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LEPA and trickle irrigation of cotton in the Southeast Anatolia Project (GAP) area in Turkey
Agricultural Water Management 54 (2002) 189±203
LEPA and trickle irrigation of cotton in the Southeast Anatolia Project (GAP) area in Turkey Attila Yazar*, S. Metin Sezen, Sertan Sesveren Irrigation and Agricultural Structures Department, Cukurova University, 01330 Adana, Turkey Accepted 20 September 2001
Abstract This study was designed to evaluate the yield response of low-energy precision application (LEPA) and trickle-irrigated cotton grown on a clay-textured soil under the arid Southeast Anatolia Project (GAP) area conditions during the 1999 growing season at Koruklu in Turkey. The effects of four different irrigation levels (100, 75, 50, and 25% of cumulative Class-A pan evaporation on a 6day basis) for LEPA, and two irrigation intervals (3-day and 6-day) and three different levels (100, 67, and 33% of cumulative Class-A pan evaporation on a 3-day and 6-day basis) for the trickle system on yield were investigated. Water was applied to alternate furrows through the double-ended Fangmeier drag-socks in the LEPA system. Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m. A total of 814 mm of water was applied to the full-irrigation treatments (100%) for both irrigation systems. Seasonal water use ranged from 383 to 854 mm in LEPA treatments; and 456 to 868 mm in trickle treatments. Highest average cotton yield of 5850 kg/ha was obtained from the full-irrigation treatment (100%) in trickle-irrigated plots with 6day intervals. The highest yield in LEPA plots was obtained in LEPA-100% treatment with an average value of 4750 kg/ha. Seed cotton yields varied from 2660 to 5040 kg/ha and 2310 to 5850 kg/ha in trickle irrigation plots with 3-day and 6-day intervals, respectively, and from 2590 to 4750 kg/ha in LEPA plots. Irrigation levels both in LEPA and trickle-irrigated plots signi®cantly increased yield. However, there was no signi®cant yield difference between 100 and 67% irrigation levels in trickle-irrigated plots. Maximum irrigation water use ef®ciency (IWUE) and water use ef®ciency (WUE) were found as 0.813 and 0.741 kg/m3 in trickle-irrigated treatment of 67% with 6-day interval. Both IWUE and WUE values varied with irrigation quantity and frequency. The research results revealed that both the trickle and LEPA irrigation systems could be used successfully for irrigating cotton crop under the arid climatic conditions of the GAP area in Turkey. # 2002 Elsevier Science B.V. All rights reserved. Keywords: LEPA; Cotton; Trickle; GAP; De®cit irrigation
* Corresponding author. Tel.: 90-322-338-6516; fax: 90-322-338-6386. E-mail address: [email protected] (A. Yazar).
0378-3774/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 1 ) 0 0 1 7 9 - 2
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1. Introduction Irrigation is an increasingly important practice for sustainable agriculture in the arid and semi-arid southeast Anatolia region of Turkey as well as in other dry regions of the world. Crop yield is primarily water-limited in this least developed region in the country. Irrigation water supplies are mainly from the reservoirs of a series of dams constructed on the Euphrates and Tigris rivers. In order to reduce the socio-economic gap between this region and in more developed parts of the country, the Turkish Government initiated an integrated water resources development project called Southeast Anatolia Project (GAP) in the mid-1980s. With the implementation of GAP, 1.7 million hectares of land will be irrigated within a time span of 30 years. Within this developmental framework, application of advanced irrigation and agricultural technologies has gained the utmost importance. Unless new irrigation and agricultural technologies are introduced, soil degradation and salinity build-up in the soil profile will be inevitable due to high clay content and flat slopes in addition to very high evaporative demand. Water shortage will arise if traditional methods of irrigation are to be practised (Yazar et al., 1999a). Cotton is the most important crop in the GAP region in Turkey. From 1996 to 1999, Turkey annually produced an average 814 000 tons of lint cotton, 40% of which was grown in the GAP area. Average lint yield in the region is 1150 kg/ha (Killi and Gencer, 1999). Common irrigation methods used for cotton production in this region are wild flooding, furrow and basin. In general, the farmers overirrigate, resulting in high losses and low irrigation efficiencies, and thus creating drainage and salinity problems. Micro-irrigation is one of the technologies, which offers unique agronomic, water conservation, and economic advantages needed to address the challenges for irrigated agriculture in the future. The use of micro-irrigation systems continues to increase in the world. According to a survey carried out by ICID in 1991, micro-irrigation systems are used on 1.8 million hectare of land in the world (Bucks, 1993). This constitutes only 1% of total irrigated land in the world. Low energy precision application (LEPA) irrigation concept was developed by Lyle and Bordovsky (1981) to maximize the utilization of seasonal rainfall and increase irrigation efficiencies by reducing sprinkler irrigation losses associated with droplet evaporation and drift in high winds which commonly occur in Texas. LEPA is a selfpropelled circular or linear irrigation system that applies water at or near the soil surface. The primary purpose of LEPA is to efficiently apply irrigation water for the production of crops and forage in an energy efficient manner. Lyle and Bordovsky (1983) tested the LEPA concept and compared with sprinkler and furrow methods. The LEPA system was found to be superior to sprinkler and furrow methods in terms of application efficiency, water use efficiency (WUE), and energy savings potential. They also reported advantages for alternate-furrow LEPA compared to every-row LEPA in addition to the obvious reduction in hardware costs. Irrigation runoff, prevention from the furrows as well as rainfall retention is achieved with furrow diking which enhances surface water storage. Currently, LEPA devices are commercially available to operate in bubble, chemigation (inverted spray) modes as well as in doubleended socks mode (Howell et al., 1991).
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Cotton yield is dependent upon the production and retention of bolls, and both can be decreased by water stress (Guinn and Mauney, 1984). Development of economically viable micro-irrigation systems could improve the precision of water placement and reduce energy requirements. Two major disadvantages of micro-irrigation are high initial system cost and annual replacement of many system components (Camp et al., 1995). Drip-irrigated cotton was first used commercially in Texas in 1984. The economic benefit derived from drip-cotton comes from labor savings, reduced cultivations, increased yield on the drip-irrigated plots and a corresponding increase in yields on the conventionally irrigated fields (Henggeler, 1995). LEPA irrigation of corn and sorghum was evaluated on Pullman clay loam soil at Bushland, TX by Howell et al. (1991, 1995) and Yazar et al. (1999b) who concluded that both crops responded similarly to LEPA compared with more traditional methods such as graded furrow and sprinkler; however, LEPA permitted greater partitioning of the applied water into actual crop water use by minimizing application losses and getting applied water into the soil. Bordovsky et al. (1992) reported that deficit, high frequency irrigation with LEPA methods enhanced cotton lint yields and provided efficient use of limited water on the southern high plains region of Texas. Spurgeon and Makens (1992) also evaluated LEPA system at the southwest Kansas Research-Extension Center at Garden City, KS on corn and soybean. They recommended furrow diking for all LEPA systems. It has been shown that water losses from center pivot systems operating in windy environment can reach almost one-half of the water applied, and over the growing season almost 30%. LEPA and low elevation spray application (LESA) have been investigated as a technology to conserve water and reduce energy costs. These approaches use drop tubes to discharge irrigation water at low pressure near the soil surface, and have been applied to row crops (in the case of LEPA) and to free standing crops (in the case of LESA) in the United States where application efficiencies typically exceed 95% (Fipps and New, 1990; Lyle and Bordovsky, 1983; Schneider and Howell, 1995). A research was carried out to determine the effects of LEPA, drip, sprinkler, mobile drip, and furrow irrigation methods on the yield and WUE of cotton in the Harran Plain of the GAP area in Turkey during the years 1991±1992. The results revealed that LEPA and mobile drip did not show any significant water savings as compared to furrow method of irrigation. Highest seed cotton yield was obtained from the drip-irrigated plots with 4650 kg per hectare followed by sprinkler with 3710 kg/ha and LEPA with 3210 kg/ ha, and furrow method resulted in a yield level of 3120 kg/ha. The amount of irrigation water applied varied from 726 mm by conventional sprinkler, 1059 mm by mobile drip, 1076 mm for LEPA, 1003 mm by furrow and 987 mm by drip method (Cetin et al., 1994). Shanmughan et al. (1977) compared furrow and trickle irrigation methods for cotton crop in India and found out that the two methods resulted in similar yields. However, the amount of irrigation water applied with trickle method was almost 50% less than the furrow method. The objective of this article is to report the results of a research on the adaptation of LEPA and trickle irrigation methods for irrigating cotton crop in the southeast Anatolia in Turkey. In addition, WUE and the yield response of cotton to LEPA and trickle systems on a slowly permeable soil in the region were investigated.
