TECHNICAL ARTICLE

Performance of Pitcher Irrigation System
Altaf A. Siyal,1 Martinus Th. van Genuchten,2 and Todd H. Skaggs3

Abstract: Pitcher irrigation is an ancient, but very efﬁcient irrigation
system used in many arid and semiarid regions. Small pitchers are often
used because they are less expensive than large ones. However, questions
exist about whether the patterns and extent of soil wetting obtained withsmall pitchers are comparable to those achieved with larger pitchers.
This work addresses these questions through a combination ofexperimental and simulation studies involving three pitcher sizes,
identiﬁed here as large (20 L), medium (15 L), and small (11 L).
Saturated hydraulic conductivities of the pitcher materials were
measured using a constant head method; the measured values ranged
from 0.07 cm dj1 for the large pitcher to 0.14 cm dj1 for the smaller
sizes. To determine the zone of wetting, the pitchers were buried down totheir necks in a sandy loam soil and ﬁlled with water. Water content
distributions were determined after 1 and 10 days at locations 20, 40, and60 cm away from the pitcher center at soil depths of 0, 20, 40, and 60 cm.
Moisture distributions predicted with the HYDRUS-2D simulation
model were found to be in close agreement with the experimental results,
showing root-mean-square-error values between 0.004 and 0.023. The
close agreement suggests that HYDRUS-2D is a suitable tool forinvestigating and designing pitcher irrigation systems. Experimental andnumerical results showed that a small pitcher half the size of a larger one,but with double the hydraulic conductivity, will produce approximately
the same wetting front as the larger pitcher. Simulations for the large
pitcher further showed, as expected, more horizontal spreading of waterin a ﬁne-texture soil as compared with a coarse-texture soil.
Key words: Pitcher irrigation, wetting zone, hydraulic conductivity,
HYDRUS-2D.
(Soil Sci 2009;174: 312Y320)

The dramatic increase in world population has resulted ingreater demand for food and ﬁber. Meeting the growing
demand requires optimizing agricultural production per unit
volume of water application (Theib and Ahmed, 2004), particularly in arid and semiarid regions of the world. Althoughmodern irrigation methods such as sprinkler and subsurface drip
systems may save up to about half of the water presently used
for irrigation, technical, economic, and sociocultural factors
hinder the adoption of these technologies. Thus, developing
traditional, low-cost, water-saving technologies for sustainablecrop production, particularly in semiarid and arid areas, remains
a major challenge in science and engineering, one that has
been ignored by most international developmental programs

1
Department of Land and Water Management, Sindh Agriculture University,
Tandojam, Pakistan;2
Department of Mechanical Engineering, Federal University of Rio deJaneiro, UFRJ, Rio de Janeiro, RJ, Brazil. Dr. van Genuchten is corresponding
author. E-mail: rvangenuchten@yahoo.com
3
U.S. Salinity Laboratory, USDA, ARS, Riverside, CA.
Received January 8, 2009, and in revised form April 8, 2009.
Accepted for publication April 8, 2009.
Copyright * 2009 by Lippincott Williams & Wilkins, Inc.
ISSN: 0038-075X
DOI: 10.1097/SS.0b013e3181a97532

