This study was conducted to determine the effects of phosphite and phosphate fertilisers on broccoli’s yield, growth, and nutritional status (Brassica oleracea L. var. italica cv. ‘Fiorentino’). In factorial combinations, experiments were conducted at three pH levels (5.5, 7.0, and 8.5) and three phosphorus source levels [Pi (phosphate), Phi (phosphite), and Pi + Phi]. Phi had a statistically significant negative effect on yield, producing immature and button-like flower heads. Decreases in chlorophyll index, Fv/Fm [ratio of variable fluorescence (Fv) to maximum fluorescence (Fm)], and leaf area were observed using the Phi treatment. These results indicate that fertilisation with Phi alone did not affect plant growth and yield. P (phosphorus) and K (potassium) concentrations in plants were increased by root fertilisation with Phi (floating system), but did not affect growth characteristics; increased Pi uptake in Phi-treated plants increased P and K concentrations in the sink source, resulting in reduced growth, phytotoxicity, and no head formation. While it may appear that Phi is upsetting the balance of solution nutrients and stressing the plants, the Phi-induced stress condition was identified by measuring proline levels and electrolyte leakage. Thus, phosphite could not be used as a P source for plants. However, Phi could be used as a plant nutrient source combined with conventional Pi fertilisers.
