Vol.3, No.5, 714-722 (2012) Agricultural Sciences
http://dx.doi.org/10.4236/as.2012.35086
Evapotranspiration and water-use efficiency of
irrigated colored cotton cultivar in semiarid regions
Pedro V. de Azevedo1*, José R. C. Bezerra2, Vicente de P. R. da Silva1
1Federal University of Campina Grande, Campina Grande, Brazil; *Corresponding Author:
2Brazilian Company for Agriculture and Animal Research (Embrapa Algodão), Campina Grande, Brazil
Received 5 June 2012; revised 16 July 2012; accepted 2 August 2012
ABSTRACT
Irrigation studies provide a framework for eva-
luating agricultural production and the water
resource management in locations where water
is scarce. Field experiments were conducted at
Barbalha—CE (Northwestern Brazil) during 2004
and 2005 cropping seasons to investigate the
effects of different irrigation water depths on the
water-use efficiency and yield of the BRS 200-
brown cotton cultivar (Gossypium hirsutum L.).
Three irrigation treatments were applied: T1 =
80%; T2 = 100% and T3 = 120% of the potential
evapotranspiration (ETp). The Bowen ratio-en-
ergy balance was used to obtain crop evapotr-
naspiration (ETc) while daily reference evapo-
transpiration (ETo) was obtained by the Penman-
Monteith approach. Irrigation water was applied
by a sprinkler system during both cropping sea-
sons. The daily evapotranspiration ranged from
2.59 mm·day−1 at the emergence to 5.89 mm·day−1
at first square growth stage with an accumulated
value of 528.7 mm as a mean of the two cropping
seasons. The average crop coefficient across
both years (2004-2005) was 0.90, with minimum
and maximum values of 0.46 and 1.17 at emer-
gency and first flower growth stages, respec-
tively. The results also showed that the increase
in irrigation from 80% to 120% of ETp resulted in
a significant increase in the seedcotton yield
(from 2476.0 to 3289.5 kg·ha−1), while lint per-
centage and water-use efficiency (WUE) were
slightly reduced from 35.7% to 35.6% and from
0.60 to 0.53 kg·m−3, respectively. These results
suggests that the cotton crop (cultivar BRS-200
brown) reaches higher water-use efficiency
when irrigated with 80% of the crop evapotran-
spiration obtained as a function of the reference
evapotranspiration and the crop coefficient pro-
posed by FAO. However, the maximum seed-
cotton yield is obtained when irrigated with
120% of that crop evapotranspiration.
Keywords: Bowen Ratio; Crop Evapotranspiration;
Irrigation Treatments; Seed-Cotton Yield
1. INTRODUCTION
Agriculture is largely responsible for the increase in
world water consumption due to the worldwide increases
in agricultural irrigation areas that were needed to main-
tain a satisfactory level of food production for the human
population. In semiarid regions, determining the timing
of irrigation and quantifying the amount of complemen-
tary irrigation that is required are important due to the
irregularity of rainfall events. Increasing crop water-use
efficiency (WUE) to increase agricultural production
without increasing the volume of water that is used for
irrigation has become more challenging for these regions.
Some studies have shown that an increase in irrigation
water volume does not necessarily result in crop yield
increases [1,2], but WUE values generally decrease with
increasing irrigation water levels for all productivity pa-
rameters [3]. Many studies have demonstrated an in-
crease in food production by increasing WUE. In other
studies, a higher WUE resulted in either the same food
production from fewer water resources or higher produc-
tion from the same water resources [4]. There is an ur-
gent need in the agricultural sector to use dwindling wa-
ter resources efficiently to enhance WUE at the farm
level [5]. These authors have observed that the water-use
efficiency could be enhanced by reducing evapotranspi-
ration through irrigation deficit and by identifying the
crop growth stage that is most sensitive to water stress.
