Introduction

In many arid and semi-arid countries, water is becoming a scarce resource which must be used economically and effectively to promote further development. At the same time, with the population expanding at a high rate, the need for increased agricultural production is apparent.

Many countries have included wastewater reuse as an important dimension of water resources planning. Many communities have practised excreta reuse and effluent reuse for hundreds of years and it is part of their culture. The quality of river water used in some irrigation projects is such that reuse of human and animal waste is continually taking place, albeit in an uncontrolled fashion. Rapid increases in population and industrial growth have led to more treatments of wastewater in order to reduce pollution and protect receiving waters. It is then a natural progression to seek direct reuse of this treated effluent for lower grade purposes, such as irrigation.

Irrigation of forest species, used for fuel and timber, with wastewater is an approach that helps overcome health hazards associated with sewage farming. Growing green belts around the cities with forest trees under wastewater irrigation also helps in renewal of the ecological balance and improves environmental quality by self-treatment of wastewater through the application and forest irrigation.

The use of primary and secondary effluents in irrigation can improve the quality of soil and plant growth, because they are considered as natural conditioners through their nutrient elements and organic matter. However, the direct application of wastewater on agricultural land is limited by the extent of contamination with heavy metals, toxic organic chemicals and pathogens (Salem et al. 2000; Sebastiani et al. 2004; EL-Sayed 2005; Singh and Bhati 2005).

Tipuana speciosa (Benth.) Kuntze (rosewood) is one of the true mahoganies. It is a large tropical tree with heavy-weight woods and, also, is one of the most valuable timber trees. Rosewood is extremely strong, hard, stable and decay resistant. This wood is used for decorative veneers, interiors and pattern making, as well as in shipbuilding and interiors of fine boats.

As available data on the use of sewage for irrigating forest trees of Egypt are limited, this study aims to explore the effects of irrigation with sewage effluent on the vegetative growth and chemical composition of T. speciosa, as well as the chemical properties of the planted soil.

Materials and methods

This study was carried out at a greenhouse in the nursery of Timber Trees Research Department, Sabahia Horticulture Research Station, Alexandria, Egypt, to investigate the effects of sewage effluent on vegetative growth, chemical composition of Tipuana speciosa (Benth.) Kuntze and chemical properties of planted soil throughout three stages (8, 16 and 24 months after treatment).

One-year-old seedlings of T. speciosa (Benth.) Kuntze were used for this study so that they averaged 28 cm in height and 3.6 mm in diameter (at 5 cm from the soil surface). Moreover, two types of sewage effluents were used to irrigate the seedlings, after 1 month from planting: primary- and secondary-treated wastewaters that were taken from oxidation ponds of a sewage effluent treatment station in New Borg El-Arab City, Alexandria. The sewage effluent contains a mixture of domestic and industrial sources. On the other hand, tap water was used as control treatment. The analysis of the used water in irrigation is shown in Table 1; Table 2 demonstrates the physical and chemical analysis of the planting soil. The tree seedlings were irrigated to field capacity to standardize the irrigation rate for the three treatments.

Table 1 Average of water composition used in irrigation treatments in the experiment
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Table 2 Physical and chemical analyses of soil
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Trace elements in samples were analyzed using atomic absorption spectrophotometer. Soluble N was determined by the Kjeldahl method (Page et al. 1982). Soluble P was determined by the ascorbic acid molybdenum blue method (Watanabe and Olsen 1965). Dissolved oxygen (DO) was determined by the azide modification of Winkler method and chemical oxygen demand (COD) by dichromate oxidation method. Five-day biochemical oxygen demand (BOD5) was determined from the amount of oxygen lost after incubation for 5 days in the dark at 20°C (APHA 1995).

At the end of each stage (8, 16 and 24 months), three seedlings from each treatment were chosen randomly to measure the parameters of vegetative growth and chemical composition of leaves, shoots and root. Otherwise, at the end of each stage, soil samples were taken from each treatment to measure their chemical properties according to Page et al. (1982). Heavy metals (Cd, Fe, Ni, Pb, Cu, Mn and Zn) were extracted by DTPA and then measured in solution by atomic absorption spectrophotometer (Lindsay and Norvell 1978).