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2. Materials and methods This study was conducted at the Koruklu Research Station of the Scientific and Technical Research Council of Turkey (TUBITAK) in the Sanlõurfa Province in Southeast Anatolia Project (GAP) area during 1999. The station has a latitude of 368410 N and a longitude of 388580 E, and is at 375 m above mean sea level. The soil of this site is classified as Harran soil series (Vertic Calciorthid aridisol) and clay textured. Volumetric soil water contents at field capacity and permanent wilting point are 0.439 and 0.292 cm3/ cm3, respectively. Total available water within the top 120 cm of soil depth is 176 mm. Mean bulk density varies from 1.31 to 1.45 g/cm3. A hose-reel boom sprinkler system (48 m long) was modified into LEPA system by installing LEPA heads on the drop tubes at alternate rows. LEPA drag-socks mode was utilized in this study. The LEPA system consisted of a hose-reel system and LEPA heads on the drop tubes, which were spaced 140 cm apart. PE pipe sections (1 m long, 12.7 mm in diameter) were used as drop tubes on which pressure regulators (100 kPa, 19.0 mm), nozzles (four different sizes were used on the system), LEPA adapters and double-ended Fangmeier LEPA drag-socks were connected. Water to the system was pumped from a deep well at the research station. The design nozzle sizes were determined from qi CA where qi is the ¯ow rate in liters per second (l/s); C the system capacity in liters per second per square meter (l/s m2); and A the service area per LEPA head in m2. In this study, the largest nozzle size was selected to simulate an irrigation capacity of 15 mm/day, which is equivalent to daily maximum evaporation from Class-A pan in the experimental station. The spray nozzles with proper diameters were selected from the Nelson Irrigation Cor. catalog for 100 kPa pressure rating. Irrigation application amounts were determined by the application rates and system travel speed controlled at the hosereel system. The trickle system consisted of a control unit and distribution lines. The control unit of the system contained a Venturi injector (25.4 mm), fertilizer tank (75 l), disk filter, control valves, and a water flow meter. Distribution lines consisted of PE pipe manifolds (supply and discharge) for each plot. Irrigation laterals of 16 mm in diameter and 30 m in length had inline emitters spaced 0.7 m apart, each delivering 4 l/h at a pressure of 100 kPa. Each discharge manifold had removable end caps for flushing. Trickle irrigation lines were spaced at 1.40 m apart, equally spaced between every other row of cotton. Water was supplied from a pressurized hydrant and filtered through disk filter. Commercial farm equipment was used for agronomic practices. Experimental field was planted with a 4-row planting machine at 70 cm row spacing at 5 cm depth. Stonville-453 cotton variety was planted on May 18, 1999. Plants were thinned to an approximate spacing of 15 cm apart when the plants were about 15 cm in height. Fertilizer applications were based on soil analysis recommendations. All treatment plots received the same amount of total fertilizer. A compound fertilizer of (20-20-0) was applied (80 kg N and 80 kg P2O5 as pure matter per hectare) at a rate of 400 kg ha at planting on May 18. At first irrigation, on July 1, 45 kg of ammonium nitrate per hectare was applied to all treatment plots. The rest of the N was applied to the experimental area
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of LEPA plots in the form of urea (CO(NH2)2) incorporated to soil by a lister. In trickle plots, remaining nutrient requirements (UAN 32-0-0) were applied by chemical injection using a Venturi injector (Netafim) with irrigation water. LEPA plots received the same total amount of N in granular form. In the study, two experiments were set-up in the same field. One half of the field was allocated for the LEPA and the other half was used for the trickle system. The experimental design was a complete randomized block design with three replications for LEPA system, and split-plot design with three replications for trickle irrigation system. Irrigation water was applied based on cumulative Class-A Pan evaporation within the irrigation intervals. In the study, two irrigation intervals of 3 and 6 days for trickle, and only 6 days in LEPA were used. ``LEPA-100'' treatment designated to receive 100% of cumulative Class-A pan evaporation on a 6 days basis was used to guide irrigation applications for LEPA, and treatments ``IF3-100'' and ``IF6-100'' designated to receive 100% of cumulative Class-A pan evaporation on a 3- and 6-day basis, respectively, were used to guide irrigation applications for the trickle method. Deficit irrigation treatments of LEPA-75, LEPA-50 and LEPA-25 received 75, 50 and 25% of full irrigation treatment (LEPA-100), respectively, for LEPA, and two deficit irrigation treatments received 67 and 33% of the full-irrigation treatments of IF3-100 and IF6-100 for trickle irrigation system. The soil water content measurements were made at 12-day intervals until harvest in the three replications for all treatments by gravimetric sampling in 0±30 cm, and using a neutron probe (Campbell Pacific Model 503DR Hydroprobe) at 30 cm depth increments over 120 cm deep with 15 s counts. The probe was field calibrated for the experimental soil. Each plot dimension was 120 m long and 2.80 m wide (four plant rows) for LEPA method, and 30 m long and 5.6 m wide (eight plant rows) for trickle method. Plant and soil water measurements and observations were started 21 days after planting, and were terminated 121±145 days after planting depending on the harvest date. In order to determine the leaf area index (LAI) and total dry matter above the ground level, all plants within 0.5 m of a row section in each plot were cut at the ground level at 12-day intervals till harvest. The cotton leaves were separated from the stem and leaf area of plants was measured by using an optical leaf area meter. Plant samples were dried at 65 8C until constant weight was achieved. Yield was determined by hand harvesting the 12 m sections of the two adjacent center rows in each plot 121, 133, and 145 days after planting depending on the physiological maturity of plants in different treatment plots. The harvest area in each plot was 16.8 m2 (two rows, each 12 m long). Five uniform rate applications varying from 20 to 80 mm were made during the plant establishment period. The first and second applications were made on June 6 and June 26 in the spray mode with LEPA system. The third and fourth applications were made on July 2 and July 6 with a sprinkler system. The final uniform application was made on July 8 with drip and LEPA in spray mode on their respective plots. Treatment irrigations were started on July 15. Water use evapotranspiration (ET) was estimated based on a one-dimensional water balance method using soil water measured by the neutron method. Furrow dikes were constructed manually at approximately 10 m intervals in LEPA-100 and LEPA-75 treatment plots, thus no runoff was allowed in LEPA plots. It was assumed that deep
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percolation was negligible. Water use was the total of seasonal water depletion (planting to harvest) plus rainfall and irrigations during the same period. WUE was computed as the ratio of cotton yield to water use. Irrigation water use efficiency (IWUE) was determined as the ratio of cotton yield for a particular treatment which is less than the non-irrigated yield, which is zero under the study area, to the applied irrigation water for that treatment (Howell et al., 1994). 3. Results and discussion The 1999 cotton growing season climatic conditions were typical of the conditions that prevail in the GAP area. Table 1 summarizes the monthly climate data compared with the long-term mean climatic data for the Harran Plain, where the experiments were carried out. No rainfall was received during the growing season. The total amount of water applied to LEPA and trickle irrigation plots is given in Table 2. As shown in this table, the amount of irrigation water applied varied from 333 to 814 mm in LEPA plots. Trickle-irrigated plots received irrigation water varying from a low of 384 mm in heavy stress plots (IF3- and IF6-33%) to a high of 814 mm in nonstress plots (IF3- and IF6-100%). Seasonal maximum water use and irrigation water requirements of cotton under Harran Plain conditions has been reported to be 1670 and 1555 mm under surface irrigation conditions (Kanber et al., 1992). The amount of irrigation water applied to cotton by conventional sprinkler, mobile drip, LEPA, furrow and drip methods were 726, 1059, 1076, 1003 and 987 mm, respectively, in the Harran Plain (Cetin et al., 1994). As the amount of water applied with LEPA and trickle irrigation systems in this study is Table 1 Historical monthly and growing season climatic data of the experimental area Climatic parameters
April
May
June
July
August
September
Long-term (means 1929±1999) Minimum air temperature (8C) Maximum air temperature (8C) Average temperature (8C) Rainfall (mm) Relative humidity (%) Wind speed (m/s) Evaporation, CAP (mm)
3.4 34.8 15.2 25.4 54 1.6 118.6
1.0 43.0 21.4 25.6 42 1.9 195.6
9.4 45.4 28.0 4.8 35 2.5 320.5
11.0 46.8 31.4 0.1 33 2.6 403.9
9.2 46.6 30.4 ± 36 2.1 376.5
3.4 44.0 25.6 0.1 34 1.5 280.4
