RESEARCH ARTICLE
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The effects of deficit irrigation on nitrogen consumption, yield, and
quality in drip irrigated grafted and ungrafted watermelon
Selçuk Özmen
1, 2, Rıza Kanber
2, Nebahat Sarı
3, Mustafa Ünlü
21 University of Düzce, Department of Biosystem Engineering, Düzce 81620, Turkey
2 University of Çukurova, Department of Irrigation and Drainage Engineering, Adana 01330, Turkey 3 University of Çukurova, Department of Horticulture, Adana 01330, Turkey
Abstract
The aim of this study is to determine the effects of deficit irrigation on nitrogen consumption, yield, and quality in grafted and ungrafted watermelon. The study was conducted in Çukurova region, Eastern Mediterranean, Turkey, between 2006 and 2008, and employed 3 irrigation rates (full irrigation (I100) with no stress, moderate irrigation (DI70), and low irrigation
(DI50); DI70 and DI50 were considered deficit irrigation) on grafted (CTJ, Crimson Tide+Jumbo) and the ungrafted (CT,
Crim-son Tide) watermelon. The amount of irrigation water (IR) applied to the study plots were calculated based on cumulative pan evaporation that occurred during the irrigation intervals. Nitrogen consumption was 16% lower in CTJ plants than in CT plants. On the other hand, consumption of nitrogen was 28% higher in DI50 plants than in DI70 plants while it was 23%
higher in DI50 plants than in I100 plants. By grafting, the average amount of nitrogen content in seeds, pulps and peels for
CTJ was 30, 43 and 56% more than those of CT, respectively. The yield and the quality were not significantly affected by the deficit irrigation. In this respect, grafting of watermelon gave higher yield, but, it had a slight effect on fruit quality. The highest yield values of 16.90 and 19.32 kg plant–1 in 2008 were obtained with I
100 and in CTJ plants, respectively. However,
DI50 treatment could be taken into account for the development of reduced irrigation strategies in semiarid regions where
irrigation water supplies are limited. Additionally, the yield increased by applying CTJ treatment to the watermelon production.
Keywords: deficit drip irrigation, yield, evapotranspiration, grafted watermelon, nitrogen, fruit quality
after China, producing 3.9 million t of fruit from 146 018 ha each year (FAO 2012). In Çukurova region of Eastern Mediterranean (Turkey) annual watermelon production is approximately 580 000 t (Anonymous 2012).
During the growing season, availability of irrigation water is very important for watermelon production in Çukurova region, the Eastern Mediterranean, Turkey. However, in this region, there is a serious problem about the water availability for agriculture management. This problem can be solved by effective irrigation strategies. Availability of limited water can cause large yield losses for all crop plants, inducing important physiological and biochemical changes (Proietti et al. 2008). Kirnak et al. (2009) stated that irrigation
Received 4 April, 2014 Accepted 10 August, 2014 Correspondence: Selçuk Özmen, Tel: +90-380-5412294, Fax: +90-380-5412295, E-mail: selcukozmen@hotmail.com © 2015, CAAS. All rights reserved. Published by Elsevier Ltd. doi: 10.1016/S2095-3119(14)60870-4
1. Introduction
Worldwide, watermelon (Citrullus lanatus (Thunb.) Mat-sum&Nakai) production is agriculturally very important. Turkey is the second largest watermelon producing country
of watermelon is quite necessary to obtain high yield due to its high growth rate, short growing period, and its water content of about 92%. In this respect, drip irrigation is the most appropriate irrigation method for fruit production. In this irrigation technique, water is applied directly to the soil as optimal irrigation is the supply of adequate water to meet plant needs in the root zone, avoiding the leaching of nutrients into deeper soil layers (Wakindiki and Kirambia 2011). Furthermore, Erdem et al. (2001) has demonstrated watermelon yield and quality improvements using drip irrigation method.
Plant nutrition is another important parameter to consider for obtaining high yield from watermelon (Santos et al. 2009). Andrade Junior et al. (2006) reported that the marketable yield of watermelon could be increased by applying nitrogen via fertigation without affecting fruit quality. Yadav et al. (1989) reported that the yield, the number of edible fruit, and the length of the watermelon stem could be increased in response to application of nitrogen. On the other hand, the number of fruit per plant and total soluble solids (TSS) were not affected by nitrogen, whereas, application of excessive nitrogen decreased the watermelon yield, but increased the speed of plant development (Colla et al. 2011). It can be concluded that nitrogen consumption and nitrogen content in the plant parts of watermelon should be needed to know. In the watermelon growing area, the problems caused by soil-borne disease, in particular, Fusarium wilt can be seen in the continuous cropping in watermelon area (Lee 1994). Yücel et al. (1989) pointed out that crop rotation using ≥5-year intervals for watermelon in the same field due to Fusarium wilt can be a classical solution for this problem. At the same time, McCreight et al. (1993) reported that a combined breeding program might be used to control soil-borne diseases. However, developing new cultivars resistant to diseases is time-consuming and increases the threat of resistant cultivars becoming susceptible to new pathogens. Hence, grafting onto resistant rootstocks may be a solution for such problems (Uygur and Yetişir 2009).
