The Link Between High Vigor and Physiological Parameters of Alfalfa Grown in Two Fertilization Modes: Classic Based on Chemical Fertilizers and Manure and Modern Based on Biocompost and Biochar Under and Without Deficit Water

Amid severe global drought, investigating diverse substrates’ impact on plant productivity, alongside physiological changes during water stress, addresses the challenge of enhancing crop yield without relying heavily on chemical fertilizers. This open-air pot study focuses on comparing the effects of biochar and biocompost treatments with conventional methods on the growth of alfalfa. Biochar samples were subjected to physicochemical, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses to characterize their properties. Pearson correlation was used to deduce the different physiological parameters linked to high vigor. Results revealed varying chemical compositions among substrates. The botanical origin of biochars played a role in atomic arrangement in their crystal lattice, as XRD revealed cellulose in plant biomass-sourced biochars. FTIR analysis identified prevalent hydroxyl and aromatic groups. Vigor was highest in treatments with ample organic manure without chemical fertilizers, and those including 3% industrial agri-food sewage sludge biochar and 6% biocompost. Protein levels and enzyme activity increased under water stress. Pearson correlation revealed a partial positive connection solely between seedling vigor index I (SVI I) and photosynthesis. Conversely, a partial negative correlation was found between superoxide dismutase (SOD) and seedling vigor index II (SVI II). No discernible correlation was observed between vigor and protein levels, stomatal characteristics. Alfalfa vigor was influenced by cation exchange capacity (CEC) and water holding capacity (WHC) in both irrigation regimes. Findings indicate that utilizing biochar and biocompost treatments holds promise for enhancing alfalfa growth when contrasted with conventional methods. Additionally, the study reveals complexities beyond the partial correlation observed between photosynthesis and vigor, making it challenging to definitively determine parameters directly responsible for vigor.