The changes in the physical and hydraulic properties of a loamy soil under irrigation with simpler-reclaimed wastewaters

Agricultural Water Management 158 (2015) 213–224

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The changes in the physical and hydraulic properties of a loamy soil under irrigation with simpler-reclaimed wastewaters Talip Tunc a,∗ , Ustun Sahin b a b

East Anatolia Agricultural Research Institute, 25090 Erzurum Turkey Department of Agricultural Structures and Irrigation, Faculty of Agriculture, Ataturk University 25240 Erzurum Turkey

a r t i c l e

i n f o

Article history: Received 23 January 2015 Received in revised form 6 May 2015 Accepted 10 May 2015 Available online 26 May 2015 Keywords: Aggregate stability Bulk density Infiltration Pore size distribution Water retention

a b s t r a c t Soil physical properties (bulk density, particle density, total porosity, pore size distribution and aggregate stability) and hydraulic properties (water retention and infiltration) may be affected significantly from wastewater irrigation. In addition, environmental conditions may change the magnitude of these effects. Therefore, we examined the effects of irrigation with simpler-reclaimed wastewaters on the certain soil properties under cauliflower and red cabbage planting with two-year study in a semi-arid region with a cool climate. W1 (filtered wastewater), W2 (filtered and aerated wastewater) and W1-FW (mix of filtered wastewater with the freshwater at the ratio of 1:1 as volume) were the wastewater treatments. Control plots were irrigated with freshwater (FW) provided from groundwater. Soil electrical conductivity and organic C content in wastewater irrigated plots were higher than the freshwater irrigated plots. Moreover, exchangeable sodium percentage was low in wastewater plots (<2.25%). Therefore, irrigation with especially W1 and W2 wastewaters markedly increased the aggregate stability. Particle density was not changed with wastewater applications. Although bulk density and porosity increased under the wastewater irrigation conditions, changes were not meaningful in terms of practical conditions. While available soil moisture increased with the increase of micropores, infiltration rate decreased with the decrease of macropores. This was probably because of the clogging of pores with suspended solids in wastewater. According to research findings, it was expressed that soil aggregation and available water content could be improved under irrigation with the mix of filtered wastewater and freshwater in a semi-arid region with a cool climate and the infiltration rate could also be protected. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Treated or untreated urban wastewater has been used commonly for agricultural irrigation in arid and semi-arid regions of the world. According to the estimations, at least 20 million hectares of agricultural land worldwide is irrigated with treated and untreated wastewaters (Corcoran et al., 2010). Its use has increased recently because there are inadequate freshwater resources. While the population suffering from water scarcity is presently 11% of the total worldwide population, it is estimated that the population with inadequate water will be 38% in 2025 and 50% of the total worldwide population in 2050 (Jiménez and Asano, 2008). Urban wastewater contains higher levels of organic matter, nutrients and pollutants (heavy metals and suspended solids) compared to freshwater. Although wastewater application provides positive effects on soil properties and crop productivity because

∗ Corresponding author. Tel.: +90 4423271440; fax: +90 4423271364. E-mail address: [email protected] (T. Tunc). http://dx.doi.org/10.1016/j.agwat.2015.05.012 0378-3774/© 2015 Elsevier B.V. All rights reserved.

of its high organic matter and macro and micronutrient contents, the pollutants in wastewater may cause some problems to soil and crops (Pescod, 1992). Wastewater compounds especially affect soil porosity and therefore hydrological properties (Coppola et al., 2004). Nadav et al. (2013) indicated that the physico-chemical properties of soils were altered with treated wastewater irrigation, because long-term wastewater application caused the accumulation of organic matter in soil. High organic matter in wastewater is cement for the improvement of soil aggregates. Therefore, lower bulk density and higher infiltration and water retention have been obtained under the wastewater irrigation conditions. However, suspended solids in wastewater negatively affect the soil porosity. Many researches obtained lower bulk density or higher porosity values under wastewater irrigation (Mojiri, 2011; Mojid and Wyseure, 2013; Vogeler, 2009). Conversely, Mollahoseini (2013) determined higher bulk density values under wastewater irrigation. In addition, Wang et al. (2003) indicated that wastewater irrigation caused a slight increase in soil compaction. Especially high-suspended solid concentration in wastewater may increase the bulk density, while lower concentrations may not significantly affect it (Kunhikrishnan et al., 2012).

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Water retention, infiltration and hydraulic conductivity are among the soil hydraulic properties affected by soil porosity and pore size distribution (Gonc¸alves et al., 2010; Wang et al., 2003). Mojid and Wyseure (2013) determined enhanced saturated hydraulic conductivity and water retention capacity values in the wastewater irrigation conditions compared to freshwater irrigation. However, some researchers reported that wastewater application to soil may decrease the hydraulic conductivity and infiltration rate. Gharaibeh et al. (2007) observed that the infiltration rate of an area irrigated with wastewater for 2 and 5 years was reduced compared to a rain-fed area. Mollahoseini (2013) found that saturated hydraulic conductivity in the top soil layer of 20 cm decreased significantly with wastewater irrigation. Adhikari et al. (2012) indicated that soil hydraulic conductivity may decrease due to the accumulation of dispersed clay and suspended solid particles in the soil pores under saline/sodic wastewater application. Similarly, Gharaibeh et al. (2007) concluded that the presence of sodium in wastewater-irrigated soil can cause swelling and dispersion of soil particles. Especially, the wastewater containing high levels of sodium leads to soil structure deterioration (Qadir et al., 2010). In addition, Fernández-Cirelli et al. (2009) reported that deteriorated soil physical properties due to irrigation with waters having high sodicity and low salinity affect the water movement in soil. Microbiological activity may also decrease the infiltration rate (Bedbabis et al., 2014). In the regions with a cool climate, soils are exposed to freeze–thaw cycles, especially in the spring period. Aggregation and therefore soil structure may be either positively or negatively affected by freeze–thaw cycles (Sahin et al., 2008). Therefore, the impacts of wastewater irrigation on main soil properties in agricultural areas under cool climate conditions may be different. Moreover, we observed that the studies examining the effects of wastewater irrigation on physical and hydraulic properties of soils in semi-arid regions with a cool climate are limited. Trials were carried out under irrigated conditions using plant material. Two Brassica vegetables were irrigated frequently due to the fact that low effective root depth (40 cm) was selected as plant material. These crops are also cool climate plants. Two plants in the same vegetable group were considered to offer more reliable results with more data about the irrigated soils. The fresh water resources potential of Turkey is not sufficient considering the agricultural areas. Agriculture is the sector in which water is used the most with 73% (32 × 109 m3 ) (SHW, 2013). Treated wastewater amount in Turkey in 2012 was 3.26 × 109 m3 . Proportion of the population served by wastewater treatment plants to the total population was 58% (TSI, 2014). Therefore, wastewaters are used in irrigation by applying simpler reclamation processes in water deficit regions which had no wastewater reclamation plant with sufficient number and capacity. For the above-mentioned reasons, we examined the effects of simpler reclaimed wastewater irrigation applications by drip irrigation system, which decreases the crop contamination on the physical and hydraulic properties of soil, with the production of two Brassica vegetables in a semi-arid region with a cool climate compared to freshwater. The plants were only used to form the irrigation conditions. Therefore, additional evaluations for the determination of plant properties were not made.

