482
Bulgarian Journal of Agricultural Science, 16 (No 4) 2010, 482-492
Agricultural Academy
DETERMINING WATER-YIELD RELATIONSHIP, WATER USE EFFICIENCY,
SEASONAL CROP AND PAN COEFFICIENTS FOR ALFALFA
IN A SEMIARID REGION WITH HIGH ALTITUDE
Y. KUSLU*, U. SAHIN, T. TUNC and F. M. KIZILOGLU
Ataturk University, Faculty of Agriculture, Department of Agricultural Structures and Irrigation,
25240 Erzurum, Turkey
Abstract
KUSLU, Y., U. SAHIN, T. TUNC and F. M. KIZILOGLU, 2010. Determining water-yield relationship,
water use efficiency, seasonal crop and pan coefficients for alfalfa in a semiarid region with high altitude.
Bulg. J. Agric. Sci., 16: 482-492
A field study was conducted to determine effects of seasonal deficit irrigation on plant dry forage yield and
water use efficiency of alfalfa for a 2-year period in the semiarid region with high altitude. In addition, the
seasonal crop and pan coefficients kc and kp of alfalfa was determined in full irrigation conditions. Irrigations
were applied when approximately 50% of the usable soil moisture was consumed in the effective rooting depth at
the full irrigation treatment. In deficit irrigation treatments, irrigations were applied at the rates of 80, 60, 40, 20
and 0% of full irrigation treatment on the same day. Irrigation water was applied by hose-drawn traveler with a
line of sprinklers. Seasonal actual evapotranspiration, total dry forage yield and water use efficiency was the
highest in full irrigation conditions and the lowest in continuous stress conditions. The linear relationship between
seasonal actual evapotranspiration and total dry forage yield was obtained. According to the averaged values of
2 years, yield response factor (ky) was 1.33. Both seasonal kp and kc were determined as 0.86 for alfalfa, when
combined values of 2 years.
Key words: Alfalfa; crop coefficient; pan coefficient; water deficit; yield response factor
Abbreviations: ETo - reference evapotranspirasyon (mm); ky - seasonal yield response factor
kc - seasonal crop coefficient; kp - seasonal pan coefficient; ETa - actual evapotranspiration, mm; I - the amount
of irrigation water applied (mm); P – precipitation, mm; Cr - capillary rise (mm); Dw - amount of drainage water
(mm); Rf - amount of runoff (mm); Δ S - change in the soil moisture content (mm); Ya - actual harvested yield;
Ym - maximum harvested yield, ETm - maximum evapotranspiration, mm; Yd - relative yield reduction; ETd relative evapotranspiration reduction, mm; Epan - evaporation of Class A pan, mm; Rn - net radiation at the crop
surface, MJ m-2 day-1; G - soil heat flux density, MJ m-2 day-1; T - mean daily air temperature at 2 m height, °C;
u2 - wind speed at 2 m height, m s-1; es - saturation vapour pressure, kPa; ea - actual vapour pressure, kPa; es ea - saturation vapour pressure deficit, kPa; Δ - slope of the saturation vapour pressure curve, kPa/°C; γ psychrometric constant, kPa/°C; WUE - water use efficiency, kg ha-1 mm-1
E-mail: [email protected] or [email protected]
Determining Water-yield Relationship, Water Use Efficiency, Seasonal Crop and Pan Coefficients...
Introduction
Alfalfa has a high water requirement compared to
other crops. Evapotranspiration is between 800 and
1600 mm growing period depending on climate and
length of growing period (FAO, 2002a). Seasonal
evapotranspiration of alfalfa reported by Sahin and
Hanay (1996) was approximately 700 mm in the
Erzurum region. In addition, Evren and Sevim (1998)
determined evapotranspiration of alfalfa as 678 mm
in Erzurum plain conditions.
In Erzurum region with semiarid climate, summers
are short, hot and dry. Water is the main factor limiting yield production in the hot and dry summer period
of semiarid regions. The great challenge for coming
decades in arid and semiarid regions will be focusing
on increase food production by using less water
(FAO, 2002b). Therefore, studies are needed to increase the efficiency of the water use that is available.
