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Effect of the micro-sprinkler irrigation method with treated effluent on soil physical and chemical properties in sea reclamation land
Agricultural Water Management 213 (2019) 222–230
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Effect of the micro-sprinkler irrigation method with treated effluent on soil physical and chemical properties in sea reclamation land
T
⁎
Na Lia,c, Yaohu Kanga,b, , Xiaobin Lia, Shuqin Wana, Jiachong Xua,c a
Key Laboratory of Water Cycle and Related Land Surface Process, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, Beijing, 100101, China b College of Resources and Environment, University of Chinese Academy of Science, Beijing, 100049, China c University of Chinese Academy of Sciences, Beijing, 100049, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Salt leaching Irrigation management Tall fescue Saline soil
To develop a micro-sprinkler method with treated effluent for tall fescue (Festuca arundinacea) cultivation in sea reclamation land and test its effect on soil physical and chemical properties, a field experiment with five treatments of water quality was conducted in 2015–2016. The five treatments of water quality were created with a mixture of treated effluent (EC, 4.2–6.9 dS/m) and fresh groundwater, and the percentage of treated effluent was 0%, 25%, 50%, 75% and 100%. Saline soil contained a gravel-sand layer imbedded at depth of 60 cm. Irrigation management was divided into three stages, enhanced salt leaching stage (continuous irrigation), water-salt regulation stage (irrigation based on the soil matric potential (SMP) at −5 KPa) and normal irrigation stage (irrigation based on the SMP at −20 KPa). The results indicated that the first stage lasted for 10 days, while the electrical conductivity of saturated extracts (ECe) of the surface 10 cm from 38.29 dS/m dropped to 4.23–6.28 dS/m. After the second stage (3.5 months), the ECe in the 0–60 cm soil layer dropped to 1.42–3.16 dS/ m. During these stages, treatment with 50% treated effluent led to relatively good infiltration and lower salinity and was therefore good at enhancing the salt leaching efficiency. In the third stage, the observed ECe of the 0–60 cm changed slightly, but ≤75% treated effluent could maintain the soil salinity below the threshold salinity of tall fescue, even in the rainless season. During the process, soil sodium adsorption ratio decreased, while soil pH increased first and then decreased. Soil available phosphorus content showed a close correlation with treated effluent and the biomass of tall fescue. Moreover, the tall fescue maintained normal growth. Therefore, it is possible to use treated effluent to micro-sprinkler irrigation on tall fescue in sea reclamation land.
1. Introduction Sea reclamation has been a common approach to increase the land area for living and developing along the coastal areas in many parts of the world. In China, a total reclamation area of 2469 km2 was approved by the State Council in 2011–2020 for economic development (Wang et al., 2014). In sea reclamation land, bare ground is exposed, which not only affects the landscape, but also leads to sandstorms. Landscape construction is required to meet the demands of living and developing environments. Sea reclamation land is usually very saline; for example, the mean electrical conductivity of saturated-soil extracts (ECe) is more than 30 dS/m in our study area (Li et al., 2015a). Moreover, the salt composition in the study area is similar to that of seawater, with chlorine and sodium being the main ions, accounting for 60–80% of the total,
respectively. There is also a high water table at 0.5–3 m, and the aquifer contains saline water. Traditional reclamation methods, such as applying gypsum, combining surface irrigation and water drainage technologies have made it difficult to improve saline soil for plants. Although some halophyte plants, such as Tamarix chinensis can survive under such conditions, they are not sufficient to create a better landscape. Replacing saline soil with non-saline soil is the most popular method used in our research area, but this is limited by high economic input and the increasing difficulty in identifying large amounts of nonsaline soil resources. Recently, several studies have been conducted in the Bohai Gulf region, east China. Sun et al. (2013) found that a gravel-sand layer at depth of 80 cm was effective at preventing the upward movement of salt into the surface soil from shallow saline groundwater during winter. Li et al. (2015b) found that the technology of surface drip
⁎ Corresponding author: Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A Datun Road, Anwai, Beijing, 100101, China. E-mail address: [email protected] (Y. Kang).
https://doi.org/10.1016/j.agwat.2018.10.023 Received 8 May 2018; Received in revised form 13 October 2018; Accepted 17 October 2018 0378-3774/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Planting pattern, soil treatment and installation of tensiometer.
approximately 555 mm, most of which occurs from July to September. The soil of the study area is sandy loam soil and the region was reclaimed from the sea in 2007. The soil salt composition was similar to that of seawater, with chlorine and sodium comprising the main ions. The average electrical conductivity, pH (pHe) and sodium adsorption ratio (SARe) of the saturated-soil extracts above a soil depth of 60 cm were ECe = 38.3 dS/m, pHe = 7.68, and SARe = 69.4 (mmol/L)0.5; Water table 0.8–1.2 m. The average soil bulk density of the initial saline soils was 1.69 g/cm3 in the 0–60 cm soil layers, which was reduced to 1.55 g/cm3 after soil tillage. The soil nutrient characteristics for 0–60 cm soil layers were: organic matter content 11.4 g/kg, total N 0.24 g/kg, available phosphorus 8.1 mg/kg, available potassium 464 mg/kg.
irrigation with phased irrigation management could enhance salt leaching and maintain good plant growth. The drip irrigation was started based on the soil matric potential (SMP) at 20 cm, and the SMP target value was adjusted according to the process of salt-leaching, irrigation water quality and plant growth. Li et al. (2015a) found that when the SMP was controlled at above −5 and −10 KPa in the two irrigation stages, drip irrigation with 4.01 dS/m saline water could maintain a 50% survival rate for salt-sensitive plants. In a study investigating drip irrigation with freshwater, Chen et al. (2015a) controlled the SMP threshold into three stages of −5, −10 and −20 KPa. In addition, micro-sprinkler irrigation of tall fescue (Festuca arundinacea) with freshwater was also conducted when the SMP was controlled above −5, −15 and −20 KPa (Chu et al., 2014). The freshwater supply of the Bohai Gulf region, including the research area, is very limited, with only 660 m3 per capita (Sun, 2007). Moreover, there were about 3.9 billion m3 of treated effluent in the coastal cities of the Bohai Gulf region in 2015 (Li, 2016; Liu, 2016; Wei, 2016; Wu and Peng, 2016), while the utilization rate was only 8.3% (Li, 2016), which is far lower than the 80% in Israel (OECD, 2015). There has been a great deal of research on irrigation with treated effluent, and the results of these studies have identified potential salinity as a restriction to the use of treated effluent. The characteristics of treated effluent, such as the salt content and concentration of specific chemical elements, may cause soil salt accumulation, plant damage or soil permeability problems (Al-Hamaiedeh and Bino, 2010; Asano and Pettygrove, 1987; Oster, 1994; Toze, 2006). Furthermore, spraying plants with saline water may cause foliar damage because many plants absorb salts directly through their leaves (Shalhevet, 1994; Tanji, 1990). Tall fescue is a plant widely used in landscapes that has a salt tolerance threshold of 3.9 dS/m (Maas and Hoffman, 1977). The present study was conducted to develop a micro-sprinkler irrigation for application of treated effluent to tall fescue in sea reclamation land. The specific goals were (1) to test the process and effect of soil salinity leaching during irrigation with different levels of treated effluent; and (2) to find the correct percentage of treated effluent for use as long-term irrigation water and to maintain normal growth of plants and soil health.
2.2. Experimental design 2.2.1. Plot layout and experiment design Based on the successful reclamation of the coastal saline soil (Chen et al., 2015a, 2015b; Chu et al., 2014; Li et al., 2016, 2015a, 2015b; Sun et al., 2012), the soil treatments before planting were as follows: soil was removed to a depth of about 60 cm A 10-cm thick gravel layer and a 5-cm thick sand layer were laid in the bottom to cut off the capillary porosity (Fig.1). Several polyvinyl chloride tubes were placed at the low edge of the gravel-sand layer, with spacings of 10 m, to allow the leaching water to flow out, after which the saline sodic soil was backfilled and levelled. The irrigation water was a mixture of treated effluent and fresh water. The treated effluent, which was from the Caofeidian District Sewage Treatment Plant maintained by the Tangshan-Caofeidian drainage operating companies, was transported and stored in a small reservoir. The quality of treated effluent met the first-grade national standard for wastewater discharge (GB18918-2002, 2003). Fresh water was pumped from a deep-layer groundwater well located at the experimental site. There were five irrigation water treatments with percentages of treated effluent were: 0% (GG1), 25% (GG2), 50% (GG3), 75% (GG4) and 100% (GG5). All treatments were replicated three times with the experimental plots arranged in a complete randomized block design. The area of each plot was 9.0 by 6.0 m, and the distance between the plots was 2.5 m. Each plot contained 6 micro-sprinklers with a 3.0 m space between them. According to Chu et al. (2013), a micro-sprinkler (Beijing Luckrain Plastic Industry Ltd., China) with a flow rate of 120 L/ h at 0.2 MPa operating pressure and a wetted diameter of about 3.1 m was selected. The tall fescue (Houndog V) turf sod covered over the saline-sodic soil directly. The irrigation water quality and its degree of restriction on permeability are presented in Tables 1 and 2. The salt concentration of the treated effluent (electrical conductivity of irrigation water, ECiw,
2. Materials and methods 2.1. Experimental site Experiments were conducted in 2015–2016 at the Industrial Zone (39°03′N, 118°48′E), located in the Caofeidian District in the south of Tangshan City, east China. This region is located in the northern portion of the Bohai Gulf, which borders the Pacific Ocean. The station has a typical semi-humid monsoon climate and annual precipitation of 223
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Table 1 Concentrations of main ions and compounds in irrigation water. Irrigation water
Main ion and some substances concentration (mg/L)
Fresh Water Treated effluent
Ca2+
Na+
K+
Mg2+
SO42−
CO32−
HCO3−
Cl−
B
COD
TN
TP
9.6 72.0
214.2 802.8
1.6 29.5
8.3 97.7
6.2 260.4
41.0 18.0
407.0 312.3
56.0 1160.0
0.4 0.6
10.0 66.0
36.6 41.9
0.5 1.5
Calcium = Ca2+, sodium = Na+, potassium = K+, magnesium = Mg2+, carbonate = CO32−, bicarbonate = HCO3-, chlorion = Cl-, boron = B, chemical oxygen demand = COD, total nitrogen = TN, total phosphorus = TP.
