Soil Hydraulic Properties as Influenced by Grass and Agroforestry Buffer Strips Tshepiso Seobi...
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Soil Hydraulic Properties as Influenced by Grass and Agroforestry Buffer Strips Tshepiso Seobi Graduate Adviser: Dr. Stephen Anderson Department of Soil, Environmental & Atmospheric Sciences
Soil Hydraulic Properties as Influenced by Grass and Agroforestry Buffer Strips Tshepiso Seobi Graduate Adviser: Dr. Stephen Anderson Department of Soil,
Soil Hydraulic Properties as Influenced by Grass and
Agroforestry Buffer Strips Tshepiso Seobi Graduate Adviser: Dr.
Stephen Anderson Department of Soil, Environmental &
Atmospheric Sciences
Slide 2
Significant concerns regarding soil erosion, water runoff and
yield loss from row crop production still persist. Conservation
tillage has increased over the past few decades which has improved
soil conservation. Other methods exist for controlling soil erosion
such as agroforestry and grass buffer strips. Rationale
Slide 3
Slide 4
Recently, agroforesty has been suggested as an alternative to
traditional row crop production to stabilize against variable
economics. Work has not been done in temperate climatic zones until
the past decade. Effects of agroforestry practices on soil
hydraulic properties has received little attention. Rationale
Slide 5
Research by Udawatta et al. (2002) indicated that
grass/agroforestry buffer strips reduce water runoff (by about 9%)
and soil loss (by about 12%) in small watersheds compared to a
control watershed. This study will attempt to evaluate the effects
of agroforestry and grass buffer strips on soil hydraulic
properties. Rationale
Slide 6
Project Objectives This study evaluated the effects of grass
buffers, agroforestry buffers, and row crop areas on the following
properties: - ponded infiltration - saturated hydraulic
conductivity - soil water retention - pore size distributions - dry
bulk density, and - CT-determined pore characteristics (CT =
computed tomography)
Slide 7
Additional Measurements Soil water content was continuously
monitored at selected locations in the watershed to allow
comparisons between the agroforestry buffers and the row crop
areas.
Slide 8
Project Hypotheses Soil infiltration properties are not
influenced by agroforestry and grass buffer strips. Saturated
hydraulic conductivity is not influenced by buffer strips. Soil
water retention, pore size distributions and dry bulk density are
not modified by buffer strips. Soil water content throughout the
year is not influenced by buffer strips. CT-measured macropore
characteristics are not affected by buffer strips.
Slide 9
Materials and Methods Three paired watersheds were established
at the Greenley Research Center near Novelty, Missouri. These
North-facing watersheds were demarcated in 1991 and corn and
soybeans were grown in rotation. No-till management was used with
contour planting. 1992-2000 average yields were 8.5 t/ha for corn
and 2.8 t/ha for soybeans. Treatments were established in 1997.
Contour buffer strips are 4.5m wide and 36.5m apart (22.8m at the
lower slope positions). Study Site
Slide 10
Grass species planted in the grass buffers included redtop,
brome grass and birdsfoot trefoil. Tree species planted in the
agroforestry buffers included pin oak, swamp white oak and bur oak.
Soils are mapped as Putnam silt loam (upslope, 0- 1% slope) and
Kilwinning silt loam (downslope, 2- 5% slope) with a water
restrictive argillic B horizon that occurs at a 4-37cm depth.
Slide 11
Slide 12
Slide 13
Field Methods Treatments were agroforestry buffers, grass
buffers and row crop areas. Six replicate locations were selected
in the Agroforestry Watershed for comparison. Three pin oak trees
were selected on each of the second and third agroforestry buffers
for measurement. Grass buffer areas midway between trees and row
crop areas midway between buffers were also selected for
measurement.
Slide 14
Ponded infiltration with single rings (25 cm diam.) were
conducted in June 2003. Rings were driven 18 cm into the soil which
was 5 cm into the claypan horizon. Infiltration rings were placed
on the west side of the tree, 20 cm from the trunk for agroforestry
measurements, midway between two trees for grass buffer
measurements, and midway between buffers north of the selected
trees for row crop measurements. Row crop measurements were made in
non-trafficked interrows. Field Methods Ponded Infiltration
Slide 15
Slide 16
Slide 17
Undisturbed cores (76 mm diam. x 76 mm long) were removed to
determine saturated hydraulic conductivity, water retention, pore
size distributions and bulk density. These cores were taken 20 cm
southwest from the trees for the agroforestry treatment, midway
between two trees for the grass buffer treatment, and midway
between buffers north of the selected tree for the row crop
treatment. Cores were taken at four depths: 0-10, 10-20, 20- 30 and
30-40 cm. Field Methods Soil Cores
Slide 18
Slide 19
Field Methods Undisturbed soil cores in plexiglas rings were
taken 15 cm east from the trees for the agroforestry treatment,
midway between trees for the grass buffer treatment, and midway
between buffers for the row crop treatment. Six replicate cores
were at one depth, 0-10 cm. CT (computed tomography) Soil
Cores
Slide 20
Soil Water Monitoring Campbell CS-616 TDR (time domain
reflectometry) automated samplers were placed in the agroforestry
and row crop treatments in May 2003. Sensors were installed at the
5, 10, 20 and 40 cm depths. Calibration data were collected during
wet and dry water content periods. Field Methods
Slide 21
Saturated Hydraulic Conductivity Soil cores were covered with
nylon mesh at the bottom end and an empty ring was connected with a
rubber band to the top of the sample core. Cores were slowly
saturated over 48 hours in tubs. Cores were removed from the tubs
and hydraulic conductivity was measured with the constant head
method. Some samples were evaluated using the falling head method.
Laboratory Methods
Slide 22
Water Retention Water retention was conducted with Buchner
funnels for higher soil water pressures (-0.4, -1.0, -2.5, -5.0,
-10.0, and -20.0 kPa). Pressure chambers were used for lower soil
water pressures (-33, -100, and -1500 kPa). Laboratory Methods
Slide 23
Slide 24
CT-Measurements Core samples were drained at 3.5 kPa water
pressure. Samples were scanned using a medical Siemens X-ray CT
scanner. Image software (Image-J) was used to evaluate macropore
characteristics. Laboratory Methods
Slide 25
Geometric means of ponded infiltration parameters Treatment
ParameterRCGBAG Green-Ampt K (mm h -1 )1.05 a 3.42 a 3.16 a
Green-Ampt S (mm h -1/2 ) 16.7 a 17.6 a 12.8 a Quasi-steady rate
(mm h -1 ) 10.2 a 13.9 a 17.0 a Results and Discussion
Slide 26
P>F values for saturated hydraulic conductivity (Ksat) and
bulk density Source of varianceKsatBulk density ----------- P >
F ----------- Treatment