One approach is the development of new irrigation
scheduling techniques such as deficit irrigation (Bekele
and Tilahun, 2007). Deficit irrigation has potential
benefits such as increasing irrigation efficiency, decreasing the cost of irrigation and water opportunity
cost (English and Raja, 1996).
The lack of water in plant and resulting water stress
has an important effect on water consumption and
yield. Alfalfa is very responsive to water stress
(Guitjens, 1993; Orloff et al., 2004; Frate and Roberts, 2006). Various researchers (Smeal et al., 1991;
Grimes et al., 1992; Saeed and El-Nadi, 1997; Bai
and Li, 2003) recognized a positive linear relationship between alfalfa yield and evapotranspiration.
Doorenbos and Kassam (1979) developed a relation
between water applied and yield that can measure
yield per applied water unit which can largely be practiced with a certain mistake level and can be performed
in the conditions of sufficient and deficit water resource.
On the other hand, an understanding of water use
efficiency was essential for evaluating the field crops
in semiarid regions where irrigation water was a limiting factor (Johnson and Henderson, 2002). Several
alfalfa water use efficiency studies have been reported.
483
Mean annual values fluctuate between 10 and 23 kg
ha-1 mm-1 (Grimes et al., 1992; Saeed and El-Nadi,
1997; Hirth et al., 2001).
The reference evapotranspirasyon (ETo) is a measurement of the water use for that reference crop. In
the case of ETo, grass is used as the reference; however, other crops may not use the same amount of
water as grass due to changes in rooting depth, crop
growth stages and plant physiology. The crop coefficient takes into account the crop type and crop development to adjust the ETo for that specific crop.
The FAO Penman-Monteith equation is recommended for determining ETo (Allen et al., 1998;
Cuiping, 2005).
Class A pan data is also used extensively throughout the world to estimate ETo (Grismer et al., 2002;
Irmak et al., 2002). However, reliable estimation of
ETo using pan evaporation depends on the accurate
determination of pan coefficients.
Alfalfa is the most important forage crop in
Erzurum, in Turkey. Erzurum is accepted as one of
the most important animal breeding regions of Turkey. According to last statistics given by Turkish Statistical Institute the alfalfa growing area in the Erzurum
region is 37480 ha, and the green, hay and seed production are 188761, 259198 and 143 ton, respectively. However, the studies with water consumption
of alfalfa plants in the region are not sufficient.
Predicting yield response to water use of alfalfa is
important in developing strategies and decision-making for use by farmers and their advisors, and researchers for irrigation management under limited water conditions. In semiarid climatic regions with high altitude,
however, little attempt has been made to assess the
water–yield relationships and optimum water management programs for alfalfa.
The objectives of this research are: (1) to determine the effect of seasonal water deficit treatments on
the plant dry forage yield and water use efficiency of
alfalfa in the semiarid conditions with high altitude, (2)
to determine the seasonal yield response factor (ky)
that would contribute to irrigation scheduling programs
in deficit irrigation treatments for semiarid climatic
zones with high altitude, (3) to determine pan and crop
484
Y. Kuslu, U. Sahin, T. Tunc and F. M. Kiziloglu
coefficients kp and kc enabling the estimation of actual
evapotranspiration of alfalfa grown under semiarid
conditions with high altitude from Class A pan evaporation.
Material and Methods
This study was conducted during the growing periods (April-September) of 2005 and 2006, at the
Agricultural Research Station of Ataturk University in
Erzurum, in Turkey. The coordinates of the experimental area are 39º55' N and 41º16' E. Its altitude is
1835 m from the sea level.
The experimental region has a semiarid climate.
The climatic variables for growing period of experimental years are given in Table 1. Temperature, humidity, wind speed and sunshine data were taken from
Erzurum meteorological station (39º57' N, 41º11' E,
1757 m a.s.l., 3 km distance than experimental field).
Precipitation and evaporation data were measured with
a standard pluviometer and a Class A pan, respectively, located in the experimental area. The pan was
placed in a fallow area. Pan readings were taken by
daily at the morning time.
The soil was classified as an Aridisol according to
the US Soil Taxonomy (Soil Survey Staff, 1992) with
parent materials mostly consisting of volcanic, marine
and lacustrine transported materials. Before establishment of the experiment, soil samples were taken with
an auger from the soil layers of 0-30, 30-60 and 6090 cm. Some physical and chemical properties of the
experimental field soil were determined according to
the methods used Klute (1986) and Page et al. (1982)
and they were given in Table 2.
