The invention relates to a formula and a film-
coating preparation method for biological
carbon coated urea. The biological
carbon coated urea is characterized in that the outside of a
fertilizer core is coated with
solid-
powder-shaped biological carbon,
sulfur, dicyandiamide and
bentonite by using granular
urea with a size of 3 to 4 mm as the
fertilizer core and oxidized
corn starch as bonding liquid, wherein the above-mentioned components have weight proportions as follows: 50 to 80 parts of the urea, 10 to 30 parts of the biological carbon, 2 to 10 parts of the
sulfur, 2 to 3 parts of the dicyandiamide, 2 to 3 parts of the
bentonite and 3 to 5 parts of the
corn starch. The film-
coating preparation method for the biological
carbon coated urea comprises the following steps: placing the urea into a disc granulator, carrying out preheating with hot air for 5 min, spraying the bonding liquid on the surface of the urea with a high-pressure spray gun, blowing the hot air for 3 to 5 min, adding a mixed film-
coating material into the disc granulator in batches and carrying out rotating for 10 min, then spraying the bonding liquid again, and carrying out
drying in the air so as to obtain the biological carbon
coated urea. According to the invention, the biological carbon can improve physical and chemical properties of soil and adsorb
ammonium-
nitrogen and
nitrate-
nitrogen ions; the dicyandiamide reduces
nitrification; and S4O62- generated by
decomposition of the
sulfur can
delay decomposition of the dicyandiamide, and H+ and S2O32- generated by
decomposition of the sulfur can inhibit
nitrification. The biological carbon
coated urea provided by the invention has the advantages of low
ammonia volatilization, slow generation of
nitrate nitrogen,
low nitrogen loss and
high nitrogen effectiveness.