Tomato irrigation scheduling improved by using percent canopy cover and crop developmental stage

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1 CSIRO PUBLISHING Australian Journal of Agricultural Research, 28, 59, Tomato irrigation scheduling improved by using percent canopy cover and crop developmental stage Oner Cetin A,C, Demet Uygan B, and Hasan Boyaci B A Dicle University, Agricultural Faculty, Department of Irrigation Engineering, 2128 Diyarbakir, Turkey. B Soil and Water Resources Research Institute, Department of Water Management, Eskisehir, Turkey. C Corresponding author. oner_cetin@yahoo.com Abstract. The aim of this study was to evaluate whether it is possible to conserve water and improve yield using canopy cover in order to adjust the amount of water needed for drip-irrigated tomatoes. The experiments were carried out using field-grown tomatoes (Lycopercion esculentum cv. Dual Large, F1) in Central Anatolia, Turkey from 23 to 25. The experimental design used split-plots in randomised blocks with 3 replications. The main plots in this study were: I 1, constant Class A pan evaporation (Ep) (i.e. K = 1.) throughout the irrigation season; I 2, varying Ep proportion according to crop development stage (i.e. planting time to flowering stage.5; flowering stage to first harvesting 1.; and first harvest to last harvest.75. In subplots, wetted area percentages or canopy cover were used. In K 1, the wetted area percentage measured 9% of the experimental site. In K 2, the wetted area percentage varied depending on the canopy cover. In K 3, the percentage of wetted area was set to a value of 65% throughout the irrigation season. The maximum yield of t/ha was obtained with the I 2 K 2 treatment, with a seasonal irrigation requirement of 515 mm. A tomato yield of t/ha was obtained under conditions of 552 mm seasonal irrigation water applied using the I 1 K 2 treatment. Although 37 mm less water was used in the I 2 K 2 treatment, the yield obtained from that treatment was higher by 12. t/ha than the I 1 K 2 treatment. In addition, the yield with all other treatments was lower than the I 2 K 2 treatment. Similarly, the maximum irrigation water-use efficiency (IWUE) of 26.2 kg/m 3 was obtained with the I 2 K 2 treatment. Thus, use of different coefficients of Ep varying with crop growth stages and percentage of canopy cover to estimate irrigation water requirement (i.e. irrigation scheduling) maximised the yield of tomatoes and improved the IWUE. Additional keywords: tomato, drip irrigation, irrigation scheduling, wetted area, canopy cover, water use efficiency. Introduction One of the major benefits of drip irrigation is that it allows the grower to use less water and fertiliser than conventional irrigation methods such as surface and sprinkler irrigation (Shock et al. 27). Tomatoes are grown on 41% of the land used for vegetable production in Turkey and on 25% of the total vegetable acreage in the study area in Eskisehir Province, where the average yield of tomatoes is 57 t/ha (Uysal 26). The furrow irrigation technique has been used to grow tomatoes there until about 5 years ago. Use of drip irrigation by farmers growing tomatoes has increased enormously in recent years in study region, and agronomists predict the use of drip irrigation will increase further. The development of more precise irrigation scheduling approaches will encourage the adoption of scientific irrigation scheduling (Fereres et al. 23). With high-value crops such as tomatoes, net productivity is twice that achieved with furrow irrigation (Luquet et al. 25). Thimme and Gowda (199) showed that drip irrigation gives higher yields of tomatoes than other irrigation methods because the soil moisture level in the root-zone can be maintained near field capacity throughout growing period. Efficient water application is critical to successful production of vegetables. The grower needs to know when to start irrigation and how much water to apply in order to satisfy crop water needs, conserve water, and avoid nutrient leaching. Several approaches have been used for scheduling drip irrigation for tomatoes; one of these is to consider pan evaporation (Ep; Shock et al. 27). El-Shafei (1989) studied the response of tomatoes grown in sandy soil to various water application levels and found that irrigation at a rate of 8% Ep was required to avoid yield loss. Locassio and Smajstrla (1996) applied water at,.25,.5,.75, or 1. Ep for drip-irrigated tomatoes; total