Quality Assessment of Irrigation Waters used in Agricultural Fields of Mersin Mezitli District and Irrigation-Induced Soil Salinity Assessments

Irrigation water salinity, measured as electrical conductivity (EC), is the most effective water quality indicator for crop productivity. Crops cannot compete with ions in the soil solution for water incase of high EClevels of irrigation water, then salinity-induced yield losses are encountered. The higher the EC, the less water is available to plants, even though the soil appears to be wet [1].

Soil salinity and alkalinity are common processes that characterize arid areas in particular. These processes can be attributed to natural conditions or anthropogenic activities. Natural conditions include climate, lithology, topography and pedology, while human-induced activities are mostly related to agricultural land use and in particular to irrigation. Over time, the extent of saline, alkaline and saline-alkaline agricultural lands has increased, such a case then resulted in accelerated land degradation and desertification, reduced agricultural productivity and ultimately jeopardized environmental health and food safety. Mapping and monitoring saline soils is an important management tool aimed at determining the extent and severity of salinization processes. Recent advances in remote sensing methods have increased the effectiveness of mapping and monitoring processes of saline soils. The knowledge and experience regarding the prevention, reduction and improvement of soil salinity and alkalinity have increased significantly overtime [2]. [3] indicated that in modern irrigation systems, quality of irrigation water is as important as the amount, timing and method of irrigation. When sufficient and good-quality water is not available, water that is unsuitable for irrigation is commonly used. Such a case then increases soil salinity levels. Therefore, to evaluate the water quality in the ponds used for irrigation in Hakkari province, water samples were taken from 10 irrigation ponds in June, July, August and September. The water samples were analyzed for electrical conductivity (EC), pH, anions and cations (Ca²⁺, Mg²⁺, K⁺, Na⁺, SO₄²⁻, NO₃²⁻, CO₃²⁻, HCO₃⁻, and Cl⁻). Additionally, using the resultant data, Sodium Adsorption Ratio (SAR), Residual Sodium Carbonate (RSC) and Sodium Percentage (% Na) values were calculated. It was observed that the pH, EC, SAR, RSC and % Navalues of irrigation pond waters did not exceed the limit values, but the Mg+2 and K+ values of the pond water in the Kanatlı area of Akçalı Village and the K+ value of the pond water in the Şişer area of Kırıkdağ Village exceeded the threshold values.

The SAR value of irrigation water is the primary parameter designating water quality class. Therefore, results obtained from studies conducted with sodium salt without considering the SAR value represent sodium damage rather than salt damage. To determine the level of irrigation water salinity that maize lants can tolerate, germination and pot experiments were conducted with irrigation waters of different salt concentrations by setting the SAR value below 1. Germination experiments revealed that root lengths, seedling dry weights and germination rates decreased with increasing irrigation water salinity levels. Root lengths began to be negatively affected at an irrigation water salinity level of 3 dS m-1 ECi, while seedling dry weights and germination rates began to be affected at a level of 5 dS m-1 ECi. In pot experiments, plant heights and plant dry weights decreased with increasing irrigation water salinity levels and were negatively affected at salinity level of 8 dS m-1 ECi [4]. It was determined in a study on the effect of irrigation water of different qualities on alfalfa that growth slowed down in alfalfa irrigated with saline water and harvest yield and quality decreased. Contrarily, when leaching (washing) was performed and salts were removed from the environment, plant growth returned to normal levels. Accordingly, it was determined that for high alfalfa yields, irrigation water salinity should be below 1.5 dSm-1 [5].

