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Effect of saline water on cucumber (Cucumis sativus L.) yield and water use under drip irrigation in North China
Agricultural Water Management 98 (2010) 105–113
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Effect of saline water on cucumber (Cucumis sativus L.) yield and water use under drip irrigation in North China Shuqin Wan a , Yaohu Kang a,∗ , Dan Wang b , Shi-ping Liu a a Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographical Sciences and Natural Resource Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing 100101, China b Beijing Xinhua Water Saving Products Certification Co. LTD, 10, Nanxiange, Xuanwu District, Beijing 100053, China
a r t i c l e
i n f o
Article history: Received 18 March 2010 Accepted 6 August 2010
Keywords: Cucumber Drip irrigation Saline water irrigation Management strategy
a b s t r a c t Saline water has been included as an important substitutable resource for fresh water in agricultural irrigation in many fresh water scarce regions. In order to make good use of saline water for agricultural irrigation in North China, a semi-humid area, a 3-year field experiment was carried out to study the possibility of using saline water for supplement irrigation of cucumber. Saline water was applied via mulched drip irrigation. The average electrical conductivity of irrigation water (ECiw ) was 1.1, 2.2, 2.9, 3.5 and 4.2 dS/m in 2003 and 2004, and 1.1, 2.2, 3.5, 4.2 and 4.9 dS/m in 2005. Throughout cucumber-growing season, the soil matric potential at 0.2 m depth immediately under drip emitter was kept higher than −20 kPa and saline water was applied after cucumber seedling stage. The experimental results revealed that cucumber fruit number per plant and yield decreased by 5.7% per unit increase in ECiw . The maximum yield loss was around 25% for ECiw of 4.9 dS/m, compared with 1.1 dS/m. Cucumber seasonal accumulative water use decreased linearly over the range of 1.5–6.9% per unit increase in ECiw . As to the average root zone ECe (electrical conductivity of saturated paste extract), cucumber yield and water use decreased by 10.8 and 10.3% for each unit of ECe increase in the root zone (within 40 cm away from emitter and 40 cm depths), respectively. After 3 years irrigation with saline water, there was no obvious tendency for ECe to increase in the soil profile of 0–90 cm depths. So in North China, or similar semi-humid area, when there is no enough fresh water for irrigation, saline water up to 4.9 dS/m can be used to irrigate field culture cucumbers at the expense of some yield loss. © 2010 Published by Elsevier B.V.
1. Introduction The availability of fresh water for agricultural use is declining in many areas of the world due to the increasing water needs of industries and municipalities. Thus, agriculture faces challenges of using low quality wastewater and saline water for crop production. Many studies indicate that these water resources traditionally classified as unsuitable for irrigation can be used successfully to grow crops without long-term hazardous consequences to crops and soils if proper management strategies are established. These strategies include adopting advanced irrigation technology, selecting appropriately salt-tolerant crops, leaching salts below the crop root zone (Rhoades et al., 1992; Oster, 1994; Shalhevet, 1994). In China, especially in North China, the increasing water shortages make it urgent to develop safe and efficient management of saline water resource for agricultural irrigation.
∗ Corresponding author. Tel.: +86 10 64856516; fax: +86 10 64856516. E-mail address: [email protected] (Y. Kang). 0378-3774/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.agwat.2010.08.003
Saline water has been successfully used to irrigate field-grown tomato and oleic sunflower in North China in recent years (Wan et al., 2007; Chen et al., 2009). It was found that when several management strategies were adopted, saline water up to 4.9 dS/m and 10.9 dS/m can be applied respectively to irrigate tomato and oleic sunflower without obviously negative effects on the yields and soil salinity. The main management strategies include applying saline water with mulched drip irrigation, keeping the soil matric potential (SMP) at 0.2 m depth immediately under emitter higher than −20 kPa throughout the growing season. Cucumber (Cucumis sativus L.) is one of the most popular and widely grown vegetable crops in the world, and is considered moderately sensitive to salt stress, since it can tolerate an ECe (electrical conductivity of saturated paste extract) of about 2.5 dS/m and fruit yield decrease by 13% with each unit of ECe increasing above the threshold value (Maas and Hoffman, 1977). The responses of cucumber to saline water irrigation were recorded by some investigators. Sonneveld and Voogt (1978) indicated when the electrical conductivity of irrigation water (ECiw ) ranged from 0.1 to 4.5 dS/m, greenhouse cucumber yields decreased linearly as ECiw increased, and the yield reduction was about 17% per unit increase
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in ECiw. Jones et al. (1989) found that ECiw of 4.0 dS/m significantly decreased cucumber yield. Chartzoulakis (1992) reported cucumber (cv. Pepinex) growth reduced significantly when the ECiw was higher than 1.2 dS/m, and the relative yield reduced by 16% per unit increase in ECiw above 1.3 dS/m. Al-Harbi indicated that cucumber (cv. Farbiola) was able to tolerate nutrient solution with ECiw higher than 4.5 dS/m without a significant reduction in yield (AlHarbi, 1994a), and high ECiw had a greater effect during the day than during the night due to its effect on cucumber water uptake (Al-Harbi, 1994b). Ho and Adams (1994) demonstrated that dry weight of cucumber (cv. Corona) fruit was not affected until the ECiw was higher than 5.5 dS/m, and the reduction was 9% for each unit of ECiw increasing between 5.5 and 8 dS/m. All of these mentioned studies were performed in greenhouse or in hydroponics cultures, which are relatively well controlled growing conditions. In North China, cucumbers are often planted in open field in early spring or later summer, and supplemental irrigation is essential. In open field, rainfall may contribute a substantial amount of water to crop need, and reduce the need of irrigation water required for salt leaching. The objectives of the study were (1) to study the responses of open cultivated cucumber to saline water irrigation, and explore the possibility of using saline water for supplement irrigation of cucumber in North China; and (2) to optimize saline water irrigation management strategies to maintain cucumber productivity and the salt balance in the soil.
Cangzhou area, one of the largest areas with moderately saline water (2–5 dS/m) resource in North China. The average ECiw were 2.2, 2.9, 3.5 and 4.2 dS/m in 2003 and 2004, and were 2.2, 3.5, 4.2 and 4.9 dS/m in 2005, respectively. Ionic composition for local groundwater and saline water in this trial is listed in Table 1. All of the treatments were replicated three times following a completely randomized design. The locations of the treatments at the experimental site was kept unchanged each year, in order to observe accumulative salinity hazards on crop and soil. 2.3. Agronomic practices Each plot consisted of three raised beds, with a width of 1.4 m between bed centers. The beds were 0.6 m wide, 4.4 m long and 0.15 m high. The area of each plot was 18.48 m2 . Every treatment plot was a gravity drip system. In the front of each plot, a tank, with volume about 120 L, was installed at a 1 m level. Drip tube (Xinjiang Tianye Co.) with 0.2 m emitter spacing and a flow rate of 3.0 L/h at the operating pressure of 0.1 MPa was placed on the center of each raised bed. Under this gravity drip irrigation system, the actual operating pressure was between 0.012 and 0.017 MPa, and the actual flow rate was about 0.9 L/h. Cucumber (C. sativus L.) seeds cv. ‘zhongnong’ were used in the 3 years. The seeds were sown in the field on May 4, May 14 and April 30 in 2003, 2004 and 2005, respectively. Double row plantings (in a zigzag) spaced 0.3 m apart per bed and interplant spacing was 0.4 m. About three weeks later, cucumber seedlings were thinned to leave only one seedling at each location maintaining a plant density of approximate 35,720 plants/ha. Cucumbers were allowed to grow naturally without pruning. Plant protection was needed each year, and disease control and pest management were the same for all treatments. Black polyethylene mulches (1.2 m wide by 0.08 mm thick) were applied over the beds on May 31 (27 days after sowing: DAS), May 12 (2 days before sowing), and June 2 (33 DAS) in 2003, 2004 and 2005, respectively. Because rainfall helps wash the soluble salts out of the soil profile, the polyethylene mulches were removed after each growing season.
2. Methods and materials 2.1. Experimental site A 3-year (2003–2005) field experiment was conducted at Tongzhou Experimental Station for Water Cycle and Modern Water-saving Irrigation Research, Institute of Geographic Science and Natural Resource Research. The Station (latitude: 39◦ 36 N; longitude: 116◦ 48 E; 20 m above sea level) is located in the southeast region of Beijing, about 60 km away from Beijing city. It is a temperate semi-humid monsoon climate, with mean annual temperature 11.3 ◦ C and mean annual global radiation 5.24 GJ/m2 . Average annual precipitation is 620 mm, with 80% concentrated during the July-September period. The dominant soil in the experiment was a silt loam. In 0–30 cm plow layer, its average bulk density was 1.35 g/cm3 , and soil organic matter content was about 1.3%.
2.4. Irrigation During cucumber-growing periods in the 3 years, irrigation was applied only when the SMP at 0.2 m depth immediately under drip emitter was close to −20 kPa, except at seeding stage. In order to ensure plants grow normally, fresh water was applied immediately after seeding and during the cucumber seedling stage (0–35 days after seeding). The treatment was initiated at the end of seedling stage, which was on June 7 (34 DAS), June 15 (32 DAS), and June 16 (47 DAS) in 2003, 2004 and 2005, respectively. In 2005, treatments were delayed about 10 days because of prolonged seedling period due to bad weather on seeding days.