Grafting onto resistant rootstocks in the vegetable may facilitate control of such soil-borne diseases as Fusarium wilt, improve nutritional mineral uptake, and have a positive impact on plant yield and fruit quality. Additionally, grafting protects plants against soil temperature extremes and iron chlorosis in calcareous soils. Moreover, grafting enhances nutrient absorption, and improves salt tolerance and plant water use (Lee 1994; Lopez-Galarza et al. 2004). Grafting is widely used for the production of fruit-bearing vegetables in Japan, Korea, other Asian countries and Europe, where intensive and continuous cropping is performed. Grafting of vegetables was firstly performed in Korea and Japan in the late 1920s by grafting watermelons onto ground root-stocks (Oda 1995). In 2007 there were 51.7 million grafted
seedlings used in Turkey, of which 27.5 million (53%) were grafted watermelon (Yılmaz et al. 2007).
Besri (2008) found that the average yield of grafted watermelon was 84% higher than that of ungrafted wa-termelon. Moreover, grafted watermelon consumed more nitrogen than ungrafted watermelon (Colla et al. 2011) while the fruit quality of watermelon reported by Rouphael et al. (2008) was not negatively affected by grafting. Proietti et al. (2008) determined that yield of mini-grafted watermelon was not significantly affected by moderate deficit drip irrigation. In production planning, estimating the yield in response to water deficit for different crops is a critical point. Moreover, crop evapotranspiration (ET) and crop yield were significant-ly affected by water deficit in crops which gives rise to water stress on plants. Thus, the investigation of water deficit on crops is quite important to determine the water saving for the region where limited water is available (Erdem and Yüksel, 2003; Proietti et al. 2008).
Drip irrigation for grafted and ungrafted watermelon is still very limited, especially in Çukurova region in Turkey. Therefore, objective of the present study is to examine nitrogen consumption, yield, and quality in grafted and ungrafted watermelon in response to deficit drip irrigation in Çukurova region.
2. Results and discussion
2.1. Crop water use
Seasonal water use varied according to the treatments. The highest and lowest ET was 520.6 mm for grafted watermen-lons (CTJ, Crimson Tide+Jumbo) with full irrigation (I100) and
311.2 mm for ungrafted watermenlons (CT, Crimson Tide) with low irrigation (DI50), respectively, in 2006 (Table 1).
Seasonal water use was the highest in 2006, which might have been due to climatic events; for example, higher pan evaporation (Epan) values and the lower rainfall amounts in
2006 (Ertek 2011). The differences of seasonal water use between grafted watermelon and ungrafted watermelon were not significant. Seasonal water use in ungrafted wa-termelon was 4% lower than in grafted wawa-termelon using I100, which is similar to what was observed using deficit
irrigation (Table 1). The lowest seasonal water use was observed in ungrafted watermelons for all 3 years, which might have been due to more efficient consumption of water by grafted watermelon because of their strong root structure, as reported earlier by Rouphael et al. (2008) and Abe et al. (2006). Rouphael et al. (2008) reported that seasonal water use in grafted and ungrafted watermelon was 273.9–189 and 248.3–162.1 mm, respectively. On the other hand, seasonal water use in ungrafted watermelon was reported to be 677–700 mm by Kirnak and Doğan (2009), 417–720 mm
by Şimşek et al. (2004), and 362–408 mm by Erdem et al. (2001). Differences in the reported findings could be at-tributed to differences in the environments in which the plants were grown.