gravel layer) were collected in mid-July, mid-September, and early November 2015, as well as in mid-March, early-July, and early-November 2016. The soil was obtained horizontally at 0, 50, 100, 150 cm from the micro-sprinkler and all sample depths in the vertical apart were the same: 0–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm. The soil ECe, pHe, inorganic nitrogen (Nmin) and soluble cations were based on extracts of saturated soil. The ECe and pHe were determined by a conductivity meter (DDS-307, REX, Shanghai, China) and a pH meter (PHS-3C, REX, Shanghai, China), respectively. Nmin included nitrate nitrogen and ammonium nitrogen, which were measured by means of colorimetry (Bao, 2000), respectively. Soluble cations such as Na+, K+, Ca2+ and Mg2+ were measured with ICP-OES (Optima 5300DV, USA). Available phosphorus was extracted with 0.5 mol/L NaHCO3 (Bao, 2000). The SAR was calculated as follows:
Table 2 Irrigation water electrical conductivity (ECiw), pH (pHiw), sodium adsorption ratio (SARiw) and its restrictions on permeability. Irrigation water
ECiw (dS/m)
pHiw
SARiw (mmol/L)0.5
Degree of restriction on permeability
GG1 GG2 GG3 GG4 GG5
1.0 1.8 2.7 3.5 4.4
9.1 8.8 8.6 8.4 8.2
12.2 11.4 12.4 13.4 14.5
Severe Slight to moderate Slight None None
(0%) (25%) (50%) (75%) (100%)
Values of ECiw, pHiw, and SARiw of irrigation water sampled in October 2015.
4.2–6.9 dS/m) was several times higher than that of the fresh water (ECiw, 1.0 dS/m), similar to the nutrient concentration. The ECiw and sodium adsorption ratio of irrigation water (SARiw) increased and the pH of the irrigation water (pHiw) decreased as the percentage of treated effluent increased. According to the evaluation of permeability using ECiw and SARiw proposed by Ayers and Westcot (1976), the irrigation water of the GG1 treatment posed a “severe” degree, while the GG2 and GG3 treatments posed a “slight to moderate” degree and a “slight” degree, respectively. There was no restriction on permeability of GG4 and GG5 treatments. The number of fecal coliforms in treated effluent was 130–1700 cfu/L, while the heavy metals levels were suitable for irrigation, except for Se, which was present at 0.029 mg/L (Ayers and Westcot, 1976). The irrigation management was divided into three stages, including enhanced salt leaching stage (1st stage), water-salt regulation stage (2nd stage), and normal irrigation stage (3rd stage). The first two stages were the two main salt leaching periods. The 1st stage was designed to leach salt from the 0–10 cm layer of the soil with continuous irrigation, during which time about 10–20 mm of water was applied per day. The stage ended when the soil ECe of the 0–10 cm layer was close to or less than 6 dS/m. During the 2nd stage, salt was leached from the soil above the gravel-sand layer by ensuring the net downward movement of water (Asano and Pettygrove, 1987). According to the successful reclamation of drip irrigation with saline water in coastal saline soil (Li et al., 2015a), the irrigation was based on the SMP at a depth of 0.2 m, which was controlled at −5 KPa. The stage terminated when the average soil ECe was < 4 dS/m above the gravel-sand layer, since the salinity tolerance threshold of tall fescue was about 3.9 dS/m. The 3rd stage was normal irrigation, during which irrigation was applied when the SMP reached the target value, −20 KPa. During the second and last stages, the depth of water for each irrigation event was 10 mm, and the target value could be adjusted uniformly according to the tall fescue growth and the soil salinity. Fertilizer was applied uniformly to each treatment in early October 2015 and July 2016, respectively. The rates of N, P2O5 and K2O application were 20 g/m2/y, 5 g/m2/y and 10 g/m2/y, respectively. In addition, tall fescue was trimmed and weeded regularly.
SAR =
([Ca2 +]
[Na+] + [Mg 2 +])0.5
(1)
where the concentration of each cation was in mmol/L. In this experiment, average ECe, pHe, SARe and Nmin within the soil profile was calculated as follows:
ECe (t ) or pHe (t ) or SAR e (t ) or Nmin (t ) n, m
∑ j, k ECe (t , j, k )[or pHe (t , j, k ); or SAR e (t , j, k ); or =
Nmin (t , j, k )] × S (j, k ) n, m ∑ j, k S (j, k )
(2)
in which, t represents the time when soil samples were obtained; j the four horizontal distances (n) from the micro-sprinkler where soil samples were obtained; k the depth (m) of the soil sample and S (j, k) the depth interval of the soil layer. The growth biomass of tall fescue was determined when it has sufficient height for harvesting (> 20 cm). All the plots were trimmed at the same time. There was five times harvest during the study period. The fresh biomass in each plot was weighted, and some was used to determine the water content. The growth biomass (Qgr ) was calculated as follows:
Qgr (t ) = Qfre (t ) × (1 − w )
(3)
where Qfre is the weight of the fresh tall fescue (kg/ha), w is the water content of the fresh tall fescue (%), and t is the moving time.
2.3. Statistical procedures Data were analyzed using IBM SPSS Statistics ver.19.0 (IBM Co., Armonk, NY, USA). The differences in growth biomass of tall fescue among treatments were compared using one-way Analyses of variance (ANOVA), the least significant difference test at a significance level of 0.05. The figures were prepared using Sigma Plot 10.0 (Systat Software, Inc., Chicago, IL, USA).
2.2.2. Observation and measurements There was one tensiometer installed in one plot for each treatment for observation of SMP at a depth of 0.2 m (Fig. 1), and observations were made daily at 8:00 and 16:00. Soil samples of each plot (above the 224
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Fig. 2. Precipitation during the study period.
3. Results and discussion
3.2. Effect of treated effluent irrigation on soil salinity (ECe)
3.1. Precipitation, irrigation amount and soil matric potential
ECe is the electrical conductivity of a saturated-soil extract. At the experimental site, the soil ECe in the 0–60 cm soil layer before planting tall fescue turf was relatively uniform, with an average of 38.29 dS/m.
3.1.1. Precipitation Fig. 2 shows the precipitation for the area during the study period. From July to November 2015, about 120 days after planting, the total precipitation was 395 mm. There was no rain during the 1st stage, and almost all of the rain was concentrated in the 2nd stage. During the 3rd stage (March–November 2016), the total precipitation was 539 mm. The rainfall events mainly occurred from mid-July to September 2015, mid-late June 2016, and late July to early September 2016. There is no rain data for the period from November to March, but the average amount was 32 mm in the same period during the past 30 years.
3.2.1. Effect of treated effluent on soil salt leaching Fig. 4 shows the spatial distribution of ECe in the vertical transects for each treatment at different soil sampling times. The salinity changed significantly in the 1st stage and the 2nd stage (Fig. 4a–c). The 1st stage lasted for 10 d, and the salinity of upper soil was well leached. The average ECe in the 0–10 cm soil profile for the GG1–GG5 treatments decreased to 3.73, 4.09, 3.81, 4.91 and 6.28 dS/m, respectively, the corresponding reductions were 90.27%, 89.32%, 90.04%, 87.17% and 83.61% of the initial soil ECe (Fig. 4a). The 2nd stage lasted for 3.5 months, as the soil salinity above the gravel layer continued to decline. In November of 2015 (Fig. 4c), the average ECe values of the 0–40 cm soil layer for the GG1–GG5 treatments decreased to 0.66, 1.44, 1.57, 1.91 and 2.22 dS/m, with an average value of 1.56 dS/m. For 0–60 cm, the values decreased to 1.42, 2.46, 2.25, 2.72 and 3.01 dS/m, respectively. Although the ultimate soil salinity increased with increasing percentages of treated effluent, the ECe values were lower than the salt tolerance threshold for tall fescue, indicating that the 2nd stage was completed. The 1st stage and the 2nd stage were two main soil salt leaching periods. Based on the ultimate soil salinity at the end of each stage, the 1st stage was the fastest desalination period, with an average decrease in ECe of 2.40 dS/m per day in the 0–60 cm soil layer. In addition, the salt leaching efficiency of the five treatments was different, even when they were irrigated with an equivalent amount of water (110 mm, Table 3). At the end of the 1st stage, the average ECe in the 0–60 cm soil profile for the GG1–GG5 treatments was 14.48, 14.02, 13.25, 13.59 and 15.87 dS/m. The salt leaching efficiency increased as the percentage of treated effluent increased to 50%, then decreased, while for the surface soil, the GG1 and GG3 treatments leached salinity faster than the other treatments. These results suggested that irrigation with 50% treated effluent could enhance the desalting process in the experimental region, and that using freshwater tend to rapidly reduce the salinity of the surface soil (Oster, 1994). Based on the information presented above, lower water salinity and
3.1.2. Irrigation The irrigation for each treatment during the tall fescue growing season is shown in Table 3. The 1st stage and 2nd stage lasted for 10 days and 3.5 months, respectively. A total of approximately 410–500 mm irrigation water was applied, and no obvious patterns were obtained among treatments. During the 3rd stage, the irrigation amount ranged from 280 to 400 mm for treatments GG1–GG5 over the growing season (about 7.5 months), and the irrigation amount increased with the increasing percentage of treated effluent, except for GG3.
3.1.3. Soil matric potential Fig. 3 presents the change in SMP at a depth of 20 cm during the study period. In the 2nd stage, the SMP threshold was controlled well above −5 KPa, then adjusted to −10 KPa in the later period of 2015 to promote root growth to the deep layer for winter survival. During most of this stage, the SMP changed above the controlled values, but some SMP values were beyond the controlled threshold. This was likely because the twice-daily monitoring data from the tensiometer showed a bit of a lag. In the 3rd stage, the SMP threshold was mostly controlled at −20 KPa, except for one period that was controlled at −10 KPa to alleviate the salt damage to plants in a rainless season. The SMP fluctuated increasingly, because the soil water changed greatly as water consumption and evapotranspiration increased on hot days. Table 3 Precipitation and irrigation amount for each treatment during the study period. Treatments
GG1 GG2 GG3 GG4 GG5
(0%) (25%) (50%) (75%) (100%)
Enhanced salt leaching stage (Jul. 5, 2015–Jul. 14, 2015)
Water-salt regulation stage (Jul. 2015–Nov. 2015)
Normal irrigation stage (Mar. 2016–Nov. 2016)
Rainfall amount (mm)
Irrigation amount (mm)
Rainfall amount (mm)
Irrigation amount (mm)
Rainfall amount (mm)
Irrigation amount (mm)
0
110 110 110 110 110
395
380 300 340 390 390
539
300 340 280 370 400
225
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Fig. 3. Change of SMP (soil matric potential) at a depth of 20 cm during the growing season of tall fescue in 2015–2016.