marketable yields were highest at 1.Ep (87. t/ha) and.75ep, (79.3 t/ha), compared with 3.7 t/ha for control. Total water use was higher with the.75ep schedule. Tuzel et al. (1999) recommended.6ep in loamy soils for an optimum irrigation program for processing tomatoes applying 386 mm to obtain 82.8 t/ha. Cetin et al. (22) investigated irrigation scheduling for drip-irrigated tomatoes using Ep in Central Anatolia, by applying irrigation water at.5,.75, 1., and 1.25 Ep with different irrigation intervals (2, 4, and 6 days). Significant differences in fruit yields were obtained in each of the treatments. Marketable fruit yield ranged from to t/ha, with a maximum at 1.Ep and a 4-day interval. The amount of irrigation water applied and irrigation water-use efficiency (IWUE) were 62 mm and 23.8 kg/m 3, respectively. Ó CSIRO /AR /8/121113

2 1114 Australian Journal of Agricultural Research O. Cetin et al. Oweis et al. (1988) determined a quadratic relationship between total yield and transpiration for drip-irrigated tomatoes. A maximum yield of about 158 t/ha could be produced with 6 mm of net irrigation. Weekly crop-pan coefficients (Kpc) were derived using transpiration data observed and Ep data from the site. Kpc increased from.15 after planting to a maximum of.7 and dropped to.5 after the harvest was completed. Crop-pan coefficients can be used as a simple and accurate method for scheduling irrigation. Cevik et al. (1997) irrigated tomatoes using a drip system. The highest tomato yield, t/ha, was obtained by applying irrigation water at.3,.9, 1.2, and 1.2 Ep during planting flowering, flowering fruit formation, fruit maturity first harvest, and first harvest last harvest stages, respectively. Cevik et al. (1997) showed that application of different rates of pan evaporation considering crop development stages was appropriate in producing maximum yield. Reference evapotranspiration multiplied by a crop coefficient based on estimated percentage canopy coverage might be the most appropriate approach for maximising water-use efficiency and crop productivity and for scheduling the drip-irrigation of tomatoes (Hartz 1993). This approach has been widely used by growers of many crops in the western United States (Wright 1982). One of the most important advantages of drip irrigation is that a grower does not need to irrigate the whole surface of the soil. Drip irrigation systems normally wet only a portion of the soil area and soil volume. No single correct or proper minimum value for percentage of wetted area (P w ) has been established. A reasonable objective when plotting a design for widely spaced crops is to consider that as much as two-thirds of the potential horizontal cross-sectional area of the root system is 33% < P w < 67%. However, when growing crops with rows and drip lines spaced <1.8 m apart, P w can approach 1%. Keller and Bliesner (199) presented and demonstrated equations for computing the wetted area as a percentage of the total crop area for a range of crop geometry and lateral layouts based on the dimensions of the spacing between emitters and lines. The amount of irrigation water to apply to the root-zone by drip irrigation is dependent on the criteria chosen, for example the percentage of wetted area or canopy cover. Irrigation system design and operation has always been a high research priority, and taking advantage of micro irrigation application demands precise design and management (Shock 23). The percentage of wetted area can be used as a multiplier to reduce the total water applied under drip irrigation. The use of an appropriate percentage of wetted area or another scheduling approach could have considerable impact in terms of both the system design and efficient irrigation management to improve water use efficiency for drip irrigation. The aim of this study was to evaluate whether irrigation efficiency was improved by using the canopy cover to calculate the drip irrigation scheduling of tomatoes. Thus, data on crops watered using canopy cover were compared with crops watered employing other strategies that ignored canopy cover. Material and methods Experimental site Field experiments were conducted at the research station (39846 N, 3831 E) of the Soil and Water Resources Research Institute in the Eskisehir Province of Turkey, This area receives an average annual rainfall of 339 mm with summer the driest season. The average annual and daily maximum Ep values are 976 and 8.4 mm, respectively. The research