2.2. Nitrogen consumption
Nitrogen consumption was calculated for each of treatments and the results are shown in Table 2. Nitrogen consump-tion varied according to year and treatment. Ungrafted watermelon consumed about 16% more nitrogen than grafted watermelon in 2006 and 2008. In contrast, Ruiz and Romero (1999) and Colla et al. (2011) reported that grafted watermelon consumed more nitrogen than ungraft-ed watermelon because graftungraft-ed watermelon has a strong root structure. During calculation of nitrogen consumption, some components such as ammonium denitrification and volatilization, nitrogen transport due to leaching, rainfall and capillary rise, nitrogen use by weeds, and the nitrogen content of roots were ignored due to lack of data where it should be included (Pathak et al. 2007). Most probably, the differences in findings between the results of the present and the previous studies by Ruiz and Romero (1999) and Colla et al. (2011) might be due to a lack of the above-mentioned oversight. The highest nitrogen consumption was obtained using I100 in 2006, and DI50 in 2007 and 2008 in terms of
irrigation (Table 2), which was unexpected because nitrogen
was added to the irrigation water only in 2006. However, higher nitrogen consumption using DI50 in 2007 and 2008
may have been due to the absence of the above-mentioned oversight because there was no deep percolation during the study years. Moreover, watermelon in the treatment of DI50
consumed 28 and 23% more nitrogen than watermelon in the treatments of DI70 and I100, respectively, between 2006
and 2008.
Mean nitrogen content in the plants and fruit parts was evaluated for each treatment at the end of each harvest (Figs. 1 and 2). The following nitrogen findings are the cumulative results for all 3 years of the study. The highest mean nitrogen content was measured in the leaves (Fig. 1) for all treatments. The leaves contained 48 and 50% more nitrogen than the stems and fruits, respectively. In addition, 50, 26, and 24% of the total nitrogen content in the plants were in the leaves, stems, and fruits, respectively. In the leaves and stems, nitrogen content was 3–24% and 19–35% higher for DI70 and DI50, respectively, than for I100. In the fruit
of plants treated with DI70, nitrogen content was 9% higher
than that obtained using DI50 and 10% higher than that
obtained using I100. As compared to CTJ, mean nitrogen
content in CT leaves, stems, and fruit, respectively, was 48, 61, and 46% higher (Fig. 1). These findings indicate that nitrogen content in the grafted plant parts was higher than in the ungrafted plant parts, as reported by Ruiz and Romero (1999) and Uygur and Yetişir (2009). The present Table 1 Irrigation results of treatments in experimental years
Year Treatments1) Number of
irrigation ∆W 2) (mm) IR 3) (mm) (mm)Rain ET 4) (mm) Relative ET(%) 2006 CTJI100 12 60.1 413.5 47.0 520.6 100 CTJDI70 12 71.6 285.7 47.0 404.3 77.7 CTJDI50 12 75.3 205.3 47.0 327.6 62.9 CTI100 12 40.6 413.5 47.0 501.1 96.3 CTDI70 12 44.8 285.7 47.0 377.5 72.5 CTDI50 12 58.9 205.3 47.0 311.2 59.8 2007 CTJI100 13 10.9 266.2 156.0 433.1 100 CTJDI70 13 34.1 188.0 156.0 378.1 87.3 CTJDI50 13 51.5 135.8 156.0 343.3 79.3 CTI100 – – – 156.0 – – CTDI70 – – – 156.0 – – CTDI50 – – – 156.0 – – 2008 CTJI100 16 34.2 361.7 79.0 474.9 100 CTJDI70 16 36.3 256.1 79.0 371.4 78.2 CTJDI50 16 69.5 185.6 79.0 334.1 70.4 CTI100 16 14.0 361.7 79.0 454.7 95.7 CTDI70 16 16.0 256.1 79.0 351.7 74.0 CTDI50 16 54.6 185.6 79.0 319.2 67.2
1) Three irrigation rates, full irrigation (I
100), moderate irrigation (DI70) and low irrigation (DI50), were employed on grafted (CTJ, Crimson
Tide+Jumbo) and ungrafted (CT, Crimson Tide) watermelons.
2) ∆W, the change in the soil water content. 3) IR, total irrigation water depth.
4) ET, evapotranspiration.