2. Materials and methods 2.1. Experimental site and soil properties The field experiments were conducted at the Agricultural Research Station of Ataturk University, Erzurum, Turkey (39.933◦ N, 41.236◦ E and the altitude of 1798 m a.s.l.). In the experimental

Table 1 Monthly temperature, pan evaporation, and precipitation at the time of cauliflower and red cabbage cultivation. o

Year

Month

Temperature, C Pan evaporation, mm

Precipitation, mm

2010

Maya June July August Septemberb Septemberc June July August Septemberd Septembere

11.7 15.9 19.5 20.3 21 17.9 14.6 19.6 19.4 14.9 14.2

1.1 51.5 59 12.8 – 4 52.7 15 16 2 15

2011

a b c d e

32.5 171.3 220.1 254.2 49.3 131.8 174.5 236.5 259.4 86.7 151.7

Calculated from data between 25 and 31 May. Calculated from data between 1 and 6 September. Calculated from data between 1 and 19 September. Calculated from data between 1 and 14 September. Calculated from data between 1 and 28 September.

region, the annual rainfall is 406.1 mm and the average annual temperature is 5.6 ◦ C according to the long-term climatic data (1960–2012) (TSMS, 2013). The hottest and coldest months are July (19.3 ◦ C average) and January (−9.4 ◦ C average), respectively. Average air temperatures during December-March are below zero degrees. Erzurum region with high altitude has Dsc climate (D: snow, s: summer dry, c: cool summer) according to the Köppen–Geiger Climate Classification (Kottek et al., 2006). Two Brassica vegetables (cauliflower and red cabbage) from cool climate crops produced in this region were selected as experimental plant material. The cauliflower growing period was from 25 May to 6 September in 2010 and from 1 June to 14 September in 2011, while the red cabbage growing period was from 25 May to 19 September in 2010 and from 1 June to 28 September in 2011. Monthly average temperature, total evaporation and precipitation values in the growing periods are given in Table 1. Evaporation and precipitation data was measured using a Class A pan and a pluviometer located in the experimental area, respectively. Temperature values were provided from the data of Erzurum meteorology station at approximately 5 km distance from the experimental area. The soils of the region were Aridisol according to the US Soil Taxonomy (Soil Survey Staff, 1992). Basal properties of the experimental field soil prior to trial in 2010 are given in Table 2. The texture of trial field soil determined by the Bouyoucos hydrometer method was loam containing 27.45% clay, 33.55% silt and 39.0% sand in the top 40 cm soil profile based on the effective rooting depth of the crops (Demiralay, 1993). The available water holding capacity calculated from the difference between field capacity and wilting point was 55 mm (Cassel and Nielsen, 1986). Table 2 Baseline soil properties of experimental field. Parameter

Texture Clay, % Silt, % Sand, % Bulk density, Mg m−3 Field capacity, % of weight Wilting point, % of weight pH EC, dS m−1 Organic C, g kg−1 CaCO3 , %

Soil depth, cm 0–20

20–40

Clay loam 30.2 34.4 35.4 1.22 31.7 19.2 7.70 2.12 4.81 2.93

Loam 24.7 32.7 42.6 1.25 28.1 18.3 7.37 2.75 4.81 0.65

T. Tunc, U. Sahin / Agricultural Water Management 158 (2015) 213–224

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Fig. 1. Turkey map showing Karasu and Euphrates rivers (www.wikipedia.org).

2.2. Wastewater reclamation processes and irrigation water quality Cauliflower and red cabbage plots were irrigated using W1 (filtered wastewater), W2 (filtered and aerated wastewater), W1-FW (mix of filtered wastewater with the freshwater at the ratio of 1:1 as volume) and FW (freshwater; control treatment). Urban wastewater of Erzurum, Turkey was used in the wastewater treatments. Resource of freshwater was groundwater obtained from this region. The wastewater is discharged into the Karasu River in the north of Erzurum city centre (Fig. 1). The river located in the upper basin of the Euphrates River is the most important water resource for Karasu plain. The planned area amount for irrigated agriculture through Karasu plain is 15,757 ha (Özbek, 2003). “Pre-treated” wastewater was the W1 wastewater. For preparing it, raw-wastewater collected from main wastewater discharge line by a pump was filtered using a 2 mm diameter mesh filter, ensuring the coarse materials were removed from the wastewater. Moreover, for the preparation of the W2 wastewater, the wastewater free from coarse material was filled into polyethylene tanks with a volume of 2000 L and then continuously aerated by circulation using a pump 2 days before each irrigation. The irrigation waters were sampled in three periods (June, July and August) and analysed for pH, electrical conductivity (EC), total suspended solids (TSS), total N, total P, cations (Ca, Mg, Na and K), anions (CO3 , HCO3 , SO4 and Cl) and 5-day biochemical oxygen demand (BOD5 ), faecal coliforms and the results are shown in Table 3. The sodium adsorption ratio (SAR) was also calculated and the results were given in Table 3. The pH and EC was directly measured during sampling using the portable pH-meter and the conductivity-meter, respectively (Kanber and Unlu, 2010). TSS, total N, total P and BOD5 analyses were carried out in accordance with the standard methods described by APHA (1995). For determining of TSS, water was filtered with suction and then the material on filter paper dried and weighted. Nitrogen content was determined by the Kjeldahl method. Total P was found by orthophosphate measurement applying acid-hydrolysis method. BOD analyses were done by dilution method using allylthiourea of 5 mg l−1 as a nitrification inhibitor. Ca, Mg, Na and K concentrations in waters were measured using an ICP-AES spectrophotometer (Inductively Couple Plasma spectrophotometer PerkinElmer, Optima 2100 DV, ICP-AES, Shelton, CT 6484-4794, USA). HCO3 and CO3 ions were determined by the titration method with sulphuric acid, while the Cl ion was determined by the titration method with silver nitrate (Richards, 1954). SO4

contents were analysed with the Spectrophotometric method using test kits. Faecal coliforms were determined by the membrane filtration method (AOAC, 1995). The sodium adsorption ratio (SAR) values of waters were calculated using the below equation (Kanber and Unlu, 2010): SAR =



Na Ca+Mg 2

where Na, Ca, and Mg are in me l−1 . 2.3. Plant cultivation and irrigation applications Snowball F1 type cauliflower (Brassica oleracea var. botrytis) and Royale F1 type red cabbage (Brassica oleracea L. var. rubra) seedlings were planted in 5 rows with 50 × 50 cm intervals on experimental plots. Two separate experimental areas for two different crops were established side by side in experimental field. Each experiment was conducted applying randomized complete block design with three replications. Four plots in each block considering different quality water treatments (W1, W2, W1-FW and, FW) were arranged. Total 12 plots (4 treatments × 3 replications) with measuring 2.5 m × 12 m were arranged for each experimental crop. Before planting in the first trial year, 180 kg ha−1 N, 52.4 kg ha−1 P, and 124.5 kg ha−1 K were applied to all plots as a basal fertilizer. Irrigation water was applied with a drip irrigation system under 0.1 MPa operation pressure. A hydrocyclone and a disc filter were used for the filtration of wastewaters in the irrigation system. PE driplines of 16 mm in diameter were placed with 0.50 m intervals on the plots. There were 5 driplines with the length of 12 m in each plot. Driplines had in-line type emitters with a flow rate of 2 litre h−1 and the emitters’ interval on driplines was 0.50 m. The irrigations were initiated when consuming approximately 40% of the available soil water at an effective rooting depth of 40 cm of freshwater irrigated plots. Soil moisture contents were measured using tensiometers (Irrometer-Model R, IRROMETER Company, Inc.). Irrigation water depth and volume applied in each irrigation were calculated with the below equations: I = AWC × Ry V = I× A × WR where I is the irrigation water depth (mm), AWC is the available soil water content (mm), Ry is the water consumption ratio (0.40), V is the irrigation water volume (l), A is the plot area (m2 )