Table 1
Climatic data of the experimental area in the growing periods of 2005 and 2006
Years
2005
2006
Climatic parameters
Mean
Mean
Mean
Mean
Mean
Total
Total
maximum
minimum
relative wind
daily
precipitation, evaporation,
temperature, temperature, humidity, speed, sunshine,
mm
mm
ºC
ºC
%
h
m s-1
Months
1
April
May
June
July
August
14.0
17.2
20.6
28.6
29.3
2.7
4.1
6.2
9.9
10.5
74.8
72.2
67.9
55.0
54.8
2.5
3.4
2.7
2.7
2.6
4.3
7.2
9.1
11.6
10.8
41.3
93.5
92.7
31.3
38.8
20.7
120.6
141.7
217.8
202.5
September2
April1
May
June
July
August
22.4
5.1
61.6
2.9
9.3
11.3
67.4
11.6
18.9
27.2
27.2
31.7
2.0
2.7
6.5
12.4
12.3
76.8
67.3
56.7
62.5
50.9
2.6
2.9
2.7
4.0
2.7
3.7
9.4
11.9
10.3
9.6
64.8
49.8
25.9
29.5
18.5
19.3
134.0
219.4
223.2
246.9
25.8
6.6
57.4
3.0
9.3
2.0
77.7
3
September
1
2
3
Calculated from the data between 20 and 30 April
Calculated from the data between 1and 15 September
Calculated from the data between 1and 14 September
485
Determining Water-yield Relationship, Water Use Efficiency, Seasonal Crop and Pan Coefficients...
Table 2
Some physical and chemical properties of the experimental field soil
Properties
Texture
Clay, %
Silt, %
Sand, %
Field capacity, Pw
Wilting point, Pw
Bulk density, g cm-3
pH*
-1
Electrical conductivity, dS m *
Carbonates, %
Organic matter, %
*: in saturated soil extract
0-30
Loam
20.90
33.20
45.90
17.80
10.20
1.48
8.11
0.49
0.79
0.88
Soil layer, cm
30-60
Clay loam
28.20
36.30
35.50
18.90
11.10
1.41
7.97
0.50
0.81
0.47
Fig. 1. The design of experimental field
60-90
Clay loam
27.60
43.20
29.20
21.90
13.80
1.37
8.10
0.52
0.68
0.25
486
The experiment was laid out as six main plots with
an area of 1500 m2 (50 x 30 m) representing five
treatments and the control (Figure 1). Each treatment
and the control have three replicated sub-plots with
an area of 500 m2 (50 x 10 m). There was a 5 m
space between main plots in order to minimize water
movement among treatments.
Alfalfa (Medicago sativa L. cv. Prosementi) seeds
were sown at a rate of 20 kg ha-1 on 20 April 2005.
All plots received at the same amount of P2O5 (120
kg ha-1) and N (50 kg ha-1) fertilizer during the sowing
and P2O5 (150 kg ha-1) fertilizer after the third harvest
in 2005 year (Serin and Tan, 2001). No pesticides
were applied. Soil moisture contents in all plots were
increased to the field capacity after the sowing in 2005
and April 20 in 2006. The total usable soil water content within the top 0.9 m of the soil profile was 100
mm. Irrigations were applied when approximately 50%
of the usable soil moisture was consumed in the effective rooting depth (0.9 m) at the full irrigation (control) treatment (T-100) in both years (Allen et al.,
1998). In deficit irrigation treatments, T-80, T-60, T40, T-20 and T-0 (non-irrigation) irrigations were applied at the rates of 80, 60, 40, 20 and 0% of full
irrigation treatments (T-100) on the same day, respectively. Irrigations were started on June 25 in 2005 and
May 24 in 2006. Irrigation water was applied by the
hose-drawn traveler with a line of sprinklers (Figure
1). The total length of sprinkler line is 50 m. The sprinkler line was mounted to a trolley from the central
point. During the irrigation water application, the trolley moves toward the irrigation machine. Total 40
sprinkler heads with a nozzle diameter of 8 mm and
equal flow rate have been mounted on the sprinkler
line with an interval of 1.25 m. The total flow rate of
the system is 73.4 m3 h-1 at the operational pressure
of 2 atm. The duration of irrigation water application
for each plot has been determined according to the
required water amount to be applied to each plot. In
this situation, the duration of irrigation water application for T-100, T-80, T-60, T-40 and T-20 plots was
1.02, 0.82, 0.61, 0.41 and 0.20 h, respectively. Surface flow in plots has not been observed during the
water application. In order to obtain irrigation unifor-
Y. Kuslu, U. Sahin, T. Tunc and F. M. Kiziloglu
mity, irrigation was performed in hours when no wind
or low wind (<2 m s-1) occurred. Irrigation water was
of high quality with an electrical conductivity of 0.29
dS/m, a sodium adsorption ratio of 0.41, and a pH of
7.55.