findings are consistent with those reported by Hegde (1988). The highest mean nitrogen content was measured in the fruit peel for all treatments (Fig. 2). The nitrogen content in peels was 29 and 36% higher than in seed and pulp, respectively. In addition, 43, 30, and 27% of total nitrogen content in the fruits were in the peels, seeds, and pulps, respectively. Mean nitrogen content in the peel obtained with DI70 was 16 and 22% higher than that obtained with
I100 and DI50, respectively. Mean nitrogen content in seeds
was 5% higher for DI50 and DI70 than for I100. Mean nitrogen
content in the pulp was 15% higher for DI50 than for DI70
and I100. Deficit irrigation increased the nitrogen content in
watermelon seeds, pulps, and peels. The nitrogen content of CTJ peels, seeds, and pulps was higher than that of CT. Compared to CT, mean nitrogen content in CTJ seeds, pulps, and peels was 30, 43 and 56% higher, respectively (Fig. 2). The fruit of grafted plants contained more nitrogen than the fruit of ungrafted plants, which is similar to Ruiz and Romero’s findings (1999). Proietti et al. (2008) reported that
Table
2
Nitrogen budget (kg ha
–1) for the experimental treatments in 2006–2008
2006 2007 2008 CTJ CT CTJ CT CTJ CT I100 DI70 DI50 I100 DI70 DI50 I100 DI70 DI50 I100 DI70 DI50 I100 DI70 DI50 I100 DI70 DI50
Input In the soil (beginning)
NH 4 2.80 2.80 2.80 2.80 2.80 2.80 4.80 4.80 4.80 – – – 4.90 4.90 4.90 4.90 4.90 4.90 NH 3 2.60 2.60 2.60 2.60 2.60 2.60 5.50 5.50 5.50 – – – 3.80 3.80 3.80 3.80 3.80 3.80
Nitrogen application (in the season) via
irrigation 103.40 77.40 51.70 103.40 77.40 51.70 12.60 12.60 12.60 – – – 0.00 0.00 0.00 0.00 0.00 0.00 as Granules 0.00 0.00 0.00 0.00 0.00 0.00 87.40 87.40 87.40 – – – 100.00 100.00 100.00 100.00 100.00 100.00 Total 108.80 82.80 57.10 108.80 82.80 57.10 110.30 110.30 110.30 – – – 108.70 108.70 108.70 108.70 108.70 108.70
Output Remaining in the soil after harvest
NH 4 3.10 2.40 3.10 2.40 4.40 2.40 4.10 3.20 3.70 – – – 4.00 3.20 3.70 3.40 4.70 3.60 NH 3 2.80 1.90 3.50 2.60 7.10 5.10 3.40 2.30 3.60 – – – 2.40 2.10 1.80 10.60 1.80 2.10
Remaining in the plant after harvest
27.60 23.90 25.80 12.40 17.40 12.50 43.00 49.70 34.80 – – – 49.50 27.00 36.00 19.90 28.00 15.30 Total 33.50 28.10 32.30 17.40 28.90 20.00 50.50 55.20 42.10 – – – 55.90 32.30 41.50 33.90 34.50 21.00
Total input–Total output (∆N)
75.30 54.70 24.80 91.40 53.90 37.10 59.90 55.10 68.20 – – – 52.80 76.40 67.20 74.80 74.20 87.70
Fig. 1 Average nitrogen amounts of leaves, stems and fruits
for experimental treatments in three experimental years. Three irrigation rates, full irrigation (I100), moderate irrigation (DI70) and low irrigation (DI50), were employed on grafted (CTJ, Crimson Tide+Jumbo) and ungrafted (CT, Crimson Tide) watermelons. The same as below.
Fig. 2 Average nitrogen amounts of seeds, pulps and peels
for treatments in three experimental years.
Leaves Stem Fruit 25.00 20.00 15.00 10.00 5.00 0.00
CTJI100 CTJDI70CTJDI50CTI100 CTDI70 CTDI50
Treatments
Nitrogen amounts (kg ha
–1)
CTJI100 CTJDI70CTJDI50CTI100 CTDI70 CTDI50
Treatments
Average nitrogen amounts
(kg ha –1) Seed Pulp Peel 5.00 4.00 3.00 2.00 1.00 0.00
Table 3 Effects of deficit irrigation and grafting on fruit yield of watermelon in 2006
Treatments Yield Fruit number (piece plant–1) Average fruit weight (kg fruit–1)
(kg plant–1) (kg ha–1) Irrigation rate (%) 100 5.55 18 500.00 1.19 4.50 70 5.56 18 533.30 1.21 4.19 50 5.47 18 233.30 1.26 4.33 Grafting CTJ 6.60 a 22 000.00 a 1.33 a 4.70 CT 4.45 b 14 833.30 b 1.11 b 3.98 Significance Irrigation (IR) ns ns ns ns Grafting (G) * * * ns IR×G ns ns ns ns
ns, non-significant (P>0.05); *, significant (P≤0.05); different letters show different yield groups as statistical. The same as below. Table 4 Effects of deficit irrigation and grafting on fruit yield of watermelon in 2007
Treatments Yield Fruit number (piece plant–1) Average fruit weight (kg fruit–1)
(kg plant–1) (kg ha–1) Irrigation rate (%) 100 13.78 45 933.30 2.12 6.36 70 13.48 44 933.30 2.36 5.62 50 13.94 46 466.70 2.54 5.53 Grafting CTJ 13.73 45 766.70 2.34 5.84 CT – – – – Significance Irrigation (IR) ns ns ns ns Grafting (G) – – – – IR×G – – – –
nitrogen content was the lowest in the pulps of watermelon fruit, which is in agreement with the present findings. On the other hand, the high nitrogen content observed in the fruits of grafted watermelons is a phenomenon that warrants further detailed investigation.