Growing season (1999) Minimum air temperature (8C) Maximum air temperature (8C) Average temperature (8C) Rainfall (mm) Relative humidity (%) Wind speed (m/s) Evaporation, CAP (mm) Solar radiation (cal/cm2)
5.8 24.0 16.0 17.8 61.1 1.2 137.6 519.1
13.7 32.0 23.9 1.0 37.4 1.5 279.5 635.1
18.3 35.8 28.0 1.5 37.1 1.5 334.6 659.2
21.5 39.2 30.9 ± 42.4 1.4 370.8 671.4
19.2 38.4 28.9 ± 50.8 1.0 304.4 592.8
14.4 33.8 24.1 ± 49.1 0.9 193.3 514.6
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Table 2 Water use and WUE data for LEPA and trickle-irrigated cotton Treatment
Dry matter yield (kg/ha)
Seed cotton yield (kg/ha)
Soil water Seasonal Water WUE IWUE depletion (mm) irrigation (mm) use (mm) (kg/m3) (kg/m3)
LEPA-100 LEPA-75 LEPA-50 LEPA-25 LSD0.01
10034 9610 8160 6140
4750 4020 3270 2590 2017
a ab ab b
39.7 40.7 48.5 50.6
814 654 493 333
854 695 542 383
0.556 0.579 0.603 0.675
0.583 0.615 0.663 0.778
12680 9650 6570 15009 12150 6490
5040 4520 2660 5870 4900 2310 1627
a a b a a b
54.1 58.7 72.2 39.6 58.7 78.1
814 604 384 814 602 384
868 663 456 854 661 462
0.580 0.695 0.583 0.687 0.741 0.500
0.619 0.748 0.692 0.721 0.813 0.601
Trickle IF3-100 IF3-67 IF3-33 IF6-100 IF6-67 IF6-33 LSD0.05
considered, water saving is possible in comparison to the results from furrow irrigation studies carried out at the same location. Cotton harvest data, irrigation amounts, water use and WUE data are summarized in Table 2. The irrigation levels both in LEPA and trickle-irrigated plots significantly increased seed cotton yield (P < 0:0036 and P < 0:0001). Highest yield, averaging 5870 kg/ha, was measured in trickle-irrigated plots with 6-day interval in IF6-100% treatment, followed by IF3-100% trickle plots with 5040 kg/ha. The effect of irrigation intervals used in trickle irrigation study on cotton yield was not significantly different P < 0:1273. There was no significant difference in yield between the 100 and 67% trickle plots. The highest yield in LEPA plots was obtained in 100% plots with an average value of 4750 kg/ha. As the amount of irrigation water decreased, seed cotton yields also decreased. Dry matter yields were also significantly different among the treatments. Highest dry matter yield, averaging 1.509 kg/m2, was measured in IF6-100 treatment plot followed by IF3-100 treatment with 1.215 kg/m2. LEPA-irrigated plots resulted in slightly lower dry matter yields than the corresponding trickle irrigation plots. In addition, both dry matter and LAI remained consistently greater in 100% treatments both in LEPA and trickle-irrigated plots. Cotton yields in LEPA-irrigated plots in this study were comparable with the cotton yields from previous experiments in the Harran Plain. However, the yields from trickle-irrigated plots were significantly higher than those from the previous experiments utilizing surface and sprinkler irrigation methods (Cetin et al., 1994; Kanber et al., 1996). In the San Joaquin valley of California, Phene et al. (1984) reported ET of 633 50 mm for maximum yield of cotton with trickle irrigation compared to 645 mm for furrow irrigation. Howell et al. (1984) reported ET of 650± 700 mm for maximum lint yield of 2000 kg/ha at the same location using narrow-row cotton (0.5 m). Seasonal water used by cotton varied from 383 mm in LEPA-25 to 854 mm in LEPA100 treatment plots. In trickle-irrigated plots, water use changed from 456 mm in IF3-33
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to 868 mm in IF3-100 treatments. Water use in IF6 treatment was almost the same as those in IF3 treatment. Thus, two different irrigation intervals in trickle plots resulted in similar water use. Accumulative pan evaporation from planting to harvest was 1200 mm. A significant linear relationship between cumulative pan evaporation (Epan) and ET for the period covering onset of square (June 25) to harvest (September 17) was found as ET 0:998 Epan 22:878 r 2 0:988 for LEPA-100 treatment, and ET 0:979 Epan 30:084 r 2 0:973 for the IF3-100 treatment. Highest WUE, averaging 0.741 kg/m3, was obtained in trickle-irrigated treatment of IF6-67. In general, WUE values decreased with increasing water use. However, the WUE values in the different treatments were higher as compared to WUE values of cotton irrigated by furrow or sprinkler system in the same experimental station (Kanber et al., 1996). Irrigation water use efficiencies (IWUE) were slightly higher than the WUE values. Since there was no rainfall during the growing season, the slight differences between the two values can be attributed to water used from soil storage. Hodgson et al. (1990) reported WUE values for trickle-irrigated cotton (lint) as 0.223 kg/m3; Wanjura et al. (1996) determined WUE of cotton (lint) for high frequency drip irrigation in Texas between 0.236 and 0.333 kg/m3. Significant linear and curvilinear relationships were found between the cotton yield and ET in LEPA and trickle irrigation treatments as shown in Fig. 1. Cotton yield increased with increasing ET in the LEPA-irrigated treatments. In trickle-irrigated plots, both irrigation intervals resulted in similar curvilinear relationships between yield and ET. The slopes of the relationships between relative yield reduction and relative ET deficit are termed as yield response factor by Doorenbos and Kassam (1979) and was found to be 0.89 and 1.31 for the LEPA and trickle (IF3)-irrigated treatments, respectively (Figs. 2 and 3). Yield response factor for sprinkler irrigated cotton was found to vary between 0.8 and 1.1 in previous studies carried out in the same location by Kanber et al. (1996). Doorenbos and Kassam (1979) gave the yield response factor for cotton as 0.84. Significant linear and curvilinear relationships between dry matter yield and water use were found for LEPA and trickle-irrigatedigated cotton as shown in Fig. 4. Dry matter
Fig. 1. The relationship between cotton yield and water use for LEPA and trickle-irrigated treatments.
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Fig. 2. Relative yield reduction vs. relative ET deficit relationships for LEPA-irrigated treatments.
yields increased with increasing ET as with cotton yield. Trickle irrigation system resulted in higher dry matter yield as compared with LEPA-irrigated cotton. As with the cotton yield, dry matter yields decreased with decreasing ET. Profile soil water storage variation during the growing season for the LEPA and trickleirrigated plots are shown in Figs. 5±7, respectively. Soil water storage within the 120 cm depth decreased gradually towards the end of the season in all treatment plots. Soil water remained higher in the full irrigation treatment plots (IF3-100, IF6-100 and LEPA-100) than the other treatments considered. However, soil water contents in trickle-irrigated plots were generally higher than those in the LEPA plots. As the amount of applied irrigation water decreased, soil water storage also decreased. Heavy stress treatments in both systems resulted in soil water contents below wilting point during most of the
Fig. 3. Relative yield reduction vs. relative ET deficit relationships for trickle-irrigated treatments.
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Fig. 4. Relationship between dry matter yield and water use for LEPA and trickle-irrigated treatments.
growing season. Grimes and El-Zik (1982) reported that not more than 60±65% of the available water of clay loam soils should be allowed to be depleted in the root zone for maintaining optimum productivity. As shown in Figs. 5±7, soil water depletion levels in the full irrigation treatments remained within 50±65% of available water in the 1.20 m depth. The total length of the growing season varied from 134 days for 1±100 treatments to 122 days in fully stressed treatments in both LEPA and trickle irrigation systems. Occurrence of blooming, ball formation and ball opening stages of cotton were observed at an earlier date in the stressed treatments as compared to the full irrigation treatments. Water deficits from onset of flowering to peak flowering may cause a more negative effect on yield as compared to that which occurred after peak flowering. With severe water deficits during late flowering and early boll formation, boll shedding can be excessive. Moderate water deficits occurring during flowering, but high enough to restrict vegetative growth, will lead to good boll-set and higher yields, despite a reduction in number of flowers (Doorenbos and Kassam, 1979). Radin et al. (1992)
Fig. 5. Soil water storage variation during the growing season in LEPA-irrigated plots.
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Fig. 6. Soil water storage variation during the growing season in trickle-irrigated plots with 3-day irrigation interval.
reported that yield increases were associated with a lengthened period of profuse flowering and a delay in the onset of cutout. Both drip irrigation and mid-cycle supplements increased mid-day leaf water potential and apparent hydraulic conductance of the plants for extended period during flowering. Indicating enhanced water uptake and transport capacity compared to plants irrigated at long cycles. In addition to dry matter data, periodic LAI values were determined for trickleirrigated and LEPA cotton (Figs. 8 and 9, respectively). Highest LAI value, averaging 4.7, was measured in trickle-irrigated treatment of IF3- and IF6-100. LAI values increased with increasing water use in both irrigation methods. The highest LAI value in LEPA
Fig. 7. Soil water storage variation during the growing season in trickle-irrigated plots with 6-day irrigation interval.
