Comparative evaluation of chitosan-based biopolymer and conventional phosphorus extractants on phosphorus availability, soil pH dynamics, and maize agronomic performance in amended soils

Phosphorus (P) availability in tropical soils is commonly restricted by strong fixation processes, mainly through adsorption onto iron and aluminum oxides and precipitation with calcium compounds, which significantly reduce its mobility and plant utilization. This study evaluated the effectiveness of chitosan-based biosorbents (nZvFe-CLCB) relative to conventional extractants (Bray-1 and Olsen) in assessing soil P availability, and their relationships with soil pH dynamics and maize performance under different P amendments. Soil samples from six locations in southwestern Nigeria were experimented under screenhouse conditions in a completely randomized design, with three treatments: single superphosphate (SSP), poultry manure (PM), and a control. Soil chemical properties, extractable P, electrical conductivity (EC), pH, maize dry matter weight (DMW), and P uptake were monitored over eight weeks after planting (WAP). Results showed Olsen extractant showed 11 to 15% higher P recovery than Bray-1 and nZvFe-CLCB in amended soils. Bray-1 extracted P was nZvFe-CLCB (0.732*) > Olsen (0.688*). Bray-1 had the strongest association with maize DMW (r² = 0.777*) and P uptake (r² = 0.820**), while soil pH had a strong influence on P availability across methods (up to r² = 0.851**). The finding concluded that nZvFe-CLCB extractant as an alternative extractant for Bray 1 in predicting plant-available P in tropical soils.