ASSESSMENT OF VARIOUS CONTROL STRATEGIES FOR RECIRCULATION OF GREENHOUSE EFFLUENTS UNDER SEMIARID CONDITIONS

Rose plants (cv. Mercedes) were planted in tuff as soilless medium dur ing April 1993. Recirculation of drainage water (DrW) was started in D ecember 1993. Since then, three strategies were tested versus non-reci rculated controls: a) Electrical conductivity (EC) of irrigation water of all treatments and the control was identical. This was achieved by diluting the recycled solution with various proportions of tap and co llected rain water. As a first approximation, DrW were considered as c ontaining full strength nutritional solution. As a result, the concent ration (conc.) of applied nutrients was somewhat lower in the recircul ation treatments than in the control. No DrW discharge was done. b) Al l treatments received a quantity of fertilizer solution identical to t hat of the control, regardless of the contribution of nutrients from t he DrW. As a result, the cone. of K and N was considerably higher in t he recirculation treatments than in the control. DrW was discharged wh enever their EC passed prescribed values (3.0, 3.5, 4.0 or 4.5 dS m(-1 )). c) Irrigation was controlled according to prescribed EC values of 2.0 (control), 2.5, 3.0 and 3.5 dS m(-1) (recirculation treatments) us ing maximum possible amount of DrW. Excess DrW was discharged. The con e, of the fertilization solution was adjusted so that phosphate cone, in the DrW was similar to that of the control. The potential savings o f water and fertilizers and the reduction in environmental pollution a re described. No negative effect of DrW recycling on crop yield (quant ity and quality) was found. Frequent monitoring revealed no proliferat ion of pathogenic microorganisms.