2002-07-08_GENERAL DOCUMENTS - M2002004 ‎(4)‎

• Permit No: M2002004
• IBM Index Class Name: GENERAL DOCUMENTS
• Doc Date: 7/8/2002
• Doc Name: ATTACHMENT, PART 3
• From: HABITAT MGMT
• To: DRMS
• Media Type: D
• Archive: No

1. Highest yields were always obtained when at
least 8 inches of topsoil was applied.
2. At equal total soil depths of 28 and 36 inches,
yields were higher when 8 inches of sandy loam
topsoil was placed over clay loam subsoil than
when 24 inches of topsoil was applied.
3. Higher yields at the midpoint of the slope as
compared to the top of the slope (where total
soil depth was greater) are attributed to
moisture differences due to rainfall runoff and
snow accumulation.
4. Highest yields of all crops were obtained at
total soil depths of 36 to 52 inches.
Zap Double Wedge Experiment:
Another wedge experiment was initiated in 1975 at
the Indianhead Mine near Zap (Merrill et al., 1982b) in
which 10 inches of topsoil was uniformly placed over
three different subsoil materials which differed in
salinity, sodium content and texture. The topsoil
was a nonsaline, very slightly sodic loam (Table 13).
10
The first subsoil material (listed as "A ") was a
moderately saline, somewhat sodic silty clay; the se-
cond subsoil (listed as "B ") was a slightly saline,
somewhat sodic loam; the third (listed as "C ") was a
nonsaline, very slightly sodic loam. The underlying
spoil was a moderately saline, moderately sodic silty
clay. The subsoil materials were placed in a double
wedge which was 42 inches thick at the summit and
which sloped to zero thickness at the north and
south limits of the wedge. The south slope was 1 to 2
percent and the north slope was 5 to 6 percent
(Figure 4). Four plots parallel to the slope were laid
out over each of two blocks of subsoil materials and
seeded to spring wheat, alfalfa, crested wheatgrass,
and Russian wildrye. Yields for only spring wheat
and crested wheatgrass are discussed here.
Average crested wheatgrass and spring wheat
yields were related to topographic position, total soil
thickness and subsoil properties (Figure 5). Max-
imum yields of both crops were obtained at
midslope positions on both north and south slopes,
but higher yields were obtained at the midpoint of
the steeper north slopes than on the midpoint of the
gentler south slopes (Figure 5). As total soil thick-
ness decreased below the midslope position, yields
Figure 4. Schematic diagram illustrating the construction of the Zap double wedge experiment (Merrill et al., 1982b).