Impacts of Irrigation with Reclaimed Wastewater on Forages Production, Nutrients, and Heavy Metals Content

In order to investigate the effect of reclaimed wastewater (RWW) on soil chemical properties and heavy metal uptake of selected forages, an experiment was carried out at Dhaid Research Station, UAE during three growing seasons (2014-2016). Alfalfa, Rhodes and Buffel grass were irrigated by RWW and grown in a randomized complete block design with four replications. Composite soil samples were collected from the experimental site before starting the study and every six months from planting date to test the macro and heavy elements concentration in soil and forages tissues. Chemical analysis for soil, crops and wastewater were analyzed. RWW irrigation has significantly increased the soil salinity (1 to 8 dSm) in 2014 but soon these values were declined in 2015 and 2016 growing seasons due to the enhanced irrigation water quality and the use of good water management. Results revealed that UAE (Sharjah) domestic RWW is suitable to be reused for irrigate forages as its quality match international standards for RWW irrigation except its Na and Cl content. The results of the plants tissues analysis during 2014 season indicated a rise in the nutrients concentration, particularly nitrogen, potash, iron and boron, compared with the critical limits. While, the results have also shown a significant increase of zinc (Zn) and copper (Cu), especially in Buffel grass and Alfalfa tissues during the third season (2016) which exceeded the critical limits. The highest mean yearly dry weight yield during the study period were recorded for Buffel grass (50.5 ton ha) followed by Rhodes (44.5 ton ha) and Alfalfa (11.1 ton ha). It can be concluded that regular monitoring of recycled wastewater, soil and appropriate management are needed to mitigate the negative impacts of sodium and salts accumulations.


Introduction
Reclaimed wastewater (RWW) is a valuable source for plant nutrients and organic matter needed for maintaining fertility and productivity of arid soils.However, the reuse of RWW for irrigation may potentially create environmental problems if not properly treated and managed (Mohammad & Mazahreh, 2003).Also irrigation with municipal wastewater is considered an environmentally sound wastewater disposal practice that helps to minimize the pollution of the ecosystem subjected to contamination by direct disposal of wastewater into surface or groundwater (ICBA, 2014).RWW irrigation provides water, N and P as well as organic matter to the soils, but there is a concern about the accumulation of potentially toxic elements such as Cd, Cu, Fe, Mn, Pb and Zn from both domestic and industrial sources.
The main challenge facing agriculture development in United Arab Emirates as the rest of Arabian Peninsula countries is the limitation and scarcity of water resources.The yearly water consumption in UAE is about 4.6 × 10 9 m 3 and the agricultural sector is considered as the biggest water consumer with about 67% of the total available water resources.RWW is considered the most important water resource that will reduce the gap between the water demand and supply in agriculture sector and save the fresh water for human priorities.The main use of domestic RWW in UAE is for irrigation of landscapes and limited amount are used for irrigation of forage crops.In 2008 about 5.6 × 10 8 m 3 of tertiary RWW were produced from the treatment plants in AUE, and it estimated to increase to about 1.44 × 10 9 m 3 in 2030 (ICBA, 2010).
With this severe limitations on the availability of water in UAE, conservative and efficient use of available water resources is a major consideration for balancing future demand and supply, therefore the application of RWW is beneficial because this disposal process removes some of the pollutants, and increase crop yields by supplying essential nutrients, but this disposal requires a special agronomic practices and management guidelines to ensure practical and safe use of RWW in irrigation for the production of forages with minimum hazard to the surrounding environment.
Nutrients make RWW an effective fertilizer, while organic matter improves soil texture and enriches the humic content, which increases soil humidity, retains metals (through cationic exchange and the formation of organo-metallic compounds), and enhances microbial activity (Mohammad & Ayadi, 2004).ICBA (2014) noted that reclaimed water irrigation decreased soil pH and increased soil salinity, soil phosphorus, potassium, iron, and manganese levels, but soil organic matter was increased only in the topsoil.Darwish et al. (2015) noted that the uptake of macro and micronutrients by corn increased with RWW irrigation, implying that secondary RWW could be a source of plant nutrients and can be reused for irrigation to increase forage crop production.Ahmed (2013) conducted a review study in Qatar using scientific, economic and technical evidence to show that RWW is a valuable and safe resource for crop irrigation, posing minimal risk to the soil, groundwater, and crops, and is a key factor towards Qatar's food security.Highlighted was the real challenge of using RWW in Qatar for crop production as being social, but that highly treated domestic wastewater could be a real water resource for irrigation.Technical and economic calculations show minimum risks associated with reuse.
In Bahrain Mapanda et al. (2005) conducted a study across six farms Kingdom irrigated with RWW aimed at studying the effect of irrigation with RWW on the concentration of heavy metals in soil and Alfalfa crop.The results indicated that the concentration of heavy metals in RWW did not exceed the international standards, except for cadmium, which was double the allowable limit.He concluded that RWW can be used safely for irrigating fodder crops with continuous monitoring of heavy metal content in the soil and the crops irrigated with it.Alghobar and Suresha (2016) indicated that the use of wastewater for irrigation led to significant differences in mean values of pH, EC, N, P, Ca, Mg, Na, Mn, Cu, Zn, Cd, Ni, Pb and Cr of soil as compared to the control groundwater irrigated soil sample.
Knowledge about the selection and management of appropriate forage species and management systems that maximize the economic return and minimize the environmental hazards associated with the use of RWW is still limited and un available.This study will assess the quantities and qualities of the RWW resources, the environmental impact, and the proportion suitable for forage production, along with appropriate crop management practices suitable for the use of RWW irrigation.