station plots have clay-loam soil containing 35% sand, 27% silt, and 38% clay in the upper.9 m profile. Soil bulk density ranged from 1.15 to 1.4 g/cm 3. The infiltration rate was 9 mm/h. Other physical and chemical properties of the soil at the experimental site are given in Table 1. Irrigation system and design The lateral lines had on-line pressure-compensating emitters with discharge rates of 3.2 L/h at the operating pressure of 1 bar (1 kpa). The emitter spacing was calculated using the equation (Yildirim 23): p De ¼ ffiffiffiffiffiffiffi q=i where De is emitter spacing (m), q is emitter discharge (L/s), and I is infiltration rate (mm/h). Thus, the emitter spacing chosen was.5 m due to the calculation and soil characteristics (Papazafiriou 198). The plant row spacing and plant spacing were 1. m and.5 m, respectively. The lateral lines were laid out along each tomato row at 1. m spacing (Fig. 1). The drip system consisted of polyethylene (PE) laterals with a diameter of 16 mm. Each plot had a PE manifold pipeline with a diameter of 32 mm. The irrigation water, which was pumped from a deep well, was conveyed by means of PE pipes with a diameter of 5 mm into the manifolds along the borders of the plots. The control unit of the drip system had a vortex sand separator, sand media filters, a fertiliser tank, screen-mesh filters (12 mesh), and pressure gauges. The water meters were used to measure the amount of irrigation water applied to each plot. Table 1. Some soil properties of the experimental site EC, Electrical conductivity; OM, organic matter; FC, field capacity; WP, wilting point; BD, bulk density. Texture class: C, clay; CL, clay loam Soil depth ph EC OM Texture (%) Texture FC WP BD (m) (ds/m) (%) Sand Silt Clay class (m 3 /m 3 ) (m/m 3 ) (g/cm 3 ) CL CL C

3 Tomato irrigation scheduling Australian Journal of Agricultural Research 1115 (a) Block space: 4 m (b) Lateral pipe l1 K1 l2 K1 l1 K1 Subplot space: 2m 1 m 1 m l2 K1 l1 K1 K1 l2 Main plots Plants Subplots and/or blocks (replications) 8 m Fig. 1. (a) Experimental design and (b) schematic layout of lateral pipes and plants in the experimental plots. Irrigation treatments Irrigation treatments were tested in the experimental design of split-plots in randomised blocks with 3 replications (Fig. 1). The main factor treatments consisted of irrigation to apply water equivalent to either constant (i.e. 1. Ep, designated I 1 )or time-varying fractions (I 2 ) of Ep every 4 days over the growing season. The time-varying fractions of Ep depended on the crop development stage (Table 2). The second factor tested (i.e. treatments in the split-plots) was different percentages of wetted area (9%, K 1 ; 65%, K 3 ) and/or canopy cover (K 2 ) (Table 2). A drip-irrigation system wets only a fraction of the soil surface. On the other hand, the fraction of the soil surface that is covered by vegetation is very important for the water consumption of crops (Allenet al. 1998). Thus, constant or different proportions of Ep and wetted area and/or canopy coverage were used to calculate the amount of irrigation water to apply to the 6 treatments, designated I 1 K 1,I 1 K 2,I 1 K 3,I 2 K 1,I 2 K 2, and I 2 K 3. For the K 1 treatment, the percentage wetted area was determined using methods developed by Keller and Bliesner (199). Thus, the width of the horizontal area wetted in the top.15.3 m of the crop root-zone was divided by the total planted area. Consequently, the actual wetted area was computed as 9% Table 2. Main plots (proportion of Ep) Treatments applied for the experiment Ep, Class A pan evaporation Subplots (percentage of wetted area and/or canopy cover) following the lateral design (lateral spacing was 1. m) adopted for the K 1 treatment. The percentage of canopy cover was determined by measuring the average plant width in a row (i.e. shaded width) and dividing that value by the bed width, i.e. row space (Hartz 1993). Thus, the canopy coverage was measured before each irrigation cycle (i.e. every 4 days) on the plants in each plot. The following equation was used to calculate the irrigation water requirement for the treatments: I ¼ Ep K P where I is the irrigation water requirement applied (mm), Ep is cumulative pan evaporation (mm) measured in a Class A Pan during the irrigation interval (i.e. 4 days), K is proportion of Ep considering the treatments in the main plots, and P is a coefficient comprising plot plant coverage (Pc) or wetted area (Pw) depending on the treatments in