Open Journal of Soil Science, 2012, 2, 213-222
http://dx.doi.org/10.4236/ojss.2012.23026 Published Online September 2012 (http://www.SciRP.org/journal/ojss)
213
Field Assessment of Soil Water Storage and Actual
Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
Justice Okona Frimpong1*, Marcus Quaynor Addy1, Emmanuel Ofori Ayeh1,2,
Harry Mensah Amoatey1,2, Jacob Teye Kutufam1, Bertrand Quaye1, Joshua Osei Sintim1,
Daniel Kwasi Asare1,2
1Nuclear Agriculture Centre, Biotechnology and Nuclear Agriculture Research Institute, Ghana Atomic Energy Commission, Le-
gon-Accra, Ghana; 2Graduate School of Nuclear and Allied Sciences, University of Ghana, Kwabenya, Ghana.
Received July 15th, 2012; revised August 18th, 2012; accepted August 29th, 2012
ABSTRACT
A field experiment was carried out in a coastal savannah agro-ecological zone of Ghana to assess the dynamics of
stored soil water and actual evapotranspiration (AET) of three maize genotypes (Obatanpa, Mamaba, and Golden Crys-
tal) grown under rainfed conditions. Access tubes were installed to a depth of 120 cm for soil water content monitoring
using a neutron probe meter. The soil water balance model of plant root zone was used to estimate AET at different
crop growth stages. On average, the rate of AET for Obatanpa, Mamaba, and Golden Crystal maize genotypes were
estimated as 4.32, 4.46, and 3.72 mm·day−1, respectively, for the major cropping season as against corresponding values
of 3.88, 4.00 and 3.72 mm day−1 for the minor cropping season. Mamaba had higher values of AET from 42 DAE (days
after emergence) to 84 DAE during the minor cropping season while it had low AET values during the major cropping
season. The positive balance in stored soil water in the root zone of Obatanpa was the highest from 42 DAE to 84 DAE
followed by Mamaba and Golden Crystal during the major cropping season. Mamaba, on the other hand, had the high-
est AET from 70 DAE to 84 DAE. Obatanpa used 55.6% of stored soil water for AET, which was the highest among
the maize genotypes during the major cropping season. Golden Crystal and Mamaba followed with 53.3% and 51.5%.
For the minor cropping season, 48.5% of stored soil water was used by Mamaba for AET, followed by Obatanpa,
(46.4%) and Golden Crystal (43.2%). A strong positive significant (p ≤ 0.05) linear correlation existed between AET
and precipitation with the coefficient of determination (R2) being 69.2 for Obatanpa, 88.5 for Mamaba and 82.8 for
Golden Crystal for the major cropping season. Higher R2 values (98.0, for Obatanpa, 94.1 for Mamaba and 98.9 for
Golden Crystal) were, however, obtained for the minor cropping season. Additionally, a strong linear relationship was
found between AET and precipitation, suggesting the need to formulate strategies for enhancing effective use of pre-
cipitation in sustained rainfed maize production.
Keywords: Soil Water Balance; Actual Evapotranspiration; Stored Soil Water; Rainfed Maize Production
1. Introduction
Water, a renewable and natural resource, is the single
most important substance in the lives of both plants and
animals. It plays a very crucial role in the development
and growth of plants, especially during the process of
photosynthesis during which carbon dioxide is converted
to dry matter. It changes from one form to another and
from one environment to another as well. The transfer of
water from one form or environment to another governs
the balance of water in the soil [1]. This balance involves
fluxes between principal pools which are evapotrans-
piration, precipitation, runoff/runon, deep percolation/
drainage, and change in stored soil water. These para-
meters, which influence the amount of water stored in the
soil for plant use, contribute either positively or nega-
tively to the amount of water stored in the soil. The use
of the soil water balance model is one approach to de-
termine whether soil water is being lost or gained.
Evapotranspiration (ET) is the process whereby plants/
crops use water for growth and cooling purposes. The
water which is extracted from the soil by the root of
plants has also been shown to depend on the rooting den-
sity and soil physical properties [2]. These physical
properties of the soil include its ability to store water
*Corresponding author.