Fig. 4. Spatial distribution of ECe (electrical conductivity from saturated paste extracts) in the vertical transects for each treatment in July 2015 (A), September 2015 (B), November 2015 (C), March 2016 (D), July 2016 (E), and November 2016 (F).
SL0–20 cm = 1.722 + 0.135 SARiw + 0.646 ECiw – 0.054 SARiw ECiw, R2 = 0.982; and, SL0–60 cm = 0.065 + 0.183 SARiw + 1.105 ECiw – 0.084 SARiw ECiw, R2 = 0.990, respectively.
good infiltration capacity of the irrigation water were likely to be the main factors that clearly affected the salt leaching efficiency. A lower ECiw means that less salinity is inputted into the soil via the irrigation water, while more salinity enters the soil when the irrigation water has a higher ECiw. A high infiltration rate means that more water can move into the soil and be used for leaching salt, especially in the deeper layers. Because the infiltration rate decreased with increasing SAR and decreasing total cation concentration (Oster and Schroer, 1979), nonlinear regression equations were used to describe the relationship of the salt leaching rate (SL, dS/m/d), SARiw ((mmol/L)0.5) and ECiw (dS/m) in the soil profiles of 0–20 cm and 0–60 cm. The regression equations were as follows:
3.2.2. Change in distribution of soil salt after winter From November–March there were almost no irrigation events, except for 30 mm of winter water. When compared with the average ECe value of the surface soil (0–20 cm) in November of 2015, it increased by 0.30–0.50 dS/m in the five treatments in March of 2016 (Fig. 4d). The increase in ECe was most likely because of the upward movement of soil salinity with water from the lower layer to the upper 226
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Fig. 5. Change of soil ECe (electrical conductivity from saturated paste extracts) at 0–20 cm (A), 0–40 cm (B) and 0–60 cm (C) for each treatment at different sampling times; 3.9 dS/m is the salt tolerance threshold of tall fescue.
total amount above the gravel layer was still higher than that in March of 2016. The accumulated soil salinity was leached during the rainy season, with a total of 358 mm rainfall occurring from July to November 2016. Fig. 4f and Fig. 5 show the spatial distribution of soil salinity in November of 2016. The average ECe values ranged from 1.98 to 2.60 dS/m at depths of 0 to 60 cm for the five treatments, representing decreases of 0.29–1.41 dS/m when compared with those observed in July of 2016. Similar to the soil profiles of 0–40 and 0–20 cm, the average ECe decreased to 0.98–2.16 dS/m and 0.66–2.40 dS/m, respectively. Moreover, the linear growth in soil salinity was highly correlated with the increasing percentage of treated effluent (*P < 0.05, Fig. 6b). When compared to the average ECe in March of 2016, the soil salinity of the five treatments sampled in November 2016 also declined, except for GG1. At 0–60 cm, the ECe values changed by 0.44, −0.42, −0.16, −0.37 and −0.19 dS/m (Fig. 5c) for the GG1–GG5 treatments. At 0–20 cm, only the ECe value of the GG5 treatment was 0.36 dS/m higher than that in March (Fig. 5a). Throughout one-year of water management during the 3rd stage, the soil salinity changed slightly or declined continually. During the rainless season, temporary salt accumulation was found in all treatments, and the average ECe of GG5 was likely beyond the salt tolerance threshold of the tall fescue. However, the accumulated salt was well leached during the rainy season. Therefore, micro-sprinkler irrigation with ECiw in the range of 4.21–6.89 dS/m is possible for sea reclamation land, but periodic examination of the soil salinity may be needed, especially for periods in which there is less rainfall. To mitigate the risk of soil salinity accumulation, it is suggested that 75% treated effluent (i.e., the ECiw should be maintained below 3.5–5.5 dS/m) be used to irrigate tall fescue in the Bohai Bay coastal region.
layer. However, the average ECe value at 0–60 cm for treatments GG1–GG5 was 1.54, 2.23, 2.33, 2.81 and 2.79 dS/m, respectively (Fig. 5c). These results suggest that there was almost no salts leaching or accumulation in the soil above the gravel-sand layer during winter and indicated that little salt moved into the upper soil from the groundwater below the gravel-sand layer, similar to the results found in previous reports (Chen et al., 2015a, 2015b; Chu et al., 2014; Li et al., 2016, 2015a, 2015b; Sun et al., 2012, 2013). Moreover, the average soil ECe in the 0–60 cm layer was still below 4 dS/m, which indicated that the irrigation management entered into the 3rd stage. 3.2.3. Effect of treated effluent on soil salinity in the normal irrigation stage In the 3rd stage, the irrigation was applied to maintain soil health and ensure the normal growth of tall fescue. The soil ECe in July 2016 increased as the percentage of treated effluent increased, and there were significant positive linear correlations between the soil ECe and the percentage of treated effluent at 0–20 cm (**P < 0.01), 0–40 cm (**P < 0.01) and 0–60 cm (*P < 0.05) (Fig. 6a), which was similar to the results observed during long-term irrigation with recycled wastewater in a previous study (Qian and Mecham, 2005). Fig. 4e shows the spatial distribution of the soil salinity in early July 2016, during which time the ECe value in all soil layers except for the surface soil was higher than that in March of 2016. The average ECe value at 0–60 cm was 2.27, 3.17, 2.83, 3.38 and 4.01 dS/m for GG1–GG5, respectively, representing an increase of 0.50–1.22 dS/m (Fig. 5c). Moreover, the ECe value in the profiles of 0–40 cm ranged from 1.53 to 2.96 dS/m, representing an increase of 0.10–0.68 dS/m (Fig. 5b). The increased soil salinity may be attributed to the irrigation water quality in the rainless season (Yao et al., 2017). From March to June, there was a total rainfall of 182 mm, but approximately 120 mm of which fell in mid-late June. In truth, the average ECe at 0–40 cm in late May had been increased to 1.32, 2.82, 3.35, 3.34 and 4.44 dS/m for GG1–GG5, respectively (Fig. 5b). It should be noted that for the GG5 treatment, the average soil salinity exceeded the salt tolerance threshold of tall fescue. After the precipitation in June, the soil salinity, especially in the surface soil, was well leached and decreased, but the
3.3. Effect of treated effluent irrigation on soil SARe The SARe is the sodium adsorption ratio of a saturated-soil extract. At the experimental site, the average soil SARe in the 0–60 cm soil profile before planting tall fescue was 69.4 (mmol/L)0.5. At the end of
Fig. 6. Response of average ECe (electrical conductivity from saturated paste extracts) in July 2016 (A) and November 2016 (B) to the percentage of treated effluent. 227
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Fig. 7. Spatial distribution of SARe (sodium adsorption ratio of saturated-soil extracts) in the vertical transects for each treatment in July 2015 (A), November 2015 (B) and July 2016 (C).
soil cation exchange, precipitation, evaporation, and addition of fertilizers (Beek and Breemen, 1973). During the 3rd stage, the pHe varied noticeably. After one-year of water management, the average pHe was 7.40, while that in the GG1, GG2, GG3, GG4 and GG5 treatments was 7.54, 7.47, 7.39, 7.37 and 7.25, respectively, in 0–60 cm soil profile (Fig. 9c). As shown in Fig. 10, the soil pHe decreased with the increasing percentage of treated effluent, and significant correlations were observed at 0–20 cm (**P < 0.01), 20–40 cm (*P < 0.05) and 40–60 cm (*P < 0.05). These results were different from those reported by Qian and Mecham (2005), who found that irrigation with treated effluent led to a 0.3 unit increase in pH. This difference may have been the result of the characteristics of the irrigation water, such as the bicarbonate level. In the study by Qian and Mecham (2005), the pH and bicarbonate concentration of treated effluent were higher than those of surface water, which was the opposite of the water applied in the present study.
Fig. 8. Response of average SARe (sodium adsorption ratio of saturated-soil extracts) in different soil layers to SARiw (sodium adsorption ratio of irrigation water) in July 2016.
3.5. Effect of treated effluent irrigation on soil inorganic nitrogen and available phosphorus
the 1st stage, the average SARe value of the five treatments decreased by 57.8%–29.3 (mmol/L)0.5 (Fig. 7a), while at the end of the 2nd stage, the SARe values for GG1–GG5 decreased by 81.1%–88.0% of the initial value (Fig. 7b), after which they changed slightly. In early July of 2016, the SARe values were 9.36, 7.12, 10.86, 10.75 and 13.74 (mmol/L)0.5 for the five treatments (Fig. 7c). There was also a significant positive regression between the soil SARe and the SARiw in the soil layers of 0–20 cm and 20–40 cm, respectively (*P < 0.05, Fig. 8). These findings are similar to those reported by Ayers and Westcot (1976) and may indicate that the quality of the irrigation water clearly affected the soil salinity and the relative concentration of some specific ions.
Table 4 shows the spatial distribution of inorganic nitrogen and available phosphorus in the root zone soil during the 3rd stage (before fertilizing). The inorganic nitrogen content of saturated-soil extract at 0–40 cm for GG1–GG5 was 2.75, 3.69, 3.31, 2.99, and 2.91 mg/L and the available phosphorus content of soil was 4.85, 5.69, 7.16, 5.07, and 5.90 mg/kg, respectively. From a multiple linear regression analysis, the available phosphorus content had a positive correlation with the treated effluent (**P < 0.01), and a negative correlation with the biomass of tall fescue (**P < 0.01), while the nitrogen content had no significant correlation with the treated effluent and the biomass. This result may be explained by the facts that the total phosphorus content of the treated effluent was 3 times that of the fresh water, while the total nitrogen was only 1.14 times (Table 1), and phosphorus is easily fixed in the soil. The growth of tall fescue affects the soil nutrient content, with more biomass absorbing more nutrients from the soil. However, further study is needed to evaluate the long-term effects of treated effluent irrigation on soil nutrient content.
