Geology Reference
In-Depth Information
Table 9.3
Soil parameter values used in WEPP runs.
Layer
Depth (mm)
Sand (%)
Clay (%)
OM (%)
CEC (meq/10)
Rock (%)
1
305
6.4
24.5
0.75
16
1.1
2
2032
23.3
47.5
0.25
285
1.2
Interrill erodibility
4702760 kg s m
−
4
Rill erodibility
0.0074 s m
−
1
Critical hydraulic shear
3.5 Pa
Effective hydraulic conductivity
1.44 mm h
−
1
Albedo
0.23
Initial saturation
0.75
Table 9.4
Dates and times of operations on watershed for 2-year corn-soybean-wheat
rotation with three levels of tillage.
Date
Moldboard plough
Chisel plough
No till
4/1/1
Tillage
Tandem disk
Tandem disk
-
4/15/1
Plant corn
Planter, dbl disk
Planter, dbl disk
No-till planter
9/30/1
Harvest corn
-
-
-
10/1/1
Tillage
Moldboard plough
Chisel plough
-
10/15/1
Tillage
Tandem disk
Tandem disk
-
10/16/1
Drill wheat
Drill, dbl disk
Drill, dbl disk
No-till drill
6/15/2
Harvest wheat
-
-
-
6/20/2
Tillage
Moldboard plough
Chisel plough
-
6/25/2
Tillage
Tandem disk
Tandem disk
-
7/1/2
Plant soybeans
Planter
Dbl disk
No-till planter
10/15/2
Harvest soybeans
-
-
-
11/1/2
Tillage
Moldboard plough
Chisel plough
-
(1) moldboard plough, (2) chisel plough, (3) no-till,
and (4) alfalfa production. The particular man-
agement (Table 9.4) was corn planted in the
spring followed by a fall harvest, tillage was per-
formed after harvest (for the moldboard plough
and chisel plough managements), and winter
wheat was planted. Winter wheat was harvested
in June, tillage was performed (but not for no-till
management) and soybeans planted. Soybeans
were harvested in the fall, followed by tillage
(but not for no-till management). The grass was
cut for hay on June 1, July 15 and September 1.
The managements modelled are all practised in
the Osage river watershed.
The plants selected (corn, soybean, wheat and
bromegrass) were those in the WEPP database for
high yields. Dates of operation were based on dis-
cussions with a local farmer. When compared
with published alfalfa, corn, wheat and soybean
yields for Missouri (USDA, 1997), average yields
for grass, corn and wheat were quite satisfactory,
while soybean yields were low. The soybean yield
when wheat is harvested and the land then
planted to soybeans in the same year is frequently
low in this area, and the yield results from the
WEPP plant growth reflected this. The combina-
tion of planting before the soil moisture has any
opportunity for recharge, the existence of a clay-
pan, and high transpiration during a period when
rainfall is low, does not produce many opportuni-
ties for high yields for double-cropped soybeans
in this region. Additionally, average yield for the