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
214
(soil water retention) for plant use and hydraulic con-
ductivity i.e. the ease with which water moves within and
between soil pores. Therefore, for plant growth and de-
velopment to be normal, there must be a favourable bal-
ance of water in the root zone of the plant. However, this
balance has been under the influence of the prevailling
weather conditions.
Several factors have been known to limit rainfed
maize production, the main factor being poor and erratic
rainfall patterns [3,4], particularly in the savannah agro-
ecological zone where maize production is extensively
carried out. Frimpong et al. [5] reported rainfall amount
of 502.4 mm and 290.7 mm during the major and minor
maize cropping seasons, respectively, for the Kwabenya-
Atomic area in the coastal savannah agro-ecological zone
of Ghana. This poor amount of rainfall, which shares
similar characteristics with rainfall conditions in some of
the semi-arid regions of the world [6,7], affects the
amount of stored soil water and the balance of soil water
in the plant root zone as well as crop ET. Despite these
limitations, several high yielding maize genotypes are
being grown in this prevailing harsh environment [8].
As a result of the poor, erratic rainfall in this water
stress prone environment, we assessed changes in stored
soil water and balance of soil water in plant root zone as
well as ET of three elite maize genotypes at different
growth stages under rainfed conditions in a coastal sa-
vannah agro-ecological zone. The information could be
used to formulate strategies for ensuring effective and
efficient use of stored soil water for sustainable rainfed
maize production in the coastal savannah agro-ecological
environment.
2. Materials and Methods
The experimental site was the research farm of the Bio-
technology and Nuclear Agriculture Research Institute
(BNARI) of the Ghana Atomic Energy Commission
(GAEC). The site lies on latitude 05˚40'N and longitude
0˚13'W and elevated at 76 m above the sea level. The
study area, which is located in the coastal savannah agro-
ecological zone of Ghana, receives less than 1000 mm of
rainfall annually [9]. The mean monthly weather infor-
mation for the study period is presented in Table 1. The
soil at the site is the Haatso series, a well-drained sava-
nnah ochrosol (Ferric Acrisol) [10] derived from quart-
zite schist. Some of the chemical and physical chara-
cteristics of the soil are presented in Table 2.
The size of the experimental field was 27.0 m by 22.0
m, giving a total area of 594.0 m2. The randomised com-
plete block design (RCBD) was used with four replicates.
Three maize genotypes (Obatanpa, Mamaba and Golden
Crystal) served as treatments. Each sub-plot measured
8.0 m by 4.0 m. Seeds of each maize genotype were
sown on April 28, 2008 for the major season planting and
September 01, 2008 for the minor season planting. Seed-
lings were thinned to 2 plants per hill one week after
germination to obtain a target plant density of 78,750
plants ha−1.
The planting distance was 0.4 m within rows and 0.8
m between rows. Access tubes were installed in each of
the sub plots to 120 cm soil depth before 50% seed ger-
mination was observed. Access tubes were made of the
polyvinyl chloride (PVC) pipe of 38.1 mm internal dia-
meter with the bottom capped with same PVC material to
Table 1. Monthly weather variables recorded at the experimental site during the study period.
Months Tmax
˚C
Tmin
˚C
R. H. average
%
Sradiation
M·J·m−2·day−1
Windspeed
m·s−1
ETo
mm·day−1
January 33.3 20.7 70.4 17.6 14.4 7.5
February 33.5 24.9 87.4 19.4 15.7 6.3
March 33.2 24.7 89.3 21.9 17.6 6.6
April 32.1 24.1 89.6 20.3 16.3 5.9
May 31.4 23.3 93.6 19.7 15.9 5.8
June 23.4 21.7 96.0 16.4 13.5 4.5
July 28.8 23.3 95.9 16.9 12.9 4.2
August 29.5 22.2 90.5 18.5 11.4 4.8
September 32.1 24.1 89.6 20.3 16.3 5.5
October 31.4 23.3 93.6 19.7 15.9 6.2
November 23.4 23.1 96 16.5 13.5 6.2
December 28.8 23.3 95.9 16.9 12.9 6.0
Average 30.1 23.2 90.7 18.7 14.7 5.8