2.2. Experimental design The experiment consisted of a control treatment and four saline water treatments. The control treatment was local groundwater (fresh water) with an ECiw of 1.1 dS/m. Artificial saline water were produced by adding NaHCO3 , Na2 SO4 , MgSO4 , MgCl2 and CaCl2 to local groundwater in molar proportion of 0.50:0.05:0.25:0.10:0.10, which is similar to the ionic compositions of the aquifer in Table 1 Ionic composition of local groundwater and saline water in 2003, 2004 and 2005. ECiw a (dS/m)
CO3 1.1 2.2 2.9 3.5 4.2 4.9 a b
SARb
Ionic concentration (mmol/L)
0.4 0.4 0.4 0.4 0.4 0.4
2−
HCO3 6 10.8 13.8 17.7 19.4 23.1
−
−
Cl
SO4
2.7 6.0 9.2 13.0 13.8 17.1
1.7 5.0 5.8 6.4 8.5 9.8
ECiw means the average electrical conductivity of the irrigation water. SAR means sodium adsorption ratio.
2−
2+
2+
+
+
Ca
Mg
K
Na
0.6 1.0 2.2 1.2 2.0 2.3
4 5.0 7.2 8.3 8.1 9.8
0.7 2.6 3.4 4.3 5.4 6.4
2.7 10.5 13.5 17.3 21.5 25.7
1.3 4.3 4.4 5.7 6.8 7.4
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When saline water was applied, surplus water was added to provide a leaching fraction. According to NRCS National Engineering Handbook (section 15) (USDA-NRCS, 1987), the leaching requirement ratio (LRt ) for high-frequency, daily or alternate-day irrigation can be calculated by the following equations: LRt = Fg =
ECiw 2(max ECe )
(1)
Fn 1.0 − LRt
(2)
where LRt is the leaching requirement ratio, ECiw is the electrical conductivity of the irrigation water (dS/m), ECe is the electrical conductivity of the saturated paste extract (dS/m), max ECe is the theoretical level of salinity that would reduce yield to zero (dS/m), max ECe value for cucumber is 10 dS/m, Fn is the net water requirement per irrigation (mm), and Fg is the gross water application per irrigation (mm). The applied water per irrigation for the control treatment (1.1 dS/m) was designed as 4.8 mm, that is, Fn was 4.8 mm. Because the tanks were made in advance, there was a deviation between actual volume (actual Fg ) and desired volume (desired Fg ) for each treatment. The calculated LRt , desired Fg and actual Fg for each treatments are listed in Table 2. 2.5. Fertilizer According to local farmer’s practice, about 37.5 m3 /ha wellrotted cow manure (N–P–K: 0.25–0.32:0.15–0.21:0.16–0.25) was uniformly applied to all plots before the field was ploughed in 2003. Several days later, 300 kg/ha compound fertilizers (diammonium phosphate, N–P–K: 18–46–0) were uniformly applied to the plots when the soil was bedded. In 2004 and 2005, about 600 kg/ha diammonium phosphate (N–P–K: 18–46–0) was applied. After the treatments began and until harvest, about 50 mL of fertilizer solution (30 wt.% urea solution) was added to the tank (120 L) at each irrigation event for each treatment. During the whole growing season, the total amount of urea applied with irrigation was about 270 kg/ha (125 kg/ha N) for each treatment. 2.6. Observation and equipments 2.6.1. Soil matric potential (SMP) Thirty mercurial tensiometers were installed in each treatment to measure spatial distribution of SMP. The sensor placement was same for all treatments. There were six tensiometers at depths of (10, 20, 30, 50, 70 and 90 cm) installed at five horizontal distances (0, 17.5, 35, 52.5 and 70 cm) from the drip line. Observations were made daily at 8:00. In order to determine the schedule of irrigation, one tensiometer with a vacuum gauge was installed at 0.2 m depth immediately under drip emitter for each treatment. These tensiometers were observed four times at 8:00, 11:00, 14:00 and 17:00 every day.
Table 2 The calculated LRt , desired Fg and actual Fg for each treatment.
a b
ECiw (dS/m)
Calculated LRt a
Desired Fg b (mm)
Actual Fg (mm)
1.1 2.2 2.9 3.5 4.2 4.9
0.00 0.11 0.15 0.18 0.21 0.25
4.8 5.4 5.6 5.8 6.1 6.4
4.8 5.2 5.6 6.0 6.3 6.3
LRt is the leaching requirement ratio. Fg is the gross water application per irrigation (mm).
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2.6.2. Cucumber water use For each treatment, one weighing lysimeter was installed in the center of the plot to measure cucumber water use. Each lysimeter consisted of an inner tank for crop cultivation and an outer tank for protection and drainage reservoir. The volume of the inner tank was 0.36 m3 (0.8 m × 0.5 m × 0.9 m), and a layer of coarse sand and gravel, 0.2 m thick, was overlain by a repacked soil profile of 0.7 m. The topsoil of the inner tank was shaped to the same form as field bed, and at the bottom of the inner tank, a pipe serving as a drainage outlet connected the inner tank to the outer tank. The lysimeters were also mulched with black polyethylene as the field. Drip tape (including three emitters) was installed across the lysimeter for irrigation, and three cucumbers were cultivated in each tank. The five lysimeters were weighed at 8:00 every day in 2003 and 2005, and every 2 days in 2004. 2.6.3. Weather data Meteorological measurements, such as precipitation, air temperature, relative humidity, solar radiation, and wind speed were recorded by automatic instruments in the experimental station. A 0.2-m diameter evaporation pan was installed over the canopy of cucumbers in the middle of the experiment field when cucumber seeds were sown. The starting height of the evaporation pan was 0.05 m above the ground and adjusted according to the growth of cucumber. The pan reached the highest height of 1.75, 1.35 and 1.50 m above the ground about 60 DAS in the 3 years. The pan was kept at this height till the harvest of cucumber. Pan evaporation (EW20 ) was measured at 8:00 daily. 2.6.4. Soil salinity Soil samples for each treatment were obtained from soil cores extracted between rows with an auger (0.025 m in diameter and 0.1 m high). In 2003, soil samples were taken before field ploughing (May 1), before treatment (May 27, 23 DAS) and at the end of the experiment (August 5, 93 DAS). The distances to drip tapes from the sample locations were 0, 17.5, 35, and 70 cm, and sample depths were 0–2, 2–10, 10–20, 20–40, 40–60 and 60–90 cm depth. In 2005, soil samples were also taken before field ploughing (April 11), before treatment (May 20, 20 DAS) and at the end of the experiment (August 15, 107 DAS). The distances to drip tapes from the sample locations were 0, 7, 14, 21, 28, 35, 42, 49, 56, 63 and 70 cm, and sample depths were the same as before. All soil samples were air-dried and sieved through a 2 mm sieve. The EC values were based on soil: water 1:5 extracts (EC1:5 , on a volume basis), and were determined using a conductivity meter. After the experiment, the relationships between ECe and EC1:5 were determined according to the Agriculture Handbook No. 60 (U.S. Salinity Laboratory Staff, 1954) and were used to convert EC1:5 to ECe for all samples. For different soil textures, the relationships were different for different depths: At 0–60 cm depths :
ECe = 14.77 × EC1:5
At 60–90 cm depths :
ECe = 9.55 × EC1:5
(R2 = 0.90) 2
(R = 0.92)
(3) (4)
2.6.5. Yield Harvest started on June 20 (47 DAS), June 29 (46 DAS), and June 27 (58 DAS), finished on August 4 (92 DAS), August 13 (91 DAS) and August 6 (98 DAS), and lasted 45, 45 and 40 days in 2003, 2004 and 2005, respectively. Fruits were picked by hand at 2 to 4 days intervals. The fruit number and the total fruit mass per plot were measured at each time. 2.7. Statistical analysis Analysis of variance (ANOVA) was conducted and significance of differences among treatment was tested using the least signif-
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icant difference (LSD). Differences were declared significant at P < 0.05. 3. Results and discussion 3.1. Weather Mean weekly temperatures during the whole cucumbergrowing period were 23.1, 23.5 and 23.1 ◦ C in 2003, 2004 and 2005, respectively. But mean temperature in the 2nd week in 2005 (14.5 ◦ C) was obviously lower than those in 2003 (18.2 ◦ C) and 2004 (20.6 ◦ C). Total rainfall during the experiment period was 180.6, 323.5 and 292.4 mm, and the distribution was 8, 18, and 19% in cucumber seedling establishment stage (in the first 4–5 weeks), 53, 43 and 15 in the flowering stage (about 3 weeks) and 39, 39 and 66% in the harvest stage in 2003, 2004 and 2005, respectively. Total pan evaporation (EW20 ) was 494.7, 455.2, and 575.2 mm, and the ratio of seasonal evaporation to rainfall was 2.7, 1.4 and 2.0 in 2003, 2004 and 2005, respectively. 3.2. Irrigation Prior to treatments initiation, only fresh water was applied and the irrigation depth was 57.0, 25.3 and 63.4 mm in 2003, 2004 and 2005, respectively. In 2004, much less fresh water was applied, because the mulches covered before seeds sowing. Whereas in 2005, more fresh water was applied in order to aid the cucumber seedling survival during the bad weather. Irrigation times and depths in 2004 and 2005 were less compared with those in 2003, because rainfall was less in 2003 than in the other years. In the 3 years, especially in 2003, the irrigation depths and times were reduced when saline water was applied. The higher ECiw was, the less irrigation times and depths were (Table 3). In 2003, the seasonal irrigation times and depths for 4.2 dS/m treatment were only 40 and 68% of the values for 1.1 dS/m treatment. 3.3. Soil matric potential (SMP) Fig. 1 illustrates the spatial distributions of SMP in the vertical transect perpendicular to the drip tape for each treatment at early and later growing stages in 2003. On June 5 (32 DAS) 2003, there was a tendency for SMP to increase gradually from about −20 to −12 kPa as soil depths increased. On June 6, 1 day after a uniform
irrigation of 6.3 mm, there was a wetted zone within 40 and 35 cm respectively away from emitter in vertical and horizontal direction for all treatments. Average SMP values near emitter rose to −16 kPa or higher, whereas those outside the wetted zone were almost kept unchanged. On July 20 (77 DAS), the wetting patterns were similar for all treatments. Average SMP values were around −25 kPa in the wetted zone, and were around −35 kPa in the surface layer between the beds. This day, a tank of water was applied for each treatment in the morning, and 17.4 mm rain fell in the afternoon. On July 21, average SMP values at depths of 0–40 cm increased drastically to −19 kPa or higher, and those below 60 cm depth were almost kept unchanged. Because of the relatively more humid weather in 2004 and 2005, it can be inferred that the soil moisture conditions in 2004 and 2005 were wetter than that in 2003.
