CASCADE CROPPING SYSTEM FOR GREENHOUSE SOILLESS CULTURE

     One approach to reduce the waste of water and chemicals in hydroponics and the resultant environmental pollution is the development of a drain nutrient solution reuse system, which is based on the cultivation of plants with successively higher salt tolerance. In a cascade cropping systems salt-tolerant crops would be cultivated with salt-enriched nutrient solutions flushed out of growing systems with less tolerant species. The drainage nutrient solution becomes progressively more saline as each successive species is grown and it is finally discarded when the salinity is too high for cropping, but the nutrient content (in particular that of nitrate and phosphate) is low and, therefore, environmentally-safe. An experiment was carried out to evaluate the feasibility to use a cascade cropping system (based on recirculating nutrient solution culture) with a round-fruit tomato as a drainage (exhausted) water-donor crop and a cherry tomato as a drainage water-user crop, in order to limit the fertiliser losses in the environment with a contemporaneous economic production. In this study, it was also included a treatment involving a tomato culture irrigated with a synthetic drainage water (prepared with fresh water and salts) with the aim to distinguish the genuine effects of high salinity of exhausted solution from those that may be related to the presence of potentially toxic root exudates. The results demonstrated that cherry tomato may be grown with exhausted nutrient solutions that are flushed out from a culture of more salt-sensitive tomato cultivar, thus reducing the environmental impact that is provoked by semi-closed soilless systems.

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