Cuttings were made by machine. Three cuttings
were applied in both years. First and second cuttings
were made when alfalfa was 10% blooming at the T100 treatment plots in both years. Third cuttings were
made before blooming because the insufficient climatic
conditions. Cutting dates were 30 June, 27 August
and 15 September in 2005 and 10 June, 10 August
and 14 September in 2006. Sub-plots were divided
into 6 parts each of which is 83.3 m2 areas. Plant
samples cut from the centre of each part were weighed
and then dried in an oven at 78 Cº for 24 h before
being re-weighed. Yields were then expressed on an
oven-dry weight basis.
Actual evapotranspiration (ETa) was calculated as
a daily average for 10-day periods during the growing season by the soil water balance equation (Malek
and Bingham, 1993; Rana and Katerji, 2000; Zhao
et al., 2004):
ETa = I + P+Cr - Dw – Rf ± Δ S
where ETa is the actual evapotranspiration (mm), I
is the amount of irrigation water applied (mm), P is
the precipitation (mm), Cr is the capillary rise (mm),
Dw is the amount of drainage water (mm), Rf is the
amount of runoff (mm), and Δ S is the change in the
soil moisture content (mm). Change in the soil moisture content at effective rooting depth was measured
on days 10, 20 and 30 or 31 of each month, and at all
harvests. Furthermore, additional measurements were
applied for determining the exact date of irrigation
based upon reduction in soil moisture content. In the
soil moisture content measurements were used the
TDR (TDR 300, spectrum technologies, USA) in top
soil layers (0-30 and 30-60 cm) and the conventional
oven-dry method in below soil layers (60-90 and 90120 cm). No runoff was observed during the experiments. Capillary rise was considered as negligible
Determining Water-yield Relationship, Water Use Efficiency, Seasonal Crop and Pan Coefficients...
because of the deep water table level. Drainage water consist of precipitation under the effective rooting
depth, according to the soil water content measurements in soil layer at under the effective rooting depth,
was determined.
Water use efficiency (kg ha-1 mm-1) was calculated
by dividing plant dry matter yield (kg ha-1) to actual
evapotranspiration (mm) (Howell et al., 1992; Scott,
2000).
The relationship between relative evapotranspiration reduction ( ETa) and relative yield reduction
1−
ETm
Ya
( 1 − Y ) was determined using the method
m
given by Doorenbos and Kassam (1979). The
equations are as follows.
Y
ETa
1 − a = k (1 −
)
y
Ym
ETm
or
Yd= ky ETd
where Ya is actual harvested yield, Ym is maximum
harvested yield, ky is yield response factor, ETa is actual evapotranspiration, ETm is maximum evapotranspiration, Yd is relative yield reduction, and ETd is relative evapotranspiration reduction.
Reference evapotranspiration (ETo) was calculated
as a daily average for 10-day periods during the growing season by using the CropWat for Windows (Version 4.2) program (Clarke et al., 1998). This program uses the FAO Penman-Monteith equation for
calculating ETo. The FAO Penman-Monteith equa-
tion is given by Allen et al. (1998):
where ETo is the reference evapotranspiration (mm
day-1), Rn is net radiation at the crop surface (MJ m-2
day-1), G is soil heat flux density (MJ m-2 day-1), T is
mean daily air temperature at 2 m height (°C), u2 is
487
wind speed at 2 m height (m s-1), es is saturation vapour
pressure (kPa), ea is actual vapour pressure (kPa), es
- ea is saturation vapour pressure deficit (kPa), Δ is
slope of the saturation vapour pressure curve (kPa/
°C), and γ is psychrometric constant (kPa/°C).
