NOVELTY - Slow release fertilizer comprises biomass carbon particles as matrix, binder and nitrogenous fertilizer, phosphorus fertilizer, potassium fertilizer and trace element fertilizer. The content of biomass carbon particles is 10-50 wt.% and the total nutrient content is 26-32 wt.%. The total nutrient is nitrogen, available phosphorus (in the form of phosphorus pentoxide) and/or available potassium (in the form of potassium oxide). The nitrogen fertilizer includes urea, ammonium nitrate, ammonium sulfate, ammonium chloride and other nitrogen-containing fertilizers.    USE - The fertilizer is useful as one time base fertilizer for watermelon (claimed).    ADVANTAGE - The fertilizer utilizes waste biomass particles of agriculture; is microporous; has similar characteristics of soil humus and has strong moisture and nutrient adsorption capacity; provides essential nutrients, increases soil fertility and improves soil structure to stimulate the growth of crops; has high efficiency; and is environmental friendly and suitable for large-scale production of watermelon.    DETAILED DESCRIPTION - Slow release fertilizer comprises biomass carbon particles as matrix, binder and nitrogenous fertilizer, phosphorus fertilizer, potassium fertilizer and trace element fertilizer. The content of biomass carbon particles is 10-50 wt.% and the total nutrient content is 26-32 wt.%. The total nutrient is nitrogen, available phosphorus (in the form of phosphorus pentoxide) and/or available potassium (in the form of potassium oxide). The content of nitrogen is 11-13 wt.%, available phosphorus is 6-8 wt.%, and the available potassium is 9-11 wt.%. The biomass carbon particles are corn cob granular carbon, rice husk granular carbon, peanut shell granular carbon, straw granular carbon and mushroom tray granular carbon. The nitrogen fertilizer includes urea, ammonium nitrate, ammonium sulfate, ammonium chloride and other nitrogen-containing fertilizers. The phosphorus fertilizer includes monoammonium phosphate, diammonium phosphate, calcium superphosphate, calcium magnesium phosphate, nitrophosphate and other phosphorus containing fertilizers. The potassium fertilizer includes potassium sulfate, potassium chloride, monopotassium phosphate and other potassium containing fertilizers. The trace element fertilizer includes boron, zinc, manganese, iron, copper or molybdenum fertilizers. The binder is bentonite and/or clay.