Biochar-based controlled-release ammonium phosphate fertilizer: Synthesis and impact on soil nutrient dynamics, wheat growth, and yield under controlled conditions

Current agricultural practices prioritize increasing crop yields through extensive fertilizer use. However, overreliance on nitrogen (N) and phosphorus (P) fertilizers has led to environmental degradation, including eutrophication and inefficient nutrient use, raising sustainability concerns. This study aims to develop a biochar-supported controlled-release fertilizer (BAPF) containing N and P, and evaluate its impact on soil nutrient dynamics, nutrient recovery, plant growth, and yield. BAPF was synthesized by impregnating biochar derived from oat hulls with urea and diammonium phosphate. An eight-week soil incubation experiment compared nutrient release dynamics between BAPF, conventional fertilizers (CF), oat hull biochar (OHB), and a control (CT). BAPF demonstrated consistent nutrient release, maintaining higher N and P availability over time than CF. By day 60, total N concentration in the BAPF treatment was 6 % higher than CF, while P availability was consistently 20 % higher. BAPF also exhibited lower ammonification rates compared to unfertilized treatments, while nitrification rates were 2.6 times greater compared to OHB and CT, demonstrating enhanced nitrogen conversion efficiency. In a greenhouse trial using spring wheat as a model plant, BAPF improved growth, nutrient uptake, and grain yield compared to CF, OHB, and CT. Total biomass and grain yield increased by approximately 15 % relative to CF, and nutrient recovery rates were significantly higher, with N apparent recovery (ARN) of 55.0 % compared to 36.5 % for CF. Additionally, the apparent P recovery rose from 8.9 % in CF to 18.5 % in BAPF. The findings suggest that BAPF improves nutrient use efficiency and enhances grain productivity compared to conventional methods. Its controlled-release properties lead to longer nutrient availability, better nutrient recovery, and increased crop productivity, even in high P-fixing soils. Therefore, BAPF offers an effective alternative to reduce reliance on synthetic fertilizers, enhancing sustainability in agricultural systems.