Statistical analysis

The design of the experiment was completely randomized. The three treatments were replicated three times, and each repetition contained four seedlings. The mean values among all treatments were compared by Duncan’s multiple range test, according to Snedecor and Cochran (1968).

Results and discussion

Vegetative growth

Significantly, the application of sewage effluent treatments increased all vegetative growth parameters compared with tap water treatment (Table 3). Primary effluent significantly increased vegetative growth parameters by around 1.5-fold more than secondary effluent treatment throughout the three stages (8, 16 and 24 months).

Table 3 Effect of sewage effluent on vegetative growth parameters and leaves biomass of Tipuana speciosa at the three stages
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The plant heights of T. speciosa seedlings irrigated with the primary effluent increased by 69.34, 64.96 and 60.00% more than those with tap water at the 8-, 16- and 24-month stages, respectively, whereas for the seedlings irrigated with secondary effluent, they were 30.19, 33.62 and 43.20% more than those with tap water treatment through the three stages, respectively. Consequently, plant heights of the seedlings that were irrigated with primary effluent increased by 1.3-, 1.2- and 1.1-fold after 8, 16 and 24 months, respectively, more than the seedlings irrigated by the secondary effluent.

The same was observed in the stem diameters after 8, 16 and 24 months for the seedling that were irrigated with the primary effluent: they were thicker by 132.14, 66.86 and 84.28%, respectively, more than those with tap water treatment (Table 3). Furthermore, secondary effluent increased stem diameter of the seedlings by 52.20, 37.31 and 54.64% more than control for the 8, 16 and 24 months stages, respectively. On the other hand, the stem diameters of the seedlings that were irrigated with the primary effluent increased by 1.5-fold after 8 months and 1.2-fold after both 16 and 24 months more than the seedlings irrigated by the secondary effluent.

The leaf numbers per plant of T. speciosa were counted when the seedlings were irrigated with the primary effluent and were recorded as 97.83, 234.48 and 212.43% more than those with tap water for the 8-, 16- and 24-month stages, respectively, while the seedlings that were irrigated with secondary effluent significantly recorded 47.83, 122.98 and 163.28% more than with tap water for the 8-, 16- and 24-month stages, respectively. It was clear that leaf numbers of the seedlings that were irrigated with primary effluent were 1.3-, 1.5- and 1.2-fold more than those irrigated with the secondary effluent.

Tipuana speciosa seedlings that were irrigated with the primary effluent significantly had the largest leaf area (36.46, 41.11 and 31.53% for 8, 16 and 24 months, respectively) more than control, whereas the leaf areas of the seedlings irrigated with the secondary effluent were 12.30, 18.19 and 15.42% more than the control for the three stages, respectively. Data in Table 3 indicate that the leaf area of the seedlings irrigated with the primary effluent was increased by 1.2-fold after both 8 and 16 months and 1.1-fold after 24 months more than the seedlings irrigated by the secondary effluent.

The fresh weights of the leaves of the T. speciosa seedlings irrigated with primary effluent were the heavier by 512.12, 732.95 and 224.93% more than those with tap water at the 8-, 16- and 24-month stages, respectively, while for the seedlings irrigated with the secondary effluent, they were 203.92, 243.32 and 175.96% more than those with tap water treatment through the same three stages, respectively. Consequently, leaves fresh weights of the seedlings that irrigated with primary effluent were folded by 2.0, 2.4 and 1.2 after 8, 16 and 24 months, respectively, more than the seedlings irrigated by secondary effluent. Similar trend was observed in the leaves dry weights after 8, 16 and 24 months for the seedling that irrigated with primary effluent where they were heavier by 653.00, 490.38 and 193.85%, respectively, more than tap water treatment (Table 3). In addition, secondary effluent increased leaves dry weights of the seedlings by 329.00, 181.43 and 157.33% more than control for 8, 16 and 24 months stages, respectively. On the other hand, leaves dry weights of the seedlings that irrigated with primary effluent were folded by 1.8, 2.1 and 1.1 after 8, 16 and 24 months more than the seedlings irrigated by secondary effluent.