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Fig. 8. LAI development in trickle-irrigated treatments.
treatments was measured in LEPA-100 plots as 3.4, followed by other irrigation levels. Cotton plants reached their maximum LAI on August 10 for full irrigation treatments in both the LEPA and trickle systems. Maximum leaf area for the stressed treatments occurred approximately 2 weeks earlier as compared to the full irrigation treatments. Vegetative growth declined severely as water deficit increased. Orgaz et al. (1992) determined the maximum LAI value as 4.1. Bielorai et al. (1983) and Turner et al. (1986) emphasized the sensitivity of expansive growth to water deficits in cotton. A significant linear relationship between LAI and ET for LEPA and trickle-irrigated cotton were obtained. The resulting equations are as follows: ET 136:87 LAI 231:8 R2 0:986 for trickle; and ET 277:66 LAI 43:77 R2 0:965 for LEPA-irrigated cotton. Water use increased with increasing LAI in both irrigation systems.
Fig. 9. LAI development in LEPA-irrigated treatments.
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4. Conclusions Cotton yields obtained from the trickle and LEPA irrigation systems in Harran Plain in GAP region of Turkey were found to be higher as compared to other irrigation methods such as sprinkler and furrow, in the previous experiments, in the same location. Deficit LEPA and trickle irrigation generally reduced cotton yield. Irrigating at less than 100% of pan evaporation may not produce enough leaching for a salt balance in the root zone since the average annual rainfall in the project area is only 388 mm. Thus, deficit irrigation of cotton with trickle and LEPA systems is not recommended for the region. Both trickle and LEPA systems permitted precise control of the irrigation applications. They provided uniform irrigation because LEPA heads equipped with pressure regulators and the constant system travel speed was maintained during an irrigation, and the trickle system had a high emission uniformity (93%) as measured on several trickle laterals. Applications with the double-ended Fangmeier LEPA socks performed well under arid climatic conditions. Water distribution uniformity along the direction of travel of the linear move hose-reel machine was observed to be very high compared to sprinkler and conventional furrow irrigation methods used in the region. LEPA should be managed to apply as much water as can be efficiently stored in the furrow-dike basins, and then the irrigation frequency is simply determined by the gross irrigation capacity of the system (Howell et al., 1995). With proper management, LEPA and trickle irrigation can avoid some application losses which are inevitable with sprinkler and surface methods. Although the cotton yields from the LEPA-100 and trickle IF3-100 and IF6-100 were not statistically significant, trickle irrigation with 6-day interval resulted in the highest yield among the treatments studied. However, the duration of water application in IF6100 treatment is considerably higher than that in IF3-100 or LEPA-100 treatment. A lateral spacing of 1.4 m is found to be sufficient for trickle irrigation of cotton. Research results revealed that both trickle and LEPA irrigation systems can be used successfully for irrigation of cotton under the climatic conditions of GAP area in Turkey. Acknowledgements We wish to acknowledge the financial support provided to this project by the TUBITAK (Turkish Scientific and Research Council) as TARP #1856. In addition, we would like to thank Dr. T.A. Howell at USDA-ARS, Bushland, TX for providing doubleended LEPA drag socks for this study. References Bielorai, H., Mantell, A., Moreshet, S., 1983. Water relations of cotton. In: Kozkowski, T.T. (Ed.), Water Deficits and Plant Growth. Academic Press, New York. Bordovsky, J.P., Lyle, W.M., Lascano, R.J., Upchurch, D.R., 1992. Cotton irrigation management with LEPA systems. Trans. ASAE 35 (3), 879±884.
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Bucks, D.A., 1993. Micro-irrigation worldwide usage report. In: Proceedings of the Workshop on Microirrigation Worldwide, The Hague, The Netherlands, September 2. ICID, New Delhi, India, pp. 11± 30. Camp, C.R., Hunt, P.G., Bauer, P.J. 1995. Subsurface microirrigation management and lateral spacing for cotton in the Southeastern USA. In: F.R. Lamm (Ed.), Microirrigation for a Changing World. Proc. of the fifth international microirrigation Congress. April 2±6, Orlando, Florida ASAE publication, pp. 368± 375. Cetin, O., Ozyurt, E., Sener, S., 1994. The effects of different irrigation methods on the yield and water use efficiency of cotton in Harran Plain. Proceedings of the 17th European Regional Conference on Efficient and Ecologically Sound Use of Irrigation Water with Special Reference to European Countries, Varna, Bulgaria, May 16±22. ICID. Doorenbos, J., Kassam, A.H., 1979. Yield response to water. FAO Irrigation and Drainage Paper No. 33. FAO, Italy, Rome. Fipps, G., New L.L., 1990. Six years of LEPA in TexasÐless water, high yields. In: Vision of the Future. Proceedings of the Third National Irrigation Symposium, St. Joseph, MI. ASAE, pp. 115± 120. Grimes, D.W., El-Zik, K.M., 1982. Water management for cotton. Division of Agricultural. Science Bulletin No. 1904. University of California, Davis, CA. Guinn, G., Mauney, J.R., 1984. Fruiting of cotton. I. Effects of moisture status on flowering. Agron. J. 76, 90± 94. Henggeler, J.C., 1995. A history of drip irrigated cotton in Texas. In: Lamm, F.R. (Ed.), Microirrigation for a Changing World. Proceedings of Fifth International Microirrigation Congress, Orlando, FL, April 2±6. ASAE, pp. 669±675. Howell, T.A., Hatfield, J.L., Yamada, H., Davis, K.R., 1984. Evaluation of cotton canopy temperature to detect crop water stress. Trans. ASAE 27, 84±88. Howell, T.A., Schneider, A.D., Dusek, D.A., 1991. Corn and sorghum response to LEPA irrigation. ASAE Paper No. 91-2520, St. Joseph, MI. ASAE. Howell T.A., Yazar, A., Schneider, A.D., Duser, D.A. Copeland, K.S., 1994. LEPA irrigation management for corn. ASAE paper No. 94±2098, pp. 23. Howell, T.A., Yazar, A., Schneider, A.D., Dusek, D.A., Copeland, K.S., 1995. Yield and water use efficiency of corn in response to LEPA irrigation. Trans. ASAE 38, 1737±1747. Kanber, R., Onder, S., Unlu, M., Koksal, H., Ozekici, B., Sezen, S.M., Yazar, A., Koc, K., 1996. Optimization of surface irrigation methods for cotton and comparison with sprinkler irrigation. Research Report No. 18, GAP Research Projects. Faculty of Agriculture Publication No. 155, Cukurova University, Adana, Turkey, 1995. Killi, F., Gencer, O., 1999. Cotton Production and Consumption Projections in 2000s in Turkey. Proceedings of the First Symposium on Cotton Agriculture, Fiber Technology and Textile in the Turk World, September 28± October 1, 1999, Kahramanmaras, Turkey, pp. 382±390. Lyle, W.M., Bordovsky, J.P., 1981. Low energy precision application (LEPA) irrigation system. Trans. ASAE 24, 1241±1245. Lyle, W.M., Bordovsky, J.P., 1983. LEPA irrigation system evaluation. Trans. ASAE 26, 776±781. Orgaz, F., Mateos, L., Fereres, E., 1992. Agroclimatology and modeling: season length and cultivar determine the optimum evapotranspiration deficit in cotton. Agron. J. 84, 700±706. Phene, C.J., Davis, K.R., Howell, T.A., McCormick, R.L., Nightengale, H.I., Meek, D.W., 1984. Evapotranspiration and water use efficiency of trickle-irrigated cotton. ASAE Paper No. 84-2625. Presented at 1984 Winter Meeting of the ASAE, New Orleans, FL. Radin, J.W., Reaves, L.L., Mauney, J.R., French, O.F., 1992. Yield enhancement in cotton by frequent irrigations during fruiting. Agron. J. 84, 551±557. Schneider, A.D., Howell, T.A., 1995. Grain sorghum response to sprinkler application methods and system capacity. Trans. ASAE 38 (6), 1693±1697. Shanmughan, K., Meenakshisundaram, D.C., Seshadri, V., 1977. Drip irrigation on the efficient technique. Soils Fert. 40 (6). Spurgeon, W., Makens, T., 1992. LEPA irrigation report. Southwest Kansas Research-Extension Center Report Progress 657. Agriculture Experimetal Station. 1992 Field Day Report.
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Turner, N.C., Hearn, A.B., Begg, J.E., Constable, G.A., 1986. Cotton (Gossypium Hirsutum L.): physiological and morphological responses to water deficits and their relationship to yield. Field Crops Res. 14, 153±170. Wanjura, D.F., Mahan, J.R., Upchurch, D.R., 1996. Irrigation starting time effects on cotton under high frequency irrigation. Agron. J. 88, 561±566. Yazar, A., Kanber, R, Sezen, S.M., Ozekici, B., 1999a. Adoption of LEPA and trickle irrigation systems for cotton and corn irrigation in the GAP region. TUBITAK-TARP No. 1856. Annual Research Report 1 and 2. Faculty of Agriculture, Department of Irrigation, Cukurova University, Adana, Turkey. Yazar, A., Howell, T.A., Dusek, D.A., Copeland, K.S., 1999b. Evaluation of crop water stress index for LEPA irrigated corn. Irrig. Sci. 18, 171±180.
