Mineral nutrition of winter-grown cucumbers under irrigation with effluent or fresh water

Two greenhouse experiments were conducted at the Newe Ya'ar Research Center (northern Israel) in the winter seasons of 2004 and 2006 in order to study the relationship between water quality and NPK nutrition of cucumbers. Two water sources were used for irrigation: effluent (treated sewage water) and fresh water in combination with five concentrations of NPK. Fruit yield was higher in plants irrigated with effluent water as compared to fresh water under control (no fertilizers) or low levels of NPK in both years, indicating the benefit of available nutrients in effluent water. In the 2004 experiment, when the NPK concentration was 50:21:50 mg l^-1 or higher, there were no significant differences between yields of plants irrigated with the different water sources, and maximal yields per plant (3.0- 3.5 kg) were achieved at 100-200 mg l^-1 N and K and 43-87 mg l^-1 P. Seedling growth analysis was conducted in the 2006 experiment, which revealed that concentrations of N, P and K for optimal vegetative growth was well below the concentrations of macronutrients required for maximal fruit yield. In the 2006 experiment maximal yield (3.35 kg plant^-1) was achieved at an NPK concentration of 400:174:400 mg l^-1, when irrigated with fresh water. Under this fertilizer regime the yield of plants irrigated with effluent water was significantly lower (2.65 kg plant^-1). At the highest concentration of NPK there was a significant reduction in fruit yield, and no difference in yield between the two sources of water. A main reason for the difference in maximal fruit yield between plants treated with different water sources may be the significant difference in mean Na absorption in shoot: 4.6 g kg^-1 in fresh, and 7.7 g kg^-1 in effluent water.