3.4. Effect of treated effluent irrigation on soil pHe The soil original pHe was 7.68. As the salt leached out, an alkalizing phenomenon occurred (Fig. 9a). In the 2nd stage (September 2015), the pHe of GG1–GG5 was in the range of 8.06–8.20 in the surface soil. The increased pHe may be attributed to the high pH of irrigation water, the hydrolysis of exchangeable sodium (Beek and Breemen, 1973) or that the soil calcium carbonate was partially dissolved to increase the HCO3− content in the solution because the soil Ca2+ was leached with water (Chen et al., 2000). However, the pHe decreased at the end of the 2nd stage to 7.71, 7.56, 7.76, 7.29 and 7.44 for GG1–GG5 in the 0–60 cm of soil profile, respectively (Fig. 9b). These findings are similar to the results reported in previous studies (Li et al., 2015a; Sun et al., 2012; Wang et al., 2011). The decreased pH may be attributed to the
3.6. Response of tall fescue to treated effluent irrigation Fig. 11 shows the biomass of tall fescue for each treatment during the study period. In general, the biomass of tall fescue increased by 11%–80% when micro-sprinkler irrigated with treated effluent instead of freshwater. This finding is similar to those observed in other studies 228
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Fig. 9. Spatial distribution of pHe (pH of saturated-soil extracts) in the vertical transects for each treatment in September 2015 (A), November 2015 (B) and November 2016 (C).
2016, there was a high evaporation rate and rainless season, resulting in increased soil salinity in the rootzone. In fact, the soil salinity can delay the reviving time of tall fescue, which may affect the visual attractiveness and decrease the yield of the GG5 treatment.
4. Conclusions The present study showed that micro-sprinkler irrigation worked well in combination with different levels of treated effluent when applied to tall fescue in sea reclamation land. The irrigation management included an enhanced salt leaching stage, water-salt regulation stage and normal irrigation stage. The enhanced salt leaching stage and water-salt regulation stage were two main soil salt leaching periods, in which the first stage leached the soil salinity of the 0–10 cm layer well within 10 days, while the second stage leached the soil salinity above the gravel layer drop to less than 4 dS/m in the next 3.5 months. During the normal irrigation stage, the observed average ECe in the 0–60 cm soil layer mainly changed within the range of 1.80–4.01 dS/m. Therefore, it is feasible to use treated effluent to leach soil salinity by micro-sprinkler irrigation in sea reclamation land. The soil salinity increased as the percentage of treated effluent increased. During the enhanced salt leaching stage and water-salt regulation stage, irrigation with 50% treated effluent can rapidly leach into the soil because of its relatively higher infiltration property and lower salinity. However, during the normal irrigation stage, 75% treated effluent (i.e., irrigation water with an EC below 3.5–5.5 dS/m) is suggested to better control soil salinity in the sea reclamation land because it can keep the soil salinity below the salt tolerance threshold of tall fescue, even in the rainless season of the Bohai Gulf region. With soil salt leaching, the soil ECe and SARe both decreased, while the soil pHe increased first and then decreased. Their performances
Fig. 10. Response of average pHe (pH of saturated-soil extracts) in different soil layers to the percentage of treated effluent in November 2016.
(Al-Lahham et al., 2003; Al-Nakshabandi et al., 1997; Chakrabarti, 1995), and likely occurred because nutrients such as nitrogen and phosphate in treated effluent provide fertilizer value to plants (Toze, 2006). As Fig. 11 shows, the biomass of GG1–GG5 sampled in September 2015, August 2016 and November 2011, increased with the increasing percentage of treated effluent. During these period, nutrients of treated effluent promoted the growth of the plant. During the November 2015 sampling, there was no significant differences in biomass between the five treatments (Fig. 11a). During this time, tall fescue grew slowly because of the low temperature, and adding fertilizer may have offset the effects of the nutrient value of the applied water. In June of 2016, the growth biomass of different treatments followed the order of GG4 > GG5 > GG1 > GG2, GG3 (Fig. 11b). From March to June of
Table 4 The spatial distribution of soil inorganic nitrogen and available phosphorus in the middle of 2016. Treatments
GG1 GG2 GG3 GG4 GG5
(0%) (25%) (50%) (75%) (100%)
Inorganic nitrogen (mg/L)
Available phosphorus (mg/kg)
0–10 cm
10–20 cm
20–40 cm
0–10 cm
10–20 cm
20–40 cm
5.05 6.64 5.12 4.50 2.21
3.18 4.44 3.24 2.22 2.52
1.38 1.84 1.62 2.62 3.46
4.43 6.34 6.31 4.75 5.26
5.07 5.01 8.63 7.17 7.30
4.94 5.71 6.85 4.18 5.52
Inorganic nitrogen was from a saturated-soil extract; available phosphorus was extracted with 0.5 mol/L NaHCO3. 229
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Fig. 11. Growth biomass (and standard errors) of tall fescue for each treatment in 2015 (A) and 2016 (B). Different lowercase letters indicate significant differences (*P < 0.05) among treatments.
depended on the quality of irrigation water. Moreover, a positive correlation existed between soil available phosphorus content with treated effluent, and a negative correlation with biomass of tall fescue. In addition, irrigation with higher percentage of treated effluent generally increased the biomass of tall fescue. Overall, a method of micro-sprinkler irrigation with treated effluent and three stages of irrigation management (enhanced salt leaching, water-salt regulation and normal irrigation stage) could be used for tall fescue turf planting in sea reclamation land with a gravel-sand layer, but periodic examination of soil salinity may be needed, especially for years with less rainfall.
Chu, L.L., Kang, Y.H., Chen, X.L., Li, X.B., 2013. Effect of watering intensity on characteristics of water and salt movement under sprinkle irrigation in coastal soil. Trans. CSAE 29, 76–82 in Chinese with English abstract. Chu, L.L., Kang, Y.H., Wan, S.Q., 2014. Influence of microsprinkler irrigation amount on water, soil, and pH profiles in a coastal saline soil. Sci. World J. 2014 279895. GB18918-2002, 2003. Discharge Standard of Pollutants for Municipal Wastewater Treatment Plant. Standard Press of China, Beijing in Chinese. Li, R.N., 2016. China Environment Yearbook 2016. China Environmental Yearbook Publishing, Beijing in Chinese. Li, X.B., Kang, Y.H., Wan, S.Q., Chen, X.L., Chu, L.L., 2015a. Reclamation of very heavy coastal saline soil using drip-irrigation with saline water on salt-sensitive plants. Soil. Tillage Res. 146, 159–173. Li, X.B., Kang, Y.H., Wan, S.Q., Chen, X.L., Chu, L.L., 2015b. First and second-year assessments of the rapid reconstruction and re-vegetation method for reclaiming two saline-sodic, coastal soils with drip-irrigation. Ecol. Eng. 84, 496–505. Li, X.B., Kang, Y.H., Wan, S.Q., Chen, X.L., Liu, S.P., Xu, J.C., 2016. Response of a saltsensitive plant to processes of soil reclamation in two saline-sodic, coastal soils using drip irrigation with saline water. Agric. Water Manag. 164, 223–234. Liu, X.H., 2016. Shandong Statistical Yearbook 2016. China Statistics Press, Beijing, pp. 271–283 in Chinese. Maas, E.V., Hoffman, G.J., 1977. Crop salt tolerance–current assessment. J. Irrig. Drain. Div. 103, 115–134. OECD, 2015. Water Resources Allocation: Sharing Risks and Opportunities, OECD Studies on Water. OECD Publishing, Paris. Oster, J.D., 1994. Irrigation with poor quality water. Agric. Water Manag. 25, 271–297. Oster, J.D., Schroer, F.W., 1979. Infiltration as influenced by irrigation water-quality. Soil Sci. Soc. Am. J. 43, 444–447. Qian, Y.L., Mecham, B., 2005. Long-term effects of recycled wastewater irrigation on soil chemical properties on golf course fairways. Agron. J. 97, 717–721. Shalhevet, J., 1994. Using water of marginal quality for crop production: major issues. Agric. Water Manag. 25, 233–269. Sun, X.M., 2007. Sustainable Utilization Study of Groundwater Resources in CircumBohai-Sea Region. China University of Geosciences, Beijing in Chinese. Sun, J.X., Kang, Y.H., Wan, S.Q., Hu, W., Jiang, S.F., Zhang, T.B., 2012. Soil salinity management with drip irrigation and its effects on soil hydraulic properties in north China coastal saline soils. Agric. Water Manag. 115, 10–19. Sun, J.X., Kang, Y.H., Wan, S.Q., 2013. Effects of an imbedded gravel-sand layer on reclamation of coastal saline soils under drip irrigation and on plant growth. Agric. Water Manag. 123, 12–19. Tanji, K.K., 1990. Agricultural Salinity Assessment and Management. American Society of Civil Engineers, New York. Toze, S., 2006. Reuse of effluent water- benefits and risks. Agric. Water Manag. 80, 147–159. Wang, R.S., Kang, Y.H., Wan, S.Q., Hu, W., Liu, S.P., Liu, S.H., 2011. Salt distribution and the growth of cotton under different drip irrigation regimes in a saline area. Agric. Water Manag. 100, 58–69. Wang, W., Liu, H., Li, Y.Q., Su, J.L., 2014. Development and management of land reclamation in China. Ocean. Coast. Manag. 102, 415–425. Wei, H.J., 2016. Liaoning Statistical Yearbook 2016. China Statistics Press, Beijing, pp. 219–222 in Chinese. Wu, J.D., Peng, Z.L., 2016. Tianjin Statistical Yearbook 2016. China Statistics Press, Beijing, pp. 246–255 in Chinese. Yao, R.J., Yang, J.S., Wu, D.H., Xie, W.P., Wang, X.P., Zhang, X., 2017. Scenario simulation of field soil water and salt balances using sahysmod for salinity management in a coastal rainfed farmland. Irrig. Drain. 66, 872–883.