312

www.soilsci.com(Bainbridge, 2001). A notable example of such a neglected
traditional method is pitcher irrigation.
Pitcher irrigation is an ancient irrigation method thought tohave originated in Northern Africa and Iran (Stein, 1998).
Pitcher irrigation has been mentioned in a book written some
2000 years ago in China (Sheng, 1974). The method reportedly
has been used to irrigate watermelons in India and Pakistan(Mondal, 1974; Soomro, 2002); horticultural crops in Brazil,
Germany, and Indonesia (Stein, 1997; Setiawan et al., 1998); andcorn, tomato, and okra in Zimbabwe (Batchelor et al., 1996).
Thus far, little research has been carried out on theperformance of pitcher irrigation systems, including the various
factors affecting water seepage out of the pitchers. The rate ofwater ﬂow seeping out of a pitcher and thus the number of plantsthat can potentially be irrigated by the pitcher are affected by,among other things, the saturated hydraulic conductivity of thepitcher material, pitcher wall thickness, pitcher surface area, soil
type, crop type, and the rate of evapotranspiration. Stein (1998)
found that the hydraulic conductivity of the pitcher material
was the most important of three design factors inﬂuencing theﬂow of water through the pitcher wall, followed by the surface
area of the pitcher and the wall thickness. For successful design,
installation, and operation of pitcher irrigation systems in arid
and semiarid regions, pitchers should be placed at suitabledistances from each other so that the wetted areas do not needlessly overlap, while at the same time ensuring that areas of thesoil root zone are not unintentionally left dry.
In Pakistan and other places, large pitchers cost more thansmall pitchers, and thus, the size of a pitcher affects start-up andinstallation costs. To minimize costs, it would thus be beneﬁcial to use small pitchers for irrigation. The question then arises
whether small pitchers are capable of producing soil wetting
patterns that are comparable to those produced by larger
pitchers. This article presents a combination of experimental

FIG. 1. Illustration of method used to calculate pitcher
surface area.
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Soil Science& Volume 174, Number 6, June 2009

Pitcher Irrigation Systems

TABLE 1. Summary of the Physical Characteristics (With SDs) of the Pitchers Used in This Study
Pitcher Name

Volume (mL)

Height (cm)

Mouth
Diameter (cm)WallThickness (cm)Surface
Area (cm2)

Hydraulic Conductivity(cm dj1)

Large
MediumSmall

19988 T 25
15025 T 35
11012 T 15

31 T 0.810
28 T 0.530
25 T 0.710

12 T 0.410
11 T 0.390
11 T 0.511

1.0 T 0.100
1.0 T 0.210
1.0 T 0.200

2710 T 140
2280 T 150
1840 T 200

0.070 T 0.001
0.076 T 0.001
0.140 T 0.004(Simunek et al., 1999) simulations of pitcher seepage withexperimental data for three different-size pitchers and assessthe utility of using simulation to design and manage pitcher
irrigation practices. We note that in a recent article, Zhang et al.
(2007) also used HYDRUS-2D to study inﬁltration from a completely buried pitcher into an Andisol. They obtained good
agreement between measured and calculated inﬁltration rates
obtained for different supply pressures, and between measured
and calculated soil-moisture contours around the pitcher in thelaboratory-scale experiments.

FIG. 2. Schematic of measurement of the saturated hydraulicconductivity of pitchers using the constant head method.

and numerical simulation research that addresses this question. Speciﬁcally, we investigate the effect of pitcher size andcomposition on soil wetting by comparing the performance oflarge pitchers with low hydraulic conductivity to that of smaller
pitchers with a higher hydraulic conductivity. Numerical simulation is an effective approach for investigating optimal
irrigation practices, for example, by comparing different irrigation scenarios before implementing them (Powis, 2002;
Skaggs et al., 2004). In this article, we compare HYDRUS-2D

FIG. 3. Typical geometry and ﬁnite element mesh used for the
HYDRUS-2D simulations.
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FIG. 4. Measured and predicted water contents for irrigation fromthe large pitcher, 1 day after initiating irrigation. The upper plotshows the predicted water content contour map, whereas thelower plots compare measured (solid circles) and predicted(solid line) water contents along selected vertical transects.
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Siyal et al.

METHODS AND MATERIALS
Pitcher Types
Field trials were carried out at the experimental site of
Sindh Agriculture University in Tandojam, Pakistan. A skilled
potter from that area was asked to prepare pitchers of threedifferent sizes, with the small pitchers being more porous thanthe large ones. The pitchers were made of clay and ﬁred in a kiln;
the potter knew how to alter the porosity and permeability of thepitchers by mixing donkey dung or rice husks with the clay.
Three sizes of pitchers (having different volumes) were
produced. They are identiﬁed here as large (20 L), medium(15 L), and small (11 L). Each pitcher size was replicated fourtimes. Pitcher heights on average ranged from 25 cm (small) to
31 cm (large). Physical properties of the pitchers are summarized in Table 1.
The thicknesses of the pitcher walls (L) were determined bybreaking up three pitchers from each category at the end ofexperiment and measuring the thickness of the broken pieces
with a Vernier caliper. The surface area of each pitcher was
calculated by plotting its actual surface curvature as a function ofheight, as shown in Fig. 1. This was done by ﬁrst using chalk to& Volume 174, Number 6, June 2009

