Integrated production of dual‐function fertilizers from poultry litter incineration ash via sulfuric acid leaching: Linking ash fraction characteristics with nutrient recovery and agronomic functionality

Sustainable recycling of biomass ash is critical for circular nutrient management, requiring proper modification before agricultural use. This study converted poultry litter‐derived boiler ash (BA) and wet ash (WA) into basal and top‐dressing fertilizers and evaluated their physicochemical properties, mineralogical changes, and agronomic performance. Both ashes were leached with sulfuric acid; the resulting filter cakes were treated with nitric acid to produce basal fertilizers with nutrient ratios expressed as N:P 2 O 5 :K 2 O (BABF 3.62:11.2:8.61; WABF 3.82:8.91:9.11), while ammonium nitrate was added to the leachates to obtain top‐dressing fertilizers with nutrient ratios (BATF 19.3:2.47:10.1; WATF 21.2:2.93:7.72). Acid treatment reduced the highly alkaline pH (11.5–12.0) to acidic levels (pH <5) and increased electrical conductivity (EC) and water‐soluble nutrients. Nitrogen (N) was enriched in top‐dressing fertilizers (up to 21.2%), whereas phosphorus (P) remained higher in basal formulations. Fertilizer applications significantly increased plant dry weight (up to 79.9 g pot −1 ) compared to control (10.4 g pot −1 ) and conventional fertilization (72.3 g pot −1 ). Plant N, P, iron (Fe), and zinc (Zn) concentrations increased markedly, with BA‐based treatments enhancing P and micronutrient uptake, and WA‐based treatments promoting biomass production. Available‐P, potassium (K), and Zn also increased after harvest. Ash‐derived fertilizers improved plant growth and soil fertility, performing comparably or better than conventional fertilizers. Producing both basal and top‐dressing fertilizers offers a promising strategy for sustainable nutrient recovery.