the split-plots. Thus, either Pc or Pw was used depending on the specific treatment. The irrigation interval was 4 days (Cetin et al. 22). Pan evaporation data were recorded daily using standard USWB- Class A open pan in the Meteorological Station of the Soil and Water Resources Research Institute. The length and width of experimental plots were 8 m and 5 m, respectively. Thus, the area of each plot was 4 m 2 (Fig. 1). Dry weight of fruit Ten fruits were harvested from the each plot to measure the fruit dry weight at the middle of the harvesting stage. Dry weights of fruits (ventilated oven 658C at least 24 h) were determined. I 1 : Constant Ep (i.e. 1.) throughout irrigation season I 2 : Different proportion of Ep according to crop development stage (i.e. planting flowering.5, flowering first harvest 1., first harvest last harvest.75) K 1 : Percentage of wetted area measuredat experimental site used to define value of Pw (9% throughout irrigation season) K 2 : Percentage of canopy cover used to define the value of Pc; Pc set at 35% from planting until canopy cover exceeded 35%, after which it was set to the measured value until last harvest K 3 : Pw set to a value of 65% throughout irrigation season Agricultural applications Tomato (Lycopercion esculentum) cv. Dual Large, F1 was used for the experiment. This variety is a widely grown and freshly consumed bush variety in this region. Tomato seeds were sown in a greenhouse at the end of March. Young tomato plants were transferred into plastic tubes at the end of April. The plants were set in the plots in mid-may each year. A total of 18 kg N and 12 kg P 2 O 5 /ha as fertiliser was applied as recommended by Sefa and Oruc (199). One-third of the P and approximately onequarer of the N was applied to the soil before planting. The remaining fertiliser, which contained N, P, K, and some minor

4 1116 Australian Journal of Agricultural Research O. Cetin et al. elements, was applied by fertigation. The harvest began at the beginning of August and finished at the beginning of October. Statistical analysis and evaluation For the statistical analysis, randomised blocks in split-plots with 3 replications were used to evaluate the effects of treatments on yield. The data were analysed using ANOVA. Variance analyses were done for each experimental year. In addition, Duncan s multiple test, an acceptable tool for comparison of discrete data, was used to compare different treatments (Yurtsever 1984). Irrigation water use efficiency (IWUE, kg/m 3 ) was calculated using the following equation to evaluate the comparative benefits of the irrigation treatments (Howell 26): IWUE ¼ Y I where Y is yield (kg/ha) and I is the amount of irrigation water applied (m 3 /ha) for the treatments. Results and discussion Effect on yield of irrigation scheduling using wetted area or canopy cover Yields varied from 74.1 to t/ha in 23 (Table 3), with significant differences (P <.5) between treatments with constant or varying proportions of Ep based on the development stages of the crop (i.e. treatments in main plots) and between different percentages of wetted area and/or canopy cover (i.e. treatments in split-plots) (Table 4). Varying proportion of Ep based on the crop development stage and using percentage of canopy cover (treatment I 2 K 2 ) produced the highest yield, t/ha. The yield of t/ha in the second range (Duncan s multiple range test) was obtained from the I 1 K 2 treatment, with constant Ep (1.) throughout the irrigation season and using percentage of canopy. The I 2 K 1 treatment, with varying proportion of Ep and using actual measured wetted area (9%), yielded t/ha. The other 3 treatments yielded less. Although 674 mm of irrigation water was applied in the I 1 K 1 treatment throughout the irrigation season, the plot produced only 74.1 t/ha. By comparison, 56 mm of irrigation water was applied in the I 2 K 2 treatment, in which the highest yield was obtained. Furthermore, 584 mm of irrigation water was applied in the I 2 K 1 treatment, but the yield obtained ranked third. The I 1 K 1 treatment had the highest irrigation application because 9% of the measured percentage of wetted area was used throughout the irrigation season. Keller and Bliesner (199) reported that significant production was achieved when only a relatively small portion of the soil volume received water; maximum production would be achieved with considerably less than full wetting. The results of this experiment are consistent with