Simplified hydroponics in Tunisia: assessing the charred straw as growing substrate for lettuce cultivation

Simplified hydroponics proves to be a viable solution for sustainable vegetable production in developing economies. In a rural area of northern Tunisia lacking commercial growing media, a three-replicated randomized block design experiment assessed the agronomic efficiency of an alternative growing substrate for lettuce cultivation. A closed-loop hydroponic system with gravity irrigation utilized recovered plastic bottles as pots, arranged in 2 m long rows and tilted to ensure nutrient solution flow. Tested substrates were commercial perlite and locally recovered wheat straw that was charred. Plants were sampled at the higher, central, and lower part of the row. Charred straw at the top of the system yielded the highest, although productivity declined in the row central and lower. When the adopted substrate was perlite yield was consistent across the different positions in the raw, with values comparable with those from plants on charred straw in the central and lower positions. These results suggest limited drainage in charred straw, impacting nutrient solution flow through the bottom of the system. Additionally, plant dry matter (%) was significantly higher in perlite, and increased at the bottom of the system for both substrates. Strategic interventions are needed to address limitations in drainage properties, thereby optimizing the potential of charred straw as a viable hydroponic substrate. Preliminary findings on using optical sensors for lettuce yield estimation in simplified hydroponics are presented, while system productivity improvements are discussed. The study provides valuable data supporting the implementation and optimization of simplified hydroponics production in northern Tunisia.