Study Site
This experiment trail was investigated at Al-Dhaid Agricultural Research Station, Sharjah, UAE (latitude 25.3° N, longitude 55.9° E).The experimental site is located in arid climate with generally light and erratic precipitation.The soil is classified as sandy and considered marginally suitable for various crop production systems under strict management conditions.

Experimental Design
This experiment was implemented using Randomized Complete Block Design (RCBD) as seen in Figure 1, with three forages (Alfalfa, Buffel and Rhodes grass) in four replications for each treatment (Experimental unit area 16 m 2 ).
Planting seeds and transplants of the forages was implemented on February 2014.Seedlings of two different grass Buffel (Cenchrus ciliaris) and Rhodes (Chloris gayana) in 0.50 m rows and 0.25 m between plants while Alfalfa (M using drip Irrigation the referen the Station

Yearly RW analysis (E and wastew
Three soil represent t soil sampl interval du Fresh and Rhodes an using TRIM

Irrigat
The

Conclusions and Recommendations
On the light of the results obtained from using RWW in irrigation of three selected forages, the main conclusions and recommendations can be summarized as follows: (1) The heavy metals contents in RWW were below the critical levels but the Na and Cl concentrations were more than the recommended levels especially during 2014 growing season.
(2) The contents of toxic element s in the plant tissues of the forage crops were found to be below the critical level except the Ni in Alfalfa crop during 2014 but it reduced during 2015 growing season due to enhancement of reclaimed water quality.
(3) Soil salinity and some heavy metals were accumulated in the soil profile as a result of using RWW in irrigation.
(4) The RWW used in this trail contain sufficient nutrients for forage crops production, and the highest mean yearly dry weight yield during the study period were recorded for Buffel grass (50.45 ton ha -1 ) followed by Rhodes (44.51 ton ha -1 ) and Alfalfa (11.1 ton ha -1 ) (5) Irrigation water, soil and crop should be monitored and tested for chemical and biological analysis in addition to evaluate crop management practices that maximize production and reduce the negative impact of RWW irrigation on plant products.
(6) The quality of forages produced on Reclaimed wastewater and their impact on animal health and productivity should be assessed.

Table 2 .
Total dry yield (ton ha -1 year -1 ) of the three studied forage species irrigated with reclaimed wastewater during the period 2014-2016 in UAE