Poster prepared by Tigist Tebebu, Christine Baver, Cathelijne Stoof, and Tammo Steenhuis for the Nile Basin Development Challenge (NBDC) Science Workshop, Addis Ababa, Ethiopia, 9–10 July 2013

1. Methods
Introduction
Restrictive soil layers commonly known
as hardpans restrict water and airflow in
the soil profile and impede plant root
growth below the plow depth (Busscher
and Bauer 2003). Preventing hardpans
to form or ameliorate existing hardpans
will allow plants root more deeply,
increase water infiltration and reduce
runoff, all resulting in greater amounts
of water available for the crop (i.e.
green water).
However, there has been a lack of
research on understanding the influence
of transported disturbed soil particles
(colloids) from the surface to the
subsurfaceto form restrictivesoil layers,
which is a common occurrence in
degraded soils.
In this study we investigated the effect
of disturbed soil particles on clogging
up of soil poresto form hardpans.
Tigist Tebebu*, ChristineBaver, CathelijneStoof, and T
ammo Steenhuis
Department of Biological and Environmental Engineering, Cornell University
Visualizing clogging up of soil poresin thetropical degraded soilsand their impact on green water productivity
*: Presenter, e-
mail tyt7@cornell.edu
a
Results& Discussion
Time series images in Fig 4. & a decrease in leachate
sediment concentration with time in thelight absorbance
graph in Fig 5. showed that accumulation of significant
amount of soil particles occur in between sand particles
and at air-
water interfaces, indicating theclogging of soil
pores occurs as a result of disturbed fine soil particles
transported from thesoil surfaceto thesubsurface.
FutureWork
Further infiltration measurements are in progress to determine
theeffect of moisturecontent, clay mineralogy, ionic strength,
pore structure and infiltration rate on the transport and
accumulation of clay particlesto form hardpans.
Fig. 2Apictureshowing compacted soilsin the
upper 60 cmabovethemacro porenetworksin a
soil profilein theEthiopian highlands.
Fig 3. Illustration of infiltration measurement showing
themicroscopeconnected to thecamera capturing the
vertical movement of soil solution in thecolumn. Image
adapted from(Sang, 2012).
References
1.Busscher, W. and P
. Bauer. 2003. Soil strength, cotton root growth and lint yield in a
southeastern USA coastal loamy sand. Soil and tillageresearch 74:151-
159
2.FAO. 2005. Field preparation and planting. http://www.fao.org.Accessed February, 2013.
3.Sang, W., 2012. How Hydrofracking Flowback WastewaterInfluencesColloid
Transport in Unsaturated PorousMedia.
Soil and Water Lab
Fig 1. Illustration of plant root deformed bya
hardpan (left) and plant root growth in a
ripped hardpan (right) (FAO, 2005).
10-
60
cm
Hardpan
Unsaturated sand column infiltration
measurements were performed by applying
0.04g/ml soil/DI water solution on
0.00025-
0.000425 & 0.000425-
0.000625
mm diameter sand texture. The sand
columns were exposed to constant influent
rate of 0.5 ml/min for an hour and half
controlling the inflow rate by a peristaltic
pump.
The leachates draining from the sand
column were collected in cuvettes at five
minute intervals at a five cm suction that
was controlled by the bubble tower.
Concurrently, transportation, circulation
and deposition of clay particles (soil
colloids) were visualized using a bright
field microscope and time series images
and short videos were captured. The
experimental set up isshown in Fig.3
Soil solution
Sediment concentration in the leachate was
measured by determining the absorbance of
radiation at a wavelength of 590 nm with a
spectrophotometer.
y = -0.0003x + 3.0
R² = 0.55
2.95
2.96
2.97
2.98
0 20 40 60 80
Light
Absorbance
Time to leachate collection (minutes)
Light absorbance at
590nm
Linear (Light
absorbance at 590nm)
Figure4: Imagesof infiltration measurement showing thesand column at
thestart of themeasurement, 30minutesof soil solution application, 1hr
application and 2hrsafter thesecond soil solution infiltration on the
previoussand column respectively.
Figure5: Light absorbance
plotted against leachates
collection time.
Our experiment show that forming of the hardpan in the
Ethiopian soils can be related to the infiltration of sediment
rich water after the soils are tilled and the soil cover is
removed by plowing. Ameliorating of these pores clogging
or preventing them to form can help to improve the
rainwaterstoragecapacity of degraded soils.
NBDC Science Workshop, 9-10 July, 203, Addis Ababa, Ethiopia
This document is licensed for use under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 Unported License July 2013