Maize responses to circular biogenic nano-hydroxyapatite and conventional phosphorus fertilization in a P-sufficient soil

Improving phosphorus management requires the development of circular nutrient sources together with agronomic evidence defining the conditions under which they can be evaluated. Here, we conducted an exploratory greenhouse assessment of maize responses to circular biogenic nano-hydroxyapatite (nHAP) derived from agri-food residues in a P-sufficient agricultural soil. In a factorial pot experiment, two thermally differentiated nHAP materials were compared with triple superphosphate (TSP) and an unfertilized control, with or without inoculation with the phosphate-solubilizing bacterium Pseudomonas alloputida. Maize phenology, gas exchange, biomass allocation, kernel P concentration, total plant P, and grain-quality traits were assessed. The experimental system did not generate a measurable yield response to external P addition, and no significant differences between the unfertilized control and the fertilized treatments were detected for grain dry weight, harvest index, kernel P concentration, kernel P content, or total plant P. No consistent treatment-related differences were detected in gas-exchange variables, whereas selected differences were observed in biomass allocation and grain composition. PSB effects were limited and did not consistently modify maize responses. Because the soil was P-sufficient, the experiment did not allow discrimination of fertilizer-source efficacy or attribution of plant P uptake to the applied materials. The study therefore represents an exploratory agronomic screening step between material characterization and subsequent evaluation in P-responsive soils and field-scale cropping systems.