Water dispersible carbon nanomaterials reduced N, P, and K leaching potential in sandy soils: A column leaching study

Carbon nanomaterials (CNMs) - amendments with carbon in nanoscale form -could potentially enhance fertilizer delivery efficiency in agriculture, but their interaction with soil properties and nutrient co-mobility, especially in coarse-textured soils, remain poorly understood. We conducted a column leaching study in repacked soil columns to compare the co-leaching of novel water-dispersible CNMs and soil nutrients across two levels of CNMs applications (200 & 400 mg kg^-1), two fertilization rates (low:80 mg kg^-1 of N, P and K and high: 200 mg N kg^-1, 100 mg P kg^-1, 200 mg K kg^-1, applied as ammonium nitrate, potassium phosphate, and potassium nitrate) and two soils (Spodosol with pH = 5.1, Alfisol with pH = 6.5). We imposed 12 leaching events to each column, with each leaching event adding water equivalent to the soil-pore volume (250 mL), resulting in cumulative leaching of 3000 mL of water through each column. CNMs applications reduced cumulative leaching losses of NO₃-N (Spodosol: 8-12 %, Alfisol: 9-19 %), NH₄-N (Spodosol: 2-14 %, Alfisol: 9-14 %), P (Spodosol: 23-27 %, Alfisol: 23-36 %) and K (Spodosol: 17-23 %, Alfisol: 24-26 %) compared to fertilized columns without CNMs. CNMs increased soil pH by up to 0.3 units (Spodosol) or 0.5 units (Alfisol), while lowering electrical conductivity by 15-20 % at the high fertilization rate in both soils. Columns with water-dispersible CNMs accumulated 25-30 % more total C in the base sections of the Alfisol compared to the Spodosol, indicating faster downward movement through the soil profile. Overall, we demonstrated that CNMs have the potential to reduce nutrient leaching in coarse-textured soils, which could be particularly beneficial in high-input intensive agricultural systems.