Shoots fresh weights of T. speciosa seedlings which irrigated by primary effluent were the heaviest by 455.52, 415.65 and 305.70% more than tap water for 8, 16 and 24 months stages, respectively. While, they were 217.88, 163.08 and 190.42% more than tap water treatment throughout the same three stages, respectively, for the seedlings that irrigated with secondary effluent. Hence, shoots fresh weights of the seedlings which irrigated by primary effluent were folded by 1.7, 2.0 and 1.4 after 8, 16 and 24 months, respectively, more than the seedlings irrigated by secondary effluent. The dry weights of shoots had similar trend after 8, 16 and 24 months for the seedling which irrigated by primary effluent where they were heavier by 915.88, 629.56 and 318.14%, respectively, more than tap water treatment (Table 4). Also, secondary effluent increased shoots dry weights of the seedlings by 322.35, 255.33 and 190.67% more than control for 8, 16 and 24 months stages, respectively. On the other hand, shoots dry weights of the seedlings that irrigated with primary effluent were folded by 2.4, 2.1 and 1.4 after 8, 16 and 24 months more than the seedlings irrigated by secondary effluent.

Table 4 Effect of sewage effluent on the shoots and roots biomass, shoot/root ratio and root length of Tipuana speciosa at three stages
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These results explained by many investigators, who found that sewage effluent had stimulation effect on vegetative growth of trees, provided the soil with plant nutrients and organic matter as well as improved the physical properties of the soil, that reflected on the growth by enhancing either the cell elongation and division (Kaneker et al. 1993 on Acacia nilotica; Hassan Fatma et al. 2002 on Acaciasaligna and Leucaena leucocephala; Berbec et al. 1999 on poplar; Guo and Sims 2000 on Eucalyptus globules; Abbaas 2002 on Casuarina glauca, Taxodium distichum and Populus nigra; Bhati and Singh 2003 on Eucalyptus camaldulensis; EL-Sayed 2005 on Ceratonia siliqua, A. saligna and Acacia stenophylla, and Singh and Bhati 2005 on Dalbergia sissoo).

Root characteristics

Table 4 exhibited that roots weights of T. speciosa had the same trend of the leaves and shoots along the three investigated stages (Table 4). Therefore, roots fresh weights of the seedlings that irrigated with primary effluent were the heaviest by 251.08, 341.54 and 235.01% more than tap water for 8, 16 and 24 months stages, respectively. While, they were 124.63, 142.12 and 110.13% more than tap water treatment through the same three stages, respectively, for the seedlings that irrigated with secondary effluent. Hence, roots fresh weights of the seedlings that irrigated with primary effluent were folded by 1.6, 1.8 and 1.6 after 8, 16 and 24 months, respectively, more than fresh roots of the seedlings irrigated by secondary effluent.

The same trend was detected in the roots dry weights after 8, 16 and 24 months for the seedling that irrigated with primary effluent where they were heavier by 424.93, 240.26 and 187.64%, respectively, more than tap water treatment (Table 4). Also, secondary effluent increased roots dry weights of the seedlings by 113.01, 96.75 and 84.75% more than control for 8, 16 and 24 months stages, respectively. Further, roots dry weights of the seedlings that irrigated with primary effluent were folded by 2.5, 1.7 and 1.6 after 8, 16 and 24 months more than dry roots of the seedlings irrigated by secondary effluent.

In contrast, secondary effluent treatment gave the shortest roots length (16.03, 14.93 and 9.75% less than tap water treatment for 8, 16 and 24 months stages, respectively). Consequently, it followed by primary sewage effluent treatment (5.83, 8.71 and 2.90% less than tap water treatment for 8, 16 and 24 months stages, respectively). This action could be explained by the accumulation of soluble salts and heavy metals in root zone, as a result of applying sewage effluent, which might adverse root elongation. This results are in harmony with these of Nessel et al. (1982) on Pond cypress, Hopmans et al. (1990) on E. camaldulensis and Pinus radiata, Gogate et al.(1995) on Tectona grandis, Hassan Fatma et al. (2002) on Albizzia lebbek, Taxodium distichum and T. speciosa and Ali et al. (2011) on Swietenia mahagoni.

Data of the root characteristics are in agreement with those of Sebastiani et al. (2004) on poplar and EL-Sayed (2005) on Ceratonia siliqua.

Chemical composition

Generally, irrigation with primary effluent gave the highest concentrations of N, P, k, Cd, Ni, Pb and Fe in leaves, shoots and roots of T. speciosa followed by secondary effluent treatment (Tables 5, 6).

