Another factor influencing the productivity of plants is potassium. Potassium was added to the influent of sand filters in the form of potassium carbonate to serve as a buffer. This action sought to maintain an appropriate pH for nitrification process that occurred in the sand filter. According to Woodson and Boodley (1982) under high potassium concentration, roses absorb most of the nitrogen in the ammonium form instead of nitrogen as nitrate. As shown in Table 2, the nitrified effluent from the sand filter possessed predominantly nitrogen as nitrate. Thus, high concentrations of potassium can be prevented better yield compared to that obtained with the anaerobic effluent irrigation.