Previous studies have reported that the WUE for cot-
ton is a key element for long-term, strategic water re-
source planning [6-8]. Other researchers have investi-
gated furrow and drip irrigation scheduling as well as
computer models for evaluating alternative irrigation
strategies for cotton production in arid, semiarid and hu-
mid environments [9]. A cotton field experiment was
performed to compare drip to furrow (conventional) irri-

P. V. de Azevedo et al. / Agricultural Sciences 3 (2012) 714-722 715
gation for a deep silt loam soil in Uzbekistan over three
consecutive years [10]. They found that WUE values
were always significantly higher for drip than for furrow
irrigation. All of these studies have greatly contributed to
an increase in crop productivity by using less water and
improving new drought-tolerant cotton varieties. Also,
some studies have been conducted for increasing cotton
crop yield with less water consumption [11-14]. By com-
paring irrigation systems, a single-row cotton crop was
more water efficient when irrigated by furrow line while
a double-row crop was more water efficient when a drip-
ping irrigation system was used [5]. Also, [15] observed
that water-use efficiency increased with increasing irri-
gation frequency.
Cotton crops have been widely cultivated in semiarid
and other wet regions of the world using rain-fed systems.
However, cotton growth under full or supplementary
irrigation may be an alternative method for increasing
crop productivity. The loss of productivity due to the lack
of rainfall events has threatened farming systems. Also,
cotton crops are sensitive to low temperatures and excess
soil water when the plants are emerging from the soil. In
many rainy years the rain-fed cotton crop has resulted in
yield reductions and quality deterioration [16]. These
challenges do not completely prevent cotton crop growth
in the semiarid regions because air temperature is always
approximately 20˚C and the annual mean rainfall is be-
low 800 mm [17]. Therefore, as an alternative agricul-
tural practice for improving the rain-fed system, the cot-
ton crops have been grown in a polyculture system with
maize (Zea mays) and beans (Phaseolus vulgaris). In
other regions of Brazil, cotton is typically grown in rota-
tions with at least three other crops, such as soybeans
(Glycine max L.), millet (Pennisetum glaucum L.) and
soybean-millet-cotton, which has resulted in better weed
control than rotations with fewer crops [18]. [19] has
mentioned the effects of growing cereal and leguminous
crops in rotation with dry land cotton on the physical and
chemical properties of grey vertisol soil. Sowing other
crops in rotation with cotton has been a successful strat-
egy for reversing yield decline and maintaining soil qual-
ity [20]. These alternative agricultural management prac-
tices have been proposed to reduce soil degradation in
cotton cropping systems.
Cotton was one of the most important crops in Brazil,
particularly in the semiarid region of northeastern Brazil,
before the appearance of the boll weevil (Anthonomus
grandis Boheman). This cotton pest was introduced to
Brazil in 1983, and it causes serious damage to crops,
including the removal of flower buds, destruction of
bolls and reduced lint production. In 2000, the Brazilian
Company for Agriculture and Animal Research (EM-
BRAPA) released a genetically modified cotton crop
(BRS 200-brown) cultivar that was more resistant to the
boll weevil pest. However, there is little information on
how this cultivar responds to changes in soil water con-
tent, which would be useful for irrigation scheduling
strategies. Additionally, little is known about the eco-
nomic viability of this new cultivar which has strong
vegetative development when grown in soil with high
water content. Therefore, it is necessary to carry out
more studies for identifying the best irrigation water
depth to obtain higher cotton yields as well as to evaluate
new cultivation techniques for reducing the cost and in-
creasing the yields of this cultivar. Therefore, the purpose
of this study was to evaluate the effect of the water
treatment on the evapotranspiration and water use-effi-
ciency of the BRS 200-brown cotton cultivar grown in
semiarid regions under sprinkler irrigation.
