CASCADE CROPS: AN ALTERNATIVE SOLUTION FOR INCREASING SUSTAINABILITY OF GREENHOUSE TOMATO CROPS IN MEDITERRANEAN ZONE

Nitrate pollution due to excessive N fertirrigation in greenhouse tomato production is a persisting environmental concern in the Mediterranean region. Closed or re-circulating hydroponic systems can significantly reduce fertilizer run-off but not eliminate it, and the spent nutrient solution has to be ultimately collected and treated at the end of the crop cycle. Also, closed systems involve greater installation and running costs, need a high degree of automation and technical skill, and their economic viability is a question of debate in southern Europe horticulture. As a consequence, the majority of the high-value horticultural production in Mediterranean countries is done using ‘open’ systems. The aim of this paper is to present an alternative way to reduce fertilizer use and, hence, reduce the pollution potential of leachate in soilless crops by collecting and re-using it for a second greenhouse crop. Avoided environmental impact quantification was performed by using LCA tool. Results showed a slight decrease in yield for the soil crop, in comparison with the soilless system, but marketable production (15 kg m^-2) for this treatment was higher than the average production of soil grown tomatoes (12 kg m^-2). Nitrogen balance for the two combined systems showed an important decrease in N leachate (more than 60% referred to the soilless system). The adoption of the cascade crop system reduced environmental impact for climate change category by 21%, but increased eutrophication category by 10% because of the yield reduction. Further research will be oriented to look for the optimum management of lixiviates combined with organic and/or mineral fertilizers for these cascade crops.