draw the outer pitcher circumference. The radii of the outersurface at different heights were then measured using thread.
The surface area of each incremental height, and therefore of theentire pitcher, was calculated by integration using:ai ¼ 2Pri ðzi  zi1 Þn

A ¼ ~ ai

ð1Þ
ð2Þ

i¼1

where ai is the surface area of the ith segment (L2), ri is theexternal radius of the ith segment, zi is the height of the ith
segment above the base of the pitcher, n is the number ofsegments, and A is the total surface area of the pitcher (L2).

Pitcher Hydraulic Conductivities
The saturated hydraulic conductivities of the pitcher
materials were measured using the constant head method as
described by Abu-Zreig and Atoum (2004). Following thismethod, a pitcher was ﬁlled with water and placed on top of a ﬂat
surface. Water seeped from the pitcher while a constant head
condition was maintained with a Marriotte bottle, as shown in

FIG. 5. Measured and predicted water contents for irrigation from the large pitcher, 10 days after initiating irrigation. The upper left
plot shows the predicted water content contour map, whereas the lower plots compare measured (solid circles) and predicted(solid line) water contents along selected vertical transects.

314

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Soil Science& Volume 174, Number 6, June 2009

Pitcher Irrigation Systems

Fig. 2. The daily decrease in the water volume in the Marriotte
bottle was assumed to be equal to the daily seepage volume.
The saturated hydraulic conductivity (Ks) of the pitcher
walls was determined by applying Darcy’s law to the outﬂow
data. Because the hydraulic head inside the pitcher varied withdepth, Darcy’s law was applied to the individual pitcher
segments and then summed to yield:Ks  nQ¼~ ai ðyi  hs Þ
ð3Þ
L i¼1
from which Ks can be calculated:
QL
KS ¼ n~ ai ðyi  hs Þ

ð4Þ

i¼1

where Q is the seepage rate (L3 Tj1), n is the number of segments, yi is the average pressure head inside the pitcher at theith segment (equal to the depth of the center of the ith segment
below the water level in the pitcher), and hs is the pressure headat outer surface of pitcher (hs = 0 for an atmospheric seepage
boundary condition).

Field Installation
Before burying the pitchers, the top 60 cm of soil was
cultivated to a ﬁne tilth with spade. Cavities for burying thepitchers were dug about three times as wide and two times as
deep as the pitchers. Any clods in the excavated soil were broken
up. Pitchers of all three sizes (large, medium, small) were buriedin the soil down to their necks, with the mouth openings left
2 cm above the soil surface. To avoid evaporation, the mouths
were covered with baked clay lids. The pitchers were reﬁlled totheir initial level every 8 h, and the required volume of water
recorded. Potential evaporation rates from the soil surface during
the study as measured with a pan evaporimeter were found to beapproximately 0.4 cm dj1.

Soil Sampling and Analysis
One and ten days after burying the pitchers, soil samples
were taken from depths of 0, 20, 40, and 60 cm at distances 20,
40, and 60 cm from the pitcher center. Because of the presumed
symmetry of the wetted zone, two samples for each depth anddistance were taken from opposite sides of the pitcher and averaged for data analysis. Gravimetric water contents of the soil samples were determined by recording the weight loss after ovendrying at 105-C for 24 h. The hydrometer method was used todetermine the soil particle size distribution. Soil texture (USDAsystem) was found to be sandy loam, with the sand content
ranging from 56 to 69%, silt from 12 to 27%, and clay from 14 to
19%. The soil bulk density was determined at several locations
down to 60-cm depth using a core sampler with 1.5-cm diameter.
The density measurements ranged from 1.42 to 1.47 g cmj3.
Because no obvious trend in the bulk density was observed, weused the average value of 1.44 g cmj3 to convert gravimetricwater content data to volumetric water contents.

