Comparison of organic substrates in urban rooftop agriculture, towards improving crop production resilience to temporary drought in Mediterranean cities.

BACKGROUND Urban agriculture contributes to meeting the growing food production demand in cities. In the context of low water availability, it is important to consider alternatives that are able to maintain production. Through a circular economy vision, this study aimed to assess the use of substrates made from local materials as an alternative for urban agriculture in periods of low water availability, due to water supply cuts. The substrates used were coir commercial organic substrate, vegetable compost from urban organic waste, perlite commercial standard substrate, and a mixture of the urban compost and perlite (1:1) were used for 3 consecutive crop cycles of lettuce (Lactuca sativa L. var. crispa). The crop cycles were performed in the spring and summer periods of 2018 to observe the performance during warmer periods of the year in an integrated rooftop greenhouse near Barcelona. Each substrate was assessed under conventionally irrigation (0-5 kPa) and temporary water restricted conditions (irrigation stopped until the water tension reached -20 kPa perlite). RESULTS In terms of yield, our results show that the compost and mixture were similar to those obtained from perlite (11.5% and 3.7% of more production in a restricted water condition). Organic substrates increased the crop's resilience to water restriction in contrast with the perlite. In particular, water lost took longer in coir (1 and 2 crop cycle); however, when dryness began, it occurred quickly. CONCLUSION The vegetable compost and the substrate mixture presented tolerance to temporary water restriction when water restriction reached -20 kPa. This article is protected by copyright. All rights reserved.