Articles
MINIMAL WATER DISCHARGE GROWING SYSTEM: CHARACTERISTICS AT A STEADY-STATE SITUATION
Water salinity, on the other hand, dictates high (ca. 40%) leaching factor (LF) in intensive, soilless run-to-waste systems.
Due to the luxury feeding practiced in these systems, the discharged water is a major source of nitrates (and pesticides) that, when reaching groundwater are causing a further deterioration of their quality.
Recycling greenhouse effluents may be, therefore, beneficial from both environmental and economical aspects.
Two main problems may hinder drainage water (DW) recirculation: a.
The risk of a rapid spread of potentially pathogenic soil-borne pathogens; b.
The damage inflicted by accumulated salts that are present in the tap water when their concentration in the system exceed certain level.
The present paper addresses the second problem as experience shows that for cut roses the first one is nor severe.
Rose plants (cv. “Mercedes”) were planted in tuff medium at April 1993. Recirculation started at December 1993. During the first 20 months the tuff acted as an ion exchanger, releasing nutritional ions such as calcium and magnesium (which were not supplied with the fertigation solution) and adsorbed sodium.
During all this period water were rarely discharged without any effect on yield quantity or quality.
When steady state was achieved, water were discharged whenever the EC of the DW exceeded predetermined values (3.0 for the non-recirculated control, 3.5, 4.0, and 4.5 dS m-1 for three recirculation treatments). At these regimes discharge rates were 38%, 23%, 10% and 8%, respectively, again with no negative effect on yield.
Periodical plating of samples derived from DW, roots and tuff on selective media, revealed no indication for the development of any soil-borne disease.
The potential water savings as well as the degree of pollution prevention will be described and discussed.