Simulated Wetting Patterns
Water seepage from the buried pitchers into the soil was
simulated using the HYDRUS-2D software package (Simunek
et al., 1999). Assuming a homogeneous and isotropic soil,
axisymmetric unsaturated ﬂow was calculated using thefollowing form of the Richards equation:¯5 1 ¯
¯h
¯
¯h
¯K
¼
rK
þ
K
þ
ð5Þ
¯t
r ¯r
¯r
¯z
¯z
¯z
where 5 is the volumetric water content (L3 LY3); h is the soilwater pressure head (L); t is time (T); r and z are the radial andvertical (positive upward) space coordinates, respectively; and K
is the hydraulic conductivity (L Tj1). The soil hydraulicproperties 5(h) and K(h) were described using the functionsof van Genuchten (1980):
8
5r
<
5r þ
hG0
5ðhÞ ¼
ð6Þ
ð1 þ j>hjn Þm:
5s
hQ0
FIG. 6. Measured and predicted water contents for irrigation fromthe medium pitcher, 1 day after initiating irrigation. The upper
plot shows the predicted water content contour map, whereas thelower plots compare measured (solid triangles) and predicted(solid line) water contents along selected vertical transects.
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mKðhÞ ¼ K s S le 1  ð1  S 1=m
e Þ



2

ð7Þ

where 5r and 5s are the residual and saturated water contents(L3 LY3), respectively; Ks (L TY1) is the saturated hydraulicwww.soilsci.com

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315

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Siyal et al.

conductivity; > (LY1), n (unitless), and : are empirical shapeparameters; m = 1Y1/n, and Se is effective saturation:: ¼

5  5r5s  5r

A ﬁnite element mesh was created with the axis ofsymmetry along the left edge (the center of a pitcher). The
boundary of the ﬂow domain was rectangular (100  100 cm),
except near the upper left corner where the pitcher was located.
The boundary of the mesh there curved inward, following thecontour of the pitcher perimeter (Fig. 3). The ﬂow domain
comprised two materials, a 1-cm-thick layer along the curved
boundary representing the pitcher material, and the remainder ofthe domain representing the assumed homogeneous soilmaterial. The boundary nodes along the pitcher wall wereassigned a constant pressure head, with the pressure head being
zero at the height of the water surface in the pitcher andincreasing linearly with depth to a maximum at the bottom of thepitcher (equal to the depth of the water in pitcher). The
remaining portion of the left boundary was a zero-ﬂux boundary
condition (due to symmetry considerations). A constantpotential evaporation rate of 0.4 cm dj1 was assigned to the& Volume 174, Number 6, June 2009

soil surface boundary, whereas the bottom boundary was set as
free drainage. The ﬂow domain was made large enough toensure that the assumed no-ﬂow condition on the outer (right)
boundary did not affect the simulations.
The soil hydraulic parameters (5r, 5s, >, n, and : ) needed
for the simulations were estimated with the Rosetta pedotransfer
functions (Schaap et al., 2001), which predict the hydraulicparameters from soil texture and related data. We used themeasured soil texture and bulk density data in Rosetta to obtainthe following parameter estimates: 5r = 0.051, 5s = 0.403, Ks =42.7 cm dj1, > = 0.025 cmj1, n = 1.45, and : = 0.5. The initialwater content in the soil proﬁle was determined from soil
samples taken during installation of the pitchers. In view of thosemeasurements, we assumed that the water content was uniform horizontally and varied only slightly with depth, from0.100 cm3 cmY3 at the soil surface to 0.105 cm3 cmY3 at thebottom of the ﬂow domain (100 cm). The simulations used themeasured Ks values for the pitcher materials, which were 0.070,
0.076, and 0.140 cm dj1 for pitchers large, medium, and small,respectively. The pitcher porosity (and hence 5s) was estimatedto be 0.350 cm3 cmj3. Other pitcher parameters were assumed
to be 5r = 0.042, > = 0.000001 cmj1, n = 1.3, and : = 0.5. The
small value of > ensured that the pitcher material would remain

FIG. 7. Measured and predicted water contents for irrigation from the medium pitcher, 10 days after initiating irrigation. The upper
plot shows the predicted water content contour map, whereas the lower plots compare measured (solid triangles) and predicted(solid line) water contents along selected vertical transects.