3.4. Cucumber yield Fruit number per plant and cucumber yield under different treatments are presented in Table 4. Average total yield of the five treatments in 2003 was 113.0 Mg/ha, about 2.7 and 4.3 times of that in 2004 and 2005, respectively. Cucumbers are quite sensitive to oxygen deficiency in the soil, waterlogging for hours or days will do great harm to the growth of cucumbers. The relatively low yield in 2004 and 2005 can be attributed to waterlogging during the middle and later growing periods. Besides, bad weather at the seedling stage in 2005 may have negative effect on the development of cucumbers, and resulted in low yield. Statistical analysis showed a significant (P < 0.05) effect of ECiw on fruit number and yield in 2003 and 2005, and both of them decreased as ECiw increased. But in 2004, there was no significant difference, for less saline water was applied. Relative yield (Yr ) and relative fruit number per plant (Nr ) responding to ECiw are presented in Fig. 2. The relationship between the correlated magnitudes was quite linear, and same slope coefficients can be distinguished. Yr and Nr decreased 5.7% per unit increase in ECiw . The maximum yield loss was about 25% for ECiw of 4.9 dS/m, compared to 1.1 dS/m. In the experiment, the major contribution to total yield reduction under saline condition was fruit number. This is in accordance with the results of Sonneveld and Voogt (1978), Jones et al. (1989), and Chartzoulakis (1992). They suggested that the differences in cucumber yield among different saline treatments were mainly
Table 3 The irrigation times and water depths for each treatment during cucumber-growing period in 2003, 2004 and 2005. Years
Treatments
Seasonal water depths (mm)
Fresh water for seedlings (mm)
During treatment
Irrigation times
Water depths (mm)
2003
1.1 2.2 2.9 3.5 4.2
177.7 161.1 157.5 146.4 120.4
57.0 57.0 57.0 57.0 57.0
25 20 18 15 10
120.7 104.1 100.5 89.4 63.4
2004
1.1 2.2 2.9 3.5 4.2
49.5 51.4 53.3 49.2 44.4
25.4 25.4 25.4 25.4 25.4
5 5 5 4 3
24.1 26.0 27.9 23.8 19.0
2005
1.1 2.3 3.5 4.2 4.9
106.8 94.6 96.9 99.1 101.4
63.4 63.4 63.4 63.4 63.4
9 6 6 6 6
43.4 31.2 33.5 35.7 38.0
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Fig. 1. The spatial distributions of soil matric potential in the vertical transect perpendicular to the drip tape for each treatment at early and later growing stages in 2003.
reflected in fruit number, and less in a low fruit weight. This is mainly because of the time of cucumber fruit picking. Generally, cucumber fruits are picked at 8–10 days after bloom or when they have reached a certain size. 3.5. Cucumber water use consumption Fig. 3 demonstrates 10-day water use for all treatments during the whole cucumber-growing season and corresponding 10-day 20 cm pan evaporation (EW20 ). The temporal patterns of 10-day water use variations were similar for different treatments. In the first 3 or 4 weeks (during cucumber seeding and seedling stages), cucumber 10-day water use for all treatments was low, and obviously lower than the corresponding EW20 values. The 10-day water use of the five treatments in the 3 years was no more than 20 mm, which meant that the average water use of cucumber was no more than 2 mm per day during seeding and seedling stages.
Cucumber water use increased gradually and reached its maximum values in the early harvest stage, the 5th 10-day in 2003 and 2004, and the 7 the 10-day in 2005. The maximal values for each treatment with ECiw from low to high were 51.7, 53.3, 43.7, 53.6 and 38.0 mm in 2003, 43.9, 46.2, 44.9, 39.8, and 39.9 mm in 2004, and 35.4, 26.9, 22.8, 25.0 and 24.7 mm in 2005, respectively. There was a decreasing tendency for cucumber water use with the increase of ECiw , and the maximal daily water use of cucumber was no more than 5.4 mm. Cucumber water use began to decrease gradually from the middle harvest stage. At the last 2–3 weeks, the 10-day water use was no more than 20 mm, which meant that average daily water use of cucumber was less than 2 mm in the late growing season. Seasonal accumulative cucumber water use for different treatments is listed in Table 4. Cucumber seasonal accumulative water use decreased with the increase of ECiw , and every 1 dS/m increase in ECiw resulted in 6.9, 1.5 and 4.4% decrease of seasonal accumulative water use in 2003, 2004 and 2005, respectively.
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Table 4 Fruit number per plant, yield, seasonal water use, water use efficiency and irrigation water use efficiency for different treatments in 2003, 2004 and 2005.
a b
Year
Treatment (dS/m)
ECe (dS/m)a
Fruit number per plant
Total yield (Mg/ha)
Seasonal water use (mm)
Water use efficiency (Mg/ha/mm)
Irrigation water use efficiency (Mg/ha/mm)
2003
1.1 2.2 2.9 3.5 4.2
3.2 3.3 3.8 4.4 4.3
20.9a 19.2b 18.3bc 17.3cd 16.7d
128.9ab 120.1ab 108.4bc 104.8bc 103.1c
230.4 213.2 208.9 198.0 177.4
0.56 0.56 0.52 0.53 0.58
0.73 0.75 0.69 0.72 0.86
2004
1.1 2.2 2.9 3.5 4.2
7.9a 7.8a 7.3a 7.3a 7.0a
45.8a 42.3a 41.2a 41.5a 40.0a
166.5 166.0 161.4 161.9 159.0
0.28 0.25 0.26 0.26 0.25
0.93 0.82 0.77 0.84 0.90
2005
1.1 2.3 3.5 4.2 4.9
5.7a 5.2ab 5.0ab 4.5b 4.6b
30.9a 27.0ab 26.0b 24.3b 24.2b
186.1 181.1 181.2 167.0 150.8
0.17 0.15 0.14 0.15 0.16
0.29 0.29 0.27 0.25 0.24
3.0 3.4 3.8 4.3 4.3
ECe means the average electrical conductivity of saturated paste extract within rooting depth integrated over time. The same letters are not significantly different at 0.05 level, and different letters mean significant difference at 0.05 level.
3.6. ECe 3.6.1. ECe in the soil profile Figs. 4 and 5A–C demonstrates the spatial distributions of ECe in the vertical transect perpendicular to the drip tape for each treatment before ploughing, before treatment and at the end of the experiment in 2003 and 2005, respectively. Before ploughing in 2003, there was a tendency for ECe to decrease as soil depths increased, and the average ECe values were 7.1, 4.8, 2.9 and 2.1 dS/m in 0–2, 2–10, 10–40 soil layers and below 40 cm depths, respectively (Fig. 4A). The ECe values were high in 0–10 cm depths, especially in 0–2 cm soil layer. Because only fresh water was applied during the seeding and seedling stages, there was an obvious low ECe zone within about 10 cm distance from the drip emitter at 0–10 cm depth, and the average ECe value was 2.7 dS/m, reduced by 63% compared to the original value. The highest salt concentration occurred in the ridge of the bed, with the average ECe value of 14.2 dS/m, increased by 58% compared to the original value (Fig. 4B). The average ECe value in
Fig. 2. Relative cucumber yield and fruit number per plant response to ECiw (electrical conductivity of irrigation water).
Fig. 3. 10-day water use curves for different treatments and the corresponding 10day evaporation curve during the whole cucumber-growing period in 2003, 2004 and 2005.
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Fig. 4. The spatial distributions of ECe (electrical conductivity of saturated paste extract) in the vertical transect perpendicular to the drip tape before field ploughing (A), before treatment (B), and at the end of the experiment (C) in 2003.
Fig. 5. The spatial distributions of ECe (electrical conductivity of saturated paste extract) in the vertical transect perpendicular to the drip tape before field ploughing (A), before treatment (B), and at the end of the experiment (C) in 2005.
