favorable chemical
properties. In contrast, natural ecosystem restoration typically requires loose soil
conditions and does not require smooth surfaces. On such lands, even minor amounts
of compaction can influence rooting by inhibiting native plant species which have
less-aggressive rooting systems than commonly used reclamation grasses. Smooth
soil surfaces, even when slightly compacted can inhibit water infiltration, increasing
water runoff and erosion; while less intensive grading leaves loosened, and often
rougher surfaces, which enhances soil moisture infiltration and retention. In addi-
tion, several studies have found that surface roughness can aid in establishment
of unseeded volunteer plants that arrive as live seed [46,47].