Yield of Tomato Crop Irrigated with Untreated Industrial Sewage Effluent and Remediated with Potassium Silicate and Compost Applications

An experiment was conducted for the two successive seasons of 2017 and 2018 to investigate the deleterious effect of irrigating tomato plants with untreated industrial waste water and the possible ameliorating effects of compost and potassium silicate applications on the growth and production of the grown plants. Tomato seedlings of hybrid K186 were transplanted at the four-true leaf stage and irrigated with untreated waste effluent. Compost was applied during the soil preparation at rates of 0 (control), 10, 20, and 30 m/feddan. Potassium silicate was sprayed on the plants three times; at 20, 40 and 60 days after transplanting in the concentrations of 0 (control), 3, 4 and 5 cm/l. Results revealed that vegetative growth and fruit yield of treated plants were increased by increasing compost and potassium silicate rates compared by the control (without compost and potassium silicate).The interaction effect of the treatment showed an added effect of both treatments on all measured parameters. Plant length, number of leaves and number of branches increased as the application rate of compost and potassium silicate increased. Similarly, SPAD readings showed similar positive and significant trend. In the contrary, contents of Zn, Pb, Ni, Cd and Mnresponded negatively and significantly to the interaction effect of the treatments showing the highest effect with the treatment 5 cm potassium silicate associated with 30 m compost application compared to the control. Similar to the positive effect on vegetative growth, the positive additive effect of both treatments was clear on total fruit yield where the highest effect was recorded with the treatment combining the highest rate of application of both potassium silicate and compost. It could be concluded that potassium silicate and compost applications can ameliorate the harmful effects of heavy metals in the soil.


Introduction
Egypt was classified as an arid land with a very little amount of rain fall mainly in the north coast and having the Nile Rivera's the main source of irrigation water. Officials revealed that with the ongoing agricultural expansion and climate changes, Egypt is facing a serious shortage of fresh water supply forcing the country to recycle all available sources of water. Some growers in remote areas are using raw industrial sewage effluent to fulfill their crop water needs ignoring the possible dangerous of contamination of heavy metals of such water.
The negative effects of heavy metal on many aspects of agriculture have been reported. For example, heavy metal can be leached to the underground water (He et al 2004, Rattan et al 2005 causing the spread of pollution to other layers of the aquifers. Heavy metal polluted soil can negatively affect plant growth and production causing serious economic losses (Nagajyoti et al 2010). Moreover, Arao et al (2010) and Khan et al (2008) reported high health risks for people exposed to polluted agricultural soil. The problem of heavy metal pollution to the soil is

Rana, Eman, Hashim, El-Shinawy, Abd El-Gawad
more difficult compared to other types of pollution such organic contamination because they cannot be degraded by microorganisms and last in the soil for longer time.
The application of compost decreased heavy metal concentration in plants (Ramachandran and D'souza 1998). In this respect, Sharma and Dhaliwal (2019) found that decreased concentrations of toxic metals in soils with regular application of wastewater sewage sludge with compost treatments.
Some researchers used soil amendments to change the mobility and bioavailability of such heavy metals (Bolan et al 2014, Udeigwe et al 2011. One of such amendments was compost (Paradelo et al 2011). Compost is rich with mineral ions, humic substances, and microbes which influence the immobilization of heavy metals resulting in reduction of the ecological and environmental risk of heavy metals in agricultural soils (De la Fuente et al 2011, Udovic andMcBride 2012). Adsorption, complexation, precipitation, and redox reactions may all be one or more process involving heavy metal immobilization (Huang et al 2010, Lagomarsino et al 2011, Park et al 2011, Vaca-Paulin et al 2006. Thus, in addition to the benefit of compost as an alternative for waste management, its application can reduce the harmful effects on the crop, lower economic losses, and decrease human health risks from heavy metals existing in the root zone. Beneficial effects of compost on the growth and production of some vegetable crops such as green beans were reported under different levels of irrigation (Abdel-Mawgoud 2005) as well as salinity (Abdel-Mawgoud et al 2010).
Another alternative to reduce heavy metals deteriorating effects on plants is the application of some nutritional and/or beneficial elements such as silicon (Emamverdian et al 2018). Epstein (1999) described silicon (Si) as a beneficial and possibly essential element for plants, which plays important roles in plant growth and development Yamaji 2006, Gu 2012). Many researchers reported various evidence that the application of Si to soils can alleviate Cd or Zn toxicity in many plant species, including rice , maize (Liang et al 2005), wheat (Hussain et al 2015) and cotton (Farooq et al 2013).
Therefore, this work aims to investigate the effect of compost and potassium silicate applications, on the growth and production of tomato crop grown in soils irrigated with untreated industrial sewage effluent.

Materials and Methods
Seeds of tomato plant (Solanum lycopersicum L.) hybrid K186 were sown on 24 th and 28 th of April 2017 and 2018, respectively. After one month when the seedlings reached the fourth true leaf, they were transplanted in the open field in a sandy soil at a private farm in the area of Borg Al-Arab, Alexandria Governorate, Egypt. The soil physical and chemical analyses are shown in Table 1. Individual transplants were grown at the bottom of ridges 100 cm width and at 50 cm apart. Planting distances between plants are 50 cm . The furrow irrigation was used and plants were irrigated using water from an industrial sewage channel. The chemical analysis of the irrigation water is shown in Table 1. Also, heavy metals analyses in soil and irrigation water during the two seasons of study are shown in Table 2.  All standard agricultural practices other than experimental treatments were applied according to the recommendations of the ministry of Agriculture, Egypt.