Acknowledgements This study was supported by the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant No. QYZDJ-SSWDQC028), the National Science Foundation for Young Scientists of China (Grant No. 51709251) and the National Key Research and Development Program of China (Grant No. 2016YFC0501304, 2014 BAD12B05 and 2016YFC0501305). References Al-Hamaiedeh, H., Bino, M., 2010. Effect of treated grey water reuse in irrigation on soil and plants. Desalination 256, 115–119. Al-Lahham, O., El Assi, N.M., Fayyad, M., 2003. Impact of treated wastewater irrigation on quality attributes and contamination of tomato fruit. Agric. Water Manag. 61, 51–62. Al-Nakshabandi, G.A., Saqqar, M.M., Shatanawi, M.R., Fayyad, M., Al-Horani, H., 1997. Some environmental problems associated with the use of treated wastewater for irrigation in Jordan. Agric. Water Manag. 34, 81–94. Asano, T., Pettygrove, G.S., 1987. Using reclaimed municipal wastewater for irrigation. Calif. Agric. 41, 15–18. Ayers, R.S., Westcot, D.W., 1976. Water Quality for Agriculture. FAO Irrig. And Dr., Rome. Bao, S.D., 2000. Soil and Agriculture Chemistry Analysis. China Agriculture Press, Beijing in Chinese. Beek, C., Breemen, N.V., 1973. The alkalinity of alkali soils. Eur. J. Soil. Sci. 24, 129–136. Chakrabarti, C., 1995. Residual effects of long-term land application of domestic wastewater. Environ. Int. 21, 333–339. Chen, W., Chen, B.B., Shen, Q.R., 2000. Study on the pH change and alkali in the salt leaching process of coastal saline soil. Acta Pedol. Sin. 37, 521–527 in Chinese. Chen, X.L., Kang, Y.H., Wan, S.Q., Chu, L.L., Li, X.B., 2015a. Chinese rose (Rosa chinensis) cultivation in Bohai bay, China, using an improved drip irrigation method to reclaim heavy coastal saline soils. Agric. Water Manag. 158, 99–111. Chen, X.L., Kang, Y.H., Wan, S.Q., Li, X.B., Guo, L.P., 2015b. Influence of mulches on urban vegetation construction in coastal saline land under drip irrigation in north China. Agric. Water Manag. 158, 145–155.
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Effect of the micro-sprinkler irrigation method with treated effluent on soil physical and chemical properties in sea reclamation land
T
⁎
Na Lia,c, Yaohu Kanga,b, , Xiaobin Lia, Shuqin Wana, Jiachong Xua,c a
Key Laboratory of Water Cycle and Related Land Surface Process, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Science, Beijing, 100101, China b College of Resources and Environment, University of Chinese Academy of Science, Beijing, 100049, China c University of Chinese Academy of Sciences, Beijing, 100049, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Salt leaching Irrigation management Tall fescue Saline soil
To develop a micro-sprinkler method with treated effluent for tall fescue (Festuca arundinacea) cultivation in sea reclamation land and test its effect on soil physical and chemical properties, a field experiment with five treatments of water quality was conducted in 2015–2016. The five treatments of water quality were created with a mixture of treated effluent (EC, 4.2–6.9 dS/m) and fresh groundwater, and the percentage of treated effluent was 0%, 25%, 50%, 75% and 100%. Saline soil contained a gravel-sand layer imbedded at depth of 60 cm. Irrigation management was divided into three stages, enhanced salt leaching stage (continuous irrigation), water-salt regulation stage (irrigation based on the soil matric potential (SMP) at −5 KPa) and normal irrigation stage (irrigation based on the SMP at −20 KPa). The results indicated that the first stage lasted for 10 days, while the electrical conductivity of saturated extracts (ECe) of the surface 10 cm from 38.29 dS/m dropped to 4.23–6.28 dS/m. After the second stage (3.5 months), the ECe in the 0–60 cm soil layer dropped to 1.42–3.16 dS/ m. During these stages, treatment with 50% treated effluent led to relatively good infiltration and lower salinity and was therefore good at enhancing the salt leaching efficiency. In the third stage, the observed ECe of the 0–60 cm changed slightly, but ≤75% treated effluent could maintain the soil salinity below the threshold salinity of tall fescue, even in the rainless season. During the process, soil sodium adsorption ratio decreased, while soil pH increased first and then decreased. Soil available phosphorus content showed a close correlation with treated effluent and the biomass of tall fescue. Moreover, the tall fescue maintained normal growth. Therefore, it is possible to use treated effluent to micro-sprinkler irrigation on tall fescue in sea reclamation land.
1. Introduction Sea reclamation has been a common approach to increase the land area for living and developing along the coastal areas in many parts of the world. In China, a total reclamation area of 2469 km2 was approved by the State Council in 2011–2020 for economic development (Wang et al., 2014). In sea reclamation land, bare ground is exposed, which not only affects the landscape, but also leads to sandstorms. Landscape construction is required to meet the demands of living and developing environments. Sea reclamation land is usually very saline; for example, the mean electrical conductivity of saturated-soil extracts (ECe) is more than 30 dS/m in our study area (Li et al., 2015a). Moreover, the salt composition in the study area is similar to that of seawater, with chlorine and sodium being the main ions, accounting for 60–80% of the total,
respectively. There is also a high water table at 0.5–3 m, and the aquifer contains saline water. Traditional reclamation methods, such as applying gypsum, combining surface irrigation and water drainage technologies have made it difficult to improve saline soil for plants. Although some halophyte plants, such as Tamarix chinensis can survive under such conditions, they are not sufficient to create a better landscape. Replacing saline soil with non-saline soil is the most popular method used in our research area, but this is limited by high economic input and the increasing difficulty in identifying large amounts of nonsaline soil resources. Recently, several studies have been conducted in the Bohai Gulf region, east China. Sun et al. (2013) found that a gravel-sand layer at depth of 80 cm was effective at preventing the upward movement of salt into the surface soil from shallow saline groundwater during winter. Li et al. (2015b) found that the technology of surface drip
⁎ Corresponding author: Key Laboratory of Water Cycle and Related Land Surface Processes, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, 11A Datun Road, Anwai, Beijing, 100101, China. E-mail address: [email protected] (Y. Kang).
https://doi.org/10.1016/j.agwat.2018.10.023 Received 8 May 2018; Received in revised form 13 October 2018; Accepted 17 October 2018 0378-3774/ © 2018 Elsevier B.V. All rights reserved.
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Fig. 1. Planting pattern, soil treatment and installation of tensiometer.
approximately 555 mm, most of which occurs from July to September. The soil of the study area is sandy loam soil and the region was reclaimed from the sea in 2007. The soil salt composition was similar to that of seawater, with chlorine and sodium comprising the main ions. The average electrical conductivity, pH (pHe) and sodium adsorption ratio (SARe) of the saturated-soil extracts above a soil depth of 60 cm were ECe = 38.3 dS/m, pHe = 7.68, and SARe = 69.4 (mmol/L)0.5; Water table 0.8–1.2 m. The average soil bulk density of the initial saline soils was 1.69 g/cm3 in the 0–60 cm soil layers, which was reduced to 1.55 g/cm3 after soil tillage. The soil nutrient characteristics for 0–60 cm soil layers were: organic matter content 11.4 g/kg, total N 0.24 g/kg, available phosphorus 8.1 mg/kg, available potassium 464 mg/kg.
irrigation with phased irrigation management could enhance salt leaching and maintain good plant growth. The drip irrigation was started based on the soil matric potential (SMP) at 20 cm, and the SMP target value was adjusted according to the process of salt-leaching, irrigation water quality and plant growth. Li et al. (2015a) found that when the SMP was controlled at above −5 and −10 KPa in the two irrigation stages, drip irrigation with 4.01 dS/m saline water could maintain a 50% survival rate for salt-sensitive plants. In a study investigating drip irrigation with freshwater, Chen et al. (2015a) controlled the SMP threshold into three stages of −5, −10 and −20 KPa. In addition, micro-sprinkler irrigation of tall fescue (Festuca arundinacea) with freshwater was also conducted when the SMP was controlled above −5, −15 and −20 KPa (Chu et al., 2014). The freshwater supply of the Bohai Gulf region, including the research area, is very limited, with only 660 m3 per capita (Sun, 2007). Moreover, there were about 3.9 billion m3 of treated effluent in the coastal cities of the Bohai Gulf region in 2015 (Li, 2016; Liu, 2016; Wei, 2016; Wu and Peng, 2016), while the utilization rate was only 8.3% (Li, 2016), which is far lower than the 80% in Israel (OECD, 2015). There has been a great deal of research on irrigation with treated effluent, and the results of these studies have identified potential salinity as a restriction to the use of treated effluent. The characteristics of treated effluent, such as the salt content and concentration of specific chemical elements, may cause soil salt accumulation, plant damage or soil permeability problems (Al-Hamaiedeh and Bino, 2010; Asano and Pettygrove, 1987; Oster, 1994; Toze, 2006). Furthermore, spraying plants with saline water may cause foliar damage because many plants absorb salts directly through their leaves (Shalhevet, 1994; Tanji, 1990). Tall fescue is a plant widely used in landscapes that has a salt tolerance threshold of 3.9 dS/m (Maas and Hoffman, 1977). The present study was conducted to develop a micro-sprinkler irrigation for application of treated effluent to tall fescue in sea reclamation land. The specific goals were (1) to test the process and effect of soil salinity leaching during irrigation with different levels of treated effluent; and (2) to find the correct percentage of treated effluent for use as long-term irrigation water and to maintain normal growth of plants and soil health.