The crop coefficient (kc) is the ratio of ETa to ETo,
and, similarly, the pan coefficient (kp) is the ratio of
ETo to Epan. kc and kp were estimated with the following equations (Allen et al., 1998; Sentelhas and
Folegatti, 2003, Snyder et al., 2005; Sahin et al.,
2007):
kc = ETa/ETo
kp = ETo/Epan
Regression technique was used to determine
evapotranspiration-dry forage yield relationship, crop
and pan coefficient. Analysis of variance (General Linear Model-ANOVA) was conducted to evaluate the
effects of treatments on the dry forage yield using
MINITAB statistical package (release 11.12, 1996;
Minitab Inc.). Duncan’s multiple range test was used
to compare and rank the treatment means (MSTATC, 1988).
Results and Discussion
Water-Yield Relationship
The total number of irrigation, the amount of irrigation water and actual evapotranspiration (ETa) values of alfalfa for the experimental years was presented
in Table 3. The total number of irrigations, the applied
irrigation water and the seasonal ETa in 2005 growing
period were lower than in 2006. This may be attributed to the differences in climatic conditions. While
mean temperature, wind speed and daily sunshine in
2005 growing period was lower than in 2006, precipitation and mean relative humidity in 2005 growing period was higher than in 2006 (Table 1). In the
control treatment, T-100, the amount of total irrigation water applied and seasonal ETa values were
349.6, 563.7 mm in 2005, 548.5, and 687.8 mm in
2006, respectively. As expected, the highest seasonal
ETa occurred in the T-100 obviously owing to an adequate soil water supply during the growing period.
Other treatments underwent water deficits and pro-
488
Y. Kuslu, U. Sahin, T. Tunc and F. M. Kiziloglu
Table 3
Total numbe r of irrigation, amount of irrigation water, se as onal actual e vapotranspiration (ETa),
total dry forage yie ld (DFY) and wate r us e e fficie ncy (WUE) values of alfalfa in the growing
pe riods of 2005 and 2006
Year Treatment
Number of Irrigation water Water
irrigation
applied, mm saving, %
2005
Seasonal
Eta, mm
Total DFY,
ton ha
-1
WUE,
T-100
7.0
349.6
0.0
563.7
7.849 b*
T-80
7.0
279.7
20.0
499.4
6.436 c
T-60
7.0
209.7
40.0
445.0
4.793 e
T-40
7.0
139.8
60.0
379.3
3.904 f
T-20
7.0
69.9
80.0
330.1
3.069 g
T-0
100.0
277.9
2.407 h
2006
T-100
11.0
548.5
0.0
687.8
10.239 a
T-80
11.0
438.8
20.0
577.8
7.601 b
T-60
11.0
329.1
40.0
472.3
5.597 d
T-40
11.0
219.4
60.0
371.9
3.917 f
T-20
11.0
109.7
80.0
281.5
2.793 gh
T-0
100.0
187.6
1.687 ı
* Different letters in the column indicate significant differences at P<0.01 using Duncan’s multiple
range test
duced lower seasonal ETa. The lowest seasonal ETa
was observed in the continuous stress treatments (T0), 277.9 mm in 2005 and 187.6 mm in 2006. The
decreasing ratio of seasonal ETa by the increasing water
deficit in 2006 growing period was higher than in 2005.
This situation could be explained by higher water requirement in 2006 (Table 3). The seasonal ETa of the
full-irrigated alfalfa plants in this study was low compared to that reported by FAO (2002a), but was similar to those obtained by Sahin and Hanay (1996) and
Evren and Sevim (1998) in Erzurum conditions.