2. MATERIALS AND METHODS
2.1. Experimental Site and Weather Data
Field experiments were conducted at the Experimental
Station of the Brazilian Company for Agriculture and
Animal Research (Embrapa Algodão) in Barbalha, CE,
Brazil (7˚19'S; 39˚18'W and 415.7 m elevation above
mean sea level). The local climate was a tropical wet
climate with tropical savanna vegetation and the soil type
was Lixisols (FAO soil taxonomy). The air temperature
ranged from 19˚C (rainy season) to 34˚C (dry season),
and the annual mean rainfall was 1000 mm [17]. The
weather data (Air temperature, Class A pan evaporation,
relative humidity and rainfall) were collected from a
weather station adjacent to the experimental field during
the two cropping seasons (Table 1).
The total rainfall plus irrigation (Figure 1) and the
temporal course of solar radiation and wind speed (Fig-
ure 2) during the cropping seasons of 2004 (July to No-
vember) and 2005 (September to December) were also
determined.
2.2. Crop and Water Management
Crop phenology was divided into four growth stages
(Table 2) based on field observations from both cropping
seasons as a function of days after sowing (DAS). Cotton
crop (Gossypium hirsutum L.), cultivar BRS 200-brown,
was cultivated using different soil water contents during
the 2004 (July 29 to November 10) and 2005 (September
02 to December 15) cropping seasons (Table 3). Three
irrigation treatments were applied: T1: 80% ETp; T2:
100% ETp and T3: 120% ETp where ETp is the potential
evapotranspiration obtained as the product of the refer-
ence evapotranspiration—ETo [21] by the crop coeffi-
cient (Kc) suggested by FAO [22].
Irrigation water was applied with a sprinkler system
during both cropping seasonsprinklers (Agropolo) . The s

P. V. de Azevedo et al. / Agricultural Sciences 3 (2012) 714-722
716
Table 1. Long-term monthly (1911-2004) means and 2004 (July-Dec) and 2005 (Sept-Dec) growing seasons air temperature (maxi-
mum, minimum and average), pan evaporation, relative humidity and rainfall at Barbalha, CE, Brazil.
air temperature (˚C)
years months
Tmax T
min T average
pan evaporation (mm)relative humidity (%) rainfall (mm)
1911-2004 Jul 29.9 19.1 23.8 224.8 61.0 11.6
Ago 31.7 18.1 24.9 268.7 53.0 7.4
Sept 33.3 20.1 26.2 292.8 49.0 12.4
Oct 34.1 21.1 26.7 262.9 51.0 36.3
Nov 33.9 21.8 26.8 223.7 53.0 35.5
Dec 33.1 21.7 26.3 216.1 55.0 98.2
mean 32.7 20.3 25.8 248.1 53.7 33.6
2004 Jul 32.3 15.6 24.0 - 68.9 2.6
Ago 35.8 17.5 25.2 388.6 61.0 6.9
Sept 37.2 18.0 26.7 284.3 52.7 0.0
Oct 37.1 18.5 28.0 403.6 54.2 0.0
Nov 38.1 19.2 27.8 274.6 57.6 32.6
mean 36.1 17.8 26.3 337.8 58.9 8.4
2005 Sept 36.3 17.2 26.7 356.4 50.2 0.0
Oct 37.4 20.2 28.4 372.9 45.8 0.4
Nov 37.7 20.4 28.5 306.5 49.1 0.0
Dec 35.9 20.3 26.9 437.4 65.7 194.5
mean 36.8 19.6 27.6 368.3 52.7 48.7
Figure 1. Temporal course of rainfall plus irrigation during the 2004 (July 29 to November 10) and 2005 (September 02 to December
15) cropping seasons at Barbalha, CE, Brazil.

P. V. de Azevedo et al. / Agricultural Sciences 3 (2012) 714-722 717
Figure 2. Pattern of solar radiation and wind speed over the cotton crop (cultivar BRS 200 Brown) during the 2004 (from September
02 to December 15) and 2005 (from July 29 to November 10) cropping seasons at Barbalha, CE, Brazil.
Table 2 . Growth stages of the cotton crop (cultivar BRS-200 brown) during the 2004 (from September 02 to December 15) and 2005
(from July 29 to November 10) cropping seasons at Barbalha, CE, Brazil.
