Enhancing germination and seedling development in lettuce and tomato using sustainable organic substrates

Aim of study: The aim of this study was to evaluate the effects of organic substrates formulated with different proportions of acerola (Malpighia glabra) bagasse and carnauba palm (Copernica prunifera) bagana on the initial development of tomato and lettuce seedlings, with a focus on enhancing the sustainability of horticultural practices. Area of study: This research was conducted in a controlled greenhouse environment at the Center for Agricultural Sciences, Federal University of Piauí, in Teresina, Piauí, Brazil. Material and methods: The experiment involved 12 different substrates, each formulated from an organic compost mixed with acerola bagasse and carnauba palm bagana. Basaplant®, a commercially available substrate, was used as the control. This study evaluated the following variables: seed emergence (SE), emergence speed index (ESI), total dry mass (TDM), shoot dry mass (SDM), root volume (RV), dry root mass (DRM), seedling height (SH), leaf area (LA), stem diameter (SD), fresh root mass (FRM), fresh shoot mass (FSM), and Dickson quality index (DQI). The statistical analysis included principal component analysis (PCA) and cluster analysis to determine the effectiveness of the substrates. Main results: For tomato, substrates with 50% carnauba bagana displayed higher volumetric density, which positively correlated with RV and DRM. This benefited seedling stability and water retention. Fine particles (<0.25 mm) enhanced TDM, while particles between 0.5–0.25 mm negatively affected SE. In lettuce, substrates with 50% acerola bagasse promoted higher aeration and drainage, which was beneficial for this crop. Larger particles (2.0–1.0 mm) correlated positively with LA, while finer particles reduced root dry mass. PCA and clustering grouped substrates by growth performance, with the G3 cluster favoring tomato and the G5 cluster favoring lettuce. Research highlights: This study demonstrates that organic substrates with 50% carnauba bagana improve root growth and water retention in tomato seedlings, while substrates with 50% acerola bagasse enhance aeration and drainage, thereby bene- fiting lettuce growth. Fine particles positively influence biomass accumulation in tomato but limit root development in lettuce. Conversely, larger particles support greater leaf area in lettuce while reducing root depth. PCA revealed distinct substrate pref- erences for tomato and lettuce, underscoring the importance of tailoring substrate composition to crop-specific needs.