LEPA and trickle irrigation of cotton in the Southeast Anatolia Project (GAP) area in Turkey Attila Yazar*, S. Metin Sezen, Sertan Sesveren Irrigation and Agricultural Structures Department, Cukurova University, 01330 Adana, Turkey Accepted 20 September 2001
Abstract This study was designed to evaluate the yield response of low-energy precision application (LEPA) and trickle-irrigated cotton grown on a clay-textured soil under the arid Southeast Anatolia Project (GAP) area conditions during the 1999 growing season at Koruklu in Turkey. The effects of four different irrigation levels (100, 75, 50, and 25% of cumulative Class-A pan evaporation on a 6day basis) for LEPA, and two irrigation intervals (3-day and 6-day) and three different levels (100, 67, and 33% of cumulative Class-A pan evaporation on a 3-day and 6-day basis) for the trickle system on yield were investigated. Water was applied to alternate furrows through the double-ended Fangmeier drag-socks in the LEPA system. Trickle irrigation laterals were laid out on the soil surface at a spacing of 1.40 m. A total of 814 mm of water was applied to the full-irrigation treatments (100%) for both irrigation systems. Seasonal water use ranged from 383 to 854 mm in LEPA treatments; and 456 to 868 mm in trickle treatments. Highest average cotton yield of 5850 kg/ha was obtained from the full-irrigation treatment (100%) in trickle-irrigated plots with 6day intervals. The highest yield in LEPA plots was obtained in LEPA-100% treatment with an average value of 4750 kg/ha. Seed cotton yields varied from 2660 to 5040 kg/ha and 2310 to 5850 kg/ha in trickle irrigation plots with 3-day and 6-day intervals, respectively, and from 2590 to 4750 kg/ha in LEPA plots. Irrigation levels both in LEPA and trickle-irrigated plots signi®cantly increased yield. However, there was no signi®cant yield difference between 100 and 67% irrigation levels in trickle-irrigated plots. Maximum irrigation water use ef®ciency (IWUE) and water use ef®ciency (WUE) were found as 0.813 and 0.741 kg/m3 in trickle-irrigated treatment of 67% with 6-day interval. Both IWUE and WUE values varied with irrigation quantity and frequency. The research results revealed that both the trickle and LEPA irrigation systems could be used successfully for irrigating cotton crop under the arid climatic conditions of the GAP area in Turkey. # 2002 Elsevier Science B.V. All rights reserved. Keywords: LEPA; Cotton; Trickle; GAP; De®cit irrigation
* Corresponding author. Tel.: 90-322-338-6516; fax: 90-322-338-6386. E-mail address: [email protected] (A. Yazar).
0378-3774/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 3 7 7 4 ( 0 1 ) 0 0 1 7 9 - 2
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1. Introduction Irrigation is an increasingly important practice for sustainable agriculture in the arid and semi-arid southeast Anatolia region of Turkey as well as in other dry regions of the world. Crop yield is primarily water-limited in this least developed region in the country. Irrigation water supplies are mainly from the reservoirs of a series of dams constructed on the Euphrates and Tigris rivers. In order to reduce the socio-economic gap between this region and in more developed parts of the country, the Turkish Government initiated an integrated water resources development project called Southeast Anatolia Project (GAP) in the mid-1980s. With the implementation of GAP, 1.7 million hectares of land will be irrigated within a time span of 30 years. Within this developmental framework, application of advanced irrigation and agricultural technologies has gained the utmost importance. Unless new irrigation and agricultural technologies are introduced, soil degradation and salinity build-up in the soil profile will be inevitable due to high clay content and flat slopes in addition to very high evaporative demand. Water shortage will arise if traditional methods of irrigation are to be practised (Yazar et al., 1999a). Cotton is the most important crop in the GAP region in Turkey. From 1996 to 1999, Turkey annually produced an average 814 000 tons of lint cotton, 40% of which was grown in the GAP area. Average lint yield in the region is 1150 kg/ha (Killi and Gencer, 1999). Common irrigation methods used for cotton production in this region are wild flooding, furrow and basin. In general, the farmers overirrigate, resulting in high losses and low irrigation efficiencies, and thus creating drainage and salinity problems. Micro-irrigation is one of the technologies, which offers unique agronomic, water conservation, and economic advantages needed to address the challenges for irrigated agriculture in the future. The use of micro-irrigation systems continues to increase in the world. According to a survey carried out by ICID in 1991, micro-irrigation systems are used on 1.8 million hectare of land in the world (Bucks, 1993). This constitutes only 1% of total irrigated land in the world. Low energy precision application (LEPA) irrigation concept was developed by Lyle and Bordovsky (1981) to maximize the utilization of seasonal rainfall and increase irrigation efficiencies by reducing sprinkler irrigation losses associated with droplet evaporation and drift in high winds which commonly occur in Texas. LEPA is a selfpropelled circular or linear irrigation system that applies water at or near the soil surface. The primary purpose of LEPA is to efficiently apply irrigation water for the production of crops and forage in an energy efficient manner. Lyle and Bordovsky (1983) tested the LEPA concept and compared with sprinkler and furrow methods. The LEPA system was found to be superior to sprinkler and furrow methods in terms of application efficiency, water use efficiency (WUE), and energy savings potential. They also reported advantages for alternate-furrow LEPA compared to every-row LEPA in addition to the obvious reduction in hardware costs. Irrigation runoff, prevention from the furrows as well as rainfall retention is achieved with furrow diking which enhances surface water storage. Currently, LEPA devices are commercially available to operate in bubble, chemigation (inverted spray) modes as well as in doubleended socks mode (Howell et al., 1991).
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Cotton yield is dependent upon the production and retention of bolls, and both can be decreased by water stress (Guinn and Mauney, 1984). Development of economically viable micro-irrigation systems could improve the precision of water placement and reduce energy requirements. Two major disadvantages of micro-irrigation are high initial system cost and annual replacement of many system components (Camp et al., 1995). Drip-irrigated cotton was first used commercially in Texas in 1984. The economic benefit derived from drip-cotton comes from labor savings, reduced cultivations, increased yield on the drip-irrigated plots and a corresponding increase in yields on the conventionally irrigated fields (Henggeler, 1995). LEPA irrigation of corn and sorghum was evaluated on Pullman clay loam soil at Bushland, TX by Howell et al. (1991, 1995) and Yazar et al. (1999b) who concluded that both crops responded similarly to LEPA compared with more traditional methods such as graded furrow and sprinkler; however, LEPA permitted greater partitioning of the applied water into actual crop water use by minimizing application losses and getting applied water into the soil. Bordovsky et al. (1992) reported that deficit, high frequency irrigation with LEPA methods enhanced cotton lint yields and provided efficient use of limited water on the southern high plains region of Texas. Spurgeon and Makens (1992) also evaluated LEPA system at the southwest Kansas Research-Extension Center at Garden City, KS on corn and soybean. They recommended furrow diking for all LEPA systems. It has been shown that water losses from center pivot systems operating in windy environment can reach almost one-half of the water applied, and over the growing season almost 30%. LEPA and low elevation spray application (LESA) have been investigated as a technology to conserve water and reduce energy costs. These approaches use drop tubes to discharge irrigation water at low pressure near the soil surface, and have been applied to row crops (in the case of LEPA) and to free standing crops (in the case of LESA) in the United States where application efficiencies typically exceed 95% (Fipps and New, 1990; Lyle and Bordovsky, 1983; Schneider and Howell, 1995). A research was carried out to determine the effects of LEPA, drip, sprinkler, mobile drip, and furrow irrigation methods on the yield and WUE of cotton in the Harran Plain of the GAP area in Turkey during the years 1991±1992. The results revealed that LEPA and mobile drip did not show any significant water savings as compared to furrow method of irrigation. Highest seed cotton yield was obtained from the drip-irrigated plots with 4650 kg per hectare followed by sprinkler with 3710 kg/ha and LEPA with 3210 kg/ ha, and furrow method resulted in a yield level of 3120 kg/ha. The amount of irrigation water applied varied from 726 mm by conventional sprinkler, 1059 mm by mobile drip, 1076 mm for LEPA, 1003 mm by furrow and 987 mm by drip method (Cetin et al., 1994). Shanmughan et al. (1977) compared furrow and trickle irrigation methods for cotton crop in India and found out that the two methods resulted in similar yields. However, the amount of irrigation water applied with trickle method was almost 50% less than the furrow method. The objective of this article is to report the results of a research on the adaptation of LEPA and trickle irrigation methods for irrigating cotton crop in the southeast Anatolia in Turkey. In addition, WUE and the yield response of cotton to LEPA and trickle systems on a slowly permeable soil in the region were investigated.