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
215
Table 2. Chemical and physical properties of soil at the experimental site.
Particle size fraction
Soil layer (cm) pH (H2O) (1:2)
Sand (%) Silt (%) Clay (%)
Textural
class
Bulk density
(g·cm−3)
0 - 20 7.33 41.4 43.2 15.4 Sandy Loam 1.34
20 - 40 7.39 40.4 44.7 14.9 Sandy Loam 1.22
40 - 60 7.83 45.3 43.8 10.9 Sandy Loam 1.41
60 - 80 7.99 48.0 41.1 11.1 Sandy Loam 1.33
80 - 100 7.79 46.3 43.0 10.7 Sandy Loam 1.47
100 - 120 7.85 55.8 36.4 7.8 Sandy Loam 1.38
prevent soil water from entering the tube. The tubes were
installed in between two centre rows within each sub-
plot.
The water content of the soil at 20, 40, 60, 80, 100, and
120 cm depth profile was monitored using the neutron
probe meter [Campbell Pacific Nuclear (CPN®), 503DR
Hydroprobe]. The soil water data were used to estimate
depth of water stored in the plant root zone (0 - 100 cm)
based on the Simpson’s integration method [11]:
0
12345
d
52 421
33 333
L
L
Sz
z











(1)
where SL is the depth of water stored in the soil profile
(cm), θ is the volumetric water content (cm3 per cm3) and
∆z is the thickness of each soil layer (cm). The water
balance method which has been used widely to estimate
the crop water use of field growing crops [12-16], was
used to estimate actual evapotranspiration (AET) for the
three maize genotypes at 14, 28, 42, 56, 70, 84, and 98
DAE during the major and minor cropping seasons:
L
L
PIETRQ S  (2)
where P is the rainfall (mm), I is the irrigation (mm), ET is
the evapotranspiration (mm), R is the runoff (mm), QL
(mm) is deep drainage below the 100 cm soil depth or
capillary rise of water above the 100 cm soil depth, ΔSL
(mm) is the change in soil-water storage in the 0 - 120 cm
soil depth and ∆t is the time set up (days), Runoff was
assumed negligible and, therefore, set to zero since the
slope of the field at the site is less than 1%. Irrigation was
also set to zero because maize crops were grown under
rain-fed conditions. A µMETOS weather station located
about 50 m away from the experimental plots recorded the
daily weather variables.
The soil water flux (QL) at the lower bottom of the soil
profile layer (i.e. 100 - 120 cm) during the period ∆t was
estimated by the relation:
0
d
t
L
Qq


where q is the Darcy’s water flux density, determined as



d
gm
qK z



 (4)
Equations (3) and (4) were combined as


0
d
d
t
L
t
QK z




 (5)
where K(θ) is the unsaturated hydraulic conductivity
(kg·s·m−3) at specific volumetric soil water content
(m3·m−3), ψg is the gravitational potential (J·kg−1), ψm is
the matric potential (J·kg−1) and z is the thickness of the
soil layer (cm).
The estimation of the unsaturated hydraulic conducti-
vity requires the estimate of saturated hydraulic conduc-
tivity. The hydraulic conductivity of the saturated soil was
estimated using the procedure given by Campbell [17] and
the unsaturated hydraulic conductivity estimated as

1.3
31300
410exp 6.93.7
b
s
atcl si
b
K
mm


 

 (6)

23b
sat
s
KK





 (7)
with
0.5 0.2
g
g
bd


 (8)
1b
s
s



 (9)


exp lnlnln
g
cl clsi si sa sa
dmdmdmd (10)

0.5
2
33
2
11
exp lnln
giiii
md md 












 (11)
where mcl, msi, and msa are clay, silt, and sand mass frac-
tions respectively dcl, dsi, and dsa are the particle size limits
separating clay, silt, and sand, respectively (dcl = 0.001
mm, dsi = 0.026 mm, dsa = 1.025 mm), b is the power of
soil moisture characteristic function, dg is the geometric
t

(3)

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
216
mean particle diameter (mm), σg is the geometric standard
deviation (mm), Ksat is the saturated hydraulic conducti-
vity (kg·s·m−3), ρb is the soil bulk density (kg·m−3), K(θ) is
the unsaturated hydraulic conductivity (kg·s·m−3), θ is the
unsaturated moisture content (m3·m−3), θs is the saturated
moisture content (m3·m−3).
The matric potential (ψm) of soil at 80 - 100 cm and 100
- 120 cm soil layers was estimated based on the procedure
given by Campbell [17]:
b
me
s