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the soil profile (0–90 cm depths) were 3.2 dS/m, equal to the value before field ploughing. Due to the frequent irrigation and rainfall, salt leaching occurred in the growing season for each treatment. The ECe value decreased obviously in 0–40 soil layers, whereas no obvious change could be observed below 40 cm depths. The average ECe values in the whole soil profile for 1.1, 2.2, 2.9, 3.5 and 4.2 dS/m treatment were 2.6, 2.7, 2.9, 3.6 and 2.5 dS/m at the end of the experiment, lower than the original value, except for 3.5 dS/m treatment, which may be the result of spatial variability (Fig. 4C). Before field was ploughed in 2005, average ECe values for 4.2 dS/m treatment were 12.5, 4.1, 2.8 and 2.1 dS/m in 0–2, 2–10, 10–40 soil layers and below 40 cm depths, respectively (Fig. 5A). Evaporation in late winter and early spring resulted in salts built up in 0–10 cm depths, especially in 0–2 cm soil layer. Compared to the original value in 2003, no obvious change in ECe was found below 40 cm depths. Similarly, before saline water was applied, an obvious low ECe zone was found within about 15 cm distance from the drip emitter at 0–10 cm depth and the highest ECe zone was in the ridge of the bed. Compared to the value before ploughing in 2005, the average ECe value was 4.4 dS/m in the low ECe zone, reduced by 44%, and was 15.0 dS/m in the ridge of the bed, increased by 67% (Fig. 4B) The average ECe of the whole soil profile of 0–90 cm depths was 3.8 dS/m, similar to the value before ploughing in 2005(3.6 dS/m). At the end of the experiment, because the black polyethylene mulches had been already removed when soil samples were taken, some salts accumulated in 0–2 cm soil layer. After 3 years of saline water irrigation, the average ECe in the whole soil profile (0–90 cm) were 2.3, 2.8, 2.9, 2.6 and 3.2 dS/m for 1.1, 2.2, 3.5, 4.2 and 4.9 dS/m, respectively (Fig. 5C). 3.6.2. Average ECe within the root zone (ECe ) Under drip irrigation system, active root water uptake of plants was concentrated mainly within 40 cm depth (Chartzoulakis and Michelakis, 1990; Bassoi et al., 2003; Kang and Wan, 2005; Wan and Kang, 2006; Wang et al., 2007). In this experiment, ECe within the root zone were integrated to take account of both spatial and temporal variation, and was calculated in the soil about 40 cm horizontally to the center of raised beds at the depth of 0–40 cm (Table 4). Relative yield (Yr ) and relative water use (WUr ) responding to ECe in the root zone are presented in Fig. 6. Yr and WUr decreased 10.8 and 9.0% for 1 dS/m increase in ECe . According to Maas and Hoffman (1977), crop salt tolerance could be expressed as the following equation: Yr = 100 − Yd (ECe − ECt )
(5)
where Yr is relative crop yield (actual yield at the given salinity level divided by yield with no salinity effect), ECe represents the average root zone salinity (electrical conductivity of saturated paste extract, dS/m), ECt represents the threshold salinity level (the maximum allowable salinity that does not reduce yield measurably below that of a non-saline condition, dS/m), and Yd is the yield decrease per unit of salinity increase beyond the threshold. In order to compare the results with the work of other researchers, the equations in Fig. 6 were expressed as the Maas–Hoffman equation form: Yr = 100–10.8 × (ECe − 2.4) WUr = 100–9.0 × (ECe − 2.8)
2
(R = 0.85) 2
(R = 0.61)
(6) (7)
It can be inferred from the about two equations that Yr and WUr began to decline when the ECe in the root zone above the threshold value of 2.4 dS/m and 2.8 dS/m, respectively.
Fig. 6. Relative cucumber yield and season water use response to average ECe (electrical conductivity of saturated paste extract) in the root zone.
According to Maas and Hoffman (1977), cucumber fruit yield decreased by 13% for each unit of ECe increase in the root zone above 2.5 dS/m. Compared with their results, the threshold value of ECe was very close to that of Maas and Hoffman (1977) in spite of a lower slope value. Allen et al. (1998) reported the ECe threshold between 1.1 and 2.5 dS/m and the slope between 7 and 13% for cucumber based on climate, soil conditions and cultural practice. The ECe threshold and slope values in this experiment were between reported values of Allen et al. (1998). 3.7. Cucumber water use efficiency (WUE) and irrigation water efficiency (IWUE) In this study, water use efficiency (Mg/ha/mm) is defined as the ratio of cucumber yield (Mg/ha) to seasonal accumulative water use consumption (mm), and irrigation water use efficiency is computed based on cucumber yield dividing by the total irrigation water. The average WUE values were 0.55, 0.26 and 0.15 Mg/ha/mm, and average IWUE values were 0.75, 0.85 and 0.27 Mg/ha/mm in 2003, 2004 and 2005, respectively (Table 4). The relationships between WUE/IWUE and ECiw /ECe in the 3 years were not clear. This is not in agreement with the findings by Katerji et al. (2003). They pointed out that the tolerant crops show more or less constant water use efficiency, and the sensitive crops show a decrease of water use efficiency with increasing salinity, for the yield of sensitive crops decreases stronger than the evapotranspiration. The difference can partly be attributed to different agronomy, water and soil management strategies. 4. Summary and conclusions In the 3-year open field experiment in North China, a semihumid area, saline water (EC ≤ 4.9 dS/m) was applied to irrigate cucumber with mulched drip irrigation after seedling stage. It can be known when the SMP at 0.2 m depth immediately under emitter was kept higher than −20 kPa throughout cucumber-growing season, a favorable soil moisture condition (ranging from −15 to −25 kPa) was maintained for the whole growing period in the root zone (within 40 cm away from emitter and 40 cm depths). Due
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to the soil evaporation, salts accumulated in the upper 0–10 cm soil layer, especially in 0–2 cm soil layer in non-growing season. A relatively low ECe zone gained in the root zone in the growing season for the periodic salt leaching by frequent irrigation and rainfall. Cucumber fruit number per plant and yield decreased by 5.7% for 1 dS/m increase of ECiw , and yield decreases were mainly reflected in fruit number. The maximal daily water use of cucumber was no more than 5.4 mm, and seasonal water use decreased linearly by 1.5–6.9% with increasing of ECiw in the 3 years. As to the mean soil salinity within the root zone, cucumber yield and water use decreased by 10.8 and 10.3% for each unit of ECe increase in the root zone. So in North China, or similar semi-humid areas, where there is no enough fresh water for irrigation, saline water up to 4.9 dS/m can be applied to irrigate field culture cucumbers after adopting some appropriate management strategies. The main strategies include adopting drip irrigation with black polyethylene mulch, keeping the SMP at 0.2 m depth immediately under drip emitter higher than −20 kPa throughout growing season. In this way, it can not only save valuable fresh water, but also reduce numbers of irrigations and total amount of water applied. The highest cucumber yield loss is about 25% compared to fresh water irrigation, and soil salinity does not increase in the soil profile of 0–90 cm depths. The conclusions in this study were based on only 3-year data. To assess the sustainability of saline water irrigation in North China, additional research is needed. Acknowledgements This study was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences, Grant No. (KSCX2-YW-N003), the Action Plan for the Development of Western China of the Chinese Academy of Sciences Grant No. (KZCX2-XB2-13), the Key Technologies R&D program (06YFGZNC00100) supported by Tianjin Municipal Science and Technology Commission, and the Project for 100 Outstanding Young Scientists supported by Chinese Academy of Sciences.
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References Al-Harbi, A.R., 1994a. Influence of salinity on the growth and nutrient composition of cucumber plants (Cucumis sativus L.). J. King Saud. Univ. Agric. Sci. 6, 263–271. Al-Harbi, A.R., 1994b. Effect of manipulating nutrient solution salinity on the growth of cucumber (Cucumis sativus L.) grown in NFT. Acta Hort. 361, 267–273. Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. In: FAO Irrigation and Drainage Paper 56, FAO, United Nations, Rome. Bassoi, L.H., Hopmans, J.W., De Jorge, L.A.C., De Alencar, C.M., E Silva, J.A.M., 2003. Grapevine root distribution in drip and microsprinkler irrigation. Sci. Agric. 60, 377–387. Chartzoulakis, K., Michelakis, N., 1990. Effects of different irrigation systems on root growth and yield of greenhouse cucumber. Acta Hort. 278, 237–243. Chartzoulakis, K.S., 1992. Effects of NaCl salinity on germination, growth and yield of greenhouse cucumber. J. Hort. Sci. 67, 115–119. Chen, M., Kang, Y., Wan, S., Liu, S.P., 2009. Drip irrigation with saline water for oleic sunflower (Helianthus annuus L.). Agric. Water Manage. 96, 1766–1772. Ho, L.C., Adams, P., 1994. Regulation of the partitioning of dry matter and calcium in cucumber in relation to fruit growth and salinity. Ann. Bot. 73, 539–545. Jones, R.W., Pike, L.M., Yourman, L.F., 1989. Salinity influences cucumber growth and yield. J. Am. Soc. Hort. Sci. 114, 547–551. Kang, Y., Wan, S., 2005. Effect of soil water potential on radish (Raphanus sativus L.) growth and water use under drip irrigation. Sci. Hort. 106, 275–292. Katerji, N., Van Hoorn, J.W., Hamdy, A., Mastrorilli, M., 2003. Salinity effect on crop development and yield, analysis of salt tolerance according to several classification methods. Agric. Water Manage. 62, 37–66. Maas, E.V., Hoffman, G.J., 1977. Crop salt tolerance-current assessment. J. Irrig. Drain. Div. ASCE 103, 115–134. Oster, J.D., 1994. Irrigation with poor quality water. Agric. Water Manage. 25, 271–297. Rhoades, J.D., Kandiah, A., Mashali, A.M., 1992. The use of saline waters for crop production. In: FAO Irrigation and Drainage Paper 48, FAO, United Nations, Rome. Shalhevet, J., 1994. Using water of marginal quality for crop production: major issues. Agric. Water Manage. 25, 233–269. Sonneveld, C., Voogt, S.J., 1978. Effects of saline irrigation water on glasshouse cucumbers. Plant Soil 49, 595–606. USDA-NRCS, 1987. National Engineering Handbook, Irrigation Section 15, Chapter 7, Trickle Irrigation. US Department of Agriculture, Natural Resource and Conservation Service, Washington, DC. U.S. Salinity Laboratory Staff, 1954. Diagnosis and Improvement of Saline and Alkali Soils. Agriculture Handbook No. 60. Washington, DC, US Department of Agriculture, Agricultural Research Service. Wan, S., Kang, Y., 2006. Effect of drip irrigation frequency on radish (Raphanus sativus L.) growth and water use. Irrig. Sci. 24, 161–174. Wan., S., Kang, Y., Wang, D., Liu, S.P., Feng, L.P., 2007. Effect of drip irrigation with saline water on tomato (Lycopersicon esculentum Mill) yield and water use in semi-humid area. Agric. Water Manage. 90, 63–74. Wang, F.X., Kang, Y., Liu, S.P., Hou, X.Y., 2007. Effects of soil matric potential on potato growth under drip irrigation in the North China plain. Agric. Water Manage. 88, 34–42.