Experimental treatments
During the preparation of the soil and before transplanting, four levels of compost were applied namely, 0 (control), 10, 20, and 30 m 3 /feddan and mixed well with the upper 50 cm of soil. A complete analysis of the applied compost is shown in Table  3.

Measurements
Plant destructed samples were taken in the end of the seasons to determine plant height, and number of leaves and branches. Total yield/plant was measured by the end of the season when all ripe fruits were harvested. Zn, Mn, Pb, Ni and Cd contents were determined with a Model SOLAR 969 Atomic Absorption Spectrometer (FAO/WHO, 2001). SPAD readings at 90 days after transplanting was measured in fully expanded leaves using Minolta SPAD 501 chlorophyll meter.

Experimental design and statistical analysis
The treatments were arranged in a split plot design with four replicates where potassium silicate treatments were in the main plot and compost treatments in the sub main plots. All data collected were subjected to the statistical analysis according to Snedecor and Cochram (1968). The data of treatments were compared, using least significant difference (LSD) method at 0.05 as mentioned by Gomez and Gomez (1984). Table 4 show that potassium silicate spraying increased significantly plant length and number of leaves and branches per plant as the concentration of the application increased in both growing seasons.

Data in
As for the effect of compost adding, compost application showed a gradual positive effect on plant length, and number of leaves and branches per plant with the highest effect recorded with the highest rate of application (30 m 3 /fed.) Table 4.
The interaction effect of potassium silicate and compost showed an added effect of both treatments on all measured parameters. The highest concentration of potassium silicate with the highest rate of compost gave the tallest plants and highest number of leaves and branches. Data in Table 5 indicate that potassium silicate spraying increased significantly SPAD reading and total yield per plant as the concentration of the application increased in both growing seasons.
As for the effect of compost adding, compost application showed a gradual positive effect on SPAD reading and total yield per plant with the highest effect recorded with the highest rate of application (30 m 3 /fed.) Table 5.
The interaction effect of potassium silicate and compost showed an added effect of both treatments on all measured parameters. The highest concentration of potassium silicate with the highest rate of compost gave the highest SPAD reading and total yield per plant. Table 6 indicated that Zn and Mn contents responded negatively and significantly to the increment in potassium silicate application rates Table 6.

Data in
Also, increasing compost application rate significantly decreased the contents of Zn and Mn in the tissue of the plants with the highest negative effect recorded with the highest rate of application (30 m 3 /fed.) in two seasons of study Table 6.
Data in Table 6 showed Zn and Mn contents responded negatively and significantly to the interaction effect of the treatments showing the highest effect with the treatment 5 cm 3 potassium silicate associated with 30 m 3 compost application compared to control. Data in Table 7 indicated that Pb, Ni and Cd contents responded negatively and significantly to the increment in potassium silicate application rates Table 7.

Yield of tomato crop irrigated with untreated industrial sewage effluent and remediated with potassium silicate and compost applications
Also, increasing compost application rate significantly decreased the contents of Pb, Ni and Cd in the tissue of the plants in two seasons of study Table 7. Table 7 showed Pb, Ni and Cd contents responded negatively and significantly to the interaction effect of the treatments showing the highest effect with the treatment 5 cm 3 potassium silicate associated with 30 m 3 compost application compared to control.

Discussion
Heavy metals have been reported to cause deteriorating effects on different plant growth aspects resulting in reduction in plant production and quality. Cd, Ni and Pb are such example of those heavy metals exist in agricultural soils because of misuse of agrochemicals and/or pollution from other sources such as irrigation of raw untreated sewage effluent. In this study, the deteriorating effect of heavy metal polluted irrigation water has been observed leading to the lowest growth and production of tomato plants as well as the highest contents of heavy metals in plant tissue. Such accumulation has been observed earlier in many crops (Nagajyoti et al 2010). In this study, compost application reduced the harmful effect of heavy metals existed in irrigation water. This can be due to changing the physicochemical property of soils and reacting with heavy metals (Bolan et al 2014, Liu et al 2009. The beneficial effect of compost application in reducing the harmful effects of heavy metals has been reported earlier by Huang et al (2016). On the other hand, potassium silicate showed also an ameliorating effect on plant growth and production as revealed from our data. These positive effects are Rana, Eman, Hashim, El-Shinawy, Abd El-Gawad mainly due to the presence of Si. These beneficial effects have been explained on the basis that Si increase plant resistance to some heavy metals such as Cd by inhibiting Cd uptake in roots and the enhancement of light-use-efficiency in leaves (Nwugo and Huerta 2008 a&b). Silicon has been reported to have a beneficial effect on growth and yield for various horticultural plant species such as bean, cucumber (Zhu et al 2004), tomato (Romero-Aranda et al 2006) and Zucchini squash (Savvas et al 2015).
Because of the different mode of action for compost and potassium silicate against heavy metals, the interaction of the two treatments was additive and its combination resulted in enhancing the effect of each other which reflected on higher plant growth and production.

Conclusion
It can be concluded that the treatment with compost and potassium silicate, as well as the interaction between them, reduced the harmful effect of irrigation with untreated industrial wastewater, as well as increased the vegetative growth and yield of the tomato plants under study.