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Table 3 Characteristics (mean ± SEM) of wastewaters and freshwater used for irrigation in trail years. 2010

2011

Characteristic

W1

W2

W1-FW

FW

W1

W2

W1-FW

FW

pH EC, dS m−1 TSS, mg l−1 Total N, mg l-1 Total P, mg l-1 BOD5 , mg l−1 SAR FC, cfu 100 ml−1

7.95 ± 0.04 1.85 ± 0.04 105 ± 5 13.8 ± 0.22 7.64 ± 1.19 442 ± 7 4.15 ± 0.34 1682 ± 395

7.86 ± 0.02 1.86 ± 0.03 110 ± 4 13.9 ± 0.09 6.96 ± 0.94 263 ± 35 4.62 ± 0.30 1400 ± 457

7.46 ± 0.20 1.25 ± 0.05 57 ± 4 6.95 ± 0.10 5.70 ± 0.37 189 ± 34 3.48 ± 0.26 867 ± 152

7.13 ± 0.05 0.46 ± 0.01 – – – – 0.29 ± 0.02 –

7.86 ± 0.03 1.87 ± 0.02 111 ± 2 13.7 ± 0.40 8.48 ± 0.37 415 ± 20 4.87 ± 0.34 1265 ± 62

7.83 ± 0.02 1.86 ± 0.03 102 ± 3 13.8 ± 0.64 8.07 ± 0.73 251 ± 5 4.18 ± 0.35 1086 ± 111

7.49 ± 0.14 1.20 ± 0.01 52 ± 1 6.84 ± 0.48 4.50 ± 0.31 189 ± 23 2.86 ± 0.20 689 ± 107

7.15 ± 0.08 0.40 ± 0.01 – – – – 0.32 ± 0.03 –

Cations, me l−1 Ca Mg Na K

4.10 ± 0.16 1.03 ± 0.08 6.67 ± 0.50 3.25 ± 0.10

4.17 ± 0.32 1.50 ± 0.19 7.78 ± 0.40 4.15 ± 0.38

2.97 ± 0.10 0.93 ± 0.10 4.87 ± 0.43 3.16 ± 0.34

2.35 ± 0.14 1.15 ± 0.03 0.39 ± 0.02 2.67 ± 0.05

4.07 ± 0.33 1.03 ± 0.07 7.79 ± 0.69 3.87 ± 0.44

4.51 ± 0.40 1.11 ± 0.36 7.01 ± 0.59 4.32 ± 0.18

2.88 ± 0.64 1.05 ± 0.17 4.03 ± 0.57 2.39 ± 0.47

1.52 ± 0.21 1.18 ± 0.08 0.37 ± 0.02 1.64 ± 0.12

Anions, me l−1 CO3 HCO3 SO4 Cl

0.66 ± 0.15 6.23 ± 0.44 5.28 ± 0.60 1.01 ± 0.07

0.60 ± 0.20 6.33 ± 0.23 5.82 ± 0.28 1.06 ± 0.14

0.11 ± 0.11 4.67 ± 0.29 3.54 ± 0.23 0.62 ± 0.12

– 3.43 ± 0.20 0.51 ± 0.03 0.28 ± 0.03

0.56 ± 0.05 6.67 ± 0.13 5.52 ± 0.18 1.59 ± 0.04

0.54 ± 0.02 6.30 ± 0.10 5.64 ± 0.21 1.56 ± 0.13

0.27 ± 0.03 4.50 ± 0.21 3.17 ± 0.12 0.59 ± 0.08

– 3.17 ± 0.03 0.48 ± 0.02 0.30 ± 0.05

EC: Electrical conductivity; TSS: Total suspended solids; BOD5: 5-day biochemical oxygen demand; SAR: Sodium adsorption ratio; FC: Faecal coliform.

and WR is the wetting ratio. The AWC value was 55 mm in 40 cm top soil layer. Therefore, the quantity of each irrigation was calculated as 660 L for each plot considering 22 mm irrigation water depth, 30 m2 plot area (2.5 m × 12 m) and 1.0 wetting ratio. While the irrigation number in red cabbage plots was 20 in 2010 and 22 in 2011, cauliflower plots were irrigated 18 times in 2010 and 20 times in 2011. Therefore, seasonal irrigation quantities in 2010 and 2011 were 440 and 484 mm in red cabbage and 396 and 440 mm in cauliflower, respectively. In order to provide free chlorine at 1 mg l−1 concentrations, chlorination with sodium hypochlorite was applied for the prevention of biological contamination and system clogging in all wastewater treatments. 2.4. Soil sampling, analysis and measurements After the harvest in trial years, tested soils were sampled separately from two soil layers (0–20 and 20–40 cm) between the plants, in the middle three rows of each plot for the determination of pH, EC, organic matter, CaCO3 , exchangeable Na, cation exchange capacity (CEC), bulk density, particle density, aggregate stability and the amount of water held at different tensions (−0.001 MPa, −0.010 MPa, −0.033 MPa, −0.101 MPa and −1.52 MPa). For the determination of each parameter, three sub samples were used. In addition, exchangeable sodium percentage (ESP), total porosity, available soil water and pore size distribution were calculated from the measured values. We determined the pH by a pH-meter in saturation extract (Mc Lean, 1982), EC by a conductivity-meter in saturation extract (Rhoades, 1982a), organic matter by the wet combustion method (Nelson and Sommers, 1982), carbonates by the calcimeter method (Nelson, 1982), exchangeable Na by the standard method in Thomas (1982) and CEC by the sodium acetate method (Rhoades, 1982b). The ESP (%) was calculated using the below equation (Richards, 1954): ESP = (Na+ /CEC) × 100 where Na+ is the measured exchangeable Na concentration (cmol kg−1 ) and CEC is the cation exchange capacity (cmol kg−1 ). The determined soil organic matter (SOM) values determined were expressed as soil organic carbon (SOC). SOM values (%) were transformed to SOC values (%) by dividing SOM values by a con-

ventional conversion factor of 1.724 (Chaudhari et al., 2013; Sleutel et al., 2007). SOC density was also determined for the estimation of organic C mass in the soil layers (Han et al., 2010; Xu et al., 2011). The SOC density was expressed as follows: SOCD = BD × SOC Where SOCD is the soil organic carbon density (kg m−3 ), BD is the bulk density (Mg m−3 ) and SOC is the soil organic carbon content (g kg−1 ). Undisturbed soil samples collected using a cylindrical soil sampler (5 cm long × 5 cm in diameter) were used to determine the bulk density and the amount of water held at different tensions (−0.001 MPa, −0.010 MPa, −0.033 MPa, −0.101 MPa and −1.52 MPa). Bulk density was calculated with the ratio of the ovendry mass to its bulk volume (Blake and Hartge, 1986a). Particle density was determined by the pycnometer method (Blake and Hartge, 1986b). Total porosity was calculated with the standard formula using the measured bulk density and particle density (Danielson and Sutherland, 1986). The wet-sieving method was used to measure the water stable aggregation (Kemper and Rosenau, 1986). Stability measurements of the aggregates in the 1 and 2 mm diameter size range were made using a Yoder-type wetsieving device (Demiralay, 1993). The amount of water retained at different water tensions was determined with a pressure plate (Klute, 1986). Available soil moisture was calculated from the retained water at the field capacity (−0.033 MPa) and wilting point (−1.52 MPa) (Cassel and Nielsen, 1986). Pore size distribution was determined using the soil water retention curve (pF curve). The pressure plate method as a standard method was used to get the pF curve (Braudeau et al., 2014). For drawing the pF curve, the volumetric water contents retained at different tensions were plotted against the matric potentials. In addition, second y axis showing the pore diameters that obtained from the capillary rise equation was added in the graph (Demiralay, 1993). In this curve, the volume at pF 1 indicates the amount of pores greater than 300 ␮m, the volume at pF 2 indicates the amount of pores greater than 30 ␮m, the volume at pF 3 indicates the amount of pores greater than 3 ␮m and so on. Infiltration rate measurements under constant water head of 10 cm were made with three replicates by double ring infiltrometers for 180 minutes on treatment plots in both trial years after approximately one month from the harvest. Cumulative infiltration