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Effect of saline water on cucumber (Cucumis sativus L.) yield and water use under drip irrigation in North China Shuqin Wan a , Yaohu Kang a,∗ , Dan Wang b , Shi-ping Liu a a Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographical Sciences and Natural Resource Research, Chinese Academy of Sciences, 11A, Datun Road, Chaoyang District, Beijing 100101, China b Beijing Xinhua Water Saving Products Certification Co. LTD, 10, Nanxiange, Xuanwu District, Beijing 100053, China
a r t i c l e
i n f o
Article history: Received 18 March 2010 Accepted 6 August 2010
Keywords: Cucumber Drip irrigation Saline water irrigation Management strategy
a b s t r a c t Saline water has been included as an important substitutable resource for fresh water in agricultural irrigation in many fresh water scarce regions. In order to make good use of saline water for agricultural irrigation in North China, a semi-humid area, a 3-year field experiment was carried out to study the possibility of using saline water for supplement irrigation of cucumber. Saline water was applied via mulched drip irrigation. The average electrical conductivity of irrigation water (ECiw ) was 1.1, 2.2, 2.9, 3.5 and 4.2 dS/m in 2003 and 2004, and 1.1, 2.2, 3.5, 4.2 and 4.9 dS/m in 2005. Throughout cucumber-growing season, the soil matric potential at 0.2 m depth immediately under drip emitter was kept higher than −20 kPa and saline water was applied after cucumber seedling stage. The experimental results revealed that cucumber fruit number per plant and yield decreased by 5.7% per unit increase in ECiw . The maximum yield loss was around 25% for ECiw of 4.9 dS/m, compared with 1.1 dS/m. Cucumber seasonal accumulative water use decreased linearly over the range of 1.5–6.9% per unit increase in ECiw . As to the average root zone ECe (electrical conductivity of saturated paste extract), cucumber yield and water use decreased by 10.8 and 10.3% for each unit of ECe increase in the root zone (within 40 cm away from emitter and 40 cm depths), respectively. After 3 years irrigation with saline water, there was no obvious tendency for ECe to increase in the soil profile of 0–90 cm depths. So in North China, or similar semi-humid area, when there is no enough fresh water for irrigation, saline water up to 4.9 dS/m can be used to irrigate field culture cucumbers at the expense of some yield loss. © 2010 Published by Elsevier B.V.
1. Introduction The availability of fresh water for agricultural use is declining in many areas of the world due to the increasing water needs of industries and municipalities. Thus, agriculture faces challenges of using low quality wastewater and saline water for crop production. Many studies indicate that these water resources traditionally classified as unsuitable for irrigation can be used successfully to grow crops without long-term hazardous consequences to crops and soils if proper management strategies are established. These strategies include adopting advanced irrigation technology, selecting appropriately salt-tolerant crops, leaching salts below the crop root zone (Rhoades et al., 1992; Oster, 1994; Shalhevet, 1994). In China, especially in North China, the increasing water shortages make it urgent to develop safe and efficient management of saline water resource for agricultural irrigation.
∗ Corresponding author. Tel.: +86 10 64856516; fax: +86 10 64856516. E-mail address: [email protected] (Y. Kang). 0378-3774/$ – see front matter © 2010 Published by Elsevier B.V. doi:10.1016/j.agwat.2010.08.003
Saline water has been successfully used to irrigate field-grown tomato and oleic sunflower in North China in recent years (Wan et al., 2007; Chen et al., 2009). It was found that when several management strategies were adopted, saline water up to 4.9 dS/m and 10.9 dS/m can be applied respectively to irrigate tomato and oleic sunflower without obviously negative effects on the yields and soil salinity. The main management strategies include applying saline water with mulched drip irrigation, keeping the soil matric potential (SMP) at 0.2 m depth immediately under emitter higher than −20 kPa throughout the growing season. Cucumber (Cucumis sativus L.) is one of the most popular and widely grown vegetable crops in the world, and is considered moderately sensitive to salt stress, since it can tolerate an ECe (electrical conductivity of saturated paste extract) of about 2.5 dS/m and fruit yield decrease by 13% with each unit of ECe increasing above the threshold value (Maas and Hoffman, 1977). The responses of cucumber to saline water irrigation were recorded by some investigators. Sonneveld and Voogt (1978) indicated when the electrical conductivity of irrigation water (ECiw ) ranged from 0.1 to 4.5 dS/m, greenhouse cucumber yields decreased linearly as ECiw increased, and the yield reduction was about 17% per unit increase
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in ECiw. Jones et al. (1989) found that ECiw of 4.0 dS/m significantly decreased cucumber yield. Chartzoulakis (1992) reported cucumber (cv. Pepinex) growth reduced significantly when the ECiw was higher than 1.2 dS/m, and the relative yield reduced by 16% per unit increase in ECiw above 1.3 dS/m. Al-Harbi indicated that cucumber (cv. Farbiola) was able to tolerate nutrient solution with ECiw higher than 4.5 dS/m without a significant reduction in yield (AlHarbi, 1994a), and high ECiw had a greater effect during the day than during the night due to its effect on cucumber water uptake (Al-Harbi, 1994b). Ho and Adams (1994) demonstrated that dry weight of cucumber (cv. Corona) fruit was not affected until the ECiw was higher than 5.5 dS/m, and the reduction was 9% for each unit of ECiw increasing between 5.5 and 8 dS/m. All of these mentioned studies were performed in greenhouse or in hydroponics cultures, which are relatively well controlled growing conditions. In North China, cucumbers are often planted in open field in early spring or later summer, and supplemental irrigation is essential. In open field, rainfall may contribute a substantial amount of water to crop need, and reduce the need of irrigation water required for salt leaching. The objectives of the study were (1) to study the responses of open cultivated cucumber to saline water irrigation, and explore the possibility of using saline water for supplement irrigation of cucumber in North China; and (2) to optimize saline water irrigation management strategies to maintain cucumber productivity and the salt balance in the soil.
Cangzhou area, one of the largest areas with moderately saline water (2–5 dS/m) resource in North China. The average ECiw were 2.2, 2.9, 3.5 and 4.2 dS/m in 2003 and 2004, and were 2.2, 3.5, 4.2 and 4.9 dS/m in 2005, respectively. Ionic composition for local groundwater and saline water in this trial is listed in Table 1. All of the treatments were replicated three times following a completely randomized design. The locations of the treatments at the experimental site was kept unchanged each year, in order to observe accumulative salinity hazards on crop and soil. 2.3. Agronomic practices Each plot consisted of three raised beds, with a width of 1.4 m between bed centers. The beds were 0.6 m wide, 4.4 m long and 0.15 m high. The area of each plot was 18.48 m2 . Every treatment plot was a gravity drip system. In the front of each plot, a tank, with volume about 120 L, was installed at a 1 m level. Drip tube (Xinjiang Tianye Co.) with 0.2 m emitter spacing and a flow rate of 3.0 L/h at the operating pressure of 0.1 MPa was placed on the center of each raised bed. Under this gravity drip irrigation system, the actual operating pressure was between 0.012 and 0.017 MPa, and the actual flow rate was about 0.9 L/h. Cucumber (C. sativus L.) seeds cv. ‘zhongnong’ were used in the 3 years. The seeds were sown in the field on May 4, May 14 and April 30 in 2003, 2004 and 2005, respectively. Double row plantings (in a zigzag) spaced 0.3 m apart per bed and interplant spacing was 0.4 m. About three weeks later, cucumber seedlings were thinned to leave only one seedling at each location maintaining a plant density of approximate 35,720 plants/ha. Cucumbers were allowed to grow naturally without pruning. Plant protection was needed each year, and disease control and pest management were the same for all treatments. Black polyethylene mulches (1.2 m wide by 0.08 mm thick) were applied over the beds on May 31 (27 days after sowing: DAS), May 12 (2 days before sowing), and June 2 (33 DAS) in 2003, 2004 and 2005, respectively. Because rainfall helps wash the soluble salts out of the soil profile, the polyethylene mulches were removed after each growing season.
