Variation in soil phosphorus adsorption and desorption characteristics across agro-ecological zones in Central Nepal

Phosphorus (P) adsorption and desorption regulate P availability, soil fertility, and the risk of P loss from terrestrial ecosystems; however, these processes remain poorly characterized in Nepalese soils. Despite their significance, there is limited understanding of these processes in Nepalese soils. This study aimed to explore how P adsorption and desorption vary across agro-ecological zones in central Nepal. A total of 225 soil samples, equally distributed among the high-hills, mid-hills, and Terai regions (75 from each), were collected across diverse locations. Isothermal P adsorption and desorption experiments were conducted to evaluate these behaviors, employing Langmuir, Freundlich, and Temkin models to assess P adsorption-desorption characteristics. Adsorbed P was highest in the high-hills (28.67–525.91 µg g⁻¹), followed by the Terai (28.57–494.68 µg g⁻¹) and mid-hills (25.63–422.14 µg g⁻¹). Similarly, P desorption was also highest in high-hills (3.39 to 69.38 µg g-1), followed by the Terai (5.15 to 56.00 µg g-1) and mid-hills (3.14 to 47.91 µg g-1). The P adsorption and desorption parameters, namely P adsorption capacity, bonding energy, maximum P buffering capacity (MPBC), P sorption index (PSI), P desorption capacity, maximum P desorption capacity, standard P requirement (SPR), external P requirement (EPR) were highest in the high-hills, while lowest in the mid-hills. However, maximum P adsorption capacity and P desorption capacity were highest and lowest, respectively, in the Terai. Moreover, the P desorption intensity, readily desorbable P (RDP), degree of P saturation (DPS), and P eutrophication risk index (PERI) were highest in the mid-hills, while lowest in the Terai. In contrast, the P buffering capacity (PBC) did not significantly differ among zones. These contrasting patterns demonstrate the need for zone-specific P management: the high-hills and Terai have comparatively greater fertilizer-P requirements, whereas the mid-hills exhibit higher laboratory-derived indicators of potential P loss. This study offers valuable insights for developing improved soil P management strategies for sustainable agriculture in diverse agro-ecological zones.