ON-SITE QUALITY EVALUATION OF SUBSURFACE DRAINAGE WATER FOR SUPPLEMENTAL IRRIGATION IN MASHTOUL AL-SOUQ AREA, SHARKIA GOVERNORATE, EGYPT

The objective of this study was to assess the quality of irrigation water, groundwater and drainage water in Mashtoul El-Souq District, Sharkia Governorate, for the supplemental irrigation purposes to compensate for the lacke of fresh irrigation water required for crops grown in the study area. Six sampels from Nabtit and El-Serw irrigation canals, 26-sampels from observation wells (groundwater) and 6-sampels from the outlets of main subsurface drainage collectors (drainage water) were collected during summer (2017) and winter (2017/2018). To achieve this study, three neighboring sites with already installed subsurface drainage system were selected. Three drainage collectors were choosen (one for each site). Five pizometers (observation wells) were constructed at the first collector, 4 pizometers at the second collector and 4 pizometers at the third collector. Water samples were periodically taken from the drainage network at the dumps of drainage pools in exchange rooms. Water samples were subjected to chemical analyses and then calculating some quality parameters to assess their validity for supplemental agricultural irrigation. Cations, anions, pH and EC were determined. Results showed that P^H values ranged from7.6 to 8.0 in irrigation water samples, and the average of salinity (EC) and sodicity (SAR) values in irrigation water samples were 0.63 dSm^-1 and 2.09, respectively, low saline and alkaline water which is good for irrigation. The pH values of the drainage water ranged from 7.8 to 8.2, and the average values of EC and SAR values in drainage water samples were 2.1 dSm^-1 and 4.52, respectively. According to the division of the US Salinity Lab. (1954), it was classified as C2S1 for irrigation water samples, and for drainage water, the classification lies between C3S2 and C4S2. There were seasonal differences in the concentration of soluble ions. Salinity and sodicity of subsurface water varied from 0.78 to 3.12 dSm^-1 and 1.75 to 8.42, respectively. A better strategy for dealing with the "disposal" of subsurface agricultural drainage water is that the drainage water could be intercepted, isolated from the good-quality water, and reused for the irrigation of suitably salt-tolerant crops other than blending.