2.3. Fruit yield
Fruit yield per plant and the number of fruits per plant from experimental plots each year of the study was statistically analyzed; all the findings are presented in Tables 3, 4 and 5. According to variance analysis, in 2006 the effects of the irrigation rate and the irrigation rate-grafting interaction on yield, number of fruits, and mean fruit weight were not significant, but grafting increased the yield and number of fruits with 95% confidence (Table 3). In 2007 only a single variety (grafted) was studied and it was observed that the effect of the irrigation rate on yield, number of fruits, and mean fruit weight was not statistically significant (Table 4).
In 2008 total yields from the first and second harvests were statistically analyzed; variance analysis showed that the effects of the irrigation rate and irrigation rate-grafting interaction on yield, number of fruits, and mean fruit weight
were not statistically significant, but that grafting resulted in a higher yield and number of fruits with a 95% confidence (P≤0.05) (Table 5). Yields in the present study were similar to those reported by Alan et al. (2007), but were not similar to those reported by Kirnak and Doğan (2009) and Colla et al. (2010). The differences between the findings were due to differences in varieties, growing periods, culture practices, and study designs; however, Mohamed et al. (2012) emphasized that grafting is an alternative approach to increase plant abiotic stress tolerance, which in turn increases crop production. At the same time, Proietti et al. (2008) reported that the irrigation and grafting increased mean marketable yield per plant, the number of fruits, and fruit weight significantly. The findings related to grafting in the present study were similar to those reported by Proietti et al. (2008).
2.4. Fruit quality
Watermelon quality parameters, weight, length, width, peel thickness, TSS, and number of seeds, were analyzed statistically for the 3 years of the study (Tables 6–8). The irrigation rate, grafting, and irrigation rate-grafting interaction
Table 5 Effects of deficit irrigation and grafting on fruit yield of watermelon in 2008
Treatments Yield Fruit number (piece plant–1) Average fruit weight (kg fruit–1)
(kg plant–1) (kg ha–1) Irrigation rate (%) 100 16.90 56 333.30 3.13 5.32 70 15.87 52 900.00 2.72 5.76 50 12.74 42 466.70 2.35 5.34 Grafting CTJ 19.32 a 64 400.00 a 3.38 a 5.69 CT 11.02 b 36 733.30 b 2.09 b 5.26 Significance Irrigation (IR) ns ns ns ns Grafting (G) * * * ns IR×G ns ns ns ns
did not significantly affect fruit quality parameters, but graft-ing increased peel thickness in 2006 at the 95% confidence level, according to variance analysis of quality parameters (Table 6). In 2007 the irrigation rate did not significantly affect fruit quality parameters. The I100 treatment affected
fruit quality parameters more than DI70 and DI50, except for
TSS (Table 7).
In 2008 fruit quality analysis measurements were ob-tained from the second harvest, which had a higher yield than the first harvest. According to analysis of variance,
the irrigation rate and irrigation rate-grafting interaction did not significantly affect fruit quality parameters at the 95% confidence level. In contrast, grafting increased watermel-on fruit weight, length, width, and number of seeds at the 95% confidence level (Table 8). Fruit quality findings in the present study are consistent with those reported by Şimşek et al. (2004) and Rouphael et al. (2008); however, TSS reported by Öztekin et al. (2012) and fruit weight, length, width, and peel thickness reported by Proietti et al. (2008) were not similar with those observed in the present study.
Table 6 Effects of deficit irrigation and grafting on fruit quality of watermelon in 2006
Treatments Weight (kg) Length (cm) Width (cm) Peel thickness (mm) TSS1) (%) Number of seeds
Irrigation rate (%) 100 4.70 23.86 19.01 10.98 9.61 563.44 70 5.03 24.32 19.60 11.07 9.18 649.56 50 4.94 24.19 19.50 10.77 9.37 592.67 Grafting CTJ 5.29 24.95 19.70 11.43 a 9.43 657.18 CT 4.49 23.30 19.04 10.44 b 9.34 546.59 Significance Irrigation (IR) ns ns ns ns ns ns Grafting (G) ns ns ns * ns ns IR×G ns ns ns ns ns ns
1) TSS, total solube solids. The same as below.