those findings. The high variation in yield can be attributed to the criteria used to calculate the amount of irrigation water to apply. In 24, yield varied from to t/ha between treatments. The yield of t/ha was obtained from the I 2 K 2 treatment. The amount of irrigation water applied in the I 2 K 2 treatment was less than that used in the I 1 K 2 treatment. The other treatments using the percentage of the measured (9%) and assumed (65%) wetted area produced lower yields (Tables 3 and 5). Table 3. Marketable yields (interaction data) and amount of irrigation water applied according to treatments and experimental years Within columns, means followed by the same letter are not significantly different (at P =.5) according to a Duncan s multiple range test Treatments Amount of irrigation water applied (mm) Marketable yield (t/ha) Mean Mean I 1 K c 122.4a 88.8a 95.1 K b 143.4a 17.9a K c 111.8a 61.8a 83.5 I 2 K b 137.3a 99.5a K a 144.9a 117.3a K c 119.8a 8.5a 94.9 Table 4. Results of variance analysis for the experimental years n.s., Not significant; *P <.5; **P <.1 Variance sources d.f. F (calculated) F (table) Main factor (I) n.s. 2.8n.s. 7.n.s Error (A) 1 Subfactor (K) ** 11.2** 13.4** Interaction (I K) 2 6.7*.61n.s..2n.s Error (B) 8 Sum 17 Coeff. of variance (CV) 7.2% 7.9% 14.9%

5 Tomato irrigation scheduling Australian Journal of Agricultural Research 1117 Table 5. Separated yield according to main and subplots Within columns, means followed by the same letter are not significantly different (at P =.1) according to a Duncan s multiple range test. Data derived from Table 4 Main Yield (t/ha) Subplots Yield (t/ha) plots Mean Mean I a 125.8a 86.2a 1.4 K ab 129.9ab 94.2ab 15.8 I a 133.9a 99.1a K a 144.2a 112.6a K 3 8.6b 115.8b 71.2b 89.2 The greatest amount of irrigation water, 79 mm, was applied in the I 1 K 1 treatment, whereas the I 2 K 2 treatment, at 58 mm, received significantly less. Thus, the application in the I 2 K 2 treatment conserved 39% of water compared with the I 1 K 1 treatment. In 25, a yield of t/ha was obtained from the I 2 K 2 treatment. The effect of the treatments on yield was not statistically significant but was consistent with the results obtained in 23 and 24. Thus, the treatments in which percentage of canopy cover was used to determine the amount of irrigation water tended not only to provide higher yields but also to save water (Fig. 2). The amount of water applied in a single irrigation event in the I 1 K 1 treatment (with 1. Ep, 9% wetted area) might exceed the soil water-holding capacity of the wetted root-zone. The results showed that the amount of irrigation water to be held in the root-zone can be calculated based on the development of canopy cover. As Howell (22) reported, in periods of crop growth an adequate supply of water is critical for high yield and quality vegetable production. Cetin et al. (22) carried out an experiment to determine the irrigation scheduling for drip-irrigated tomatoes using Class A Pan evaporation in the same study area. Different proportions of Ep and different intervals of irrigation were tested. The measured percentage of wetted area (9%) according to the laterals and dripper design was used to calculate the amount of irrigation water to be applied to the root-zone. The most appropriate schedule was to apply 1. Ep and an irrigation interval of 4 days. The water requirement and the yield obtained from this irrigation schedule were 62 mm and t/ha, respectively, whereas, in the current study, the amount of irrigation water applied and yield were 515 mm and t/ha, respectively. Although yields were similar, there was a water saving of about 16% compared with the results of Cetin et al. (22). This was because irrigation water was applied depending on the percentage of canopy cover as well as varying proportion of Ep based on the development stages of the crop. The findings in this study improved the results obtained by Cetin et al. (22) in terms of an efficient irrigation schedule and water saving for drip-irrigated tomatoes. Previously, Oweis et al. (1988) and Cevik et al. (1997) showed the benefit of the use of different proportions of pan evaporation according to the crop development stages compared with using constant Ep for irrigation scheduling of tomatoes. Hartz (1993) showed that using percentage of canopy cover as the basis for calculation of the amount of irrigation water for drip-irrigated tomatoes resulted in less total water usage and greater crop