(12)
0.67
1300
b
b
ees





(13)
0.5
0.5
es g
d 

 (14)
where ψe is the air entry potential (J·kg−1) and ψes is the air
entry potential (J·kg−1) at the soil bulk density of 1300
kg·m–3.
Data on soil water in depth units, precipitation, and
change in soil water storage were represented graphically
with the aid of Microsoft excel in office 2007. Addi-
tionally, the simple linear regression was used to deter-
mine the correlation between AET and precipitation.
3. Results and Discussion
3.1. Climatic Characteristics at Experimental
Site
The highest maximum and minimum temperatures re-
corded at experimental site were 33.5◦C and 24.9◦C for
the month of February (Table 1). On the average, the
maximum and minimum temperature throughout the year
were 27.5◦C and 21.5◦C, respectively. The highest rela-
tive humidity at the experimental site was 96 % which
occurred in June and November. The mean relative
humidity was 83%. Similarly, the highest solar radiation
and wind speed at the site was 21.9 M·J·m−2·day−1 and
17.62 m·s−1, respectively, for the month of March. Ge-
nerally, air temperatures, solar radiation, and wind speed
were higher during the first half of the year as compare to
the second half (Table 1).
Generally, precipitation was higher during the major
cropping season as compare to the minor cropping sea-
son. Precipitations recorded for the major cropping sea-
son from April-July were higher compare to values for
the minor cropping season, September-December, (Fig-
ure 1). The highest monthly total precipitation was re-
corded in May (325.9 mm) during the major cropping
season with the lowest occurring in June (89.0 mm).
Similarly, during the minor cropping season, the monthly
total precipitation was high in October (118.7 mm) with
the lowest rainfall occurring in September (32.9 mm).
3.2. Soil Water Balance of Plant Root Zone
The influence of the poor and erratic rainfall pattern on the
soil water balance in the root zone of the three rainfed
maize genotypes (Obatanpa, Mamaba, and Golden Crystal)
is shown in Tables 3 an d 4. The observed trends in the
balance of soil water in the root zone are similar to those
reported by Baba-Kutigi et al. [18] for maize grown under
rainfed conditions in the northern guinea savannah in
Nigeria.
Generally, the drainage component of the balance of
soil water in the root zone for the three maize varieties was
positive throughout the major and minor cropping seasons
(Tables 3 and 4). This indicates that some amount of soil
water was lost through deep drainage below the root zone
which contributed negatively to the amount of water
stored in the profile for plant use. This evidence con-
tradicts the omission of the drainage component of the soil
water balance model by some workers, based on the as-
sumption that there was no drainage from the soil pro- file
or better still the drainage component is insignificant
under rainfed cropping systems [12-14,16,19].
400
300
200
100
0
Precipitation (mm)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Months
Figure 1. Monthly precipitation distribution at Biotechnology and Nuclear Agriculture Research Institute research station in
2008 cropping season.

