Deashed biochar as N-carrier extended the N-release by inhibiting N-losses in calcareous soils

Recently, biochar has been tested as a nutrient carrier for synthesizing slow-release fertilizers. But, such slow-release fertilizer exists which is designed specifically for alkaline calcareous soils. Biochar adsorbs/complex large quantities of nutrient ions due to extensive surface area, porosity, and surface functional groups. In addition, the indigenous properties of biochar can be tailored for specific use. Therefore, in this study, the emphasis was given to formulate a designer slow-release nitrogen fertilizer by modifying biochar by deashing to suit the alkaline calcareous soils since such soils are prone to heavy nitrogen losses. The acacia wood ( Acacia Arabica L.) biochar was made and deashed with 0.1 M HCl. Then, raw and deashed biochar was characterized to evaluate the changes in pH, CEC, ash contents, volatile matter, fixed-C, surface area, pore volume, surface morphology, mineral structure, and surface functional groups after deashing. Biochar-based slow-release nitrogen fertilizer (BSRNF) was synthesized by impregnating the urea onto biochar while starch and polyvinyl alcohol were used as binders. The effect of BSRNF on N release, NH 3 -volatilization, NO 3 -leaching, and N 2 O emission was examined in two different soils compared to conventional urea. It was found that deashing significantly modified the properties of biochar which favored urea sorption onto biochar which was confirmed by SEM images, XRD patterns, and FTIR spectra of raw and deashed biochar. The evaluation of BSRNF in two different alkaline calcareous soils showed that N release was extended up to ≥ 60 days. Consequently, BSRNF, compared to conventional urea, significantly decreased the NH 3 -volatilization up to 38.09%, NO 3 -leaching up to 49.66%, and N 2 O-emission up to 52.39% of applied N. The BSRNF significantly delayed the nitrogen release in soil, resulting in decreased nitrogen losses compared to conventional urea. The mechanism behind this was the sorption of nitrogen onto biochar which was further enhanced by deashing. The deashing also made biochar suitable for alkaline calcareous soils. In addition, the application rate of biochar has also economized.