Alternative to tomato soilless culture in open system in the Canary Islands: Preliminary results

In order to reduce the pollution of agricultural origin, we are studying recirculation strategies in three different substrates as an alternative to tomato soilless culture in open system in the Canary Islands. The three tested substrates were rockwool (widely used in canary tomato crop), picon (volcanic tuff) and coir, a less extended substrate in this area, which generate a reduced environmental impact in their obtaining processes and waste. This research was conducted in a traditional canary screenhouse from October 2006 to May 2007 with tomato plants, cv. 'Boludo' grafted on 'Beaufort'. The nutrient solution applied in all treatments had an electrical conductivity (EC) of 2.3 to 2.5 dS·m^-1, which in the closed system was renewed when drainage EC reached 5 dS·m^-1. Compared to the open system, recirculating significantly decreased the amount of water both applied (32% less for rockwool, 45% for picon and 39% for coir) and discharged (61%, 69% and 65% less). Marketable productions in the open system were 17.5, 16.4 and 18.9 kg·m^-2 for rockwool, picon and coir, respectively, while recirculation produced around 7, 15 and 19% less, but in terms of water use efficiency the closed system produced on average 28 kg·m^-3 of marketable fruit compared to 19-to-21 kg·m^-3 in the open system.