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
217
Table 3. Soil water balance in the plant root zone of Obatanpa (O), Mamaba (M), and Golden Crystal (GC) during the major
cropping season.
Season DAE Maize Genotypes
1P (mm) 2I (mm) 3AET (mm)4D (mm) 5R (mm) 6ΔS (mm)
O 21.1 - 22.0 1.8 - −0.8
Major 14 M 21.1 - 22.8 1.7 - 0.0
GC 21.1 - 20.6 1.5 - −1.9
O 42.1 - 18.2 1.9 - −25.9
Major 28 M 42.1 - 34.2 1.7 - −9.8
GC 42.1 - 27.5 1.4 - −16.1
O 63.2 - 89.1 1.6 - 24.3
Major 42 M 63.2 - 74.7 1.7 - 9.8
GC 63.2 - 76.9 1.5 - 12.1
O 54.2 - 63 1.6 - 7.3
Major 56 M 54.2 - 62.4 1.7 - 6.6
GC 54.2 - 61.9 1.6 - 6.2
O 46.1 - 55.5 1.4 - 7.9
Major 70 M 46.1 - 50.9 1.6 - 3.1
GC 46.1 - 60.1 1.8 - 12.2
O 88.8 - 102.7 1.5 - 12.3
Major 84 M 88.8 - 101.9 1.9 - 11.2
GC 88.8 - 104.4 2 - 13.6
O 103.7 - 82.9 1.5 - −22.3
Major 98 M 103.7 - 89.9 1.2 - −15.0
GC 103.7 - 90.5 2.4 - −15.5
1Precipitation; 2Irrigation; 3Runoff; 4Evapotranspiration; 5Drainage; 6Soil Water Storage.
The balance of soil water in the root zone of the three
maize genotypes was negative after monitoring on 14
DAE during the major cropping season under a uniform
precipitation of 21.1 mm (Table 3). On the other hand, the
balance of soil water was negative for Mamaba and
Golden Crystal maize genotypes with the exception of
Obatanpa for which the soil water balance was positive for
the minor cropping season with an amount of precipitation
of 14.2 mm (Table 4). A similar trend in the balance of
soil water occurred at 28 DAE during both the major and
minor cropping seasons. Similar results have been re-
ported by Zhang et al. [20], for maize and winter wheat
grown under different soil water treatments.
For the major cropping season, the balance of water in
the root zone was negative for the three maize genotypes
with the root zone of Obatanpa losing the highest amount
of water followed by those of Golden Crystal and Ma-
maba. Soil water balance around the root of Golden
Crystal was positive during the minor cropping season
with Obatanpa and Mamaba recording a negative balance.
The magnitude of water loss from the root zone was
smaller for Obatanpa and Mamaba during minor cropping
season as compared to that of Golden Crystal which
gained water.
The soil water balance in the root zone of the maize
genotypes remained positive from 42 to 84 DAE during
the major cropping season (Table 3). Obatanpa recorded
the highest positive change in soil water storage at 42
DAE as against Mamaba which recorded the lowest at 70
DAE for the major cropping season. This gives an in-

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
218
Table 4. Soil water balance in the plant root zone of Obatanpa (O), Mamaba (M) and Golden Crystal (GC) during the minor
cropping season.
Season DAE Maize Genotype
1P (mm) 2I (mm) 3AET (mm)4D (mm) 5R (mm) 6ΔS (mm)
O 14.2 - 16.2 1.8 - 0.2
Minor 14 M 14.2 - 15.8 1.7 - −0.1
GC 14.2 - 15.5 1.5 - −0.2
O 28.4 - 30.1 1.9 - −0.2
Minor 28 M 28.4 - 29.3 1.7 - −0.8
GC 28.4 - 36.1 1.4 - 6.3
O 93.4 - 95.6 1.6 - 0.6
Minor 42 M 93.4 - 95.6 1.7 - 0.6
GC 93.4 - 88.9 1.5 - −5.9
O 57.8 - 59.3 1.6 - −0.2
Minor 56 M 57.8 - 59.4 1.7 - −0.1
GC 57.8 - 59.3 1.6 - −0.1
O 43.9 - 53.8 1.4 - 8.5
Minor 70 M 43.9 - 57.9 1.6 - 12.5
GC 43.9 - 49.8 1.8 - 4.1
O 85.3 - 92.3 1.5 - 5.5
Minor 84 M 85.3 - 94.9 1.9 - 7.8
GC 85.3 - 88.5 2.0 - 1.2
O 57.8 - 65.8 1.5 - 6.5
Minor 98 M 57.8 - 49.9 1.2 - −9.1
GC 57.8 - 58.9 2.5 - −1.5
1Precipitation; 2Irrigation; 3Runoff; 4Evapotranspiration; 5Drainage; 6Soil Water Storage.
dication that there was an increase in the amount of water
stored in the root zone of the maize genotypes but with
different magnitudes. The situation was different during
the minor cropping season, but rather the balance of soil
water in the root zone of the maize genotypes was positive
at 70 and 84 DAE, with the root zone of Mamaba re-
cording the highest change in stored soil water as against
that of Golden Crystal which had the lowest change in
stored soil water. The water balance at 56 DAE during the
minor cropping season was negative for the maize geno-
types, which indicates a decrease in stored soil water. On
the other hand, a positive soil water balance was observed
in the root zone of Obatanpa and Mamaba during the
minor cropping season at 42 DAE whereas the root zone
of Golden Crystal had a negative water balance.
Finally, at crop maturity, during the major cropping
season a negative balance in soil water was estimated for
the maize genotype under a precipitation of 103.7 mm.
High amount of water lost from the root zone of the maize
genotypes, with the root zone of Obatanpa losing the
highest amount of water while root zones of Mamaba and
Golden Crystal lost similar amount of water (Tables 3 and
4). For the minor cropping season, a positive balance in
soil water was observed for Obatanpa, which was 0.92
mm greater than that recorded at 84 DAE. This indicates
that Obatanpa maize genotype was still taking up soil
water as a result of capillary rise of water below its root
zone to satisfy evaporative and transpiration demand. On
the other hand, a negative balance in soil water storage
was recorded in the root zone of Mamaba and Golden