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Soil Science& Volume 174, Number 6, June 2009

FIG. 8. Measured and predicted water contents for irrigation fromthe small pitcher, 1 day after initiating irrigation. The upper plotshows the predicted water content contour map, whereas thelower plots compare measured (solid squares) and predicted (solidline) water contents along selected vertical transects.

saturated during the simulations. Hence, Ks was the only
parameter of the pitcher material that had a signiﬁcant impact on
the results.

RESULTS AND DISCUSSION
Figures 4Y9 show for the three pitcher sizes measured andsimulated moisture distributions obtained 1 and 10 days after
initiating irrigation. Each ﬁgure shows measured and predictedwater content proﬁles along with selected proﬁle transects, aswell as contour plots of simulated water content proﬁles. The
contour plots were drawn using a kriging interpolation
algorithm.
The transect plots provide a good comparison between
experimental and predicted results. The plots show good
agreement (R2 = 0.96Y0.98) between the experimental and* 2009 Lippincott Williams & Wilkins

Pitcher Irrigation Systems

simulated results. The good agreement is also reﬂected by theroot mean square errors (RMSEs) for the simulated andmeasured water contents along the vertical transects (Table 2).
Root-mean-square-error values range between 0.005 and 0.009
cm3 cmj3 for the large pitcher, 0.004 and 0.013 cm3 cmj3 forthe medium pitcher, and 0.006 and 0.023 cm3 cmj3 for the small
pitcher. This level of accuracy conﬁrms that HYDRUS-2D
simulations are sufﬁciently accurate to justify using this code toinvestigate and design pitcher irrigation systems.
The level of accuracy in the predictions is especially
noteworthy in view of the invoked water application boundary
condition along the pitcher boundary. Previous work by Skaggs
et al. (2004) found similarly good agreement between simulated
and measured moisture distributions around buried drip irrigation lines. However, in that study, the water application boundary was a ﬂux condition (ﬂux-controlled inﬁltration) such that
it was ensured that the actual and simulated applied water
volumes were identical. In this study, we used a constant head
condition (proﬁle-controlled inﬁltration) that causes the inﬁltration rate to depend on the applied boundary pressure headvalues, hydraulic conductivity of the pitcher material, unsaturated soil hydraulic properties, and the initial water content of
the soil. The good agreement obtained in this study for the more
complex proﬁle-controlled inﬁltration scenario is hence a signiﬁcant result. This is also in view of the fact that we used soil
hydraulic parameters estimated with Rosetta-based pedotransfer
functions, rather than direct measurements.
Figure 10 compares observed water contents and, indirectly, the wetted zones produced by the three pitchers 10 days after
irrigation at various locations in the soil. The volume of the large
pitcher was 25% greater than that of the medium pitcher, and
45% greater than that of the small pitcher (see also Table 2). The
surface area of the large pitcher was similarly 15% greater thanthat of the medium pitcher and 32% greater than that of the small
pitcher. Thus, the medium pitcher was approximately threefourths the size of the large pitcher, whereas the small pitcher
was approximately half the size of the large pitcher. On the other
hand, the hydraulic conductivity of the medium pitcher was 12%
greater than that of the large pitcher, whereas the conductivity ofthe small pitcher was twice that of the large pitcher. The resultsin Fig. 10 show that 10 days after burying the pitchers, a very
similar wetting pattern was obtained with the large and medium
pitchers. However, the small pitcher produced 40% higher watercontent at 60 cm from the pitcher center, as compared with thelarge pitcher. Thus, a pitcher half the size of a larger pitcher butwith double the hydraulic conductivity can produce soil wetting
patterns comparable to those obtained with more expensive
larger pitchers. This suggests that for given soil hydraulicconditions, the hydraulic conductivity of the pitcher material is
the most important factor determining water ﬂow into the soil,
followed by the surface area of the pitcher [consistent with theﬁndings of Stein (1998)]. The large pitcher had low hydraulicconductivity but 15 and 32% more surface area than the medium
and small pitchers, respectively, but it created similar wetting
patterns to those of obtained with the small pitcher.
The close agreement between measured and predictedwater content distributions in Figs. 4Y10 gives much conﬁdence
in using HYDRUS-2D to investigate the effects of various
pitcher irrigation parameters on resultant soil-moisture distributions. Especially of interest is the effect of soil texture on
soil wetting patterns. To study this, we carried out a series of
HYDRUS-2D simulations using hydraulic parameter values thatare typical of particular soil texture classes (Carsel and Parrish,1988). Predicted moisture distributions along the soil surface
after 10 days of irrigation are plotted in Fig. 11 for nine soil
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& Volume 174, Number 6, June 2009