As shown in Table 3, data obtained from the 2year study showed that alfalfa total dry forage yield
was significantly (P<0.01) affected by water deficit,
and the highest values were obtained in T-100. Increasing water deficits resulted in a relatively lower
plant yields. While the water saving in our study was
20% (T-80), 40% (T-60), 60% (T-40), 80% (T-20)
and 100% (T-0) of T-100, the rates of decreases in
-1
-1
kg ha mm
13.9
12.9
10.8
10.3
9.3
8.7
14.9
13.2
11.9
10.5
9.9
9.0
average dry forage yield for 2 years were found to be
22.4, 42.6, 56.8, 67.6 and 77.4% of the T-100, respectively. Therefore, it was observed that the ratio
of decreases in total dry forage yield for each percent
deficit rate was not constant. Frate and Roberts
(2006) reported that alfalfa hay yields were greatly
reduced by deficit irrigation. Guitjens (1993) indicated
that generally, alfalfa yields were significantly less for
non-irrigation conditions. Orloff et al. (2004) reported
severe yield losses when irrigation was halted in summer. Hanson et al. (2007) also determined similar results.
The relationships between seasonal ETa (mm) and
total dry forage yield (ton ha-1) have been evaluated
for 2005, 2006 and 2005–2006. The relationship
between seasonal ETa and total dry forage yield was
linear (P<0.01) (Figure 2). This result agree with those
of Bauder et al. (1987), Sheafer et al. (1988), Guitjens
(1990), Smeal et al. (1991), Grimes et al. (1992),
Saeed and El-Nadi (1997) and Bai and Li (2003).
489
Determining Water-yield Relationship, Water Use Efficiency, Seasonal Crop and Pan Coefficients...
Water Use Efficiency (WUE)
WUE calculated by dividing total dry forage yield
(kg ha-1) to seasonal ETa (mm) were different depending on the treatments (Table 3). The lowest WUE
values were determined for continuous stress conditions (T-0) in both years. WUE was increased by increasing irrigation. This could be explained that dry
matter accumulation was increased by irrigation. The
WUE of the full-irrigated alfalfa plants in this study
was low to those reported by Grimes et al. (1992)
and Hirth et al. (2001) for cooler climates, but it was
high to those obtained by Saeed and El-Nadi (1997)
and Hirth et al. (2001) for warmer climates.
Yield Response Factor (ky)
Yield response factor (ky) was determined for
2005, 2006 and 2005–2006. Total dry forage yield
(DFY) and seasonal actual evapotranspiration (ETa)
presented in Table 3 were used to determine relative
yield reduction (Yd) and relative evapotranspirasyon
reduction (ETd). A linear regression equation was fitted to the data (Figure 3). The ky values of alfalfa to
water deficit for the entire growing season were 1.47
and 1.24 in 2005 and 2006, respectively. According
12
10
0.5
0.4
0.3
0.2
0.1
0
0
Yd = 1.47ETd ; r 2 = 0.973** (2005)
Yd = 1.24ETd ; r 2 = 0.970** (2006)
Yd = 1.33ETd ; r2 = 0.973** (2005-2006)
9
0.1
8
7
Yd = 1 - (Ya/Ym)
Total dry forage yield, ton ha -1
Crop and Pan Coefficients (kc and kp)
ETa determined by the soil water balance equation, ETo calculated with the FAO Penman–Monteith
equation and Epan values measured with a Class A pan
during the 2005 and 2006 growing periods of alfalfa
were given as means of 10 days in Figure 4. ETa values varied from 1.21 to 6.21 mm day-1 in 2005. It
was 1.24-6.44 mm day-1 in 2006. ETo values varied
from 2.50 to 7.11 mm day-1 in 2005 and from 2.19 to
7.51 mm day-1 in 2006. Seasonal ETo was determined
as 702.2 mm in 2005 and 782.9 mm in 2006. Seasonal ETo was higher than seasonal ETa in both years.
Epan values varied from 1.88 to 7.80 mm day-1 in 2005
and from 1.76 to 10.04 mm day-1 in 2006. Seasonal
Epan was determined as 770.7 mm in 2005 and 920.5
mm in 2006. Seasonal Epan was higher than seasonal
ETo in both years.
0.6
y = 0.019x - 3.216 ; r2 = 0.979** (2005)
y = 0.017x - 1.981 ; r2 = 0.982** (2006)
y = 0.018x - 2.397 ; r2 = 0.974** (2005-2006)
11
to the regression equation, ky was 1.33, when the
experimental years were considered together. The
coefficient of determination (r2) was 0.97 and the relationship was statistically significant at the level of
P<0.01. The ky value of 1.33 obtained in this study
was higher than ky value of 1.1 reported by Doorenbos
and Kassam (1979) and FAO (2002a).