2. Methods and materials 2.1. Experimental site A 3-year (2003–2005) field experiment was conducted at Tongzhou Experimental Station for Water Cycle and Modern Water-saving Irrigation Research, Institute of Geographic Science and Natural Resource Research. The Station (latitude: 39◦ 36 N; longitude: 116◦ 48 E; 20 m above sea level) is located in the southeast region of Beijing, about 60 km away from Beijing city. It is a temperate semi-humid monsoon climate, with mean annual temperature 11.3 ◦ C and mean annual global radiation 5.24 GJ/m2 . Average annual precipitation is 620 mm, with 80% concentrated during the July-September period. The dominant soil in the experiment was a silt loam. In 0–30 cm plow layer, its average bulk density was 1.35 g/cm3 , and soil organic matter content was about 1.3%.
2.4. Irrigation During cucumber-growing periods in the 3 years, irrigation was applied only when the SMP at 0.2 m depth immediately under drip emitter was close to −20 kPa, except at seeding stage. In order to ensure plants grow normally, fresh water was applied immediately after seeding and during the cucumber seedling stage (0–35 days after seeding). The treatment was initiated at the end of seedling stage, which was on June 7 (34 DAS), June 15 (32 DAS), and June 16 (47 DAS) in 2003, 2004 and 2005, respectively. In 2005, treatments were delayed about 10 days because of prolonged seedling period due to bad weather on seeding days.
2.2. Experimental design The experiment consisted of a control treatment and four saline water treatments. The control treatment was local groundwater (fresh water) with an ECiw of 1.1 dS/m. Artificial saline water were produced by adding NaHCO3 , Na2 SO4 , MgSO4 , MgCl2 and CaCl2 to local groundwater in molar proportion of 0.50:0.05:0.25:0.10:0.10, which is similar to the ionic compositions of the aquifer in Table 1 Ionic composition of local groundwater and saline water in 2003, 2004 and 2005. ECiw a (dS/m)
CO3 1.1 2.2 2.9 3.5 4.2 4.9 a b
SARb
Ionic concentration (mmol/L)
0.4 0.4 0.4 0.4 0.4 0.4
2−
HCO3 6 10.8 13.8 17.7 19.4 23.1
−
−
Cl
SO4
2.7 6.0 9.2 13.0 13.8 17.1
1.7 5.0 5.8 6.4 8.5 9.8
ECiw means the average electrical conductivity of the irrigation water. SAR means sodium adsorption ratio.
2−
2+
2+
+
+
Ca
Mg
K
Na
0.6 1.0 2.2 1.2 2.0 2.3
4 5.0 7.2 8.3 8.1 9.8
0.7 2.6 3.4 4.3 5.4 6.4
2.7 10.5 13.5 17.3 21.5 25.7
1.3 4.3 4.4 5.7 6.8 7.4
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When saline water was applied, surplus water was added to provide a leaching fraction. According to NRCS National Engineering Handbook (section 15) (USDA-NRCS, 1987), the leaching requirement ratio (LRt ) for high-frequency, daily or alternate-day irrigation can be calculated by the following equations: LRt = Fg =
ECiw 2(max ECe )
(1)
Fn 1.0 − LRt
(2)
where LRt is the leaching requirement ratio, ECiw is the electrical conductivity of the irrigation water (dS/m), ECe is the electrical conductivity of the saturated paste extract (dS/m), max ECe is the theoretical level of salinity that would reduce yield to zero (dS/m), max ECe value for cucumber is 10 dS/m, Fn is the net water requirement per irrigation (mm), and Fg is the gross water application per irrigation (mm). The applied water per irrigation for the control treatment (1.1 dS/m) was designed as 4.8 mm, that is, Fn was 4.8 mm. Because the tanks were made in advance, there was a deviation between actual volume (actual Fg ) and desired volume (desired Fg ) for each treatment. The calculated LRt , desired Fg and actual Fg for each treatments are listed in Table 2. 2.5. Fertilizer According to local farmer’s practice, about 37.5 m3 /ha wellrotted cow manure (N–P–K: 0.25–0.32:0.15–0.21:0.16–0.25) was uniformly applied to all plots before the field was ploughed in 2003. Several days later, 300 kg/ha compound fertilizers (diammonium phosphate, N–P–K: 18–46–0) were uniformly applied to the plots when the soil was bedded. In 2004 and 2005, about 600 kg/ha diammonium phosphate (N–P–K: 18–46–0) was applied. After the treatments began and until harvest, about 50 mL of fertilizer solution (30 wt.% urea solution) was added to the tank (120 L) at each irrigation event for each treatment. During the whole growing season, the total amount of urea applied with irrigation was about 270 kg/ha (125 kg/ha N) for each treatment. 2.6. Observation and equipments 2.6.1. Soil matric potential (SMP) Thirty mercurial tensiometers were installed in each treatment to measure spatial distribution of SMP. The sensor placement was same for all treatments. There were six tensiometers at depths of (10, 20, 30, 50, 70 and 90 cm) installed at five horizontal distances (0, 17.5, 35, 52.5 and 70 cm) from the drip line. Observations were made daily at 8:00. In order to determine the schedule of irrigation, one tensiometer with a vacuum gauge was installed at 0.2 m depth immediately under drip emitter for each treatment. These tensiometers were observed four times at 8:00, 11:00, 14:00 and 17:00 every day.
Table 2 The calculated LRt , desired Fg and actual Fg for each treatment.
a b
ECiw (dS/m)
Calculated LRt a
Desired Fg b (mm)
Actual Fg (mm)
1.1 2.2 2.9 3.5 4.2 4.9
0.00 0.11 0.15 0.18 0.21 0.25
4.8 5.4 5.6 5.8 6.1 6.4
4.8 5.2 5.6 6.0 6.3 6.3
LRt is the leaching requirement ratio. Fg is the gross water application per irrigation (mm).
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2.6.2. Cucumber water use For each treatment, one weighing lysimeter was installed in the center of the plot to measure cucumber water use. Each lysimeter consisted of an inner tank for crop cultivation and an outer tank for protection and drainage reservoir. The volume of the inner tank was 0.36 m3 (0.8 m × 0.5 m × 0.9 m), and a layer of coarse sand and gravel, 0.2 m thick, was overlain by a repacked soil profile of 0.7 m. The topsoil of the inner tank was shaped to the same form as field bed, and at the bottom of the inner tank, a pipe serving as a drainage outlet connected the inner tank to the outer tank. The lysimeters were also mulched with black polyethylene as the field. Drip tape (including three emitters) was installed across the lysimeter for irrigation, and three cucumbers were cultivated in each tank. The five lysimeters were weighed at 8:00 every day in 2003 and 2005, and every 2 days in 2004. 2.6.3. Weather data Meteorological measurements, such as precipitation, air temperature, relative humidity, solar radiation, and wind speed were recorded by automatic instruments in the experimental station. A 0.2-m diameter evaporation pan was installed over the canopy of cucumbers in the middle of the experiment field when cucumber seeds were sown. The starting height of the evaporation pan was 0.05 m above the ground and adjusted according to the growth of cucumber. The pan reached the highest height of 1.75, 1.35 and 1.50 m above the ground about 60 DAS in the 3 years. The pan was kept at this height till the harvest of cucumber. Pan evaporation (EW20 ) was measured at 8:00 daily. 2.6.4. Soil salinity Soil samples for each treatment were obtained from soil cores extracted between rows with an auger (0.025 m in diameter and 0.1 m high). In 2003, soil samples were taken before field ploughing (May 1), before treatment (May 27, 23 DAS) and at the end of the experiment (August 5, 93 DAS). The distances to drip tapes from the sample locations were 0, 17.5, 35, and 70 cm, and sample depths were 0–2, 2–10, 10–20, 20–40, 40–60 and 60–90 cm depth. In 2005, soil samples were also taken before field ploughing (April 11), before treatment (May 20, 20 DAS) and at the end of the experiment (August 15, 107 DAS). The distances to drip tapes from the sample locations were 0, 7, 14, 21, 28, 35, 42, 49, 56, 63 and 70 cm, and sample depths were the same as before. All soil samples were air-dried and sieved through a 2 mm sieve. The EC values were based on soil: water 1:5 extracts (EC1:5 , on a volume basis), and were determined using a conductivity meter. After the experiment, the relationships between ECe and EC1:5 were determined according to the Agriculture Handbook No. 60 (U.S. Salinity Laboratory Staff, 1954) and were used to convert EC1:5 to ECe for all samples. For different soil textures, the relationships were different for different depths: At 0–60 cm depths :
ECe = 14.77 × EC1:5
At 60–90 cm depths :
ECe = 9.55 × EC1:5
(R2 = 0.90) 2
(R = 0.92)
(3) (4)
2.6.5. Yield Harvest started on June 20 (47 DAS), June 29 (46 DAS), and June 27 (58 DAS), finished on August 4 (92 DAS), August 13 (91 DAS) and August 6 (98 DAS), and lasted 45, 45 and 40 days in 2003, 2004 and 2005, respectively. Fruits were picked by hand at 2 to 4 days intervals. The fruit number and the total fruit mass per plot were measured at each time. 2.7. Statistical analysis Analysis of variance (ANOVA) was conducted and significance of differences among treatment was tested using the least signif-
