Nitrogen Use Efficiency of Microbial and Amino Acid Treatments for Organic Broccoli (Brassica oleracea L. var. italica Plenk) Seed Production

The availability and quality of organic seeds are critical challenges for organic farming, with nitrogen use efficiency (NUE) being crucial for improving productivity. This study, part of the H2020 BRESOV project, assessed the effects of three nutritional protocols (NPs) on eight broccoli genotypes (GEs), comprising two commercial F1 hybrids and six Sicilian landraces. The tested NPs included formulations containing Trichoderma species, organic nitrogen, and essential micronutrients such as iron, zinc, carbon, boron, manganese, molybdenum, and zinc. This trial was conducted on an organic farm in Adrano (CT). Plants were evaluated for key traits related to growth, development, and seed production. NUE was analyzed to measure the efficiency of nitrogen conversion from soil into seed production. Significant interactions between NPs and GEs were observed for all seed yield components and most morphometric traits, except for secondary branches and root width, varying significantly only among the tested genotypes. The Sicilian landraces Broccolo nero and Sparaceddi showed the highest seed yield, overcoming the productive performances of the commercial hybrids F1 Marathon and Gentleman. Broccolo nero, grown using amino acid microbial consortia applied solely via fertigation (NP1), exhibited the highest NUE, indicating a positive nitrogen balance relative to seed yield and soil nitrogen content. Principal component analysis (PCA) grouped the genotypes into five distinct clusters based on the analyzed bio-morphometric traits and on the effect of the treatment. The Broccolo nero and Sparaceddi genotypes formed two distinct groups, clearly differentiated by their unique morphological traits related to plant biomass and seed production. Additionally, both genotypes exhibited distinct responses to the applied nutrition protocols, with positive results compared to the control condition. These results underscore the potential of the broccoli landraces for organic farming and breeding due to their adaptability, resilience, and superior NUE.