Long-term nutrient management influences phosphorus sorption, buffering capacity, and fractionation in Vertisols of Central India

Phosphorus (P) availability in Vertisols is limited by strong fixation associated with smectitic clay, alkaline soil conditions, and calcium-rich constituents. This study evaluated the effects of long-term nutrient management on phosphorus sorption, buffering capacity, and phosphorus fractions in Central Indian Vertisols. Surface soil samples (0–15 cm) were collected from long-term experimental plots at the ICAR-Indian Institute of Soil Science, Bhopal, under five nutrient management treatments: Control (T 1 ), Soil test crop response-based fertilizer application (STCR; T 2 ), Integrated nutrient management (INM) with 75% recommended fertilizer dose + 25% farmyard manure (T 3 ), 100% organic nutrient management (T 4 ), and recommended NPK with 90% crop residue incorporation under conservation agriculture (CA; T 5 ) replicated 3 times. P sorption parameters were estimated using the Langmuir adsorption isotherm, while sequential fractionation was employed to determine soil phosphorus pools. The Langmuir adsorption model adequately described phosphorus sorption behavior across all nutrient management treatments (R 2 = 0.99). Organic nutrient management significantly reduced phosphorus sorption maximum (394 µg g⁻ 1 ), bonding energy constant (0.10 mL µg⁻ 1 ), and maximum phosphorus buffering capacity (40.57 L kg⁻ 1 ) compared with all other treatments. Although calcium-bound phosphorus remained the dominant phosphorus fraction across all treatments, organic and conservation agriculture systems significantly increased the proportions of soluble, Al-bound, and Fe-bound phosphorus fractions. The lower soil phosphorus retention (SPR) observed under organic management suggests reduced phosphorus fixation and, consequently, improved phosphorus use efficiency. The long-term Organic and Conservation agriculture (CA) treatments improved phosphorus dynamics by reducing sorption and increasing plant-available phosphorus pools, supporting sustainable nutrient management in Vertisols.