Dates
Growth Stage
Year 2004 Year 2005
Days after sowing (DAS) Time periods (days)
Emergency Jul, 29 to Aug, 11 Sept, 02 to Sept, 16 01 - 15 15
First Square Aug, 12 to Sep, 20 Sept, 17 to Oct, 25 16 - 54 39
First Flower Sept, 21 to Oct, 20 Oct, 26 to Nov, 25 55 - 85 31
Open Boll Oct, 21 to Nov, 10 Nov, 26 to Dec, 15 86 - 105 20
Total 105
Table 3. Components of seed-cotton (cultivar BRA-200 Brown) yield and water-use efficiency (WUE) as influenced by irrigation
treatments (averaged for the 2004 and 2005 cropping seasons) at Barbalha, CE, Brazil.
Irrigation treatment Seed-cotton yield (kg·ha−1) Lint percentage (%) WUE (kg·m−3)
T1 = 80% (ETp) = 411.6 mm 2476.0b 35.7ª 0.60
T2 = 100% (ETp) = 514.5 mm 2848.8ab 35.7ª 0.55
T3 = 120% (ETp) = 617.4 mm 3289.5a 35.6a 0.53
Means followed by the same letter are not significantly different by the Duncan test at the 5% significance level.
had a mouthpiece emitter discharge of 3.2 × 5.4 mm
spaced over an 18 × 12 m area with an operating pressure
of 2.5 atm. The crop was planted in double rows in a
main plot of 1006 ha with 1.0 × 0.40 m spacing between
each row and a population density of 10 plants·m−2. The
irrigation treatments were laid out in a split plot ar-
rangement in a randomized block design with four repli-
cations of three different water treatments. The crop yield

P. V. de Azevedo et al. / Agricultural Sciences 3 (2012) 714-722
718
was obtained by hand harvesting the central rows of each
sub-plot two times during the cropping seasons: the first
harvest occurred at 60% boll formation and the second
harvest occurred at 100% boll formation. The total
amount of fertilizer applied to all the plots before cotton
sowing was 30 kg·N·ha−1, 60 kg·P2O5·ha−1 and 10
kg·K2O·ha−1.
The experimental plot was fully irrigated until the
available soil content reached 100% before crop sowing.
Four days after sowing (DAS), a short period of irriga-
tion was applied to ensure good seed germination. After
the crop was fully established, the irrigation was applied
weekly as a function of the water consumption estab-
lished by crop evapotranspiration.
2.3. Environmental Measurements
Measurements of global and reflected solar radiation,
net radiation, dry and wet bulb air temperature (at 0.30
and 1.5 m above the crop canopy), wind speed (at 0.30
and 1.5 m above the crop canopy), and soil heat flux (at
0.02 m below the soil surface) were obtained during the
experimental periods. The sensors were connected to a
data acquisition system (Data logger CR 10X, Campbell
Scientific Inc.) programmed for collecting data every 5 s
and storage averages every 20 min. Wet and dry bulb
temperatures were measured by a ventilated
psychrometer held about 0.5 m above the crop canopy.
The micrometeorology tower was installed at the ex-
perimental plot with a fetch of 80 m in the main wind
direction. All of these sensors were calibrated prior to the
experimental periods.
2.4. Crop and Reference Evapotranspiration
Daily reference evapotranspiration (ETo) was obtained
by the Penman-Monteith method [21] by using climate
data from a weather station located 400 m from the ex-
perimental site. Further details regarding this method can
be found in [1].
