Evaluating Nitrogen Solubility from Fertilizers in Sandy Loam Soil Using Core-Ring Soil Extraction Method and Electrical Conductivity Sensors

Abstract Understanding fertilizer solubility and nutrient release dynamics is essential for improving nitrogen (N) use efficiency in coarse-textured soils prone to leaching. This study aimed to quantify and compare the dissolution kinetics of urea, diammonium phosphate (DAP) and pelleted poultry manure using a novel core-ring extraction method under controlled moisture condition in sandy loam soil. Fertilizers were incubated for 0.5 to 168 hours, and core (application zone) and surrounding ring soils were separately extracted to quantify N release and mobility. Nutrient mobility was further validated using TEROS 12 electrical conductivity (EC) sensors in layered soil columns. Results indicated that urea had the highest core N release index of 1.8, followed by DAP at 1.1 and poultry manure at 0.3, with statistically significant differences (p < 0.05). Temporal solubility patterns showed rapid urea- N surge in the core from 42.8 to 219.1 mg L -1 within 2 h, followed by outward migration reflected in ring N increasing to 44 mg L -1 by 168 h. DAP released N more gradually from 50.8 to 111.6 mg L -1 by 168 h with minimum lateral diffusion. Poultry manure displayed the slowest release from 20 to 34.1 mg L -1 at 4 h. EC monitoring corroborated with these results, where urea generated a strong EC accumulation in the topsoil (EC response ratio of 2.15 at 48 h), DAP produced localized EC enrichment and poultry manure induced negligible EC change. The integrated core-ring and EC monitoring approach provided a mechanistic understanding of fertilizer solubility pathways and nutrient movement under field moisture conditions.