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icant difference (LSD). Differences were declared significant at P < 0.05. 3. Results and discussion 3.1. Weather Mean weekly temperatures during the whole cucumbergrowing period were 23.1, 23.5 and 23.1 ◦ C in 2003, 2004 and 2005, respectively. But mean temperature in the 2nd week in 2005 (14.5 ◦ C) was obviously lower than those in 2003 (18.2 ◦ C) and 2004 (20.6 ◦ C). Total rainfall during the experiment period was 180.6, 323.5 and 292.4 mm, and the distribution was 8, 18, and 19% in cucumber seedling establishment stage (in the first 4–5 weeks), 53, 43 and 15 in the flowering stage (about 3 weeks) and 39, 39 and 66% in the harvest stage in 2003, 2004 and 2005, respectively. Total pan evaporation (EW20 ) was 494.7, 455.2, and 575.2 mm, and the ratio of seasonal evaporation to rainfall was 2.7, 1.4 and 2.0 in 2003, 2004 and 2005, respectively. 3.2. Irrigation Prior to treatments initiation, only fresh water was applied and the irrigation depth was 57.0, 25.3 and 63.4 mm in 2003, 2004 and 2005, respectively. In 2004, much less fresh water was applied, because the mulches covered before seeds sowing. Whereas in 2005, more fresh water was applied in order to aid the cucumber seedling survival during the bad weather. Irrigation times and depths in 2004 and 2005 were less compared with those in 2003, because rainfall was less in 2003 than in the other years. In the 3 years, especially in 2003, the irrigation depths and times were reduced when saline water was applied. The higher ECiw was, the less irrigation times and depths were (Table 3). In 2003, the seasonal irrigation times and depths for 4.2 dS/m treatment were only 40 and 68% of the values for 1.1 dS/m treatment. 3.3. Soil matric potential (SMP) Fig. 1 illustrates the spatial distributions of SMP in the vertical transect perpendicular to the drip tape for each treatment at early and later growing stages in 2003. On June 5 (32 DAS) 2003, there was a tendency for SMP to increase gradually from about −20 to −12 kPa as soil depths increased. On June 6, 1 day after a uniform
irrigation of 6.3 mm, there was a wetted zone within 40 and 35 cm respectively away from emitter in vertical and horizontal direction for all treatments. Average SMP values near emitter rose to −16 kPa or higher, whereas those outside the wetted zone were almost kept unchanged. On July 20 (77 DAS), the wetting patterns were similar for all treatments. Average SMP values were around −25 kPa in the wetted zone, and were around −35 kPa in the surface layer between the beds. This day, a tank of water was applied for each treatment in the morning, and 17.4 mm rain fell in the afternoon. On July 21, average SMP values at depths of 0–40 cm increased drastically to −19 kPa or higher, and those below 60 cm depth were almost kept unchanged. Because of the relatively more humid weather in 2004 and 2005, it can be inferred that the soil moisture conditions in 2004 and 2005 were wetter than that in 2003.
3.4. Cucumber yield Fruit number per plant and cucumber yield under different treatments are presented in Table 4. Average total yield of the five treatments in 2003 was 113.0 Mg/ha, about 2.7 and 4.3 times of that in 2004 and 2005, respectively. Cucumbers are quite sensitive to oxygen deficiency in the soil, waterlogging for hours or days will do great harm to the growth of cucumbers. The relatively low yield in 2004 and 2005 can be attributed to waterlogging during the middle and later growing periods. Besides, bad weather at the seedling stage in 2005 may have negative effect on the development of cucumbers, and resulted in low yield. Statistical analysis showed a significant (P < 0.05) effect of ECiw on fruit number and yield in 2003 and 2005, and both of them decreased as ECiw increased. But in 2004, there was no significant difference, for less saline water was applied. Relative yield (Yr ) and relative fruit number per plant (Nr ) responding to ECiw are presented in Fig. 2. The relationship between the correlated magnitudes was quite linear, and same slope coefficients can be distinguished. Yr and Nr decreased 5.7% per unit increase in ECiw . The maximum yield loss was about 25% for ECiw of 4.9 dS/m, compared to 1.1 dS/m. In the experiment, the major contribution to total yield reduction under saline condition was fruit number. This is in accordance with the results of Sonneveld and Voogt (1978), Jones et al. (1989), and Chartzoulakis (1992). They suggested that the differences in cucumber yield among different saline treatments were mainly
Table 3 The irrigation times and water depths for each treatment during cucumber-growing period in 2003, 2004 and 2005. Years
Treatments
Seasonal water depths (mm)
Fresh water for seedlings (mm)
During treatment
Irrigation times
Water depths (mm)
2003
1.1 2.2 2.9 3.5 4.2
177.7 161.1 157.5 146.4 120.4
57.0 57.0 57.0 57.0 57.0
25 20 18 15 10
120.7 104.1 100.5 89.4 63.4
2004
1.1 2.2 2.9 3.5 4.2
49.5 51.4 53.3 49.2 44.4
25.4 25.4 25.4 25.4 25.4
5 5 5 4 3
24.1 26.0 27.9 23.8 19.0
2005
1.1 2.3 3.5 4.2 4.9
106.8 94.6 96.9 99.1 101.4
63.4 63.4 63.4 63.4 63.4
9 6 6 6 6
43.4 31.2 33.5 35.7 38.0
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Fig. 1. The spatial distributions of soil matric potential in the vertical transect perpendicular to the drip tape for each treatment at early and later growing stages in 2003.
reflected in fruit number, and less in a low fruit weight. This is mainly because of the time of cucumber fruit picking. Generally, cucumber fruits are picked at 8–10 days after bloom or when they have reached a certain size. 3.5. Cucumber water use consumption Fig. 3 demonstrates 10-day water use for all treatments during the whole cucumber-growing season and corresponding 10-day 20 cm pan evaporation (EW20 ). The temporal patterns of 10-day water use variations were similar for different treatments. In the first 3 or 4 weeks (during cucumber seeding and seedling stages), cucumber 10-day water use for all treatments was low, and obviously lower than the corresponding EW20 values. The 10-day water use of the five treatments in the 3 years was no more than 20 mm, which meant that the average water use of cucumber was no more than 2 mm per day during seeding and seedling stages.
Cucumber water use increased gradually and reached its maximum values in the early harvest stage, the 5th 10-day in 2003 and 2004, and the 7 the 10-day in 2005. The maximal values for each treatment with ECiw from low to high were 51.7, 53.3, 43.7, 53.6 and 38.0 mm in 2003, 43.9, 46.2, 44.9, 39.8, and 39.9 mm in 2004, and 35.4, 26.9, 22.8, 25.0 and 24.7 mm in 2005, respectively. There was a decreasing tendency for cucumber water use with the increase of ECiw , and the maximal daily water use of cucumber was no more than 5.4 mm. Cucumber water use began to decrease gradually from the middle harvest stage. At the last 2–3 weeks, the 10-day water use was no more than 20 mm, which meant that average daily water use of cucumber was less than 2 mm in the late growing season. Seasonal accumulative cucumber water use for different treatments is listed in Table 4. Cucumber seasonal accumulative water use decreased with the increase of ECiw , and every 1 dS/m increase in ECiw resulted in 6.9, 1.5 and 4.4% decrease of seasonal accumulative water use in 2003, 2004 and 2005, respectively.
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Table 4 Fruit number per plant, yield, seasonal water use, water use efficiency and irrigation water use efficiency for different treatments in 2003, 2004 and 2005.
a b
Year
Treatment (dS/m)
ECe (dS/m)a
Fruit number per plant
Total yield (Mg/ha)
Seasonal water use (mm)
Water use efficiency (Mg/ha/mm)
Irrigation water use efficiency (Mg/ha/mm)
2003
1.1 2.2 2.9 3.5 4.2
3.2 3.3 3.8 4.4 4.3
20.9a 19.2b 18.3bc 17.3cd 16.7d
128.9ab 120.1ab 108.4bc 104.8bc 103.1c
230.4 213.2 208.9 198.0 177.4
0.56 0.56 0.52 0.53 0.58
0.73 0.75 0.69 0.72 0.86
2004
1.1 2.2 2.9 3.5 4.2
7.9a 7.8a 7.3a 7.3a 7.0a
45.8a 42.3a 41.2a 41.5a 40.0a
166.5 166.0 161.4 161.9 159.0
0.28 0.25 0.26 0.26 0.25
0.93 0.82 0.77 0.84 0.90
2005
1.1 2.3 3.5 4.2 4.9
5.7a 5.2ab 5.0ab 4.5b 4.6b
30.9a 27.0ab 26.0b 24.3b 24.2b
186.1 181.1 181.2 167.0 150.8
0.17 0.15 0.14 0.15 0.16
0.29 0.29 0.27 0.25 0.24
3.0 3.4 3.8 4.3 4.3
ECe means the average electrical conductivity of saturated paste extract within rooting depth integrated over time. The same letters are not significantly different at 0.05 level, and different letters mean significant difference at 0.05 level.