The above canopy latent heat flux was obtained by the
energy balance method by neglecting the advection ef-
fects, the energy stored in the canopy and the photosyn-
thetic energy flux. Thus, assuming equality between the
turbulent diffusion coefficients of sensible (Kh) and latent
(Kw) heat fluxes and
 
aa
the
latent heat flux (λE, in W·m−2), based on the Bowen ratio
(  = H/λE   (ΔT/Δea), was obtained as:
TzezT e 

1
n
a
RG
ETe 








(1)
where λ = 2.501 MJ·kg−1) is the latent heat of vaporiza-
tion, Rn (W·m−2) the net radiation, G (W·m−2) the soil
heat flux, γ (kPa·˚C−1) the psychrometric constant and ΔT
(˚C) and Δea (kPa) are the temperature and vapor pres-
sure differences between two measurement levels at 0.5
and 1.5 m heights above cotton canopy. The compo-
nents of the energy balance were obtained for the day-
time period (i.e., Rn > 0) and were considered positive
when upward and negative when downward crop canopy
[3,23-25]. Also, the set of criteria suggested by [26] was
adopted for selecting between reliable and unreliable
values of
 for daytime periods with Rn > 0. The crop
evapotranspiration (ETc) was then obtained in mm·day-1
by dividing
 E by  , and integrating the mean values
collected by the data acquisition system for day-time
period with Rn − G > 0 [23].
The water use-efficiency (WUE) was calculated as the
ratio of seed-cotton yield to total water use and was ex-
pressed as kg·ha−1·mm−1 [27].
2.5. Statistical Analysis
An analysis of variance (ANOVA) was conducted to
evaluate the effects of the irrigation water depths on seed
cotton yield by using ASSISTAT software [28]. The sig-
nificant difference of the means was analyzed by Dun-
can’s multiple range tests with significance levels of 1%
and 5%.
3. RESULTS AND DISCUSSION
3.1. Crop Evapotranspiration
During the 2004 growing season, the daily crop evapo-
transpiration (ETc) varied from 3.2 to 7.1 mm·day−1 with
an average and standard deviation of 5.4 ± 0.9 mm·day−1.
In 2005, the ETc values varied from 2.9 to 5.0 mm·day−1
with an average and standard deviation of 5.0 ± 0.87
mm·day−1. On the other hand, the accumulative values of
ETc were 545.0 and 512.4 mm for the growing seasons
of 2004 and 2005, respectively with an average of 528.7
mm (Table 4). Therefore, the ETc was 6.3% higher in
2004 as compared to 2005. These differences in evapo-
transpiration (ETc) between the experimental years could
be attributed to higher values in solar radiation and wind
speed during the 2004 year, which likely produced a
higher evaporative demand (Figure 2).
The lower water input (irrigation plus rainfall) in the
2004 growing season (580.1 mm) compared to that of
2005 (632.8 mm) did not significantly affected cotton
crop evapotranspiration or the crop coefficient (Figure 3 ).
According to [29] the crop evapotranspiration is higher
for days after irrigation or after rainfall events when
there is higher level of energy available to the evapo-
transpiration process. The results of this study did not
always agreed with these findings once the plants
reached the open boll growth stage (at the end of the
cotton cropping cycle) during two consecutive days of

P. V. de Azevedo et al. / Agricultural Sciences 3 (2012) 714-722 719
Figure 3. Cotton crop evapotranspiration (a), reference evapotranspiration (b) and crop coefficient (c) for the 2004 (from September
02 to December 15) and 2005 (from July 29 to November 10) cropping seasons at Barbalha, CE, Brazil. The crop coefficient is an
average for the 2004 and 2005 cropping seasons.
Table 4. Mean and accumulated daily cotton crop evapotranspiration (ETc) for each growth stages for the cropping seasons of 2004
(from September 02 to December 15) and 2005 (from July 29 to November 10) at Barbalha, CE, Brazil.
ETc (mm)
Growth stage
Mean (mm·day−1) 2004 2005 Mean (2004-2005)
Emergency (15 days) 2.59 37.7 39.9 38.8
First Square (39 days) 4.95 193.1 193.4 193.3
First Flower (31 days) 5.89 192.1 172.4 182.3
Open Boll (20 days) 5.72 122.1 106.7 114.4
Total - 545.0 512.4 -
Average 4.78
- - 528.7

P. V. de Azevedo et al. / Agricultural Sciences 3 (2012) 714-722
720
intense cloudiness and rainfall that reduced solar radia-
tion and wind speed (Figures 1 and 2). These climatic
conditions produced low values for crop evapotranspira-
tion even when the soil moisture content was high.