T. Tunc, U. Sahin / Agricultural Water Management 158 (2015) 213–224

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Table 4 Bulk density, total porosity and aggregate stability values (mean ± SEM) at two different soil layers of two Brassica vegetables plots irrigated with wastewater and freshwater after harvesting in trail years. 2010

2011

Crop

Soil layer, cm

Treatment

Bulk Density, Mg m-3

Total porosity, %

Aggregate stability, %

Bulk Density, Mg m-3

Total Porosity, %

Aggregate stability, %

Cauliflower

0–20

W1 W2 W1-FW FW P value W1 W2 W1-FW FW P value W1 W2 W1-FW FW P value W1 W2 W1-FW FW P value

1.25 c 1.26 b 1.24 c 1.28 a 0.001 1.27 bc 1.26 c 1.27 b 1.31 a 0.001 1.23 1.25 1.25 1.27 0.099 1.28 1.27 1.29 1.31 0.064

50.4 ± 0.12 a 49.9 ± 0.07 b 50.7 ± 0.13 a 49.1 ± 0.18 c 0.001 49.8 ± 0.12 ab 50.1 ± 0.07 a 49.3 ± 0.13 b 47.6 ± 0.24 c 0.001 51.3 ± 0.27 50.5 ± 0.17 50.7 ± 0.43 49.6 ± 0.23 0.058 49.1 ± 0.37 a 49.7 ± 0.46 a 48.7 ± 0.37 ab 48.0 ± 0.40 a 0.046

52.0 ± 2.08 a 43.7 ± 0.33 b 39.3 ± 0.67 c 35.3 ± 0.33 d 0.001 39.3 ± 0.88 ab 41.7 ± 0.88 a 37.0 ± 0.58 bc 34.7 ± 0.33 c 0.003 49.3 ± 5.21 a 42.0 ± 0.58 ab 38.3 ± 0.88 b 35.3 ± 0.33 b 0.027 42.3 ± 1.45 a 43.0 ± 2.52 a 36.0 ± 0.58 b 35.7 ± 0.33 b 0.015

1.25 c 1.26 b 1.25 d 1.28 a 0.001 1.27 c 1.27 c 1.28 b 1.32 a 0.001 1.24 c 1.25 c 1.27 b 1.28 a 0.001 1.27 1.28 1.29 1.29 0.136

50.4 ± 0.00 b 50.0 ± 0.00 c 50.5 ± 0.06 a 49.0 ± 0.00 d 0.001 49.6 ± 0.00 a 49.6 ± 0.00 a 49.2 ± 0.00 b 47.6 ± 0.00 c 0.001 50.7 ± 0.13 a 50.5 ± 0.13 a 49.6 ± 0.00 b 49.0 ± 0.12 c 0.001 49.5 ± 0.13 49.5 ± 0.13 48.7 ± 0.35 48.6 ± 0.31 0.095

60.7 ± 1.45 a 53.3 ± 4.18 ab 48.3 ± 3.33 b 33.7 ± 0.67 c 0.001 54.0 ± 5.03 a 52.0 ± 2.08 ab 45.7 ± 1.20 b 36.3 ± 0.67c 0.004 57.3 ± 1.86 a 54.7 ± 0.33 a 45.0 ± 1.53 b 31.7 ± 0.67 c 0.001 52.7 ± 2.33 a 55.0 ± 0.00 a 38.0 ± 1.15 b 31.0 ± 0.00 c 0.001

20–40

Red cabbage

0–20

20–40

Means marked with the different letters at each column of each soil layer are statistically different at the level of 0.01 or 0.05. Standard errors (SEM) in bulk density columns are not shown because they are extremely low (less than 0.01 Mg m−3 ).

and elapsed time data were recorded during these measurements. Infiltration rate equations were obtained by regression analysis using the recorded data considering Kostiakov infiltration model derived by the data observed in the field or under laboratory conditions (Uloma et al., 2014). Moreover, stable and mean infiltration rates of the experimental field determined by double ring infiltrometer measurements for 180 min prior to experiments were 30 and 59.7 mm h−1 , respectively. Infiltration rate reduces with time and eventually becomes almost a constant value. This basic value is considered stable infiltration rate (Brouwer et al., 1988). Mean infiltration rate also represents the average value throughout the elapsed period (Gungor et al., 2002). 2.5. Statistical analysis The effects of irrigation treatments on physical and hydraulic properties of soil were identified with variance analysis (ANOVA). Treatment means were compared by the Duncan Multiple Range test. The SPSS software (SPSS Inc., version 15) package was used for all statistical analyses. 3. Results and discussion 3.1. Particle density, bulk density, total porosity and aggregate stability Wastewater irrigation showed no significant effect on soil particle density determined between 2.51 and 2.53. The particle density changes with the composition of mineral and organic soil components (Rühlmann et al., 2006). Although organic C content in soil increased significantly under wastewater irrigation conditions, it could be said that the increase was not sufficient for the decrease of particle density. Higher porosity and lower bulk density values were obtained from wastewater irrigated plots under growing conditions of two Brassica vegetables in both years compared to freshwater irrigation plots (Table 4). Bulk densities determined after the treatments were also higher in two soil layers compared to bulk density values prior to the trials in Table 2. However, the increase under wastewater irrigation conditions was less. Considering the average values

of crops, soil layers and trial years, the bulk density values were 1.26 Mg m−3 in W1 and W2 treatments, 1.27 Mg m−3 in W1-FW treatment and 1.29 Mg m−3 in FW treatment. Total porosity values were 50.1, 50.0, 49.7 and 48.6% under W1, W2, W1-FW and FW treatments, respectively. Although the changes in bulk density and porosity values were significant as statistically, wastewaters irrigation did not provide a meaningful and practical contribution considering the effects of dynamic environmental factors including soil, climate and plant. Therefore, we can say that we were able to obtain a very little positive effect on improving the bulk density and porosity. While W1 and W2 wastewater applications generally provided similar aggregate stability, these values were higher than the values of the W1-FW and FW treatments (Table 4). Considering the average values, aggregate stability values were 51.0% in the W1 treatment, 48.2% in the W2 treatment, 41.0% in the W1-FW treatment and 34.2% in the FW treatment. Soil organic matter is one of the main factors affecting the aggregation (Ngailo and Dechen, 2010). Therefore, any increase in the organic matter of soil is important in terms of contribution to the stability of soil aggregates (Bot and Benites, 2005). Among the waters used in the experiments, W1 wastewater had the highest organic matter content due to the highest BOD5 value (Table 3). As shown in Table 5, the W1 treatment significantly increased the soil organic C content in two soil layers compared to the FW treatment under growing conditions of two Brassica vegetables. In addition, organic C contents in two soil layers before the experiments in Table 2 showed that wastewater irrigation increased the soil organic C content. Significantly higher aggregate stability values were obtained under W1 treatment compared to the FW treatment values (Table 4). Moreover, plots irrigated with W2 and W1-FW wastewaters obtained higher aggregate stability because of its considerable organic C as compared to freshwater irrigated plots (Table 5). Especially the aggregate stability values in 2011 were higher than the 2010 values. It could be explained with higher accumulation of soil organic C (SOC density) in 2011. Several studies have shown that wastewater irrigated soils had higher aggregate stability and porosity and lower bulk density because of the presence of higher organic C in wastewater irrigated soils compared to freshwater irrigated soils (Mojiri, 2011; Mojid and Wyseure,

