Evaluating impact of irrigation water quality on a calcareous clay soil using principal component analysis

Declining yields from farmland in the Bet She'an Valley, Israel, irrigated with Jordan River water, raised concerns about resource management and long term sustainability. An experiment was conducted in a commercial cotton field of the Bet She'an region, to assess the impact of irrigation water quality on soil quality. A randomized block design compared four irrigation sources: Jordan River Water, Spring Water, Treated Waste Water, and Salty Spring Water, applied via drip irrigation to a calcareous silty clay soil for 3 years. Soil samples were collected and analyzed for 20 different physical, chemical and biological attributes. Samples from an adjacent uncultivated area were used as a reference. Principal component analysis (PCA) identified electrical conductivity (EC), fluorescein diacetate enzymatic activity (FDA), exchangeable Na (Ex-Na), apparent steady state saturated hydraulic conductivity (Ksat), and available P as the most important indicators for inclusion in a minimum data set (MDS) used to evaluate soil quality. Multiple regression tested these indicators against each of 4 specified management goals, reflecting soil quality attributes, i.e., sodium adsorption ratio (SAR) of soil solution, infiltration rate, soil loss, and cotton yield. There was a significant relationship between the indicators and 3 of the goals but not with cotton yield. Soil quality indices (SQI) were calculated using a PCA weighting factor and each MDS indicator scored using linear transformation. The SQI was highest for uncultivated soil (2.945), followed by Treated Waste Water (1.471), Spring Water (0.923), Salty Spring Water (0.823) and Jordan River Water (0.582) irrigated soils. The order of relative contribution of the indicators to the SQI was FDA (35.2%), Ksat (25.0%), Ex-Na (19.2%), EC (13.4%), and available P (7.2%). The method successfully identified Jordan River Water as the most deleterious, and Treated Waste Water as the best, irrigation treatment when considering soil quality.