Also, the minimum daily evapotranspiration (2.59
mm·day−1) occurred during the emergence growth stage
while the maximum value (5.89 mm·day−1) occurred at
first square stage as a mean of the two cropping seasons
(Table 4). Then, both crop evapotranspiration and crop
coefficient increased as the plants grew to the open boll
stage (Figure 3) indicating that the crop coefficient was
dependent on crop evapotranspiration throughout the two
cropping seasons. The cotton open boll growth stage has
been shown to be sensitive to soil water deficit [5]. Dur-
ing this growth stage, the water input in 2004 and 2005
were 176.4 and 155.2 mm, respectively. Consequently,
there was not any water deficit for the cotton crop for
either experimental year. As the evapotranspiration de-
creased during this growth stage, the water input was
primarily responsible for the increase in crop evapotran-
spiration and crop coefficient. This result agrees with the
findings of [30], who observed that irrigation was largely
responsible for the boll number of cotton and about 70%
- 75% of seasonal evapotranspiration in all irrigation
treatments occurred roughly during the 85 - 92 day pe-
riod between sowing the seeds to full bloom.
3.2. Crop Coefficient
The average of the crop coefficient (Kc) values across
both years (2004-2005) was 0.90, with maximum and
minimum values of 1.17 and 0.46 at first flower and
emergency growth stages, respectively (Figure 3). Simi-
lar results were found in a study by [30] to determine
water use and the lint yield response of drip irrigated
cotton in a semiarid region. They obtained average Kc
values ranging from 0.58 at the initial growth stage to
1.10 at the mid growth stage. The accumulated ET was
642 mm for a total growing season of 134 days. Similarly,
[31] obtained a Kc of 0.53 at emergence, 1.15 at heading
and 0.40 at hard dough for cotton. The Kc values ob-
tained in this study were also similar to those reported in
FAO/56 [21], but the values were slightly higher at the
open boll growth stage. The disagreements between Kc
values from these studies could be attributed to differ-
ences in climate and cotton variety.
3.3. Seed-Cotton Yield and Water-Use
Efficiency
The effects of irrigation treatments on the components
of seed-cotton yield and water-use efficiency are shown
in Table 3. An analysis of variance showed that only
seed-cotton yield was affected by irrigation water depth.
The increases in irrigation from T1 to T3 treatment re-
sulted in a significant increase in the seed-cotton yield
(from 2476.0 to 3289.5 kg·ha−1), while lint percentage
and WUE values were slightly reduced from 35.7% to
35.6% and from 0.60 to 0.53 kg·m−3, respectively. These
lint percentage results were consistent with the values
obtained by Karam et al. (2006), who reported a reduc-
tion in the cotton lint yield values as the irrigation amounts
increased. Higher cotton yield values were obtained from
the highest irrigation treatment (T3), but the values were
slightly lower than those reported in other studies [8,9]
and much higher than those found by [2] and [32].
Although there was a slight decrease according to in-
creasing irrigation depth, no significant differences were
detected in water-use efficiency (Ta b le 3). These results
may be associated with the physiological crop response
to greater soil water availability for all of irrigation
treatments. The soil water availability also affected the
plants physiological processes, primarily the crop growth
and vegetative development [22] as well as photosynthe-
sis and leaf expansion [33]. Both seed-cotton yield and
water-use efficiency (WUE) decreased linearly with in-
creasing irrigation water treatment. Also, the increases on
irrigation treatment from T1 to T3 resulted in a 24.7%
increase in seed-cotton yield and a 11.7% decrease in
WUE values (Table 3), which are similar to the values
reported in the literature [8]. These results means that the
cotton crop (cultivar BRS-200 brown) reaches higher
water-use efficiency when irrigated with 80% of the crop
evapotrnaspiration obtained as a function of the reference
evapotranspiration and the crop coefficient proposed by
FAO. However, the maximum seed-cotton yield is ob-
tained when irrigated with 120% of that crop evapotran-
spiration.
