Evaluation of green roof structures and substrates for Lactuca sativa L. in tropical conditions

Different types of structures and substrates are used for urban extensive green roofs. However, there is not enough information about the performance of these structures and substrates for growing edible plants in tropical climate conditions. This study evaluates the best combination of three different modular extensive green roof structures and two types of local substrates (compost and soil + biochar) for Lactuca sativa L. var. crispa (lettuce) growth. Physicochemical and biological properties of substrates and growth variables of plants were measured for the different green roof structures, at the beginning and at the end of the experiment (seven weeks after), and under rainy and dry climatic conditions. According to the model obtained, the monolithic multilayer structure, high concentrations of Mg, elevated amounts of 600 μm aggregates and less substrate bulk density were linked with a higher L. sativa yield. The substrate used, however, was not associated with this result. Additionally, it was found that some of the physicochemical and microbiological properties of substrates changed at the end of the experiment. However, these properties were dependent on climatic conditions. It is recommended to use the monolithic multilayer green roof structure and a substrate with added biochar for higher L. sativa yield. Further evaluations of this structure and substrate for other edible plants may be useful for supporting vulnerable people and enhancing agroecological functions of green roofs in Latin-America.