Impacts of Sewage- Treated- Wastewater and Groundwater with Sludge Applications on Nutrients and Heavy Metals Distribution in Soil and Cucumber Plant

Abstract

The main aim of this study is to evaluate the impacts of irrigation water qualities (groundwater (GW) and tertiary treated water (TW)) and sewage sludge application rates (0, 5, 10, 15, 20 and 40%) on chemical, physical and microbiological properties of the calcareous (CS) and non-calcareous (NC) soils and the yield and yield components of the cucumber crop. The distribution of nutrients(N, P, K, Zn, Cu, Fe, and Mn) and heavy metals(Cd, C, and Ni) in the soils, leaves and fruits of grown plants were also investigated. The current study was conducted under the greenhouse conditions at the Agricultural and Veterinary Training and Research Station of the King Faisal University, Al-Hassa, Kingdom of Saudi Arabia. The obtained results revealed that application of sewage sludge significantly increased soil salinity (EC); soluble cations (Ca2+ , Mg2+ , Na+ and K+ ) and anions (Cl- , SO4 2- and NO3 - ); SAR and ESP and contents of organic matter (OM) in both CS and NC soils. While, irrigation with treated water decreased the Ece vaues and the soluble cations and anions values. Soil pH, soluble HCO3 - and CaCO3 significantly decreased with increasing application of sewage sludge. Significant improvements in soil physical properties (soil moisture characteristics, bulk density and porosity) were also observed. As a result of sewage sludge application the total nitrogen (TN), available phosphorous(Avail-P) and micronutrients (Fe, Mn, Cu and Zn) significantly increased in both CS and NC soils with increasing sewage sludge application rates. Also, applications of sewage sludge and treated wastewater irrigation water caused significant prevents of the both CS and NC soils. It decreased soil bulk density values and increased values of saturation percents, filed capacity, permanent wilting point, available water and porosity. Significant increases were also observed in values of heavy metals (Cd, Co, and Ni) in both CS and NC soils as a result of sewage sludge applications. Their soil contents were in order of Ni > Co ≥ Cd. Their values however were greatly less than the maximum permissible limits. On long term impacts, it is however worth to mention that they should be periodically monitored to observe their accumulative concentrations in soils, as many researchers suggested so. In addition, similar fear is suggested regarding the microbiological data observed in the soil, including the total bacterial count and total coli-form. These data showed that increasing the application of sewage sludge possessed significant effects on the values of these soil microbial parameters. However, their values did not exceed the suggested maximum allowed limits. Nonetheless, the long term impacts of sludge applications should be cautiously considered. Furthermore, the parameters of yield (plant height and chlorophyll content ) and yield components (number of fruits, weight) of cucumber plants showed significant increases resulting from the increased application rates of sewage sludge and irrigation by tertiary treated wastewater. The highest level of sludge application caused the biggest impacts on these parameters of the cucumber plants. The contents of the macro- (TN and avail-P) and micro- (Fe, Mn, Cu and Zn) nutrients and heavy metals (Cd, Co and Ni) in the cucumber plant parts (leaves and fruits) showed an increasing trend as a result of the applications of sewage sludge and treated wastewater irrigation. Impacts if sludge applications were significantly greater than irrigation water quality. Similar trend in the microbial data were observed under the effects of sewage sludge applications and irrigation water quality. These trends were the same on both CS and NC soils, suggesting the grate impacts of the sewage sludge application on plant growth and yield. It is concluded from the data obtained in the current study that irrigation water qualities and sewage sludge applications affect soil chemical, physical, fertility and microbiological properties that imposed significant effects on the plant yield and yield components. Soil and plant contents of heavy metals were also affected by the sewage sludge applications and irrigation water qualities. Yet, their values were much less than the permissible limits. Such effects were observed on both CS and NC soils. However, differences between the two soils were also observed. These findings imply that the tertiary treated wastewater and sewage sludge may possibly utilized on cultivated agricultural soils. It is presumed that their long term impacts are cautiously considered.