The values of water-use efficiency and seed-cotton
yield from this study are reported as the average over
two years (2004-2005) since the results were similar for
both experimental years. The seed-cotton yield range was
similar to those reported in the current literature [8,9,34].
However, the yield variation from 2476 to 3289 kg·ha−1
for the colored cotton cultivar does not offset the high
cost of sowing the cultivar (Table 5). [2] has reported
that the economic costs and values used for the full irri-
gation rate did not improve net return over the 66% rate
during the experimental years. Also, the results indicated
that the WUE values ranging from 0.53 to 0.60 kg·m−3
were well within of range reported by these studies and
close to the FAO 33 range (0.4 - 0.6 kg·m3) reported by
[22].
4. CONCLUSIONS
Field experiments were carried out during two con-
secutive years with the primary objective of evaluating
the evapotranspiration, seed yield and water-use effi-
ciency of the cotton crop (cultivar BRS-200 brown)

P. V. de Azevedo et al. / Agricultural Sciences 3 (2012) 714-722 721
Table 5. Summary of range in water use efficiency (WUE) and seed-cotton yield values in comparison with other researches values.
Literature source Irrigation system WUE (kg·m−3) Seed-cotton yield (kg·ha−1) Cost of sowing (US$·ha−1)
This study Sprinkler 0.53 - 0.60 2476 - 3289 1489.18
Dagdelen et al. (2009) Drip 0.77 - 0.96 2550 - 5760 -
Pereira et al. (2009) - - 2723 - 3722 -
Nuti et al. (2009) Furrow - 1017 - 1476a -
Martin & Hanks (2009) Furrow - 1112 - 1325a,b -
Nazirbay et al. (2007) Drip + furrow 0.50 - 0.88 3180 - 4030 -
Du et al. (2006) Furrow 0.58 - 1.99d 1611 - 2564 -
Aujla et al. (2005) Drip 0.17 - 0.23e 931 - 2144 -
Cetin & Bilgel (2002) Drip/furrow/sprinkler 0.24 - 0.49d 850 - 4900 -
aSeed-cotton yield; Bconverted values from lbs/acre to kg·ha−1; cConverted values from $/acre to US$·ha−1; dConverted values from kg·ha−1·mm−1 to kg·m−3;
eConverted values from kg/ha cm to kg·m−3.
grown under sprinkler irrigation.
The daily evapotranspiration ranged from 2.59 mm·day−1
at the emergence to 5.89 mm·day−1 at first square growth
stage with an accumulated value of 528.7 mm. For the
growing cycle the average daily value of the crop coeffi-
cient was 0.90, with minimum and maximum values of
0.46 and 1.17 at emergency and first flower growth
stages, respectively.
The results also showed that the increase in irrigation
from 80% to 120% of ETp resulted in a significant in-
creases in the seed-cotton yield (from 2476.0 to 3289.5
kg·ha−1), while lint percentage and water-use efficiency
(WUE) were slightly reduced from 35.7% to 35.6% and
from 0.60 to 0.53 kg·m−3, respectively. These results
suggests that the cotton crop (cultivar BRS-200 brown)
reaches higher water-use efficiency when irrigated with
80% of the crop evapotranspiration obtained as a func-
tion of the reference evapotranspiration and the crop co-
efficient proposed by FAO. However, the maximum
seed-cotton yield is obtained when irrigated with 120%
of that crop evapotranspiration.
5. ACKNOWLEDGEMENTS
This study was partially supported by the National Council of Scien-
tific and Technological Research—CNPq/Brazil. The authors would
like to thank the National Center for Cotton Research—CNPA and the
Brazilian Company for Agriculture and Animal Research—EMBRAPA,
for allowing us to use their facilities, including laboratories, library and
field experimental stations.
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