productivity. Moreover, Cetin and Bilgel (22) have already shown that percentage of canopy cover could be used for irrigation scheduling for drip-irrigated cotton. Thus, several previous studies and our results show that percentage of canopy cover rather than constant percentage of wetted area in the calculation of irrigation water used throughout the irrigation season results in more efficient irrigation and appropriate irrigation scheduling. Irrigation water use efficiency (IWUE) Irrigation water use efficiencies varied from 11. to 28.5 kg/m 3 depending on treatment and year. In all experimental years, the highest IWUE was obtained from the I 2 K 2 treatment. Considering the average values for the 3-year study, the maximum IWUE value was 26.2 kg/m 3 water applied in the I 2 K 2 treatment, where high marketable yield was combined with lower water Marketable yield (t/ha) Yield IWUE I 1 K 1 (66) I 1 K 2 (552) I 1 K 3 (489) I 2 K 1 (563) I 2 K 2 (515) I 2 K 3 (421) Treatments and amount of irrigation water applied (mm) IWUE (kg/m 3 ) Fig. 2. Marketable tomatoesyields and irrigationwater use efficiency(iwue) foreach treatment and amount of irrigation water applied (average values for 3 years).

6 1118 Australian Journal of Agricultural Research O. Cetin et al. application. The overall IWUE was the lowest for the I 1 K 1 treatment (Fig. 2). Most of the water savings in the current experiment occurred early in the season when crop cover was not yet complete. This was because the lower coefficient of Ep and percentage of canopy cover, which was quite low at the beginning of growing season, were used to determine the amount of irrigation water applied. This provided both water saving and the higher IWUE. These findings showed that both improving IWUE and maximising yield were possible using efficient irrigation scheduling, which is consistent with the recommendation made by Wright (1982). Fruit dry weight (DW) Considering the average results for the 3 years, the percentage DW varied from 6.1 to 7.6% (Fig. 3). DW increased as amount of irrigation water was reduced. Consequently, the minimum DW of 6.1% occurred when irrigation was 66 mm, while the maximum DW of 7.6% occurred when irrigation was 421 mm. Like fruit yield, the highest yield of DW was obtained from the treatment I 2 K 2 (Fig. 3). Sanders et al. (1989) determined that yields of red fruit and all fruit increased with increasing drip irrigation rate; concentrations of soluble solids (SS) and total solids (TS) decreased with increasing irrigation rates, while fruit colour, size, and acidity increased, as did the yield of SS and TS per ha. Similarly, water deficits improved the quality of fruits, increasing SS and acidity for tomatoes (Colla et al. 1999), irrigation for maximum yield was found to reduce SS of processing tomatoes (Hanson et al. 1997). May (1997) determined that SS were not affected by depleting levels between irrigations but were significantly increased by increasing the cut-off interval before harvest. The findings of our study are consistent with all of the above results. Wetted area, canopy cover, and plant height The percentage of wetted area measured in the experimental site for the K 1 treatment was 9% because the lateral and crop row spacing was 1. m, and the clay fraction was dominant in the soil texture. Also, for closely spaced crops with rows and emitter laterals spaced >1.8 m apart, P w often approaches 1% (Keller and Bliesner 199). For the K 3 treatment, a constant value of 65% was assumed for the wetted area. Thus, two quite different percentages of wetted area were used as the fixed values throughout the irrigation season. The canopy factor used for the K 2 treatment was the percentage area covered by plant canopy (foliage). The canopy cover gradually developed by approximately 15 3% between planting time (mid May) and mid (25 3 days after transplanting). In the following days or crop development stages, canopy cover rapidly increased, and it reached the 8 7 SS TSS 9 8 DW (%) I 1 K 1 (66) I 1 K 2 (552) I 1 K 3 (489) I 2 K 1 (563) I 2 K 2 (515) I 2 K 3 (421) TDW (t/ha) Treatments and amount of irrigation water applied (mm) Fig. 3. Dry weight ratio of fruits and total dry weight per ha for each treatment and amount of irrigation water applied (average values for 3 years) Canopy cover (%) May Sept. 24 May I 1 K 1 I 1 K 2 I 1 K 3 I 2 K 1 I 2 K 2 I 2 K Sept. Oct Sept. Crop growth period Fig. 4. Crop canopy development throughout the growth season.