218

Table 5 Some chemical parameters values (mean ± SEM) at two different soil layers (0–20 and 20–40 cm) of two Brassica vegetables plots irrigated with wastewater and freshwater after harvesting in trail years. 0–20 cm

20–40 cm

Year

Parameter

W1

W2

W1-FW

FW

P value

W1

W2

W1-FW

FW

P value

Cauliflower

2010

pH EC, dS m−1 Organic C, g kg−1 SOC density, kg m−3 CaCO3 , % Exc. Na, cmol kg−1 CEC, cmol kg-1 ESP (%) pH EC, dS m−1 Organic C, g kg−1 SOC density, kg m−3 CaCO3 , % Exc. Na, cmol kg−1 CEC, cmol kg−1 ESP (%) pH EC, dS m-1 Organic C, g kg−1 SOC density, kg m−3 CaCO3 , % Exc. Na, cmol kg−1 CEC, cmol kg−1 ESP (%) pH EC, dS m-1 Organic C, g kg−1 SOC density, kg m-3 CaCO3 , % Exc. Na, cmol kg−1 CEC, cmol kg−1 ESP (%)

7.46 ± 0.07 2.85 ± 0.13 11.2 ± 1.60 a 14.0 ± 1.98 a 1.51 ± 0.38 0.74 ± 0.02 a 37.7 ± 0.20 a 1.96 ± 0.07 a 7.46 ± 0.05 2.86 ± 0.15 a 16.1 ± 1.95 a 20.2 ± 2.44 a 1.39 ± 0.27 0.72 ± 0.04 a 35.1 ± 0.32 a 2.06 ± 0.13 ab 7.51 ± 0.03 c 2.54 ± 0.07 10.1 ± 2.22 a 12.4 ± 2.79 a 0.67 ± 0.06 b 0.68 ± 0.02 a 37.9 ± 0.20 a 1.79 ± 0.04 a 7.55 ± 0.03 2.63 ± 0.07 a 10.1 ± 1.02 a 12.5 ± 1.24 a 0.69 ± 0.03 b 0.74 ± 0.06 a 35.6 ± 0.10 a 2.08 ± 0.17 a

7.56 ± 0.13 2.77 ± 0.01 8.00 ± 0.00 ab 10.1 ± 0.00 ab 0.48 ± 0.17 0.65 ± 0.06 a 36.9 ± 0.12 b 1.76 ± 0.15 a 7.46 ± 0.05 2.81 ± 0.07 a 15.0 ± 1.83 a 18.9 ± 2.31 a 0.94 ± 0.37 0.78 ± 0.06 a 34.9 ± 0.31 a 2.23 ± 0.20 a 7.46 ± 0.06 bc 2.67 ± 0.12 6.44 ± 0.00 ab 8.03 ± 0.02 ab 0.54 ± 0.11 b 0.62 ± 0.05 a 37.0 ± 0.62 a 1.67 ± 0.10 a 7.51 ± 0.01 2.74 ± 0.11 a 8.51 ± 0.51 a 10.6 ± 0.67 a 0.65 ± 0.06 b 0.69 ± 0.06 a 34.8 ± 0.29 a 1.99 ± 0.17 a

7.58 ± 0.07 2.58 ± 0.12 6.42 ± 0.92 b 7.98 ± 1.13 b 0.87 ± 0.29 0.35 ± 0.00 b 34.0 ± 0.12 c 1.02 ± 0.01 b 7.45 ± 0.17 2.59 ± 0.13 a 10.5 ± 1.52 ab 13.1 ± 1.90 ab 1.05 ± 0.11 0.54 ± 0.02 b 32.9 ± 0.42 b 1.63 ± 0.07 bc 7.62 ± 0.03 ab 2.30 ± 0.21 5.36 ± 0.54 b 6.67 ± 0.63 b 1.52 ± 0.76 b 0.34 ± 0.04 b 34.2 ± 0.64 b 1.00 ± 0.10 b 7.28 ± 0.16 2.28 ± 0.09 b 7.08 ± 0.76 ab 8.99 ± 0.97 ab 1.00 ± 0.10 b 0.45 ± 0.05 b 33.4 ± 0.59 b 1.35 ± 0.12 b

7.58 ± 0.13 2.44 ± 0.12 4.81 ± 0.00 b 6.15 ± 0.02 b 0.98 ± 0.50 0.32 ± 0.01 b 32.0 ± 0.00 d 1.00 ± 0.02 b 7.62 ± 0.12 2.14 ± 0.02 b 4.78 ± 0.18 b 6.11 ± 0.24 b 1.67 ± 0.52 0.45 ± 0.10 b 32.1 ± 0.19 c 1.41 ± 0.32 c 7.68 ± 0.02 a 2.25 ± 0.08 4.81 ± 0.00 b 6.10 ± 0.03 b 2.72 ± 0.11 a 0.30 ± 0.02 b 32.0 ± 0.15 c 0.94 ± 0.05 b 7.52 ± 0.09 2.18 ± 0.07 b 4.62 ± 0.20 b 5.93 ± 0.27 b 2.18 ± 0.30 a 0.33 ± 0.05 b 32.5 ± 0.64 b 1.01 ± 0.12 b

0.793 0.156 0.007 0.007 0.337 0.001 0.001 0.001 0.611 0.015 0.003 0.003 0.441 0.005 0.001 0.013 0.01 0.182 0.046 0.055 0.014 0.001 0.001 0.001 0.146 0.012 0.003 0.004 0.003 0.001 0.001 0.002

7.59 ± 0.08 b 2.58 ± 0.09 ab 6.44 ± 0.00 ab 8.15 ± 0.02 ab 0.48 ± 0.17 b 0.68 ± 0.05 a 37.2 ± 0.39 a 1.83 ± 0.14 a 7.52 ± 0.03 b 2.76 ± 0.04 a 13.0 ± 0.57 a 16.5 ± 0.72 a 0.79 ± 0.31 b 0.79 ± 0.06 a 34.9 ± 0.34 a 2.25 ± 0.16 a 7.46 ± 0.05 2.70 ± 0.11 6.42 ± 0.92 8.19 ± 1.10 0.76 ± 0.29 0.72 ± 0.07 a 38.0 ± 0.03 a 1.90 ± 0.19 a 7.51 ± 0.04 2.57 ± 0.21 9.51 ± 0.68 a 12.1 ± 0.90 a 0.72 ± 0.17 b 0.74 ± 0.05 a 35.6 ± 0.38 a 2.09 ± 0.15 a

