Assessment of various control strategies for recirculation of greenhouse effluents under semi-arid conditions

Summary

Rose plants (cv. Mercedes) were planted in tuff as soilless medium during April 1993. Recirculation of drainage water (DrW) was started in December 1993. Since then, three strategies were tested versus non-recirculated 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 collected rain water. As a first approximation, DrW were considered as containing full strength nutritional solution. As a result, the concentration (cone.) of applied nutrients was somewhat lower in the recirculation treatments than in the control. No DrW discharge was done, b) All treatments received a quantity of fertilizer solution identical to that of the control, regardless of the contribution of nutrients from the DrW. As a result, the cone, of K and N was considerably higher in the recirculation treatments than in the control. DrW was discharged whenever 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) using maximum possible amount of DrW. Excess DrW was discharged. The cone, of the fertilization solution was adjusted so that phosphate cone, in the DrW was similar to that of the control. The potential savings of water and fertilizers and the reduction in environmental pollution are described. No negative effect of DrW recycling on crop yield (quantity and quality) was found. Frequent monitoring revealed no proliferation of pathogenic microorganisms.