Table 5 Effect of sewage effluent on N, P and K percentage and total uptake of leaves (L), shoots (S) and roots (R) of Tipuana speciosa at three stages
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Table 6 Effect of sewage effluent on Cd, Ni, Pb and Fe percentage and total uptake of leaves (L), shoots (S) and roots (R) of Tipuana speciosa at three stages
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As well as, the concentrations of N, P and K in leaves were much higher than that of shoots and roots. The increase of N, P, K, Cd, Ni, Pb and Fe in plant parts might be attributed to increasing them in the occupancy root zone from applying sewage effluents, which reflected on their uptake by roots.

These results are agreed with the findings of Singh and Bhati (2005) who found that concentrations of N, P and K were greater in foliage compared to the other plant parts. In contrary heavy metals (Cd, Ni, Pb and Fe) tended to be accumulated in root rather than in both leaves and shoots with few exceptions. When irrigation stage enlarged from 8 to 24 months, the uptakes of N, P, K, Cd, Ni, Pb and Fe in the whole plant were increased due to enormity increase of vegetative growth. Similarly, EL-Sayed (2005) found that irrigation with secondary effluent increased N, P, K, Ca, Mg, Na, Fe, Zn, Mn, Cu, Pb, Cd, Cr and Ni in leaves, stems and roots of Ceratonia siliqua, A. saligna and A. stenophylla compared with tap water.

After 24 months, the magnitude of increase of heavy metals in the whole plant due to primary effluent treatment ranged from 2 to 9 times more than tap water for Cd, Ni, Pb and Fe.

Soil characteristics

Data in Table 7 revealed that soil salinity in terms of electrical conductivity of saturated paste (EC), CaCO3 (%), organic matter (%) and soluble anions and cations were influenced by both primary and secondary effluent treatment. Where, pH value slightly changed by irrigation with sewage effluent. EC values of soil treated with sewage effluent were related to EC values of irrigation water treatment therefore, EC of soil treated with tap water was decreased to 1.50 and 1.44 ds/m after 16 and 24 months of irrigation, respectively. While EC of soil treated with secondary and primary effluent were ranged between 2.76 and 3.48 ds/m, respectively. However, the soluble cations and anions had the same trend of EC of soil except for Ca2+ and SO4−.

Table 7 Means of effect of sewage effluent on the soil properties of Tipuana speciosa plantation at three stages
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It is clear, from Table 7, that irrigation with primary sewage effluent decreased the CaCO3 content from 32.26 to 31.04 and 29.15% for primary sewage effluent treatments after 8, 16 and 24 months, respectively, of irrigation stage. This is probably due to the fact that same CaCO3 was dissolved by the organic acids present in sewage and leached down in soil.

Furthermore, organic matter content increased with irrigation stage was extended from 8 to 16 then 24 months, with higher values for primary effluent compared with secondary (5, 14 and 22% for former stages, respectively). Likewise, available P and N were also maximized more by primary effluent treatment compared to secondary effluent, while tape water gave the lowest values. In addition, it is clear that available P and N were accumulated more as stage of irrigation was extended from 8 to 16 then 24 months.

The results are agree with those of EL-Nennah et al. (1982) who found that use of sewage effluent in irrigation resulted in remarkable change of organic matter, available P and total and soluble N which might have been added to soils upon irrigation.

Extractable-heavy metals

Results given in Table 7 show that DTPA-extractable Cd, Cu, Ni and Pb increased as irrigation stage increased by sewage effluent treatments compared to tap water therefore, the primary effluent treatment gave the greater values (0.05, 0.59, 1.92 and 2.21 ppm for above-mentioned metals, respectively, after 24 months. Whereas, the response of extractable Fe, Mn and Zn were not consistent for different sewage effluent treatments.

Many investigators stated that heavy metals accumulated in soil resulted from continuous irrigation with sewage effluent (EL-Nennah et al. 1982; Abulroos et al. 1996; Salem et al. 2000). This increment of heavy metals in soil and consequently in edible parts of field crop plant should be considered, which adversely affect human and animal health through the food chain. It would be great advantage to grow forest trees such as T. speciosa in heavily polluted areas or soil irrigated with sewage effluent without serious problems.