7.58 ± 0.03 b 2.68 ± 0.03 a 7.48 ± 0.52 a 9.40 ± 0.64 a 1.08 ± 0.22 b 0.60 ± 0.04 a 36.7 ± 0.29 a 1.63 ± 0.13 a 7.51 ± 0.09 b 2.75 ± 0.04 a 12.2 ± 0.44 a 15.5 ± 0.55 a 1.25 ± 0.28 b 0.77 ± 0.05 a 34.1 ± 0.03 b 2.25 ± 0.15 a 7.48 ± 0.04 2.68 ± 0.09 6.96 ± 0.52 8.83 ± 0.59 0.76 ± 0.11 0.62 ± 0.06 a 36.4 ± 0.73 b 1.70 ± 0.13 ab 7.52 ± 0.13 2.59 ± 0.10 9.69 ± 0.55 a 12.4 ± 0.71 a 0.80 ± 0.04 b 0.70 ± 0.08 a 35.3 ± 0.30 a 1.98 ± 0.24 a

7.66 ± 0.08 ab 2.31 ± 0.14 bc 5.90 ± 0.54 ab 7.50 ± 0.67 ab 1.20 ± 0.39 b 0.34 ± 0.01 b 33.6 ± 0.29 b 1.01 ± 0.01 b 7.62 ± 0.11 b 2.35 ± 0.10 b 8.18 ± 0.56 b 10.5 ± 0.71 b 1.02 ± 0.17 b 0.58 ± 0.03 b 32.3 ± 0.12 c 1.81 ± 0.09 ab 7.50 ± 0.04 2.49 ± 0.10 4.81 ± 0.00 6.21 ± 0.05 1.06 ± 0.29 0.50 ± 0.04 b 34.5 ± 0.58 c 1.45 ± 0.10 b 7.54 ± 0.05 2.62 ± 0.15 5.47 ± 0.45 b 7.08 ± 0.60 b 1.14 ± 0.28 ab 0.47 ± 0.04 b 33.9 ± 0.46 b 1.38 ± 0.09 b

7.79 ± 0.02 a 2.11 ± 0.10 c 4.81 ± 0.00 b 6.32 ± 0.02 b 2.61 ± 0.50 a 0.33 ± 0.01 b 32.1 ± 0.03 c 1.03 ± 0.04 b 7.80 ± 0.01 a 2.09 ± 0.06 c 4.81 ± 0.00 c 6.35 ± 0.00 c 2.15 ± 0.37 a 0.48 ± 0.09 b 31.5 ± 0.32 d 1.53 ± 0.28 b 7.51 ± 0.08 2.46 ± 0.15 5.08 ± 0.27 6.64 ± 0.34 0.69 ± 0.04 0.30 ± 0.03 c 31.9 ± 0.09 d 0.93 ± 0.09 c 7.58 ± 0.09 2.32 ± 0.10 4.58 ± 0.07 b 5.93 ± 0.09 b 1.67 ± 0.02 a 0.34 ± 0.02 c 32.0 ± 0.18 c 1.06 ± 0.05 b

0.031 0.009 0.007 0.01 0.011 0.001 0.001 0.001 0.026 0.001 0 0 0.034 0.007 0.001 0.026 0.923 0.407 0.069 0.066 0.627 0.001 0.001 0.001 0.952 0.537 0 0 0.018 0.001 0.001 0.002

2011

Red cabbage

2010

2011

EC: Electrical conductivity; CEC: cation exchange capacity; ESP: Exchangeable sodium percentage; SOC density: Soil organic carbon density. Means marked with the different letters at each line of each soil layer are statistically different at the level of 0.01 or 0.05.

T. Tunc, U. Sahin / Agricultural Water Management 158 (2015) 213–224

Crop

T. Tunc, U. Sahin / Agricultural Water Management 158 (2015) 213–224

219

Fig. 2. Pore size distribution at two different soil layers (0–20 and 20–40 cm) of cauliflower plots irrigated with wastewater and freshwater after the harvest in 2010 and 2011. In each column, means marked with different letters are significantly different at the level of 0.01 (**) or 0.05 (*).

2013; Vogeler, 2009). However, some researchers found higher bulk density and lower porosity because of dispersion and sedimentation (Abedi-Koupai et al., 2006; Aiello et al., 2007; Coppola et al., 2004). Therefore, it could be said that practical meaningful results about bulk density and porosity have not been obtained due to possible sedimentation under wastewater irrigation. Soil aggregate stability is also controlled largely with a combination of ESP and EC. Aggregates tend to disperse under high ESP and low EC conditions. Although we obtained statistically higher exchangeable sodium percentage (ESP) values in the wastewater plots compared to FW plots (Table 5), these values were too low to cause a sodicity problem. The SAR values of wastewaters were also too low to create a sodium problem (Table 3). Electrical conductivity (EC) of the 0–20 and 20–40 cm soil layers increased with the wastewater application. The increase was significant particularly under W1 and W2 wastewater irrigations (Table 5). Initial soil EC values in Table 2 also showed that EC values in 0-20 cm soil layer increased under wastewater irrigation conditions. However, EC values after wastewater treatments in 20–40 cm soil layer were lower than the initial EC values. Wastewater applications generally decreased the soil CaCO3 content. Moreover, the CaCO3 content in the 0–20 cm soil layer decreased below the initial contents in Table 2 after the wastewater treatments. Therefore, increasing the soil EC and probably dissolved CaCO3 during wastewater application may have also contributed to higher aggregation and therefore the soil structure. Similarly, Tayel et al. (2010) determined that while the correlation between the soil structure and EC was positively significant, there

was a negative correlation between the soil structure and the CaCO3 content. 3.2. Pore size distribution Pore volumes for different pore size classes obtained from the moisture retention curve determined as experimental are shown in Figs. 2 and 3. Significant changes by water applications with different qualities were observed in the volumes occupied by the pore diameter classes of >300, 300–30, 30–0.3 and 3–0.3 ␮m. However, the changes were statistically similar in pore diameter classes of 0.3–0.03, 0.03–0.003, 0.003–0.0003 ␮m. While the maximum pore volumes were observed between the diameters of 30–3 ␮m, the lowest pore volumes were obtained for the diameters of >300 ␮m. In pore volumes with >30 ␮m diameter, wastewater applications provided negative effect. The lowest volumes for pore size of >30 ␮m were obtained under W1 treatment as 6.60 and 6.62% in upper (0–20 cm) and bottom (20–40 cm) soil layers, respectively. While the volumes for the pore size of >30 ␮m under the W2, W1-FW and FW treatments were 6.62, 7.52 and 10.10% in surface soil layer, these volumes were 7.36, 7.20 and 8.69% in the bottom soil layer, respectively. Conversely, wastewater treatments showed a more positive effect in pore volumes with diameters between 30–3 ␮m. In the upper soil layer, pore volumes between 30–3 ␮m diameters were 13.07, 12.90, 12.76 and 10.62% under the W1, W2, W1-FW and FW treatments, respectively. The volumes for the pore sizes between 30–3 ␮m in the bottom soil layer were 12.34% in

220

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Fig. 3. Pore size distribution at two different soil layers (0 20 and 20–40 cm) of red cabbage plots irrigated with wastewater and freshwater after the harvest in 2010 and 2011. In each column, means marked with different letters are significantly different at the level of 0.01 (**) or 0.05 (*).