Soil salinity and alkalinity occur in arid and semi-arid regions of the world where irrigated agriculture is practiced. Low rainfall, poor-quality irrigation water and high evaporation rates contribute to salinity and alkalinity issues in such regions. These issues also impair the structural properties of the soil ([6].; [7]). [8] conducted a study with the irrigation water resources of Ankara Haymana Soğulca Village irrigation cooperative and stated that the irrigation water samples were C (excessively saline water) and could not be used in areas with limited drainage. 3 Despite the presence of salinity issues in the irrigation water resources of the study area, it was noted that no salinity problems arose in the agricultural lands where these waters were used. It was also emphasized that although no salinity issues were observed in the agricultural lands of the region, it is essential to develop both closed and open drainage systems to prevent future salinity problems in these agricultural lands. [9] examined the possible effects of using drainage water for irrigation on the water and salt balance of the soils in the Harran Plain. It was determined that open drainage canal water in the plain contained less salt than sub-surface drainage water and that salt content decreased toward the end of the season. In areas with drainage systems, the water table level generally remains at a depth of 140–160 cm during the irrigation season. Under these conditions, the SaltMod computer model predicts that root zone salinity will decrease from 7.0 to 3.0 dSm-1 within 3 years and to 1.5 dSm-1 within 10 years. Additionally, irrigation with water having an EC of 1.5 dSm-1 will cause a decrease in soil salinity, while irrigation with water with EC=2.5-3.0 dS m-1 and above will cause an increase in soil salinity. [10] conducted a study in the Biga Plain of Çanakkale province and analyzed water samples taken from 20 wells for electrical conductivity (EC), pH, potassium (K), calcium (Ca), magnesium (Mg), Sodium (Na), Carbonate (CO3), Bicarbonate (HCO3), Chloride (Cl), Sulfate (SO4), Nitrate (NO3) and Boron (B) parameters. Considering the Water Pollution Control Regulation (SKKY) Classification System, water samples of 11 wells were classified as second class and the others as first class. The study found that apart from nitrate pollution in groundwater, no significant problems had yet emerged in the study area. [11] conducted a study in the Isparta Plain to examine the quality of irrigation water in water samples taken from 21 groundwater wells and found that the water quality in some of the wells was classified as C S (highly saline-low alkaline), 3 1 while the water quality in other wells was classified as C S (moderately saline-low alkaline). 2 1 [12] conducted a study to determine the impact of domestic and industrial waste waters on water quality of Nilüfer River. Water samples were taken from the discharge points of five wastewater treatment plants discharging into the Nilüfer River and from the streams into which these plants discharge during four different periods between August 2013 – May 2014. It was determined that the water quality parameters of Nilüfer River and some of the wastewater treatment plants discharging into the Nilüfer River varied depending on the period. Based on the classification made considering ECand SAR, water samples were classified into the C S-C S classes. It was also determined that the wastewater discharged from treatment plants had a 2 1 4 4 negative impact on the Nilüfer River, particularly in terms of pH, EC, ammonium, phosphorus, sulfate, boron and chlorine values.

It was found in a study conducted by [13] in the Sultanhisar district of Aydın Province that the quality of water used for irrigation varied between C Sand C S classes over time. It was also determined that the canal water used affected fruit quality 2 1 3 1 and boron concentrations were higher than that of the control group plants. [14] selected a total of 17 sampling sites along the Awash River and its tributaries and conducted sampling four times a year indifferent seasons to assess the water quality of the Awash River and its tributaries. Researchers assessed the overall water quality and suitability for irrigation using numerous water quality parameters such as pH, EC, SAR, RSC, Na+, K+, Ca++ , Mg++, CO 2−, HCO − and Cl−. It was determined that all quality parameters in Lake Beseka exceeded the maximum permissible limits 3 3 for irrigation, the physicochemical characteristics of the Awash River showed variations indifferent water quality parameters across different sites. Only the pH and SAR of Beseka Lake and Meteka hot spring water exceeded the permitted limit and the ECvalues in Mojo, Wonji, Beseka, Melkasedi, Werer, Ambash, Meteka and Meteka hot springs showed medium-high salinity values, while the RSC was very high. It was recommended that wastewater treatment plants should be constructed for industries to improve water quality.