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
219
Crystal maize genotypes.
3.3. Depth of Water Stored in Soil
The depth of soil water stored for plant use peaked at 28
DAE, being 239.3, 228.4 and 237.3 mm, respectively, in
the root zone of Obatanpa, Mamaba and Golden Crystal.
This high amount of stored soil water is attributed to pre-
cipitation events that occurred within 28 DAE. Mamaba
used about 14.9 % of the stored soil water for evapo-
transpiration followed by Golden Crystal and Obatanpa
which used 11.6 % and 7.6 %, respectively, at 28 DAE.
The depth of soil water stored dropped from 28 DAE to
84 DAE during the major cropping season (Figure 2(a))
but increased again from 84 to 98 DAE when crops were
already matured. The decline in the stored soil water in the
plant root zone could be attributed to decrease in pre-
cipitation and increase in AET as crop growth and deve-
lopment progressed with time. Similar amount of stored
soil water in the root zones of the maize genotypes was
observed at tasseling and silking stages of the crops (56
DAE). 29.92% of the stored soil water was absorbed by
the roots of Obatanpa for plant evapotranspiration, with
Golden Crystal and Mamaba following with 29.37% and
28.68% respectively. The use of stored soil water peaked
at 84 DAE among the maize genotypes with Obatanpa
taking up the highest (55.6%) amount of stored soil water
followed by Golden Crystal (53.3%) and Mamaba (51.5%)
for AET.
There was a constant depth of water stored in the plant
root zones of maize genotypes from 14 DAE to 56 DAE
during the minor cropping season, which declined from 56
to 84 DAE but increased from 84 DAE to 98 DAE (Figure
2(b)). The highest depth of water stored during the minor
cropping season occurred at 98 DAE when maize crops
were already matured. These high values of stored soil
water (232.92 mm for Obatanpa, 231.22 mm for Mamaba
and 235.44 mm for Golden Crystal) during the minor
cropping season were as a result of the high amount of
precipitation (Table 4). Stored soil water was the highest
for Golden Crystal at 84 DAE during the minor cropping
season as against similar levels 199.2 mm and 195.7 mm
for Obatanpa and Mamaba, respectively. Golden Crystal
used 16.5% of stored soil water at 28 DAE for AET during
the minor cropping season as against Mamaba and Oba-
tanpa which used 14.0% and 13.8%, respectively. Further-
more, the use of stored soil water peaked at 84 DAE
during the minor cropping season, with 48.5% of stored
soil water being taken up by Mamaba followed by 46.4%
by Obatanpa and 43.2% by Golden Crystal during the
major cropping season.
3.4. Rate of Actual Evapotranspiration
Statistically, the rate of AET during the major and minor
250
200
150
Obatanpa
Mamaba
Golden Crystal
0 20 40 60 80 100 120
Days after emergence
Depth of water stored (mm)
(a)
250
200
150
Obatanpa
Mamaba
Golden Crystal
0 20 40 60 80 100 120
Days after emergence
Depth of water stored (mm)
(b)
Figure 2. Depth of water stored within the rooting depth of
the three maize genotypes during (a) major (b) minor crop-
ping seasons.
cropping seasons was similar among the maize genotypes.
The rates of AET for the major cropping season for
Obatanpa, Mamaba, and Golden Crystal were signify-
cantly (p ≤ 0.05) higher than those of the minor cropping
season. For Obatanpa, the rate of AET ranged between
1.30 and 7.33 mm·day−1, averaging 4.32 mm·day−1 during
the major cropping season and also ranged between 1.16
and 6.60 mm·day−1 with an average value of 3.88
mm·day−1 during the minor cropping season. In the case
of Mamaba the rate of AET ranged between 1.63 and 7.28
mm·day−1, averaging 4.46 mm·day−1 during the major
cropping season as against the range of 1.13 - 6.78
mm·day−1 with an average value of 4.00 mm·day−1 during
the minor cropping season. Similarly, the rate of AET for
Golden Crystal ranged between 1.47 and 7.46 mm·day−1
with an average value of 4.47 mm·day−1 during the major
cropping season as against the rate of AET which ranged
between 1.11 and 6.32 mm·day−1 with an average of 3.72
mm·day−1 during the minor cropping season.
At the early vegetative stage of the maize crops (14 and
28 DAE), AET values were low (Tables 3 and 4), in re-