FIG. 9. Measured and predicted water contents for irrigation from the small pitcher, 10 days after initiating irrigation. The upper left plotshows the predicted water content contour map, whereas the lower plots compare measured (solid squares) and predicted (solid line)
water contents along selected vertical transects.

textural classes. The ﬁgure shows that, as expected, the horizontal spread of the water is larger in the ﬁner-texture soils. By
comparison, coarse-texture soils will exhibit much more verticalﬂow of water as shown by the contour plots in Fig. 12. Results
such as those presented in 12 are useful for optimizing pitcher
irrigation operational parameters. This pertains not only to thesize of the pitcher and the hydraulic conductivity of the pitcher
material, but also the spacing of the pitchers relative to eachother for a given soil texture, the extent and frequency of reﬁlling, and expected evapotranspiration rates and crop rooting
patterns.

smaller pitchers are less expensive than larger ones, the use ofsmaller, higher conductivity pitchers would reduce irrigationequipment costs in arid and semiarid regions using traditional

TABLE 2. Root-Mean-Square-Error Values for HYDRUS-2D
Simulated and Measured Data of the Volumetric Water
Content at Various Lateral Distances From the Center of the
Pitcher Down to a Depth of 60 cm
Water Content (cm3 cmj3)

SUMMARY AND CONCLUSIONS
Experimental and numerical studies were carried out toinvestigate expected wetting patterns and moisture distributions during pitcher irrigation. The experimental and simulation
results both showed that similar soil wetting patterns can beachieved with small and large pitchers if the smaller pitcher has ahigher hydraulic conductivity than the larger one. Because318

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Large
Pitcher

MediumPitcher

Small
Pitcher

Horizontal
Distance (cm)

1d

10 d

1d

10 d

1d

10 d

20
40
60

0.007
0.005
V

0.008
0.009
0.007

0.008
0.005
V

0.013
0.008
0.004

0.006
0.006
V

0.023
0.013
0.016

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Soil Science& Volume 174, Number 6, June 2009

Pitcher Irrigation Systems

FIG. 10. Comparison of measured water contents at various depths 10 days after initiating irrigation from pitchers having three different
sizes and conductivities.

irrigation methods. However, the small pitchers need more
frequent reﬁlling, which may require extra labor.
Numerical simulations with the HYDRUS-2D software
package were in close agreement with water contents measured
during pitcher irrigation of a sandy loam soil (RMSE values
ranged from 0.004 to 0.023 cm3 cmj3). These results provide

FIG. 11. Predicted water contents along the soil surface fordifferent soil textures, 10 days after initiating irrigation with thelarge pitcher.
* 2009 Lippincott Williams & Wilkins

support for using HYDRUS-2D as a tool for designing pitcher
irrigation systems.
ACKNOWLEDGMENTS
The Fulbright Foundation is gratefully acknowledged
for providing a fellowship to the senior author, as is Sindh
Agriculture University, Tandojam, Pakistan, for approving
sabbatical leave. This study was supported in part also by
CAPES, Brazil.

FIG. 12. Predicted water content contours for different soil
textures 10 days after initiating irrigation from the large pitcher.
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