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2. Materials and methods This study was conducted at the Koruklu Research Station of the Scientific and Technical Research Council of Turkey (TUBITAK) in the Sanlõurfa Province in Southeast Anatolia Project (GAP) area during 1999. The station has a latitude of 368410 N and a longitude of 388580 E, and is at 375 m above mean sea level. The soil of this site is classified as Harran soil series (Vertic Calciorthid aridisol) and clay textured. Volumetric soil water contents at field capacity and permanent wilting point are 0.439 and 0.292 cm3/ cm3, respectively. Total available water within the top 120 cm of soil depth is 176 mm. Mean bulk density varies from 1.31 to 1.45 g/cm3. A hose-reel boom sprinkler system (48 m long) was modified into LEPA system by installing LEPA heads on the drop tubes at alternate rows. LEPA drag-socks mode was utilized in this study. The LEPA system consisted of a hose-reel system and LEPA heads on the drop tubes, which were spaced 140 cm apart. PE pipe sections (1 m long, 12.7 mm in diameter) were used as drop tubes on which pressure regulators (100 kPa, 19.0 mm), nozzles (four different sizes were used on the system), LEPA adapters and double-ended Fangmeier LEPA drag-socks were connected. Water to the system was pumped from a deep well at the research station. The design nozzle sizes were determined from qi CA where qi is the ¯ow rate in liters per second (l/s); C the system capacity in liters per second per square meter (l/s m2); and A the service area per LEPA head in m2. In this study, the largest nozzle size was selected to simulate an irrigation capacity of 15 mm/day, which is equivalent to daily maximum evaporation from Class-A pan in the experimental station. The spray nozzles with proper diameters were selected from the Nelson Irrigation Cor. catalog for 100 kPa pressure rating. Irrigation application amounts were determined by the application rates and system travel speed controlled at the hosereel system. The trickle system consisted of a control unit and distribution lines. The control unit of the system contained a Venturi injector (25.4 mm), fertilizer tank (75 l), disk filter, control valves, and a water flow meter. Distribution lines consisted of PE pipe manifolds (supply and discharge) for each plot. Irrigation laterals of 16 mm in diameter and 30 m in length had inline emitters spaced 0.7 m apart, each delivering 4 l/h at a pressure of 100 kPa. Each discharge manifold had removable end caps for flushing. Trickle irrigation lines were spaced at 1.40 m apart, equally spaced between every other row of cotton. Water was supplied from a pressurized hydrant and filtered through disk filter. Commercial farm equipment was used for agronomic practices. Experimental field was planted with a 4-row planting machine at 70 cm row spacing at 5 cm depth. Stonville-453 cotton variety was planted on May 18, 1999. Plants were thinned to an approximate spacing of 15 cm apart when the plants were about 15 cm in height. Fertilizer applications were based on soil analysis recommendations. All treatment plots received the same amount of total fertilizer. A compound fertilizer of (20-20-0) was applied (80 kg N and 80 kg P2O5 as pure matter per hectare) at a rate of 400 kg ha at planting on May 18. At first irrigation, on July 1, 45 kg of ammonium nitrate per hectare was applied to all treatment plots. The rest of the N was applied to the experimental area
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of LEPA plots in the form of urea (CO(NH2)2) incorporated to soil by a lister. In trickle plots, remaining nutrient requirements (UAN 32-0-0) were applied by chemical injection using a Venturi injector (Netafim) with irrigation water. LEPA plots received the same total amount of N in granular form. In the study, two experiments were set-up in the same field. One half of the field was allocated for the LEPA and the other half was used for the trickle system. The experimental design was a complete randomized block design with three replications for LEPA system, and split-plot design with three replications for trickle irrigation system. Irrigation water was applied based on cumulative Class-A Pan evaporation within the irrigation intervals. In the study, two irrigation intervals of 3 and 6 days for trickle, and only 6 days in LEPA were used. ``LEPA-100'' treatment designated to receive 100% of cumulative Class-A pan evaporation on a 6 days basis was used to guide irrigation applications for LEPA, and treatments ``IF3-100'' and ``IF6-100'' designated to receive 100% of cumulative Class-A pan evaporation on a 3- and 6-day basis, respectively, were used to guide irrigation applications for the trickle method. Deficit irrigation treatments of LEPA-75, LEPA-50 and LEPA-25 received 75, 50 and 25% of full irrigation treatment (LEPA-100), respectively, for LEPA, and two deficit irrigation treatments received 67 and 33% of the full-irrigation treatments of IF3-100 and IF6-100 for trickle irrigation system. The soil water content measurements were made at 12-day intervals until harvest in the three replications for all treatments by gravimetric sampling in 0±30 cm, and using a neutron probe (Campbell Pacific Model 503DR Hydroprobe) at 30 cm depth increments over 120 cm deep with 15 s counts. The probe was field calibrated for the experimental soil. Each plot dimension was 120 m long and 2.80 m wide (four plant rows) for LEPA method, and 30 m long and 5.6 m wide (eight plant rows) for trickle method. Plant and soil water measurements and observations were started 21 days after planting, and were terminated 121±145 days after planting depending on the harvest date. In order to determine the leaf area index (LAI) and total dry matter above the ground level, all plants within 0.5 m of a row section in each plot were cut at the ground level at 12-day intervals till harvest. The cotton leaves were separated from the stem and leaf area of plants was measured by using an optical leaf area meter. Plant samples were dried at 65 8C until constant weight was achieved. Yield was determined by hand harvesting the 12 m sections of the two adjacent center rows in each plot 121, 133, and 145 days after planting depending on the physiological maturity of plants in different treatment plots. The harvest area in each plot was 16.8 m2 (two rows, each 12 m long). Five uniform rate applications varying from 20 to 80 mm were made during the plant establishment period. The first and second applications were made on June 6 and June 26 in the spray mode with LEPA system. The third and fourth applications were made on July 2 and July 6 with a sprinkler system. The final uniform application was made on July 8 with drip and LEPA in spray mode on their respective plots. Treatment irrigations were started on July 15. Water use evapotranspiration (ET) was estimated based on a one-dimensional water balance method using soil water measured by the neutron method. Furrow dikes were constructed manually at approximately 10 m intervals in LEPA-100 and LEPA-75 treatment plots, thus no runoff was allowed in LEPA plots. It was assumed that deep
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percolation was negligible. Water use was the total of seasonal water depletion (planting to harvest) plus rainfall and irrigations during the same period. WUE was computed as the ratio of cotton yield to water use. Irrigation water use efficiency (IWUE) was determined as the ratio of cotton yield for a particular treatment which is less than the non-irrigated yield, which is zero under the study area, to the applied irrigation water for that treatment (Howell et al., 1994). 3. Results and discussion The 1999 cotton growing season climatic conditions were typical of the conditions that prevail in the GAP area. Table 1 summarizes the monthly climate data compared with the long-term mean climatic data for the Harran Plain, where the experiments were carried out. No rainfall was received during the growing season. The total amount of water applied to LEPA and trickle irrigation plots is given in Table 2. As shown in this table, the amount of irrigation water applied varied from 333 to 814 mm in LEPA plots. Trickle-irrigated plots received irrigation water varying from a low of 384 mm in heavy stress plots (IF3- and IF6-33%) to a high of 814 mm in nonstress plots (IF3- and IF6-100%). Seasonal maximum water use and irrigation water requirements of cotton under Harran Plain conditions has been reported to be 1670 and 1555 mm under surface irrigation conditions (Kanber et al., 1992). The amount of irrigation water applied to cotton by conventional sprinkler, mobile drip, LEPA, furrow and drip methods were 726, 1059, 1076, 1003 and 987 mm, respectively, in the Harran Plain (Cetin et al., 1994). As the amount of water applied with LEPA and trickle irrigation systems in this study is Table 1 Historical monthly and growing season climatic data of the experimental area Climatic parameters
April
May
June
July
August
September
Long-term (means 1929±1999) Minimum air temperature (8C) Maximum air temperature (8C) Average temperature (8C) Rainfall (mm) Relative humidity (%) Wind speed (m/s) Evaporation, CAP (mm)
3.4 34.8 15.2 25.4 54 1.6 118.6
1.0 43.0 21.4 25.6 42 1.9 195.6
9.4 45.4 28.0 4.8 35 2.5 320.5
11.0 46.8 31.4 0.1 33 2.6 403.9
9.2 46.6 30.4 ± 36 2.1 376.5
3.4 44.0 25.6 0.1 34 1.5 280.4