7 Tomato irrigation scheduling Australian Journal of Agricultural Research 1119 Plant height (cm) May Sept May I 1 K 1 I 1 K 2 I 1 K 3 I 2 K 1 I 2 K 2 I 2 K Sept. Oct. Plant growth period Sept. Sept. Fig. 5. Plant height development throughout the growth period. maximum (7 1% depending on the treatments) by the beginning of August. Afterwards, canopy cover was almost constant to the end of the season (Fig. 4). Crop cover developed quickly, reaching 6 7% about 15 days after planting. Plants were approximately.1.15 m high when first transplanted in the plots, developing rapidly until the end of, and reaching a maximum of about.67 m, depending on the treatment; this tomato was a bush variety (Fig. 5). The minimum plant height (.55 m) was attained in the treatment I 1 K 3, which received less irrigation water. Plant height developed in parallel with canopy cover. The majority of soil wetted by irrigation may be beneath the canopy and may therefore be shaded (Allen et al. 1998), and as the growing season progresses and canopy cover increases, evaporation from the wet soil surface gradually decreases (Al-Kaisi and Broner 27). Therefore, water savings would increase as the wetted area on the soil surface decreases (Evett et al. 27). For this reason, most of the water savings occurred in the I 2 K 2 treatment early in the growth season, when crop cover was not yet complete, because evaporation from the soil surface was at its highest in this period. Conclusion Both high yield (134.8 t/ha) and high IWUE (26.2 kg/m 3 ) were obtained from the treatment in which varying proportion of pan evaporation based on crop development stage (i.e. planting time flowering stage.5; flowering first harvest 1.; first harvest last harvest.75) and percentage of canopy cover were used to calculate the amount of irrigation water. An average 515 mm of irrigation water was applied for this treatment. As a result, improvement of irrigation efficiency can be achieved using the canopy cover for drip irrigation scheduling of tomatoes. This knowledge contributes to a wide range of techniques to reduce the water requirement, increase the water availability, and raise yields. Acknowledgments This study contains a part of the research project (KHGM-322E1) carried out by the authors from 23 to 25 in Soil and Water Resources Research Institute of Eskisehir, Turkey. References Al-Kaisi MM, Broner I (27) Crop water use and growth stages. No available on Allen RG, Pereira LS, Raes D, Smith M (1998) Crop evapotranspiration (guidelines for computing crop water requirements). FAO Irrigation and Drainage Paper No. 56. (FAO: Rome) Cetin O, Bilgel L (22) Effects of different irrigation methods on shedding and yield of cotton. Agricultural Water Management 54, doi: 1.116/S (1)138-X Cetin O, Yildirim O, Uygan D, Boyaci H (22) Irrigation scheduling of drip-irrigated tomatoes using Class A pan evaporation. Turkish Journal of Agriculture and Forestry 26, Cevik B, Abak K, Sari N, Kirda C, Topaloglu F (1997) Effects of different irrigation levels on yield and quality for drip-irrigated some vegetables. In The Proceedings of 6th National Agricultural Engineering Congress , Kirazliyayla, Bursa, Turkey. pp (in Turkish). Colla G, Casa R, Cascio B, Saccardo F, Temperini O, Leoni C (1999) Responses of processing tomato to water regime and fertilization in Central Italy. Acta Horticulturae 487, El-Shafei YZ (1989) Response of tomatoes to trickle irrigation on sandy soil in an arid zone in Libya. Arid Soil Research and Rehabilitation 3, Evett SR, Colaizzi PD, Howell TA (27) Drip and evaporation. ars.usda.gov, available on Fereres E, Goldhamer