Table 7 Effects of deficit irrigation and grafting on fruit quality of watermelon in 2007
Treatments Weight (kg) Length (cm) Width (cm) Peel thickness (mm) TSS (%) Number of seeds Irrigation rate (%) 100 8.72 29.44 22.50 15.41 10.48 512.00 70 8.08 28.56 22.17 15.11 10.30 432.00 50 7.40 28.11 21.48 13.90 10.93 432.89 Grafting CTJ 8.07 28.70 22.05 14.81 10.57 917.93 CT – – – – – – Significance Irrigation (IR) ns ns ns ns ns ns Grafting (G) – – – – – – IR×G – – – – – –
Different results about fruit quality were probably due to differences in the varieties studied under different climactic and geographic conditions, and differences in culture prac-tices (Davis et al. 2008).
3. Conclusion
As a result of this 3-year study, it was concluded that yield and quality were not significantly affected by deficit irrigation. However, grafting on watermelon increased the yield dramatically but it had a slight effect on quality. Seasonal ET varied according to treatment and year as follows: 520.6–311.2 mm in 2006, 433.1–343.3 mm in 2007, and 474.9–319.2 mm in 2008. Seasonal ET in grafted and ungrafted plants were 398.6 and 385.8 mm, respectively, in 2006 and 2008. Nitrogen consumption in grafted watermelon was 16% lower than in ungrafted plants. However, watermelon in the treatment of DI50
consumed 28 and 23% more nitrogen than watermelon in the treatments of DI70 and I100, respectively, between
2006 and 2008. Grafted watermelon had the highest nitrogen concentration in plant parts (i.e., leaves, stems, and fruit), but this situation was not similar by using deficit irrigations, especially DI50. Grafted watermelon and deficit
irrigation resulted in the highest nitrogen concentration in the fruit parts (i.e., peels, pulps, and seeds). Average nitrogen content in seeds, pulp, and peel was 30, 43, and 56% higher in CTJ than in those of CT, respectively. It was concluded that DI50 treatment could be taken into
account for the development of reduced irrigation strat-egies in semiarid regions where irrigation water supplies are limited. In addition, the yield increases by applying CTJ treatment to the watermelon production.
4. Materials and methods
This experimental study was performed between 2006 and 2008 at research field (36°59´N, 35°18´E; 20 m a.s.l.), Ir-rigation and Drainage Engineering Department, Faculty of
Agriculture, Çukurova University, Adana, Turkey. The study area has a typical Mediterranean climate - hot and dry in the summer and cool and rainy in the winter. Long-term mean rainfall in the area is about 646.5 mm. The highest amount of rainfall occurs during the winter, when most plants do not grow (Table 9). The soil of the experimental area developed from alluvial deposits and covered the entire area. Soil at the study site was clayey of the Mutlu series (Özbek et al. 1974). Some general physical and chemical properties of the soil are shown in Table 10. The soil water content at field capacity (FC) and permanent wilting point (PWP, g g−1)
were determined using the pressure membranes at –33 kPa and –1.5 MPa suction pressures, respectively. The soil bulk density (As, g cm−3) was determined by the methodology
given by USSL (1954); pH was measured in the soil paste using a Beckman model glass electrode pH-meter; electrical conductivity (EC) was also measured in soil paste using the standard Wheatstone resistance bridge method (USSL 1954). The Crimson Tide (CT) F1 variety of watermelon
(Citrullus Lanatus) was used as the ungrafted type, and the grafted type was CT grafted on Jumbo rootstock (CTJ). The salinity of the irrigation water was 0.36 dS m–1 and therefore
did not contribute to crop stress.
A completely randomized block experimental design in triplicate was employed. During the first 2 years of the study each plot was 13 m long by 12 m wide (156 m2), with
4 rows and 52 watermelon seedlings. During the third year, each plot was 13 m long by 9 m wide (117 m2) for the first
2 replicate and 156 m2 for the third replicate. All plants in
the same row in each plot were covered with a low plastic tunnel-like cover. Plastic cover is 0.05 mm thick and made from transparent material. The plastic covers were removed completely when the average of ambient air temperature reached 22°C. This was done to protect the greenhouse gas in the plastic tunnel (Yetişir et al. 2003). Planting dates were 4 April 2006, 12 March 2007, and 01 March 2008. Plant-ing dates were varied in each year accordPlant-ing to changPlant-ing conditions of climate.
