Unidad de excelencia María de Maeztu CEX2019-000940-M

BACKGROUND: Urban agriculture contributes to meet food production demand in cities. In a context of low water availability, it is important to consider alternatives that are able to maintain production. This study aimed to assess the use of substrates made from local materials and high water retention capacity as an alternative for urban agriculture in periods with water stress. Different substrates were used for 3 consecutive crop cycles of lettuce (Lactuca sativa L.) during the spring and summer periods of 2018 to observe these substrates performance during warmer periods of the year in an integrated rooftop greenhouse near Barcelona. The substrates used were coir commercial organic substrate, vegetable Compost from urban organic waste, Perlite (as control) commercial standard substrate, and a Mixture of the urban Compost and Perlite (1:1). Substrate crop performance was assessed under conventionally irrigation (0-5 cbar) and water restricted conditions (irrigation stop until the water tension inside the perlite bags reached -20 cbar). RESULTS: The results demonstrate that the Compost and Mix yields were similar to those obtained from Perlite (11.5% y 3.7% of more production in a restricted water condition average values). Compared to the Perlite, the organic substrates increased the crops resilience to water restriction, through biomass accumulation comparison, it took longer for Coir to lose water (1 and 2 test); however, when dryness began, it occurred very quickly. CONCLUSION: The vegetable Compost and the substrate Mixture presented tolerance to water restriction when water restriction reached -20 cbar.