DA, Parsons LR (23) Irrigation water management of horticultural crops. HortScience 35, Hanson BR, May DM, Schwankl LJ (1997) Drip irrigation of processing tomatoes. In ASAE Annual International Meeting. Minneapolis, Minnesota, USA, 1 14 August, Hartz TK (1993) Drip-irrigation scheduling for fresh-market tomato production. HortScience 28, Howell J (22) Vegetables notes. Soil moisture and scheduling irrigation. Vol. 3, No. 4, University of Massachusetts Extension Vegetable Program. Howell TA (26) Challenges in increasing water use efficiency in irrigated agriculture. In The Proceedings of International Symposium on Water and Land Management for Sustainable Irrigated Agriculture. April 4 8, 26, Adana, Turkey. Keller J, Bliesner RD (199) Sprinkle and trickle irrigation. (Chapman and Hall: New York) Locassio SJ, Smajstrla AG (1996) Water application scheduling by pan evaporation for drip-irrigated tomato. Journal of the American Society for Horticultural Science 121, Luquet D, Vidal A, Smith M, Dauzat J (25) More crop per drop: how to make it acceptable for farmers. Agricultural Water Management 76, doi: 1.116/j.agwat

8 112 Australian Journal of Agricultural Research O. Cetin et al. May DM (1997) Water management differences between drip- and furrowirrigated processing tomatoes to maximize yield and fruit quality in California. In Proceedings of the 1st International Conference on the Processing Tomato, and the 1st International Symposium on Tropical Tomato Diseases. Recife, Pernambuco, Brazil, November 1996, and November Oweis TY, Shatanawi MR, Ghavi IO (1988) Optimal irrigation management for protected tomato in the Jordan Valley. Dirasat: Human and Social Sciences 15, Papazafiriou ZG (198) Compact procedures for trickle irrigation system design. Bulletin 29, Sanders DC, Howell TA, Hile MMS, Hodges L, Meek D, Phene CJ (1989) Yield and quality of processing tomatoes in response to irrigation rate and schedule. Journal of the American Society for Horticultural Science 114, Sefa S, Oruc S (199) Requirement of nitrogen and phosphorus for tomatoes under Bursa Conditions. Rural Affairs Research Institute, Publication No. 218, Report Series No. 168, Eskisehir (in Turkish). Shock CC (23) Micro irrigation technologies for protection of natural resources and optimum production. w128project.html, (available on ). Shock CC, Pereira AB, Hanson BR, Cahn MD (27) Vegetable irrigation. In Irrigation of agricultural crops. Agronomy Monograph 3, 2nd edn. (Eds R Lescano, R Sojka) pp (ASA, CSSA, and SSSA: Madison, WI) Thimme G, Gowda T (199) Brief review of drip irrigation in Karnataka. In Proceedings of the 11th International Congress on the use of Plastics in Agriculture. New Delhi, India, 26 February 2 March 199. pp Tuzel IH, Ul MA, Dorsan AF (1999) Effects of irrigation levels and intervals on yield and water use consumptive for drip-irrigated processing tomatoes. In The Proceedings of 3rd National Horticultural Crops Congress September 1999, Ankara, Turkey. pp (in Turkish). Uysal F (26) The crops grown in Eskisehir. The Records of Department of the Project and Statistical Branch of Agricultural Authority of Eskisehir, Turkey (in Turkish). Wright JL (1982) New evapo-transpiration crop coefficients. Journal of Irrigation & Drainage Division-ASCE 18, Yildirim O (23) Design of irrigation systems. Ankara University, Agricultural Faculty, Publication No /489, Ankara, Turkey (in Turkish). Yurtsever N (1984) Experimental statistical methods. Soil and Fertilizer Research Institute, Publication No. 121, Technical Publ. No. 56, Ankara (in Turkish). Manuscript received 2 April 28, accepted 16 September 28