Three irrigation rates were used as follows: full (I100) with
Table 8 Effects of deficit irrigation and grafting on fruit quality of watermelon in 2008
Treatments Weight (kg) Length (cm) Width (cm) Peel thickness (mm) TSS (%) Number of seeds Irrigation rate (%) 100 6.49 25.43 21.92 12.10 8.94 860.44 70 6.86 25.79 22.22 12.31 9.08 863.56 50 6.94 26.17 22.08 11.71 9.33 883.78 Grafting CTJ 7.29 a 26.53 a 22.52 a 11.78 9.15 1 017.63 a CT 6.23 b 25.06 b 21.63 b 12.31 9.09 720.89 b Significance Irrigation (IR) ns ns ns ns ns ns Grafting (G) * * * ns ns * IR×G ns ns ns ns ns *
Table 9 The meteorological data in the experimental site during the study years
Years Meteorological data March April May June
2006 Average temperature (°C) 13.9 18.1 22.0 25.6
Relative humidity (%) 73.8 68.1 64.4 65.7
Average wind speed (m s–1) 0.9 1.0 1.0 1.1
Precipitation (mm) 63.5 13.0 25.0 12.0
Total solar radiation (MJ m–² d–1) 14.5 16.0 25.2 24.3
Epan (mm) 40.5 71.3 123.9 147.0
Vapor pressure deficit (mb) 4.3 6.9 9.9 11.2
2007 Average temperature (°C) 14.0 16.1 23.3 26.0
Relative humidity (%) 69.0 61.9 68.0 63.4
Average wind speed (m s–1) 1.0 1.0 1.0 1.3
Precipitation (mm) 66.0 67.0 33.5 3.7
Total solar radiation (MJ m–² d–1) 14.8 20.1 19.8 24.6
Epan (mm) 41.8 61.2 105.0 159.5
Vapor pressure deficit (mb) 5.0 7.1 9.5 13.0
2008 Average temperature (°C) 16.2 18.8 20.8 26.4
Relative humidity (%) 62.5 64.9 64.4 58.1
Average wind speed (m s–1) 1.2 1.3 1.3 1.6
Precipitation (mm) 32.0 27.0 20.0 0.0
Total solar radiation (MJ m–² d–1) 15.0 20.0 22.5 26.8
Epan (mm) 122.1 143.3 160.2 225.4
Vapor pressure deficit (mb) 7.3 8.1 9.1 15.0
no water stress; moderate (DI70); and low (DI50). I100 was
calculated using eq. (1). This provided enough water to bring the soil profile (whole 0–120 cm) to field capacity in the I100 plots (Gençsoylu and Yilmaz 2003; Ünlü et al. 2011).
DI70 and DI50 were deficit irrigation treatments and equal to 70 and 50% of I100. Germination water per year was 4.8,
5.5 and 9.3 mm during 2006, 2007 and 2008, respectively.
IR=Epan×Kp×
Pc (1)
Where, IR is the volume of irrigation water (mm), Epan is
the cumulative free surface water evaporation at irrigation interval (mm), Kp is the pan-crop, and Pc is the plant cover
(%). Plant cover was measured with one week interval by viewing the canopy through a wooden frame (100 cm× 300 cm) divided into 100 equal sections. Free surface water evaporation was measured using a screened US Weather Bureau Class A pan located at the meteorological station
near the experimental field. The Kp coefficient was 1.0 for
the first irrigation and 1.2 for the other irrigations in 2006 and 2007. In 2008 this coefficient was 1.2 for all irrigations (Şenyiğit 1999 ).
A drip irrigation system was used in this study. A 16-mm diameter polyethylene pipe with in-line drippers at 0.5-m intervals was placed on one side of each watermelon row. Drip laterals were placed 10 cm away from the plant. The mean discharge of the emitters was 4 L h–1 at 0.1 MP. The
first irrigation of each year was applied to bring the soil moisture to field capacity. Then, irrigation was started at the stage of watermelon branch development and terminated 4–11 d before harvest. All irrigation treatments were applied once or twice each week with 3–4-d intervals.
Pre plant fertilizer was distributed (P2O5 100 kg ha–1+
K2O 100 kg ha–1 in 2006, and P
2O5 150 kg ha–1+K2O 200 kg
ha–1 in 2007 and 2008) and incorporated into the soil. During
the irrigation season, additional fertilizer (nitrogen: 103.4 kg ha–1 for I
100, 72.4 kg ha–1 for DI70, and 51.7 kg ha–1 for DI50
in 2006, and 10 kg ha–1 for I
100, DI70, and DI50 in 2007 and
2008) were applied to plots via the drip irrigation system weekly in 2006 and with bands on each row of each plot at 2-wk intervals in 2007 and 2008 (Miguel et al. 2004). Fertilizer amounts were changed according to observa-tions between each year. All ungrafted plants died due to Fusarium oxysporum disease by the 55th d after planting in 2007. Pest and disease control was performed based on the recommendations of Plant Protection Department, Faculty of Agriculture, University of Çukurova.