2.2. Experimental design 2.2.1. Plot layout and experiment design Based on the successful reclamation of the coastal saline soil (Chen et al., 2015a, 2015b; Chu et al., 2014; Li et al., 2016, 2015a, 2015b; Sun et al., 2012), the soil treatments before planting were as follows: soil was removed to a depth of about 60 cm A 10-cm thick gravel layer and a 5-cm thick sand layer were laid in the bottom to cut off the capillary porosity (Fig.1). Several polyvinyl chloride tubes were placed at the low edge of the gravel-sand layer, with spacings of 10 m, to allow the leaching water to flow out, after which the saline sodic soil was backfilled and levelled. The irrigation water was a mixture of treated effluent and fresh water. The treated effluent, which was from the Caofeidian District Sewage Treatment Plant maintained by the Tangshan-Caofeidian drainage operating companies, was transported and stored in a small reservoir. The quality of treated effluent met the first-grade national standard for wastewater discharge (GB18918-2002, 2003). Fresh water was pumped from a deep-layer groundwater well located at the experimental site. There were five irrigation water treatments with percentages of treated effluent were: 0% (GG1), 25% (GG2), 50% (GG3), 75% (GG4) and 100% (GG5). All treatments were replicated three times with the experimental plots arranged in a complete randomized block design. The area of each plot was 9.0 by 6.0 m, and the distance between the plots was 2.5 m. Each plot contained 6 micro-sprinklers with a 3.0 m space between them. According to Chu et al. (2013), a micro-sprinkler (Beijing Luckrain Plastic Industry Ltd., China) with a flow rate of 120 L/ h at 0.2 MPa operating pressure and a wetted diameter of about 3.1 m was selected. The tall fescue (Houndog V) turf sod covered over the saline-sodic soil directly. The irrigation water quality and its degree of restriction on permeability are presented in Tables 1 and 2. The salt concentration of the treated effluent (electrical conductivity of irrigation water, ECiw,
2. Materials and methods 2.1. Experimental site Experiments were conducted in 2015–2016 at the Industrial Zone (39°03′N, 118°48′E), located in the Caofeidian District in the south of Tangshan City, east China. This region is located in the northern portion of the Bohai Gulf, which borders the Pacific Ocean. The station has a typical semi-humid monsoon climate and annual precipitation of 223
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Table 1 Concentrations of main ions and compounds in irrigation water. Irrigation water
Main ion and some substances concentration (mg/L)
Fresh Water Treated effluent
Ca2+
Na+
K+
Mg2+
SO42−
CO32−
HCO3−
Cl−
B
COD
TN
TP
9.6 72.0
214.2 802.8
1.6 29.5
8.3 97.7
6.2 260.4
41.0 18.0
407.0 312.3
56.0 1160.0
0.4 0.6
10.0 66.0
36.6 41.9
0.5 1.5
Calcium = Ca2+, sodium = Na+, potassium = K+, magnesium = Mg2+, carbonate = CO32−, bicarbonate = HCO3-, chlorion = Cl-, boron = B, chemical oxygen demand = COD, total nitrogen = TN, total phosphorus = TP.
gravel layer) were collected in mid-July, mid-September, and early November 2015, as well as in mid-March, early-July, and early-November 2016. The soil was obtained horizontally at 0, 50, 100, 150 cm from the micro-sprinkler and all sample depths in the vertical apart were the same: 0–10, 10–20, 20–30, 30–40, 40–50 and 50–60 cm. The soil ECe, pHe, inorganic nitrogen (Nmin) and soluble cations were based on extracts of saturated soil. The ECe and pHe were determined by a conductivity meter (DDS-307, REX, Shanghai, China) and a pH meter (PHS-3C, REX, Shanghai, China), respectively. Nmin included nitrate nitrogen and ammonium nitrogen, which were measured by means of colorimetry (Bao, 2000), respectively. Soluble cations such as Na+, K+, Ca2+ and Mg2+ were measured with ICP-OES (Optima 5300DV, USA). Available phosphorus was extracted with 0.5 mol/L NaHCO3 (Bao, 2000). The SAR was calculated as follows:
Table 2 Irrigation water electrical conductivity (ECiw), pH (pHiw), sodium adsorption ratio (SARiw) and its restrictions on permeability. Irrigation water
ECiw (dS/m)
pHiw
SARiw (mmol/L)0.5
Degree of restriction on permeability
GG1 GG2 GG3 GG4 GG5
1.0 1.8 2.7 3.5 4.4
9.1 8.8 8.6 8.4 8.2
12.2 11.4 12.4 13.4 14.5
Severe Slight to moderate Slight None None
(0%) (25%) (50%) (75%) (100%)
Values of ECiw, pHiw, and SARiw of irrigation water sampled in October 2015.
4.2–6.9 dS/m) was several times higher than that of the fresh water (ECiw, 1.0 dS/m), similar to the nutrient concentration. The ECiw and sodium adsorption ratio of irrigation water (SARiw) increased and the pH of the irrigation water (pHiw) decreased as the percentage of treated effluent increased. According to the evaluation of permeability using ECiw and SARiw proposed by Ayers and Westcot (1976), the irrigation water of the GG1 treatment posed a “severe” degree, while the GG2 and GG3 treatments posed a “slight to moderate” degree and a “slight” degree, respectively. There was no restriction on permeability of GG4 and GG5 treatments. The number of fecal coliforms in treated effluent was 130–1700 cfu/L, while the heavy metals levels were suitable for irrigation, except for Se, which was present at 0.029 mg/L (Ayers and Westcot, 1976). The irrigation management was divided into three stages, including enhanced salt leaching stage (1st stage), water-salt regulation stage (2nd stage), and normal irrigation stage (3rd stage). The first two stages were the two main salt leaching periods. The 1st stage was designed to leach salt from the 0–10 cm layer of the soil with continuous irrigation, during which time about 10–20 mm of water was applied per day. The stage ended when the soil ECe of the 0–10 cm layer was close to or less than 6 dS/m. During the 2nd stage, salt was leached from the soil above the gravel-sand layer by ensuring the net downward movement of water (Asano and Pettygrove, 1987). According to the successful reclamation of drip irrigation with saline water in coastal saline soil (Li et al., 2015a), the irrigation was based on the SMP at a depth of 0.2 m, which was controlled at −5 KPa. The stage terminated when the average soil ECe was < 4 dS/m above the gravel-sand layer, since the salinity tolerance threshold of tall fescue was about 3.9 dS/m. The 3rd stage was normal irrigation, during which irrigation was applied when the SMP reached the target value, −20 KPa. During the second and last stages, the depth of water for each irrigation event was 10 mm, and the target value could be adjusted uniformly according to the tall fescue growth and the soil salinity. Fertilizer was applied uniformly to each treatment in early October 2015 and July 2016, respectively. The rates of N, P2O5 and K2O application were 20 g/m2/y, 5 g/m2/y and 10 g/m2/y, respectively. In addition, tall fescue was trimmed and weeded regularly.
SAR =
([Ca2 +]
[Na+] + [Mg 2 +])0.5
(1)
where the concentration of each cation was in mmol/L. In this experiment, average ECe, pHe, SARe and Nmin within the soil profile was calculated as follows:
ECe (t ) or pHe (t ) or SAR e (t ) or Nmin (t ) n, m
∑ j, k ECe (t , j, k )[or pHe (t , j, k ); or SAR e (t , j, k ); or =
Nmin (t , j, k )] × S (j, k ) n, m ∑ j, k S (j, k )
(2)
in which, t represents the time when soil samples were obtained; j the four horizontal distances (n) from the micro-sprinkler where soil samples were obtained; k the depth (m) of the soil sample and S (j, k) the depth interval of the soil layer. The growth biomass of tall fescue was determined when it has sufficient height for harvesting (> 20 cm). All the plots were trimmed at the same time. There was five times harvest during the study period. The fresh biomass in each plot was weighted, and some was used to determine the water content. The growth biomass (Qgr ) was calculated as follows:
Qgr (t ) = Qfre (t ) × (1 − w )
(3)
where Qfre is the weight of the fresh tall fescue (kg/ha), w is the water content of the fresh tall fescue (%), and t is the moving time.
2.3. Statistical procedures Data were analyzed using IBM SPSS Statistics ver.19.0 (IBM Co., Armonk, NY, USA). The differences in growth biomass of tall fescue among treatments were compared using one-way Analyses of variance (ANOVA), the least significant difference test at a significance level of 0.05. The figures were prepared using Sigma Plot 10.0 (Systat Software, Inc., Chicago, IL, USA).
2.2.2. Observation and measurements There was one tensiometer installed in one plot for each treatment for observation of SMP at a depth of 0.2 m (Fig. 1), and observations were made daily at 8:00 and 16:00. Soil samples of each plot (above the 224
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Fig. 2. Precipitation during the study period.
3. Results and discussion
3.2. Effect of treated effluent irrigation on soil salinity (ECe)
3.1. Precipitation, irrigation amount and soil matric potential
ECe is the electrical conductivity of a saturated-soil extract. At the experimental site, the soil ECe in the 0–60 cm soil layer before planting tall fescue turf was relatively uniform, with an average of 38.29 dS/m.
3.1.1. Precipitation Fig. 2 shows the precipitation for the area during the study period. From July to November 2015, about 120 days after planting, the total precipitation was 395 mm. There was no rain during the 1st stage, and almost all of the rain was concentrated in the 2nd stage. During the 3rd stage (March–November 2016), the total precipitation was 539 mm. The rainfall events mainly occurred from mid-July to September 2015, mid-late June 2016, and late July to early September 2016. There is no rain data for the period from November to March, but the average amount was 32 mm in the same period during the past 30 years.
3.2.1. Effect of treated effluent on soil salt leaching Fig. 4 shows the spatial distribution of ECe in the vertical transects for each treatment at different soil sampling times. The salinity changed significantly in the 1st stage and the 2nd stage (Fig. 4a–c). The 1st stage lasted for 10 d, and the salinity of upper soil was well leached. The average ECe in the 0–10 cm soil profile for the GG1–GG5 treatments decreased to 3.73, 4.09, 3.81, 4.91 and 6.28 dS/m, respectively, the corresponding reductions were 90.27%, 89.32%, 90.04%, 87.17% and 83.61% of the initial soil ECe (Fig. 4a). The 2nd stage lasted for 3.5 months, as the soil salinity above the gravel layer continued to decline. In November of 2015 (Fig. 4c), the average ECe values of the 0–40 cm soil layer for the GG1–GG5 treatments decreased to 0.66, 1.44, 1.57, 1.91 and 2.22 dS/m, with an average value of 1.56 dS/m. For 0–60 cm, the values decreased to 1.42, 2.46, 2.25, 2.72 and 3.01 dS/m, respectively. Although the ultimate soil salinity increased with increasing percentages of treated effluent, the ECe values were lower than the salt tolerance threshold for tall fescue, indicating that the 2nd stage was completed. The 1st stage and the 2nd stage were two main soil salt leaching periods. Based on the ultimate soil salinity at the end of each stage, the 1st stage was the fastest desalination period, with an average decrease in ECe of 2.40 dS/m per day in the 0–60 cm soil layer. In addition, the salt leaching efficiency of the five treatments was different, even when they were irrigated with an equivalent amount of water (110 mm, Table 3). At the end of the 1st stage, the average ECe in the 0–60 cm soil profile for the GG1–GG5 treatments was 14.48, 14.02, 13.25, 13.59 and 15.87 dS/m. The salt leaching efficiency increased as the percentage of treated effluent increased to 50%, then decreased, while for the surface soil, the GG1 and GG3 treatments leached salinity faster than the other treatments. These results suggested that irrigation with 50% treated effluent could enhance the desalting process in the experimental region, and that using freshwater tend to rapidly reduce the salinity of the surface soil (Oster, 1994). Based on the information presented above, lower water salinity and
3.1.2. Irrigation The irrigation for each treatment during the tall fescue growing season is shown in Table 3. The 1st stage and 2nd stage lasted for 10 days and 3.5 months, respectively. A total of approximately 410–500 mm irrigation water was applied, and no obvious patterns were obtained among treatments. During the 3rd stage, the irrigation amount ranged from 280 to 400 mm for treatments GG1–GG5 over the growing season (about 7.5 months), and the irrigation amount increased with the increasing percentage of treated effluent, except for GG3.