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
220
sponse to low growth rate and development of the maize
crop during that period. The value of AET at 14 DAE was
20.0, 22.8, and 20.6 mm for Obatanpa, Mamaba and
Golden Crystal, respectively during the major cropping
season as against corresponding value of 16.2, 15.8, and
15.5 mm for the minor cropping season. The value of AET
for Obatanpa, Mamaba, and Golden Crystal during the
major cropping was 5.9, 7.0 and 5.1 mm, respectively,
which was greater than the AET values for the minor
cropping season. The AET for the three maize genotypes
increased at the late vegetative phase of growth (42 DAE)
at the time when 50% canopy was attained. At 42 DAE,
the maize genotypes generally used more soil water dur-
ing the minor cropping season than during the major
cropping season (Tables 3 and 4). Also, Obatanpa had the
highest rate of AET (6.43 mm·day−1) during the major
cropping season whereas the rate of AET was the highest
(6.83 mm·day−1) for Mamaba during the minor cropping
season.
3.5. Changes in Soil Water Stored
The change in soil water storage in the root zone of plants
gives an indication of the net impact of AET, runoff and
deep drainage on the water balance in the root zone trend
in stored soil water reported by Baba-Kutigi et al. [18] for
rainfed maize grown in guinea savannah.
During the major cropping season, stored soil water in
the root zones of the maize genotypes was negative at 28
DAE which indicates a loss of water from the root zones
of the crops. The magnitude of water loss from the profile
was larger for Obatanpa, followed by Golden Crystal and
Mamaba. Following the trend in change in soil water
storage (∆S) as shown in Figure 3(a), ∆S remained posi-
tive for the maize genotypes from 42 DAE to 84 DAE
during the major cropping season. A similar trend in ∆S
occurred during the minor cropping season, from 70 DAE
to 84 DAE with ∆S at 70 DAE being the highest for
Mamaba compared to ∆S for Obatanpa and Golden
Crystal during the minor cropping season. This implies
that more water moved upward through the capillary rise
process in response to evapotranspiration demand of the
maize crops. The positive contribution of the capillary rise
process in AET was significant for Obatanpa, Mamaba
and Golden Crystal from 42DAE to 84 DAE during the
major cropping season. This could have accounted for the
high seasonal cumulative evapotranspiration of Obatanpa,
Mamaba, and Golden Crystal reported by Frimpong et al.
[5].
The positive ∆S in the root zone of the three maize
genotypes during the major cropping season dropped from
42 DAE to 56 DAE (Figure 3(a)) when the maize crops
needed much water for tasseling and grain filling. After 56
DAE, during the major cropping season, the positive
change in ∆S rose from 56 DAE to 84 DAE. Golden
Crystal recorded the highest positive ∆S around its root
zone followed by Obatanpa and Mamaba (Figure 3(a)).
At 84 DAE, values of ∆S in the root zone of the maize
genotypes were similar but higher than values recorded at
70 DAE. This increment is attributed to the higher amount
of precipitation recorded within 70 DAE and also dense
leaf canopy of the maize genotypes. The ∆S in the root
zones of Obatanpa, Mamaba and Golden Crystal remained
constant from 14 to 56 DAE with the exception of Golden
Crystal, which showed a significant positive and negative
∆S at 28 DAE and 42 DAE, respectively, during the minor
cropping season (Figure 3(b)). After 56 days, the ∆S
increased positively up to 84 DAE and declined thereafter
with the exception of the root zone of Obatanpa which had
a positive ∆S at crop senescence. The positive ∆S was
greater in the root zone of Mamaba followed by that of
Figure 3. Changes in soil water storage around the root zones
of the three rainfed maize genotypes during the (a) major (b)
minor cropping season.