6
5
4
3
0.2
0.3
0.4
2
2005
1
2006
0.5
0
0
100
200
300
400
500
600
700
Seasonal ETa (mm)
Fig. 2. Total dry forage yield of alfalfa as a
function of seasonal actual evapotranspiration
(ETa)
0.6
ETd = 1 - (ETa/ETm)
Fig. 3. Yield response factor, ky
490
Y. Kuslu, U. Sahin, T. Tunc and F. M. Kiziloglu
8
12
2005-ETa
11
2006-ETa
2005-ETo
2006-ETo
2005-Epan
2
ETa = 0.83ETo ; r = 0.663** (2005)
2006-Epan
7
ETa = 0.88ETo ; r = 0.627** (2006)
6
ETa = 0.86ETo ; r = 0.662** (2005-2006)
2
2
9
-1
8
Eta, mm day
ETa, ETo , Epan, mm day-1
10
7
6
5
4
5
4
3
3
2
2
1
2005
2006
1
0
0
0
10
20
30
40
50
60
70
80
90 100 110 120 130 140 150
0
1
Fig. 4. Actual evapotranspiration (ETa), reference evapotranspiration (ETo) and Class A pan
evaporation (Epan) values during the 2005 and
2006 growing periods
2
8
ET o = 0.90Epan ; r = 0.754** (2005)
ET o = 0.83Epan ; r2 = 0.854** (2006)
7
ET o = 0.86Epan ; r2 = 0.791** (2005-2006)
ETo, mm day
-1
6
5
4
3
2
2005
1
2006
0
0
1
2
3
4
5
6
Epan, mm day
7
2
3
4
ETo, mm day
Date, da ys a fter sowing
8
9
10
11
5
6
7
8
-1
Fig. 5. The relationship between seasonal
ETa and Eto
Heibloem (1986), Allen et al. (1998) and FAO
(2002a).
The values of kp was computed from ETo and Epan
data in Figure 4, and was shown in Figure 6. The
seasonal kp values was determined as 0.90 in 2005,
as 0.83 in 2006 and as 0.86 in 2005-2006. The coefficient of determination (r2) was 0.75 in 2005, 0.85
in 2006 and 0.79 in 2005-2006; and the relationships were statistically significant at the level of P<0.01.
The kp value of 0.86 obtained in this study is a result
of the ETo lower than Epan values (Figure 4). Based
on earlier investigations, the FAO sources state that
the kp values vary between 0.35 and 0.85 (Allen et
al., 1998).
-1
Fig. 6. The relationship between seasonal
ETo and Epan
The values of kc derived from ETa and ETo data in
Figure 4 are shown in Figure 5. The seasonal kc value
was determined as 0.83 in 2005, as 0.88 in 2006 and
as 0.86 in 2005-2006. The coefficient of determination (r2) was 0.66 in 2005, 0.63 in 2006 and 0.66 in
2005-2006; and the relationships were statistically
significant at the level of P<0.01. The kc value of 0.86
obtained in this study is a result of the ETa lower than
ETo values (Figure 4). The kc value determined from
this study was similar to those suggested as 0.85-1.05
by Doorenbos and Kassam (1979), Brouwer and
Conclusion
According to the results of a 2-year study, alfalfa
dry forage yield was significantly decreased by water
stress. Water use efficiency values were decreased
by the increase in water deficit. Positive linear relationship was obtained between evapotranspiration and
dry forage yield. The yield response factor (ky) was
1.33. This value could be used as a good basis for
irrigation strategy development in semiarid regions with
high altitude where irrigation water supplies are limited.
The seasonal crop coefficient was determined as
0.86 for alfalfa. The value of the seasonal pan coeffi-
Determining Water-yield Relationship, Water Use Efficiency, Seasonal Crop and Pan Coefficients...
cient was 0.86. According to these results, the actual
evapotranspiration of alfalfa under semiarid conditions
with high altitude could be considered as 74 % Class
A pan evaporation.
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Received December, 2, 2009; accepted for printing May, 4, 2010