Response of Growth Dynamics and Root Architecture of Safflower (Carthamus tinctorius L.) to Mineral Phosphorus Rate, Bio-Fertilizer type and Their Interactions

Abstract

Objective: This study evaluated the individual and interactive effects of mineral phosphorus fertilization rates and bio-fertilizer inoculations on the vegetative growth and root characteristics of safflower (Carthamus tinctorius L.) under Sharkia Governorate conditions, Egypt.

Materials and Methods: A field trial was conducted in a split-plot design with three replications during the 2024 year. Main plots received four mineral phosphorus rates (0.0, 15.50, 31.00 and 46.50 kg P2O5 feddan-1), while sub-plots comprised four bio-fertilizer regimes: un-inoculated control, Nitrobein (Azospirillum lipoferum), Phosphorein (Bacillus megaterium), and dual inoculation (nitrobein + phosphorein). Morpho-physiological and root parameters were evaluated at 110 days after sowing.

Results: Increasing mineral phosphorus up to 46.50 kg P2O5 feddan-1 significantly maximized plant height (197.33 cm), root length (44.67 cm), and root dry weight (85.26 g). Dual bio-inoculation (nitrobein + phosphorein) consistently recorded superior mean values across all traits compared to single-strain and control treatments. Crucially, the interaction of 46.50 kg P2O5 feddan-1 × (nitrobein + phosphorein) produced the highest overall growth performance, while moderate phosphorus (31.00 kg P2O5 feddan-1) combined with dual bio-inoculation efficiently optimized shoot biomass (149.70 g). Recommendation: Integrating dual bio-fertilizer inoculation (nitrobein + phosphorein) with moderate-to-high phosphorus rates (31.00 – 46.50 kg P2O5 feddan-1) is recommended to optimize safflower growth performance, maximize nutrient utilization efficiency, and support sustainable agricultural practices.