Laboratory analyses The samples of irrigation water were tested for chemical and biological components, including major elements (N, P, K) from fertilizer, minor and trace elements and heavy metals. Chemical parameters were determined by classic chemical analysis methods. The total alkalis and the chemical oxygen demand were determined volumetrically; other parameters were determined colorimetrically (Berl, 1951; Hach Chemical Company, 1979; Alexeev, 1980). Lead (Pb) and cadmium (Cd) were analysed after extraction with a chloroformic solution of dithizone. Colorimetric analyses were conducted with a Hach spectrophotometer, either a model 2000 or a model 1105.