Nanobiochar-Coating Regulates N and P Release from DAP Fertilizer in Soil and Improves Maize Crop Productivity

The crop phosphorus (P) utilization efficiency of commercial fertilizers is only 10-15%, leaving much P fixed in the soil. Coating fertilizer can lessen this problem, but most of the current available options are potentially toxic and expensive. This study-investigated nanobiochar as a coating material for engineering "smart" di-ammonium phosphate (DAP) fertilizer that controls P and nitrogen (N) release in soil, ultimately enhancing nutrient utilization by maize. Biochar was produced from farmyard manure and ball-milled to obtain nanobiochar. Different nanobiochar concentrations (2.5%, 5%, and 10% w/w) were used to coat the DAP granules in a fluidized-bed coater. The release of N and P was studied after immersing both coated and uncoated DAP fertilizers in water. In a pot experiment, five treatments, i.e.i) control (C), ii) uncoated DAP (UF), iii) 2.5% nanobiochar-coated DAP (CUNB1), iv) 5% nanobiochar-coated DAP (CUNB2), and v) 10% nanobiochar-coated DAP (CUNB3) were introduced, after which maize was sown. The presence of a uniform nanobiochar coating on DAP was confirmed by the discrete carbon peaks observed through X-ray diffraction and FTIR spectroscopic analyses. In a laboratory study, the slowest release of N and P was observed for CUNB3. Remarkably, the application of CUNB1 substantially increased the microbial biomass carbon and N by 104% and 147%, respectively, while enhancing the plant-available P, N, and potassium (K) by 40%, 70%, and 46%, respectively, compared with those of C. This treatment increased maize shoot dry matter yield by 88%, accompanied by marked increases of 229%, 205%, and 67% in maize P, N, and K uptakes compared to C, respectively. However, other coating treatments failed to increase these parameters compared with those of UF, confirming that these coatings had the slowest nutrient availability for short-duration crops. The 2.5% nanobiochar concentration can be recommended for coating DAP fertilizer to reduce problems of P fixation and enhance P availability, crop growth and nutrients uptake, hence contributing to sustainable fertilizer management practices in agroecosystem.