Table 6 Field capacity, wilting point and available water values (mean ± SEM) at two different soil layers of two Brassica vegetables plots irrigated with wastewater and freshwater after harvesting in trail years. 2010

2011

Crop

Soil layer, cm

Treatment

Field capacity, %Pw

Wilting point, %Pw

Available water, %Pw

Field capacity, %Pw

Wilting point, %Pw

Available water, %Pw

Cauliflower

0–20

W1 W2 W1-FW FW P value W1 W2 W1-FW FW P value W1 W2 W1-FW FW P value W1 W2 W1-FW FW P value

30.4 ± 0.30 b 32.2 ± 0.12 a 31.5 ± 0.46 a 30.3 ± 0.20 b 0.002 30.3 ± 0.16 a 30.0 ± 0.18 a 29.0 ± 0.37 b 29.8 ± 0.25 a 0.024 33.2 ± 0.22 a 32.5 ± 0.30 a 30.8 ± 0.61 b 29.7 ± 0.26 b 0.002 29.3 ± 0.10 a 29.1 ± 0.36 ab 27.9 ± 0.59 b 27.8 ± 0.23 b 0.05

20.1 ± 0.17 a 20.1 ± 0.12 a 20.2 ± 0.07 a 19.0 ± 0.21 b 0.006 20.1 ± 0.04 a 20.0 ± 0.11 a 20.1 ± 0.15 a 18.6 ± 0.16 b 0.001 20.0 ± 0.08 20.0 ± 0.07 20.3 ± 0.38 20.1 ± 0.09 0.678 20.1 ± 0.23 19.8 ± 0.02 19.8 ± 0.23 19.9 ± 0.17 0.703

10.3 ± 0.46 b 12.1 ± 0.15 a 11.3 ± 0.46 a 11.3 ± 0.01 a 0.023 10.2 ± 0.17 ab 10.0 ± 0.25 b 8.85 ± 0.47 c 11.2 ± 0.40 a 0.008 13.2 ± 0.15 a 12.5 ± 0.37 a 10.5 ± 0.73 b 9.60 ± 0.20 b 0.005 9.26 ± 0.33 a 9.25 ± 0.37 a 8.11 ± 0.36 ab 7.85 ± 0.30 b 0.07

31.4 ± 0.11 b 31.9 ± 0.14 a 31.0 ± 0.16 b 30.1 ± 0.10 c 0.001 30.1 ± 0.03 a 30.0 ± 0.13 a 29.1 ± 0.03 b 30.1 ± 0.03 a 0.001 32.8 ± 0.08 a 32.6 ± 0.06 b 30.1 ± 0.04 c 29.4 ± 0.02 d 0.001 30.1 ± 0.02 a 29.4 ± 0.03 b 29.0 ± 0.07 c 27.2 ± 0.05 d 0.001

20.1 ± 0.15 b 20.0 ± ±0.09 b 20.4 ± 0.04 a 19.6 ± 0.07 c 0.005 20.2 ± 0.07 a 20.1 ± 0.02 ab 19.9 ± 0.05 b 19.5 ± 0.13 c 0.003 21.0 ± 0.09 a 21.1 ± 0.08 a 20.0 ± 0.09 b 19.6 ± 0.03 c 0.001 20.0 ± 0.09 a 19.5 ± 0.02 b 20.0 ± 0.08 a 18.8 ± 0.07 c 0.001

11.3 ± 0.12 b 11.9 ± 0.15 a 10.6 ± 0.18 c 10.5 ± 0.14 c 0.002 9.93 ± 0.04 b 9.84 ± 0.11 b 9.24 ± 0.07 c 10.6 ± 0.15 a 0.001 11.8 ± 0.10 a 11.5 ± 0.08 a 10.1 ± 0.09 b 9.80 ± 0.01 c 0.001 10.1 ± 0.10 a 9.90 ± 0.02 a 9.02 ± 0.05 b 8.44 ± 0.10 c 0.001

20–40

Red cabbage

0–20

20–40

Means marked with the different letters at each column of each soil layer are statistically different at the level of 0.01 or 0.05.

T. Tunc, U. Sahin / Agricultural Water Management 158 (2015) 213–224

300

200

150

y = 682.3x-0.65 ; R² = 0.948

W1

y = 401.2x-0.55 ; R² = 0.964

W2

2010

200

y = 1205.2x-0.70; R² = 0.977

W1-FW

y = 621.9x-0.53 ; R² = 0.982

FW

100

Infiltration rate, mm h-1

250 Infiltration rate, mm h-1

250

2010

y = 235.7x-0,39 ; R² = 0.902

W1

y = 411.1x-0.52 ; R² = 0.970

W2

y = 1097.7x-0.67 ; R² = 0.983

W1-FW

y = 522.5x-0.49 ; R² = 0.981

FW

150

100

50

50

0

0 0

50

100 Elapsed time, min

150

200

0

50

300 300

100 Elapsed time, min

150

200

2011

2011 y = 470.0x-0.54 ; R² = 0.908

200

y=

150

581.6x-0.58

; R² = 0.930

W1 W2

y = 862.3x-0.62 ; R² = 0.928

W1-FW

y = 643.5x-0.53 ; R² = 0.900

FW

Infiltration rate, mm h-1

250 250 Infiltration rate, mm h-1

221

200

150

y = 334.5x-0.46 ; R² = 0.861

W1

y = 593.8x-0,59 ; R² = 0.939

W2

y = 654.3x-0.52 ; R² = 0.969

W1-FW

y = 763.7x-0,61 ; R² = 0.922

FW

100

100 50 50 0 0

0 0

50

100 Elapsed time, min

150

200

Fig. 4. Infiltration rates of cauliflower plots irrigated with wastewater and freshwater after the harvest in 2010 and 2011.

50

100 Elapsed time, min

150

200

Fig. 5. Infiltration rates of red cabbage plots irrigated with wastewater and freshwater after the harvest in 2010 and 2011.

3.3. Water retention W1, 11.45% in W2, 12.73% in W1-FW and 11.82% in FW. Wastewater irrigation also significantly increased the pore volumes with diameters between 3–0.3 ␮m compared to freshwater irrigation (Figs. 2 and 3). Sahin et al. (2002) indicated that pore sizes are divided into four general groups as macropores (>100 ␮m diameter), mesopores (100–30 ␮m diameter), micropores (30–3 ␮m diameter) and ultramicropores (<3 ␮m diameter). As shown in Figs. 2 and 3, this study results showed that while wastewater irrigation decreased the volume of macropores and mesopores, it increased the volume of micropores and ultramicropores between 3–0.3 ␮m. Alteration of pore size distribution towards narrower pores under wastewater irrigation may be due to physical and biological reasons. Wastewaters include suspended solids (Table 3). Although wastewaters were filtered by a disc filter in the control unit, small soil particles are transported into the soil by water. Therefore, larger soil pores may be narrowed from solid accumulation. Similarly, AlOthman (2009) indicated that wastewater including suspended solids at high levels could affect the amount of macropores after the irrigation. In addition, biological partial clogging in pores because of an increase in the amount of biomass could be improved (Coppola et al., 2004; Stevik et al., 2004). It can also be said that clogging of macropores was not caused by clay dispersion because of dissolved lime, higher organic C and lower ESP under wastewater irrigation conditions compared to freshwater irrigation.