During the growing season soil moisture content at a Table 10 Soil characteristics of the experimental field
Characteristics1) Soil depth (cm)
0–30 30–60 60–90 90–120 Texture Clay Clay Clay Clay Sand (%) 17.99 16.30 15.41 13.75 Clay (%) 62.61 65.24 62.92 67.71 Silt (%) 19.40 17.96 21.67 18.54 ECe (dS m–1) 0.29 0.31 0.32 0.40 pH 7.58 7.20 7.15 7.30 As (g cm–3) 1.19 1.16 1.15 1.25 FC (g g–1) 34.40 36.70 38.40 37.80 PWP (g g–1) 17.50 18.20 19.20 19.40 1) ECe, electrical conductivity; As, bulk density; FC, field capacity;
depth of 0–120 cm (in 30-cm increments) was measured gravimetrically (105°C, 24 h) just before irrigation events. Soil samples were collected with a hand-driven auger in the center of one replicate of each treatment during the study years. Evapotranspiration (ET) values (mm) for all treatments were calculated using eq. (2):
ET=P+IR+Cp–DP–TW±∆W (2)
Where, P and IR are rainfall and total irrigation water depth (mm), respectively, Cp is the capillary contribution from
the ground water table to the crop root zone (mm), DP is the deep percolation from the root zone (mm), TW is runoff (mm), and DW is the change in soil water content (final minus initial). As there was no water table or runoff in the exper-imental area, Cp and TW were set to 0; DP was assumed
to be negligible because of the drip system characteristics and high soil moisture deficiency before irrigation (Dağdelen et al. 2009). These were also confirmed via gravimetric soil moisture content measurements conducted in the 120cm soil profile during the growing seasons. Data showed that the soil moisture content was consistently less than field capacity at the lower boundary of the root zone because of the Pc component in eq. (1).
In order to determine the nitrogen consumption for all treatments soil nitrogen content in the 0–120 cm layer was measured in 20-cm increments before planting, during the mid-irrigation season, and just after harvesting. Soil samples were taken from center row in the each plot with 3 replicates to represent the whole area in terms of uniform distribution of soil water under drip irrigation. Moreover, nitrogen content in leaves, stems, peel, pulp, and seeds (plant parts) was also measured. These data were collected via the modified Kjeldahl method (Kaçar 1972). Nitrogen consumption was calculated using eq. (3):
∆N=Ninput–Noutput (3)
Where, ΔN is the amount of nitrogen lost after the study period (kg ha–1), N
input is the quantity of nitrogen in the soil at
the beginning and the quantity of nitrogen applied during the study period (kg ha–1), and N
output is the quantity of nitrogen in
the soil and in the plant parts at the end of growing season. While making these calculations ammonium denitrification and volatilization, nitrogen transport due to leaching, rainfall and capillary rise, and nitrogen use by weeds were disre-garded (Pathak et al. 2007).
Harvesting was performed when the atrium and leech of the watermelon stems were completely dried, the stems of fruit were thinned, and the color of the peels reached the brightness of maturity (Gündüz and Kara 1996). The rows in the middle of each plot were selected for harvest evaluation. Fully mature fruits were harvested on 30 June 2006, 20 June 2007, and 2–6 June 2008. Weight, length, width, peel thickness, TSS, and the number of seeds were measured in 3 fruits that were selected randomly for all treatments every
harvest year (Yetişir and Sarı 2003; Bautista et al. 2011). TSS was measured by refractometer (ATC-1 Sucrose Brix 0–32%). All data were statistically analyzed using SPSS ver.10.0 for Windows (SPSS, Inc., Chicago, IL). Grafting and irrigation rate on water melon were compared for yield and quality. Differences among means were separated by Duncan’s multiple rage test P≤0.05.
Acknowledgements
The authors would like to gratefully acknowledge the Uni-versity of Çukurova, Turkey, for providing funding through the Scientific Research Projects of Çukurova University (ZF2006D16 and ZF2008BAP1). The authors thank to Dr. Elif UZ, Department of Molecular Biology and Genetics, for her help in preparing the manuscript.
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