Effect of Phosphorus-Solubilizing Bacteria, Organic Fertilizer, and mineral phosphate fertilization on NPK Concentrations in Cabbage (Brassica oleracea var. capitata) under Calcareous Soil Conditions

Abstract

A field experiment was conducted in autumn 2025 at the fields of College of Agriculture, University of Wasit to evaluate the effect of inoculation with phosphorus solubilizing bacteria, liquid organic fertilizer Bio-60 and different levels of mineral phosphate fertilizer triple superphosphate (TSP) on nitrogen, phosphorus and potassium concentrations in cabbage plants cv. Club Star. The experiment was conducted in a randomized complete block design (RCBD) in a 2 × 2 × 3 factorial arrangements consisting of three replications. The first factor was the inoculation with phosphorus solubilizing bacteria at two levels; no inoculation (A ₀) and 12 mL plant⁻¹ (A₁). The second factor consisted of two levels of organic liquid fertilizer (Bio-60) (no application, O₀; 5 mL plant⁻¹ in the O₁). Third factor was mineral phosphate fertilizer TSP at three levels 0, 50 and 100 kg ha⁻¹ (M₀, M₁ and M₂). The effects of fertilization on all studied traits were significant at P ≤ 0.05. The control treatment (A₀O₀M₀) recorded the lowest values of N, P and K with 0.51, 0.236 and 0.755%, respectively. By contrast, the interaction between all three factors A₁O₁M₂ was significantly better and gave the maximum values of 1.89, 0.409, and 2.567% for N, P, and K, respectively. This higher efficiency can be explained by the synergistic effect of biofertilization, organic fertilization, and mineral phosphate fertilization on nutrient availability and on nutrient uptake efficiency. Phosphorus-solubilizing bacteria increase phosphorus availability and stimulate rhizosphere activity, and organic fertilizer enhances soil physical properties and nutrient holding capacity. On the other hand, mineral phosphate fertilizer provides a direct source of available phosphorus. These findings indicate that integrated fertilization is a promising approach to enhance the nutritional status of cabbage plants and the content of macronutrients under calcareous soil conditions.