Growing season (1999) Minimum air temperature (8C) Maximum air temperature (8C) Average temperature (8C) Rainfall (mm) Relative humidity (%) Wind speed (m/s) Evaporation, CAP (mm) Solar radiation (cal/cm2)
5.8 24.0 16.0 17.8 61.1 1.2 137.6 519.1
13.7 32.0 23.9 1.0 37.4 1.5 279.5 635.1
18.3 35.8 28.0 1.5 37.1 1.5 334.6 659.2
21.5 39.2 30.9 ± 42.4 1.4 370.8 671.4
19.2 38.4 28.9 ± 50.8 1.0 304.4 592.8
14.4 33.8 24.1 ± 49.1 0.9 193.3 514.6
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Table 2 Water use and WUE data for LEPA and trickle-irrigated cotton Treatment
Dry matter yield (kg/ha)
Seed cotton yield (kg/ha)
Soil water Seasonal Water WUE IWUE depletion (mm) irrigation (mm) use (mm) (kg/m3) (kg/m3)
LEPA-100 LEPA-75 LEPA-50 LEPA-25 LSD0.01
10034 9610 8160 6140
4750 4020 3270 2590 2017
a ab ab b
39.7 40.7 48.5 50.6
814 654 493 333
854 695 542 383
0.556 0.579 0.603 0.675
0.583 0.615 0.663 0.778
12680 9650 6570 15009 12150 6490
5040 4520 2660 5870 4900 2310 1627
a a b a a b
54.1 58.7 72.2 39.6 58.7 78.1
814 604 384 814 602 384
868 663 456 854 661 462
0.580 0.695 0.583 0.687 0.741 0.500
0.619 0.748 0.692 0.721 0.813 0.601
Trickle IF3-100 IF3-67 IF3-33 IF6-100 IF6-67 IF6-33 LSD0.05
considered, water saving is possible in comparison to the results from furrow irrigation studies carried out at the same location. Cotton harvest data, irrigation amounts, water use and WUE data are summarized in Table 2. The irrigation levels both in LEPA and trickle-irrigated plots significantly increased seed cotton yield (P < 0:0036 and P < 0:0001). Highest yield, averaging 5870 kg/ha, was measured in trickle-irrigated plots with 6-day interval in IF6-100% treatment, followed by IF3-100% trickle plots with 5040 kg/ha. The effect of irrigation intervals used in trickle irrigation study on cotton yield was not significantly different P < 0:1273. There was no significant difference in yield between the 100 and 67% trickle plots. The highest yield in LEPA plots was obtained in 100% plots with an average value of 4750 kg/ha. As the amount of irrigation water decreased, seed cotton yields also decreased. Dry matter yields were also significantly different among the treatments. Highest dry matter yield, averaging 1.509 kg/m2, was measured in IF6-100 treatment plot followed by IF3-100 treatment with 1.215 kg/m2. LEPA-irrigated plots resulted in slightly lower dry matter yields than the corresponding trickle irrigation plots. In addition, both dry matter and LAI remained consistently greater in 100% treatments both in LEPA and trickle-irrigated plots. Cotton yields in LEPA-irrigated plots in this study were comparable with the cotton yields from previous experiments in the Harran Plain. However, the yields from trickle-irrigated plots were significantly higher than those from the previous experiments utilizing surface and sprinkler irrigation methods (Cetin et al., 1994; Kanber et al., 1996). In the San Joaquin valley of California, Phene et al. (1984) reported ET of 633 50 mm for maximum yield of cotton with trickle irrigation compared to 645 mm for furrow irrigation. Howell et al. (1984) reported ET of 650± 700 mm for maximum lint yield of 2000 kg/ha at the same location using narrow-row cotton (0.5 m). Seasonal water used by cotton varied from 383 mm in LEPA-25 to 854 mm in LEPA100 treatment plots. In trickle-irrigated plots, water use changed from 456 mm in IF3-33
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to 868 mm in IF3-100 treatments. Water use in IF6 treatment was almost the same as those in IF3 treatment. Thus, two different irrigation intervals in trickle plots resulted in similar water use. Accumulative pan evaporation from planting to harvest was 1200 mm. A significant linear relationship between cumulative pan evaporation (Epan) and ET for the period covering onset of square (June 25) to harvest (September 17) was found as ET 0:998 Epan 22:878 r 2 0:988 for LEPA-100 treatment, and ET 0:979 Epan 30:084 r 2 0:973 for the IF3-100 treatment. Highest WUE, averaging 0.741 kg/m3, was obtained in trickle-irrigated treatment of IF6-67. In general, WUE values decreased with increasing water use. However, the WUE values in the different treatments were higher as compared to WUE values of cotton irrigated by furrow or sprinkler system in the same experimental station (Kanber et al., 1996). Irrigation water use efficiencies (IWUE) were slightly higher than the WUE values. Since there was no rainfall during the growing season, the slight differences between the two values can be attributed to water used from soil storage. Hodgson et al. (1990) reported WUE values for trickle-irrigated cotton (lint) as 0.223 kg/m3; Wanjura et al. (1996) determined WUE of cotton (lint) for high frequency drip irrigation in Texas between 0.236 and 0.333 kg/m3. Significant linear and curvilinear relationships were found between the cotton yield and ET in LEPA and trickle irrigation treatments as shown in Fig. 1. Cotton yield increased with increasing ET in the LEPA-irrigated treatments. In trickle-irrigated plots, both irrigation intervals resulted in similar curvilinear relationships between yield and ET. The slopes of the relationships between relative yield reduction and relative ET deficit are termed as yield response factor by Doorenbos and Kassam (1979) and was found to be 0.89 and 1.31 for the LEPA and trickle (IF3)-irrigated treatments, respectively (Figs. 2 and 3). Yield response factor for sprinkler irrigated cotton was found to vary between 0.8 and 1.1 in previous studies carried out in the same location by Kanber et al. (1996). Doorenbos and Kassam (1979) gave the yield response factor for cotton as 0.84. Significant linear and curvilinear relationships between dry matter yield and water use were found for LEPA and trickle-irrigatedigated cotton as shown in Fig. 4. Dry matter
Fig. 1. The relationship between cotton yield and water use for LEPA and trickle-irrigated treatments.
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Fig. 2. Relative yield reduction vs. relative ET deficit relationships for LEPA-irrigated treatments.
yields increased with increasing ET as with cotton yield. Trickle irrigation system resulted in higher dry matter yield as compared with LEPA-irrigated cotton. As with the cotton yield, dry matter yields decreased with decreasing ET. Profile soil water storage variation during the growing season for the LEPA and trickleirrigated plots are shown in Figs. 5±7, respectively. Soil water storage within the 120 cm depth decreased gradually towards the end of the season in all treatment plots. Soil water remained higher in the full irrigation treatment plots (IF3-100, IF6-100 and LEPA-100) than the other treatments considered. However, soil water contents in trickle-irrigated plots were generally higher than those in the LEPA plots. As the amount of applied irrigation water decreased, soil water storage also decreased. Heavy stress treatments in both systems resulted in soil water contents below wilting point during most of the
Fig. 3. Relative yield reduction vs. relative ET deficit relationships for trickle-irrigated treatments.
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Fig. 4. Relationship between dry matter yield and water use for LEPA and trickle-irrigated treatments.
growing season. Grimes and El-Zik (1982) reported that not more than 60±65% of the available water of clay loam soils should be allowed to be depleted in the root zone for maintaining optimum productivity. As shown in Figs. 5±7, soil water depletion levels in the full irrigation treatments remained within 50±65% of available water in the 1.20 m depth. The total length of the growing season varied from 134 days for 1±100 treatments to 122 days in fully stressed treatments in both LEPA and trickle irrigation systems. Occurrence of blooming, ball formation and ball opening stages of cotton were observed at an earlier date in the stressed treatments as compared to the full irrigation treatments. Water deficits from onset of flowering to peak flowering may cause a more negative effect on yield as compared to that which occurred after peak flowering. With severe water deficits during late flowering and early boll formation, boll shedding can be excessive. Moderate water deficits occurring during flowering, but high enough to restrict vegetative growth, will lead to good boll-set and higher yields, despite a reduction in number of flowers (Doorenbos and Kassam, 1979). Radin et al. (1992)
Fig. 5. Soil water storage variation during the growing season in LEPA-irrigated plots.
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Fig. 6. Soil water storage variation during the growing season in trickle-irrigated plots with 3-day irrigation interval.
reported that yield increases were associated with a lengthened period of profuse flowering and a delay in the onset of cutout. Both drip irrigation and mid-cycle supplements increased mid-day leaf water potential and apparent hydraulic conductance of the plants for extended period during flowering. Indicating enhanced water uptake and transport capacity compared to plants irrigated at long cycles. In addition to dry matter data, periodic LAI values were determined for trickleirrigated and LEPA cotton (Figs. 8 and 9, respectively). Highest LAI value, averaging 4.7, was measured in trickle-irrigated treatment of IF3- and IF6-100. LAI values increased with increasing water use in both irrigation methods. The highest LAI value in LEPA
Fig. 7. Soil water storage variation during the growing season in trickle-irrigated plots with 6-day irrigation interval.