3.6. ECe 3.6.1. ECe in the soil profile Figs. 4 and 5A–C demonstrates the spatial distributions of ECe in the vertical transect perpendicular to the drip tape for each treatment before ploughing, before treatment and at the end of the experiment in 2003 and 2005, respectively. Before ploughing in 2003, there was a tendency for ECe to decrease as soil depths increased, and the average ECe values were 7.1, 4.8, 2.9 and 2.1 dS/m in 0–2, 2–10, 10–40 soil layers and below 40 cm depths, respectively (Fig. 4A). The ECe values were high in 0–10 cm depths, especially in 0–2 cm soil layer. Because only fresh water was applied during the seeding and seedling stages, there was an obvious low ECe zone within about 10 cm distance from the drip emitter at 0–10 cm depth, and the average ECe value was 2.7 dS/m, reduced by 63% compared to the original value. The highest salt concentration occurred in the ridge of the bed, with the average ECe value of 14.2 dS/m, increased by 58% compared to the original value (Fig. 4B). The average ECe value in
Fig. 2. Relative cucumber yield and fruit number per plant response to ECiw (electrical conductivity of irrigation water).
Fig. 3. 10-day water use curves for different treatments and the corresponding 10day evaporation curve during the whole cucumber-growing period in 2003, 2004 and 2005.
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Fig. 4. The spatial distributions of ECe (electrical conductivity of saturated paste extract) in the vertical transect perpendicular to the drip tape before field ploughing (A), before treatment (B), and at the end of the experiment (C) in 2003.
Fig. 5. The spatial distributions of ECe (electrical conductivity of saturated paste extract) in the vertical transect perpendicular to the drip tape before field ploughing (A), before treatment (B), and at the end of the experiment (C) in 2005.
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the soil profile (0–90 cm depths) were 3.2 dS/m, equal to the value before field ploughing. Due to the frequent irrigation and rainfall, salt leaching occurred in the growing season for each treatment. The ECe value decreased obviously in 0–40 soil layers, whereas no obvious change could be observed below 40 cm depths. The average ECe values in the whole soil profile for 1.1, 2.2, 2.9, 3.5 and 4.2 dS/m treatment were 2.6, 2.7, 2.9, 3.6 and 2.5 dS/m at the end of the experiment, lower than the original value, except for 3.5 dS/m treatment, which may be the result of spatial variability (Fig. 4C). Before field was ploughed in 2005, average ECe values for 4.2 dS/m treatment were 12.5, 4.1, 2.8 and 2.1 dS/m in 0–2, 2–10, 10–40 soil layers and below 40 cm depths, respectively (Fig. 5A). Evaporation in late winter and early spring resulted in salts built up in 0–10 cm depths, especially in 0–2 cm soil layer. Compared to the original value in 2003, no obvious change in ECe was found below 40 cm depths. Similarly, before saline water was applied, an obvious low ECe zone was found within about 15 cm distance from the drip emitter at 0–10 cm depth and the highest ECe zone was in the ridge of the bed. Compared to the value before ploughing in 2005, the average ECe value was 4.4 dS/m in the low ECe zone, reduced by 44%, and was 15.0 dS/m in the ridge of the bed, increased by 67% (Fig. 4B) The average ECe of the whole soil profile of 0–90 cm depths was 3.8 dS/m, similar to the value before ploughing in 2005(3.6 dS/m). At the end of the experiment, because the black polyethylene mulches had been already removed when soil samples were taken, some salts accumulated in 0–2 cm soil layer. After 3 years of saline water irrigation, the average ECe in the whole soil profile (0–90 cm) were 2.3, 2.8, 2.9, 2.6 and 3.2 dS/m for 1.1, 2.2, 3.5, 4.2 and 4.9 dS/m, respectively (Fig. 5C). 3.6.2. Average ECe within the root zone (ECe ) Under drip irrigation system, active root water uptake of plants was concentrated mainly within 40 cm depth (Chartzoulakis and Michelakis, 1990; Bassoi et al., 2003; Kang and Wan, 2005; Wan and Kang, 2006; Wang et al., 2007). In this experiment, ECe within the root zone were integrated to take account of both spatial and temporal variation, and was calculated in the soil about 40 cm horizontally to the center of raised beds at the depth of 0–40 cm (Table 4). Relative yield (Yr ) and relative water use (WUr ) responding to ECe in the root zone are presented in Fig. 6. Yr and WUr decreased 10.8 and 9.0% for 1 dS/m increase in ECe . According to Maas and Hoffman (1977), crop salt tolerance could be expressed as the following equation: Yr = 100 − Yd (ECe − ECt )
(5)
where Yr is relative crop yield (actual yield at the given salinity level divided by yield with no salinity effect), ECe represents the average root zone salinity (electrical conductivity of saturated paste extract, dS/m), ECt represents the threshold salinity level (the maximum allowable salinity that does not reduce yield measurably below that of a non-saline condition, dS/m), and Yd is the yield decrease per unit of salinity increase beyond the threshold. In order to compare the results with the work of other researchers, the equations in Fig. 6 were expressed as the Maas–Hoffman equation form: Yr = 100–10.8 × (ECe − 2.4) WUr = 100–9.0 × (ECe − 2.8)
2
(R = 0.85) 2
(R = 0.61)
(6) (7)
It can be inferred from the about two equations that Yr and WUr began to decline when the ECe in the root zone above the threshold value of 2.4 dS/m and 2.8 dS/m, respectively.
Fig. 6. Relative cucumber yield and season water use response to average ECe (electrical conductivity of saturated paste extract) in the root zone.
According to Maas and Hoffman (1977), cucumber fruit yield decreased by 13% for each unit of ECe increase in the root zone above 2.5 dS/m. Compared with their results, the threshold value of ECe was very close to that of Maas and Hoffman (1977) in spite of a lower slope value. Allen et al. (1998) reported the ECe threshold between 1.1 and 2.5 dS/m and the slope between 7 and 13% for cucumber based on climate, soil conditions and cultural practice. The ECe threshold and slope values in this experiment were between reported values of Allen et al. (1998). 3.7. Cucumber water use efficiency (WUE) and irrigation water efficiency (IWUE) In this study, water use efficiency (Mg/ha/mm) is defined as the ratio of cucumber yield (Mg/ha) to seasonal accumulative water use consumption (mm), and irrigation water use efficiency is computed based on cucumber yield dividing by the total irrigation water. The average WUE values were 0.55, 0.26 and 0.15 Mg/ha/mm, and average IWUE values were 0.75, 0.85 and 0.27 Mg/ha/mm in 2003, 2004 and 2005, respectively (Table 4). The relationships between WUE/IWUE and ECiw /ECe in the 3 years were not clear. This is not in agreement with the findings by Katerji et al. (2003). They pointed out that the tolerant crops show more or less constant water use efficiency, and the sensitive crops show a decrease of water use efficiency with increasing salinity, for the yield of sensitive crops decreases stronger than the evapotranspiration. The difference can partly be attributed to different agronomy, water and soil management strategies. 4. Summary and conclusions In the 3-year open field experiment in North China, a semihumid area, saline water (EC ≤ 4.9 dS/m) was applied to irrigate cucumber with mulched drip irrigation after seedling stage. It can be known when the SMP at 0.2 m depth immediately under emitter was kept higher than −20 kPa throughout cucumber-growing season, a favorable soil moisture condition (ranging from −15 to −25 kPa) was maintained for the whole growing period in the root zone (within 40 cm away from emitter and 40 cm depths). Due
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to the soil evaporation, salts accumulated in the upper 0–10 cm soil layer, especially in 0–2 cm soil layer in non-growing season. A relatively low ECe zone gained in the root zone in the growing season for the periodic salt leaching by frequent irrigation and rainfall. Cucumber fruit number per plant and yield decreased by 5.7% for 1 dS/m increase of ECiw , and yield decreases were mainly reflected in fruit number. The maximal daily water use of cucumber was no more than 5.4 mm, and seasonal water use decreased linearly by 1.5–6.9% with increasing of ECiw in the 3 years. As to the mean soil salinity within the root zone, cucumber yield and water use decreased by 10.8 and 10.3% for each unit of ECe increase in the root zone. So in North China, or similar semi-humid areas, where there is no enough fresh water for irrigation, saline water up to 4.9 dS/m can be applied to irrigate field culture cucumbers after adopting some appropriate management strategies. The main strategies include adopting drip irrigation with black polyethylene mulch, keeping the SMP at 0.2 m depth immediately under drip emitter higher than −20 kPa throughout growing season. In this way, it can not only save valuable fresh water, but also reduce numbers of irrigations and total amount of water applied. The highest cucumber yield loss is about 25% compared to fresh water irrigation, and soil salinity does not increase in the soil profile of 0–90 cm depths. The conclusions in this study were based on only 3-year data. To assess the sustainability of saline water irrigation in North China, additional research is needed. Acknowledgements This study was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences, Grant No. (KSCX2-YW-N003), the Action Plan for the Development of Western China of the Chinese Academy of Sciences Grant No. (KZCX2-XB2-13), the Key Technologies R&D program (06YFGZNC00100) supported by Tianjin Municipal Science and Technology Commission, and the Project for 100 Outstanding Young Scientists supported by Chinese Academy of Sciences.
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