Field Assessment of Soil Water Storage and Actual Evapotranspiration of Rainfed Maize (Zea mays L.)
Genotypes in a Coastal Savannah Environment
221
Table 5. Relationship between precipitation (P) and actual evapotranspiration (AET) for the three maize genotypes during the
major and minor cropping seasons.
Cropping
season (s)
Maize
Genotypes
Regression
model
Correlation
coefficient p-value (s)
Major Obatanpa AET = 0.96P + 3.78 0.6917 ≤0.02**
Major Mamaba AET = 0.95P + 5.07 0.885 ≤0.002**
Major Golden Crystal AET = 0.99P + 3.47 0.8251 ≤0.004**
Minor Obatanpa AET = 0.99P + 4.39 0.9796 ≤0.00002***
Minor Mamaba AET = 1.00P + 2.68 0.9407 ≤0.003**
Minor Golden Crystal AET = 0.94P + 5.30 0.9887 ≤0.000004***
***Extremely significant; **Highly significant.
Obatanpa and Golden Crystal. This suggests that capillary
rise of soil water contributed more to the stored soil water
in the root zone of Mamaba compared to Obatanpa and
Golden Crystal from 56 DAE to 84 DAE (Figure 3(b)),
which further contributed positively to its consumptive
water use (Table 4). The rate of ∆S in the root zone of the
maize genotypes declined from 84 DAE to 98 DAE and
was comparatively the highest in the root zone of the
Golden Crystal. On the contrary, ∆S in the root zone of
Mamaba and Golden Crystal were negative while that of
Obatanpa remained positive (Figure 3(b)).
3.6. Relationship between Evapotranspiration
and Precipitation
A strong linear positive correlation existed between AET
for the maize genotypes and precipitation (P) during the
major and minor cropping seasons (Table 5). Hong-Yong
et al. [21] have reported a similar strong positive relation-
ship between AET and irrigation for winter wheat in the
Northern Plains of China. The correlation and regression
coefficients between AET and P for Obatanpa, Mamaba,
and Golden Crystal were 69.2%, 88.5% and 82.5%, re-
spectively, during the major cropping season. Thus, P
significantly (p ≤ 0.002) accounted for about 88.5 % of the
variations in AET of Mamaba, as compared to Golden
Crystal and Obatanpa where it accounted for 82.51 and
69.2%, respectively. Based on the regression analysis, an
increase in a unit of P leads to an increase AET by 0.95,
0.99 and 0.96 for Mamaba, Golden Crystal and Obatanpa,
respectively, for the major cropping season (Table 5). On
the contrary, regression and correlation coefficients of
98.0%, 94.1%, and 98.9% were estimated for Obatanpa,
Mamaba and Golden Crystal, respectively, during the
minor cropping season. Again P significantly (p ≤ 0.000004)
accounted for 98.9% of the variations in AET of Golden
Crystal during the minor cropping season, compared to
Obatanpa and Mamaba for which P accounted for 98.0%
and 94.1%, respectively, of AET (Table 5). Values of R2
generated for the correlation and regression analysis be-
tween AET and P were similar to values reported by
Hong-Yong et al. [21] for the linear relationship between
AET of wheat and irrigation.
Generally, precipitation accounted for most of the vari-
ations in actual evapotranspiration for the maize geno-
types during the minor cropping season compared to the
major cropping season where coefficients of determi-
nations were lower.
4. Conclusion
Generally, the dynamics of the water balance in the root
zone of the maize genotypes were dictated by P, drainage,
AET and stored soil water. The water balance in the root
zone was the highest for Obatanpa during the major
cropping season from 42 DAE to 84 DAE and that for
Mamaba was the highest from 70 DAE to 84 DAE during
the minor cropping season. Obatanpa used the highest
amount of stored soil water for AET during the major
cropping season at 84 DAE whereas AET for Mamaba
was the highest during the minor cropping season. Addi-
tionally, the rate of AET for the maize genotypes was
similar for both major and minor cropping seasons. How-
ever, Mamaba had the highest rate of AET during both
major and minor cropping seasons. Results of the study
are emphasizing the need to formulate effective manage-
ment strategies to enhance soil water use and productivity
by maize crop grown under rainfed environment cha-
racterised by poor and erratic rainfall patterns.
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