The field capacity and wilting point are soil moisture constants that are important in terms of irrigation. Field capacity expresses the soil moisture retained when downward drainage has stopped. It has been considered that the water and air contents of soil at this moisture levels are appropriate for plant growth. W1 and W2 treatments generally caused higher field capacity values under the growing conditions of Brassica vegetables in two soil layers and two trial years compared to freshwater irrigation (Table 6). In addition, field capacity values increased under wastewater irrigation conditions compared to field capacity values before the experiments in Table 2. Field capacity values in the bottom soil layer (20–40 cm) were lower than the values of the upper soil layer (0–20 cm). The average amount of water retained at the field capacity for soil layer of 0–20 cm was 32.0% in the W1 treatment, 32.3% in the W2 treatment, 30.9% in the W1-FW treatment and 29.9% in the FW treatment. In the 20–40 cm soil layer, mean field capacity values under W1, W2, W1-FW and FW treatments were 30.0, 29.6, 29.5 and 28.5%, respectively. There is a close relationship between the pore size distribution and soil water content due to the fact that macropores control the aeration and drainage, mesopores control the water conductivity, micropores control the water retention the most available for plants and ultramicropores control the water retention less available or mostly unavailable water for plants (Sahin et al., 2002). Therefore, it could be said that soil water content at the field capac-

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Fig. 6. Stable and mean infiltration rates of cauliflower plots irrigated with wastewater and freshwater after the harvest in 2010 and 2011. In each trial year, means marked with different letters are significantly different at the level of 0.05 (*).

Fig. 7. Stable and mean infiltration rates of red cabbage plots irrigated with wastewater and freshwater after the harvest in 2010 and 2011. In each trial year, means marked with different letters are significantly different at the level of 0.01(**) or 0.05 (*).

ity under wastewater irrigation conditions increased because of the increased micropores volume (Figs. 2 and 3). Wilting point expresses the soil moisture content which is too difficult to uptake from soil by plant roots. All wastewater applications significantly increased the soil moisture retained at the wilting point compared to the FW application in two soil layers and trial years (Table 6). After the wastewater applications, wilting point values were over the initial values as shown in Table 2. The wilting point values in the soil layer of 0–20 cm were slightly higher than the values in the bottom soil layer (20–40 cm). The average amounts of water retained at the wilting point for the soil layer of 0–20 cm were 20.3% in the W1 and W2 treatments, 20.2% in the W1FW treatment and 19.6% in the FW treatment. In the 20–40 cm soil layer, mean wilting point values under the W1, W2, W1-FW and FW treatments were 20.1, 19.9, 20.0 and 19.2%, respectively. Increased ultramicropores amount in the wastewater irrigated plots caused higher wilting point values compared to freshwater irrigated plots (Figs. 2 and 3). Similar to our results, Al-Othman (2009) determined that wilting point significantly increased in a loamy sand soil irrigated with treated domestic wastewater. The soil water content between the field capacity (−0.033 MPa) and wilting point (−1.52 MPa) is the available water content. Wastewater application significantly increased the available water content in the upper soil layer (0–20 cm) compared to freshwater application. However, although wastewater irrigations provide higher values compared to the freshwater irrigation, available water contents were lower than the values prior to the experi-

ments in Table 2. Considering the plants and trial years together, available water contents under W1, W2, W1-FW and FW treatments were 11.7, 12.0, 10.6 and 10.3%, respectively. However, the available water content in the bottom soil layer (20–40 cm) slightly increased under W1 and W2 treatments compared to the FW treatment. In the bottom soil layer, the available soil water contents were 9.87% in W1, 9.75% in W2, 8.81% in W1-FW and 9.52% in FW. It could be said that although wastewater irrigation increased the wilting point, higher increases in the field capacity provided higher available water contents under wastewater irrigation conditions. These findings are in agreement with the results of Zupanc and Justin (2010), who determined the increase in the available water amount under wastewater irrigation. 3.4. Infiltration rate As shown in Figs. 4 and 5, infiltration rates which were determined considering the average data obtained from three replicates in each treatment showed a decrease as a function of elapsed time and they were expressed with equations based on Kostiakov model with high determination coefficients (R2 ) (Uloma et al., 2014). Infiltration rates throughout the measuring time of 180 min in the W1 and W2 treatments were lower than W1-FW and FW treatments in two Brassica vegetables plots. Stable (basic) infiltration rates in the W1 and W2 treatments at the end of 180 minutes measurement were also lower than the values of W1-FW and FW treatments (Figs. 6 and 7). Considering two Brassica vegeta-

T. Tunc, U. Sahin / Agricultural Water Management 158 (2015) 213–224

bles and trial years together, stable infiltration rates in the W1, W2, W1-FW and FW treatments were averagely 34.6, 32.6, 41.9 and 44.4 mm h−1 , respectively. These results showed that the W1 and W2 treatments had significantly lower stable infiltration rates provided compared to the FW treatment. However, the stable infiltration rates under W1 and W2 wastewater irrigation conditions were close to the value (30 mm h−1 ) prior to the experiments. Similar results also provided mean infiltration rates (Figs. 6 and 7). Mean infiltration rates were 48.6 mm h−1 in the W1 treatment, 48.8 mm h−1 in the W2 treatment, 69.6 mm h−1 in the W1-FW treatment and 67.9 mm h−1 in the FW treatment when the two vegetables and trial years together were considered. In the W1 and W2 treatments, mean infiltration rates indicating the average values throughout elapsed infiltration time were also lower compared to the initial mean infiltration rate (59.7 mm h−1 ) of the experimental field. Stable infiltration rate and mean infiltration rate values in the W1 and W2 treatments were approximately 25% lower than the FW treatment values. The decreasing infiltration rates under the W1 and W2 treatments is a result of pore size distribution modified because the W1 and W2 treatments changed the pore size distribution by decreasing macroporosity and increasing microporosity (Figs. 2 and 3). Similarly, Coppola et al. (2004) and Aiello et al. (2007) indicated that the change in the pore size distribution towards narrower pores under wastewater treatment decreased the soil hydraulic conductivity. Cook et al. (1994) concluded that the changes in top soil pore size distribution under wastewater irrigation conditions led to a decrease in the infiltration rate. In addition, Abo-Ghobar (1993) and Bedbabis et al. (2014) determined that the infiltration rate under wastewater application significantly decreased through the clogging of the soil pores with suspended solids especially at the soil surface. 4. Conclusions The effects of wastewater applications on physical and hydraulic properties of the soil should be known for the sustainability of wastewater use in agriculture. This study shows that higher aggregate stability values were obtained under wastewater irrigation conditions compared to freshwater irrigation. Improving aggregate stability in soil may be a result of higher organic C density and electrical conductivity in wastewater plots. Especially the W1 (filtered wastewater) and W2 (filtered and aerated wastewater) treatments decreased macropores, although they increased micropores. Therefore, an increase in the available water retention as a result of the increase in micropores was determined. However, a decrease in macropores provided lower soil infiltration rate under wastewater irrigation. The significant reduction of the water infiltration rate could be explained with the accumulation of suspended solids in macropores. Consequently, our results showed that wastewater irrigation effects on physical and hydraulic properties of soils exposed to freeze-thaw cycles in the spring and autumn were generally similar to the results of the previous studies conducted under no-freeze conditions. Considering the positive implications of this study, it could be expressed that irrigation with the water mix of filtered wastewater and freshwater may improve the aggregation of soil and available water content compared to freshwater irrigation in a semi-arid region with a cool climate under crop production frequently irrigated due to shallow rooting depth. The infiltration rate of soils irrigated with filtered wastewater diluted with freshwater may also be improved. However, considering the negative implications of simpler-reclaimed wastewater treatments (W1 and W2) on macroporosity, it could be concluded that water infiltration and soil aeration may decrease dramatically in the long term application conditions.

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