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Fig. 8. LAI development in trickle-irrigated treatments.
treatments was measured in LEPA-100 plots as 3.4, followed by other irrigation levels. Cotton plants reached their maximum LAI on August 10 for full irrigation treatments in both the LEPA and trickle systems. Maximum leaf area for the stressed treatments occurred approximately 2 weeks earlier as compared to the full irrigation treatments. Vegetative growth declined severely as water deficit increased. Orgaz et al. (1992) determined the maximum LAI value as 4.1. Bielorai et al. (1983) and Turner et al. (1986) emphasized the sensitivity of expansive growth to water deficits in cotton. A significant linear relationship between LAI and ET for LEPA and trickle-irrigated cotton were obtained. The resulting equations are as follows: ET 136:87 LAI 231:8 R2 0:986 for trickle; and ET 277:66 LAI 43:77 R2 0:965 for LEPA-irrigated cotton. Water use increased with increasing LAI in both irrigation systems.
Fig. 9. LAI development in LEPA-irrigated treatments.
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4. Conclusions Cotton yields obtained from the trickle and LEPA irrigation systems in Harran Plain in GAP region of Turkey were found to be higher as compared to other irrigation methods such as sprinkler and furrow, in the previous experiments, in the same location. Deficit LEPA and trickle irrigation generally reduced cotton yield. Irrigating at less than 100% of pan evaporation may not produce enough leaching for a salt balance in the root zone since the average annual rainfall in the project area is only 388 mm. Thus, deficit irrigation of cotton with trickle and LEPA systems is not recommended for the region. Both trickle and LEPA systems permitted precise control of the irrigation applications. They provided uniform irrigation because LEPA heads equipped with pressure regulators and the constant system travel speed was maintained during an irrigation, and the trickle system had a high emission uniformity (93%) as measured on several trickle laterals. Applications with the double-ended Fangmeier LEPA socks performed well under arid climatic conditions. Water distribution uniformity along the direction of travel of the linear move hose-reel machine was observed to be very high compared to sprinkler and conventional furrow irrigation methods used in the region. LEPA should be managed to apply as much water as can be efficiently stored in the furrow-dike basins, and then the irrigation frequency is simply determined by the gross irrigation capacity of the system (Howell et al., 1995). With proper management, LEPA and trickle irrigation can avoid some application losses which are inevitable with sprinkler and surface methods. Although the cotton yields from the LEPA-100 and trickle IF3-100 and IF6-100 were not statistically significant, trickle irrigation with 6-day interval resulted in the highest yield among the treatments studied. However, the duration of water application in IF6100 treatment is considerably higher than that in IF3-100 or LEPA-100 treatment. A lateral spacing of 1.4 m is found to be sufficient for trickle irrigation of cotton. Research results revealed that both trickle and LEPA irrigation systems can be used successfully for irrigation of cotton under the climatic conditions of GAP area in Turkey. Acknowledgements We wish to acknowledge the financial support provided to this project by the TUBITAK (Turkish Scientific and Research Council) as TARP #1856. In addition, we would like to thank Dr. T.A. Howell at USDA-ARS, Bushland, TX for providing doubleended LEPA drag socks for this study. References Bielorai, H., Mantell, A., Moreshet, S., 1983. Water relations of cotton. In: Kozkowski, T.T. (Ed.), Water Deficits and Plant Growth. Academic Press, New York. Bordovsky, J.P., Lyle, W.M., Lascano, R.J., Upchurch, D.R., 1992. Cotton irrigation management with LEPA systems. Trans. ASAE 35 (3), 879±884.
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Bucks, D.A., 1993. Micro-irrigation worldwide usage report. In: Proceedings of the Workshop on Microirrigation Worldwide, The Hague, The Netherlands, September 2. ICID, New Delhi, India, pp. 11± 30. Camp, C.R., Hunt, P.G., Bauer, P.J. 1995. Subsurface microirrigation management and lateral spacing for cotton in the Southeastern USA. In: F.R. Lamm (Ed.), Microirrigation for a Changing World. Proc. of the fifth international microirrigation Congress. April 2±6, Orlando, Florida ASAE publication, pp. 368± 375. Cetin, O., Ozyurt, E., Sener, S., 1994. The effects of different irrigation methods on the yield and water use efficiency of cotton in Harran Plain. Proceedings of the 17th European Regional Conference on Efficient and Ecologically Sound Use of Irrigation Water with Special Reference to European Countries, Varna, Bulgaria, May 16±22. ICID. Doorenbos, J., Kassam, A.H., 1979. Yield response to water. FAO Irrigation and Drainage Paper No. 33. FAO, Italy, Rome. Fipps, G., New L.L., 1990. Six years of LEPA in TexasÐless water, high yields. In: Vision of the Future. Proceedings of the Third National Irrigation Symposium, St. Joseph, MI. ASAE, pp. 115± 120. Grimes, D.W., El-Zik, K.M., 1982. Water management for cotton. Division of Agricultural. Science Bulletin No. 1904. University of California, Davis, CA. Guinn, G., Mauney, J.R., 1984. Fruiting of cotton. I. Effects of moisture status on flowering. Agron. J. 76, 90± 94. Henggeler, J.C., 1995. A history of drip irrigated cotton in Texas. In: Lamm, F.R. (Ed.), Microirrigation for a Changing World. Proceedings of Fifth International Microirrigation Congress, Orlando, FL, April 2±6. ASAE, pp. 669±675. Howell, T.A., Hatfield, J.L., Yamada, H., Davis, K.R., 1984. Evaluation of cotton canopy temperature to detect crop water stress. Trans. ASAE 27, 84±88. Howell, T.A., Schneider, A.D., Dusek, D.A., 1991. Corn and sorghum response to LEPA irrigation. ASAE Paper No. 91-2520, St. Joseph, MI. ASAE. Howell T.A., Yazar, A., Schneider, A.D., Duser, D.A. Copeland, K.S., 1994. LEPA irrigation management for corn. ASAE paper No. 94±2098, pp. 23. Howell, T.A., Yazar, A., Schneider, A.D., Dusek, D.A., Copeland, K.S., 1995. Yield and water use efficiency of corn in response to LEPA irrigation. Trans. ASAE 38, 1737±1747. Kanber, R., Onder, S., Unlu, M., Koksal, H., Ozekici, B., Sezen, S.M., Yazar, A., Koc, K., 1996. Optimization of surface irrigation methods for cotton and comparison with sprinkler irrigation. Research Report No. 18, GAP Research Projects. Faculty of Agriculture Publication No. 155, Cukurova University, Adana, Turkey, 1995. Killi, F., Gencer, O., 1999. Cotton Production and Consumption Projections in 2000s in Turkey. Proceedings of the First Symposium on Cotton Agriculture, Fiber Technology and Textile in the Turk World, September 28± October 1, 1999, Kahramanmaras, Turkey, pp. 382±390. Lyle, W.M., Bordovsky, J.P., 1981. Low energy precision application (LEPA) irrigation system. Trans. ASAE 24, 1241±1245. Lyle, W.M., Bordovsky, J.P., 1983. LEPA irrigation system evaluation. Trans. ASAE 26, 776±781. Orgaz, F., Mateos, L., Fereres, E., 1992. Agroclimatology and modeling: season length and cultivar determine the optimum evapotranspiration deficit in cotton. Agron. J. 84, 700±706. Phene, C.J., Davis, K.R., Howell, T.A., McCormick, R.L., Nightengale, H.I., Meek, D.W., 1984. Evapotranspiration and water use efficiency of trickle-irrigated cotton. ASAE Paper No. 84-2625. Presented at 1984 Winter Meeting of the ASAE, New Orleans, FL. Radin, J.W., Reaves, L.L., Mauney, J.R., French, O.F., 1992. Yield enhancement in cotton by frequent irrigations during fruiting. Agron. J. 84, 551±557. Schneider, A.D., Howell, T.A., 1995. Grain sorghum response to sprinkler application methods and system capacity. Trans. ASAE 38 (6), 1693±1697. Shanmughan, K., Meenakshisundaram, D.C., Seshadri, V., 1977. Drip irrigation on the efficient technique. Soils Fert. 40 (6). Spurgeon, W., Makens, T., 1992. LEPA irrigation report. Southwest Kansas Research-Extension Center Report Progress 657. Agriculture Experimetal Station. 1992 Field Day Report.
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Turner, N.C., Hearn, A.B., Begg, J.E., Constable, G.A., 1986. Cotton (Gossypium Hirsutum L.): physiological and morphological responses to water deficits and their relationship to yield. Field Crops Res. 14, 153±170. Wanjura, D.F., Mahan, J.R., Upchurch, D.R., 1996. Irrigation starting time effects on cotton under high frequency irrigation. Agron. J. 88, 561±566. Yazar, A., Kanber, R, Sezen, S.M., Ozekici, B., 1999a. Adoption of LEPA and trickle irrigation systems for cotton and corn irrigation in the GAP region. TUBITAK-TARP No. 1856. Annual Research Report 1 and 2. Faculty of Agriculture, Department of Irrigation, Cukurova University, Adana, Turkey. Yazar, A., Howell, T.A., Dusek, D.A., Copeland, K.S., 1999b. Evaluation of crop water stress index for LEPA irrigated corn. Irrig. Sci. 18, 171±180.