3.1.3. Soil matric potential Fig. 3 presents the change in SMP at a depth of 20 cm during the study period. In the 2nd stage, the SMP threshold was controlled well above −5 KPa, then adjusted to −10 KPa in the later period of 2015 to promote root growth to the deep layer for winter survival. During most of this stage, the SMP changed above the controlled values, but some SMP values were beyond the controlled threshold. This was likely because the twice-daily monitoring data from the tensiometer showed a bit of a lag. In the 3rd stage, the SMP threshold was mostly controlled at −20 KPa, except for one period that was controlled at −10 KPa to alleviate the salt damage to plants in a rainless season. The SMP fluctuated increasingly, because the soil water changed greatly as water consumption and evapotranspiration increased on hot days. Table 3 Precipitation and irrigation amount for each treatment during the study period. Treatments
GG1 GG2 GG3 GG4 GG5
(0%) (25%) (50%) (75%) (100%)
Enhanced salt leaching stage (Jul. 5, 2015–Jul. 14, 2015)
Water-salt regulation stage (Jul. 2015–Nov. 2015)
Normal irrigation stage (Mar. 2016–Nov. 2016)
Rainfall amount (mm)
Irrigation amount (mm)
Rainfall amount (mm)
Irrigation amount (mm)
Rainfall amount (mm)
Irrigation amount (mm)
0
110 110 110 110 110
395
380 300 340 390 390
539
300 340 280 370 400
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Fig. 3. Change of SMP (soil matric potential) at a depth of 20 cm during the growing season of tall fescue in 2015–2016.
Fig. 4. Spatial distribution of ECe (electrical conductivity from saturated paste extracts) in the vertical transects for each treatment in July 2015 (A), September 2015 (B), November 2015 (C), March 2016 (D), July 2016 (E), and November 2016 (F).
SL0–20 cm = 1.722 + 0.135 SARiw + 0.646 ECiw – 0.054 SARiw ECiw, R2 = 0.982; and, SL0–60 cm = 0.065 + 0.183 SARiw + 1.105 ECiw – 0.084 SARiw ECiw, R2 = 0.990, respectively.
good infiltration capacity of the irrigation water were likely to be the main factors that clearly affected the salt leaching efficiency. A lower ECiw means that less salinity is inputted into the soil via the irrigation water, while more salinity enters the soil when the irrigation water has a higher ECiw. A high infiltration rate means that more water can move into the soil and be used for leaching salt, especially in the deeper layers. Because the infiltration rate decreased with increasing SAR and decreasing total cation concentration (Oster and Schroer, 1979), nonlinear regression equations were used to describe the relationship of the salt leaching rate (SL, dS/m/d), SARiw ((mmol/L)0.5) and ECiw (dS/m) in the soil profiles of 0–20 cm and 0–60 cm. The regression equations were as follows:
3.2.2. Change in distribution of soil salt after winter From November–March there were almost no irrigation events, except for 30 mm of winter water. When compared with the average ECe value of the surface soil (0–20 cm) in November of 2015, it increased by 0.30–0.50 dS/m in the five treatments in March of 2016 (Fig. 4d). The increase in ECe was most likely because of the upward movement of soil salinity with water from the lower layer to the upper 226
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Fig. 5. Change of soil ECe (electrical conductivity from saturated paste extracts) at 0–20 cm (A), 0–40 cm (B) and 0–60 cm (C) for each treatment at different sampling times; 3.9 dS/m is the salt tolerance threshold of tall fescue.
total amount above the gravel layer was still higher than that in March of 2016. The accumulated soil salinity was leached during the rainy season, with a total of 358 mm rainfall occurring from July to November 2016. Fig. 4f and Fig. 5 show the spatial distribution of soil salinity in November of 2016. The average ECe values ranged from 1.98 to 2.60 dS/m at depths of 0 to 60 cm for the five treatments, representing decreases of 0.29–1.41 dS/m when compared with those observed in July of 2016. Similar to the soil profiles of 0–40 and 0–20 cm, the average ECe decreased to 0.98–2.16 dS/m and 0.66–2.40 dS/m, respectively. Moreover, the linear growth in soil salinity was highly correlated with the increasing percentage of treated effluent (*P < 0.05, Fig. 6b). When compared to the average ECe in March of 2016, the soil salinity of the five treatments sampled in November 2016 also declined, except for GG1. At 0–60 cm, the ECe values changed by 0.44, −0.42, −0.16, −0.37 and −0.19 dS/m (Fig. 5c) for the GG1–GG5 treatments. At 0–20 cm, only the ECe value of the GG5 treatment was 0.36 dS/m higher than that in March (Fig. 5a). Throughout one-year of water management during the 3rd stage, the soil salinity changed slightly or declined continually. During the rainless season, temporary salt accumulation was found in all treatments, and the average ECe of GG5 was likely beyond the salt tolerance threshold of the tall fescue. However, the accumulated salt was well leached during the rainy season. Therefore, micro-sprinkler irrigation with ECiw in the range of 4.21–6.89 dS/m is possible for sea reclamation land, but periodic examination of the soil salinity may be needed, especially for periods in which there is less rainfall. To mitigate the risk of soil salinity accumulation, it is suggested that 75% treated effluent (i.e., the ECiw should be maintained below 3.5–5.5 dS/m) be used to irrigate tall fescue in the Bohai Bay coastal region.
layer. However, the average ECe value at 0–60 cm for treatments GG1–GG5 was 1.54, 2.23, 2.33, 2.81 and 2.79 dS/m, respectively (Fig. 5c). These results suggest that there was almost no salts leaching or accumulation in the soil above the gravel-sand layer during winter and indicated that little salt moved into the upper soil from the groundwater below the gravel-sand layer, similar to the results found in previous reports (Chen et al., 2015a, 2015b; Chu et al., 2014; Li et al., 2016, 2015a, 2015b; Sun et al., 2012, 2013). Moreover, the average soil ECe in the 0–60 cm layer was still below 4 dS/m, which indicated that the irrigation management entered into the 3rd stage. 3.2.3. Effect of treated effluent on soil salinity in the normal irrigation stage In the 3rd stage, the irrigation was applied to maintain soil health and ensure the normal growth of tall fescue. The soil ECe in July 2016 increased as the percentage of treated effluent increased, and there were significant positive linear correlations between the soil ECe and the percentage of treated effluent at 0–20 cm (**P < 0.01), 0–40 cm (**P < 0.01) and 0–60 cm (*P < 0.05) (Fig. 6a), which was similar to the results observed during long-term irrigation with recycled wastewater in a previous study (Qian and Mecham, 2005). Fig. 4e shows the spatial distribution of the soil salinity in early July 2016, during which time the ECe value in all soil layers except for the surface soil was higher than that in March of 2016. The average ECe value at 0–60 cm was 2.27, 3.17, 2.83, 3.38 and 4.01 dS/m for GG1–GG5, respectively, representing an increase of 0.50–1.22 dS/m (Fig. 5c). Moreover, the ECe value in the profiles of 0–40 cm ranged from 1.53 to 2.96 dS/m, representing an increase of 0.10–0.68 dS/m (Fig. 5b). The increased soil salinity may be attributed to the irrigation water quality in the rainless season (Yao et al., 2017). From March to June, there was a total rainfall of 182 mm, but approximately 120 mm of which fell in mid-late June. In truth, the average ECe at 0–40 cm in late May had been increased to 1.32, 2.82, 3.35, 3.34 and 4.44 dS/m for GG1–GG5, respectively (Fig. 5b). It should be noted that for the GG5 treatment, the average soil salinity exceeded the salt tolerance threshold of tall fescue. After the precipitation in June, the soil salinity, especially in the surface soil, was well leached and decreased, but the
3.3. Effect of treated effluent irrigation on soil SARe The SARe is the sodium adsorption ratio of a saturated-soil extract. At the experimental site, the average soil SARe in the 0–60 cm soil profile before planting tall fescue was 69.4 (mmol/L)0.5. At the end of
Fig. 6. Response of average ECe (electrical conductivity from saturated paste extracts) in July 2016 (A) and November 2016 (B) to the percentage of treated effluent. 227
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Fig. 7. Spatial distribution of SARe (sodium adsorption ratio of saturated-soil extracts) in the vertical transects for each treatment in July 2015 (A), November 2015 (B) and July 2016 (C).
soil cation exchange, precipitation, evaporation, and addition of fertilizers (Beek and Breemen, 1973). During the 3rd stage, the pHe varied noticeably. After one-year of water management, the average pHe was 7.40, while that in the GG1, GG2, GG3, GG4 and GG5 treatments was 7.54, 7.47, 7.39, 7.37 and 7.25, respectively, in 0–60 cm soil profile (Fig. 9c). As shown in Fig. 10, the soil pHe decreased with the increasing percentage of treated effluent, and significant correlations were observed at 0–20 cm (**P < 0.01), 20–40 cm (*P < 0.05) and 40–60 cm (*P < 0.05). These results were different from those reported by Qian and Mecham (2005), who found that irrigation with treated effluent led to a 0.3 unit increase in pH. This difference may have been the result of the characteristics of the irrigation water, such as the bicarbonate level. In the study by Qian and Mecham (2005), the pH and bicarbonate concentration of treated effluent were higher than those of surface water, which was the opposite of the water applied in the present study.
Fig. 8. Response of average SARe (sodium adsorption ratio of saturated-soil extracts) in different soil layers to SARiw (sodium adsorption ratio of irrigation water) in July 2016.
3.5. Effect of treated effluent irrigation on soil inorganic nitrogen and available phosphorus
the 1st stage, the average SARe value of the five treatments decreased by 57.8%–29.3 (mmol/L)0.5 (Fig. 7a), while at the end of the 2nd stage, the SARe values for GG1–GG5 decreased by 81.1%–88.0% of the initial value (Fig. 7b), after which they changed slightly. In early July of 2016, the SARe values were 9.36, 7.12, 10.86, 10.75 and 13.74 (mmol/L)0.5 for the five treatments (Fig. 7c). There was also a significant positive regression between the soil SARe and the SARiw in the soil layers of 0–20 cm and 20–40 cm, respectively (*P < 0.05, Fig. 8). These findings are similar to those reported by Ayers and Westcot (1976) and may indicate that the quality of the irrigation water clearly affected the soil salinity and the relative concentration of some specific ions.
Table 4 shows the spatial distribution of inorganic nitrogen and available phosphorus in the root zone soil during the 3rd stage (before fertilizing). The inorganic nitrogen content of saturated-soil extract at 0–40 cm for GG1–GG5 was 2.75, 3.69, 3.31, 2.99, and 2.91 mg/L and the available phosphorus content of soil was 4.85, 5.69, 7.16, 5.07, and 5.90 mg/kg, respectively. From a multiple linear regression analysis, the available phosphorus content had a positive correlation with the treated effluent (**P < 0.01), and a negative correlation with the biomass of tall fescue (**P < 0.01), while the nitrogen content had no significant correlation with the treated effluent and the biomass. This result may be explained by the facts that the total phosphorus content of the treated effluent was 3 times that of the fresh water, while the total nitrogen was only 1.14 times (Table 1), and phosphorus is easily fixed in the soil. The growth of tall fescue affects the soil nutrient content, with more biomass absorbing more nutrients from the soil. However, further study is needed to evaluate the long-term effects of treated effluent irrigation on soil nutrient content.
3.4. Effect of treated effluent irrigation on soil pHe The soil original pHe was 7.68. As the salt leached out, an alkalizing phenomenon occurred (Fig. 9a). In the 2nd stage (September 2015), the pHe of GG1–GG5 was in the range of 8.06–8.20 in the surface soil. The increased pHe may be attributed to the high pH of irrigation water, the hydrolysis of exchangeable sodium (Beek and Breemen, 1973) or that the soil calcium carbonate was partially dissolved to increase the HCO3− content in the solution because the soil Ca2+ was leached with water (Chen et al., 2000). However, the pHe decreased at the end of the 2nd stage to 7.71, 7.56, 7.76, 7.29 and 7.44 for GG1–GG5 in the 0–60 cm of soil profile, respectively (Fig. 9b). These findings are similar to the results reported in previous studies (Li et al., 2015a; Sun et al., 2012; Wang et al., 2011). The decreased pH may be attributed to the
3.6. Response of tall fescue to treated effluent irrigation Fig. 11 shows the biomass of tall fescue for each treatment during the study period. In general, the biomass of tall fescue increased by 11%–80% when micro-sprinkler irrigated with treated effluent instead of freshwater. This finding is similar to those observed in other studies 228
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Fig. 9. Spatial distribution of pHe (pH of saturated-soil extracts) in the vertical transects for each treatment in September 2015 (A), November 2015 (B) and November 2016 (C).
2016, there was a high evaporation rate and rainless season, resulting in increased soil salinity in the rootzone. In fact, the soil salinity can delay the reviving time of tall fescue, which may affect the visual attractiveness and decrease the yield of the GG5 treatment.
4. Conclusions The present study showed that micro-sprinkler irrigation worked well in combination with different levels of treated effluent when applied to tall fescue in sea reclamation land. The irrigation management included an enhanced salt leaching stage, water-salt regulation stage and normal irrigation stage. The enhanced salt leaching stage and water-salt regulation stage were two main soil salt leaching periods, in which the first stage leached the soil salinity of the 0–10 cm layer well within 10 days, while the second stage leached the soil salinity above the gravel layer drop to less than 4 dS/m in the next 3.5 months. During the normal irrigation stage, the observed average ECe in the 0–60 cm soil layer mainly changed within the range of 1.80–4.01 dS/m. Therefore, it is feasible to use treated effluent to leach soil salinity by micro-sprinkler irrigation in sea reclamation land. The soil salinity increased as the percentage of treated effluent increased. During the enhanced salt leaching stage and water-salt regulation stage, irrigation with 50% treated effluent can rapidly leach into the soil because of its relatively higher infiltration property and lower salinity. However, during the normal irrigation stage, 75% treated effluent (i.e., irrigation water with an EC below 3.5–5.5 dS/m) is suggested to better control soil salinity in the sea reclamation land because it can keep the soil salinity below the salt tolerance threshold of tall fescue, even in the rainless season of the Bohai Gulf region. With soil salt leaching, the soil ECe and SARe both decreased, while the soil pHe increased first and then decreased. Their performances
Fig. 10. Response of average pHe (pH of saturated-soil extracts) in different soil layers to the percentage of treated effluent in November 2016.
(Al-Lahham et al., 2003; Al-Nakshabandi et al., 1997; Chakrabarti, 1995), and likely occurred because nutrients such as nitrogen and phosphate in treated effluent provide fertilizer value to plants (Toze, 2006). As Fig. 11 shows, the biomass of GG1–GG5 sampled in September 2015, August 2016 and November 2011, increased with the increasing percentage of treated effluent. During these period, nutrients of treated effluent promoted the growth of the plant. During the November 2015 sampling, there was no significant differences in biomass between the five treatments (Fig. 11a). During this time, tall fescue grew slowly because of the low temperature, and adding fertilizer may have offset the effects of the nutrient value of the applied water. In June of 2016, the growth biomass of different treatments followed the order of GG4 > GG5 > GG1 > GG2, GG3 (Fig. 11b). From March to June of
Table 4 The spatial distribution of soil inorganic nitrogen and available phosphorus in the middle of 2016. Treatments
GG1 GG2 GG3 GG4 GG5
(0%) (25%) (50%) (75%) (100%)
Inorganic nitrogen (mg/L)
Available phosphorus (mg/kg)
0–10 cm
10–20 cm
20–40 cm
0–10 cm
10–20 cm
20–40 cm
5.05 6.64 5.12 4.50 2.21
3.18 4.44 3.24 2.22 2.52
1.38 1.84 1.62 2.62 3.46
4.43 6.34 6.31 4.75 5.26
5.07 5.01 8.63 7.17 7.30
4.94 5.71 6.85 4.18 5.52
Inorganic nitrogen was from a saturated-soil extract; available phosphorus was extracted with 0.5 mol/L NaHCO3. 229
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Fig. 11. Growth biomass (and standard errors) of tall fescue for each treatment in 2015 (A) and 2016 (B). Different lowercase letters indicate significant differences (*P < 0.05) among treatments.
depended on the quality of irrigation water. Moreover, a positive correlation existed between soil available phosphorus content with treated effluent, and a negative correlation with biomass of tall fescue. In addition, irrigation with higher percentage of treated effluent generally increased the biomass of tall fescue. Overall, a method of micro-sprinkler irrigation with treated effluent and three stages of irrigation management (enhanced salt leaching, water-salt regulation and normal irrigation stage) could be used for tall fescue turf planting in sea reclamation land with a gravel-sand layer, but periodic examination of soil salinity may be needed, especially for years with less rainfall.
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Acknowledgements This study was supported by the Key Research Program of Frontier Sciences of the Chinese Academy of Sciences (Grant No. QYZDJ-SSWDQC028), the National Science Foundation for Young Scientists of China (Grant No. 51709251) and the National Key Research and Development Program of China (Grant No. 2016YFC0501304, 2014 BAD12B05 and 2016YFC0501305). References Al-Hamaiedeh, H., Bino, M., 2010. Effect of treated grey water reuse in irrigation on soil and plants. Desalination 256, 115–119. Al-Lahham, O., El Assi, N.M., Fayyad, M., 2003. Impact of treated wastewater irrigation on quality attributes and contamination of tomato fruit. Agric. Water Manag. 61, 51–62. Al-Nakshabandi, G.A., Saqqar, M.M., Shatanawi, M.R., Fayyad, M., Al-Horani, H., 1997. Some environmental problems associated with the use of treated wastewater for irrigation in Jordan. Agric. Water Manag. 34, 81–94. Asano, T., Pettygrove, G.S., 1987. Using reclaimed municipal wastewater for irrigation. Calif. Agric. 41, 15–18. Ayers, R.S., Westcot, D.W., 1976. Water Quality for Agriculture. FAO Irrig. And Dr., Rome. Bao, S.D., 2000. Soil and Agriculture Chemistry Analysis. China Agriculture Press, Beijing in Chinese. Beek, C., Breemen, N.V., 1973. The alkalinity of alkali soils. Eur. J. Soil. Sci. 24, 129–136. Chakrabarti, C., 1995. Residual effects of long-term land application of domestic wastewater. Environ. Int. 21, 333–339. Chen, W., Chen, B.B., Shen, Q.R., 2000. Study on the pH change and alkali in the salt leaching process of coastal saline soil. Acta Pedol. Sin. 37, 521–527 in Chinese. Chen, X.L., Kang, Y.H., Wan, S.Q., Chu, L.L., Li, X.B., 2015a. Chinese rose (Rosa chinensis) cultivation in Bohai bay, China, using an improved drip irrigation method to reclaim heavy coastal saline soils. Agric. Water Manag. 158, 99–111. Chen, X.L., Kang, Y.H., Wan, S.Q., Li, X.B., Guo, L.P., 2015b. Influence of mulches on urban vegetation construction in coastal saline land under drip irrigation in north China. Agric. Water Manag. 158, 145–155.
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