NOVELTY - Modified straw fertilizer comprises 80-100 pts. wt. crop straw, 8-12 pts. wt. ammonium hydrogen carbonate, 30-50 pts. wt. biogas residue, 10-15 pts. wt. zeolite powder, 5-10 pts. wt. magnesium sulfate, 10-15 pts. wt. monoammonium phosphate, 8-15 pts. wt. potassium humate, 2-3 pts. wt. microbial agent, 3-5 pts. wt. additive and suitable amount of water. The additive comprises 1-2 pts. wt. sodium dodecyl sulfate, 6-8 pts. wt. maifanite powder, 7-10 pts. wt. vinyl acetate, 6-9 pts. wt. ethanol, 2-3 pts. wt. N,N'-methylenebisacrylamide and 30 pts. wt. water.    USE - The modified straw fertilizer is useful for increasing content of organic colloid in soil (claimed).    ADVANTAGE - The fertilizer improves toughness of soil. The method consumes less time.    DETAILED DESCRIPTION - Modified straw fertilizer comprises 80-100 pts. wt. crop straw, 8-12 pts. wt. ammonium hydrogen carbonate, 30-50 pts. wt. biogas residue, 10-15 pts. wt. zeolite powder, 5-10 pts. wt. magnesium sulfate, 10-15 pts. wt. monoammonium phosphate, 8-15 pts. wt. potassium humate, 2-3 pts. wt. microbial agent, 3-5 pts. wt. additive and suitable amount of water. The additive comprises 1-2 pts. wt. sodium dodecyl sulfate, 6-8 pts. wt. maifanite powder, 7-10 pts. wt. vinyl acetate, 6-9 pts. wt. ethanol, 2-3 pts. wt. N,N'-methylenebisacrylamide and 30 pts. wt. water. The additive is prepared by diluting ethanol using water in a reaction kettle, adding vinyl acetate and N,N'-methylenebisacrylamide to the kettle, stirring obtained mixture at 150-200 revolutions/minute (rpm) for 5-10 minutes, sequentially adding the sodium dodecyl sulfate and maifanite powder, and stirring obtained mixture at 250-400 rpm for 0.5-1 hour to obtain product. An INDEPENDENT CLAIM is included for method for preparing the modified straw fertilizer, which involves (a) crushing the crop straw using crusher to a size of 3-4 cm, adding 2-3 times water, adding ammonium hydrogen carbonate, stirring obtained mixture, subjecting the mixture to ammoniation treatment at 30-35 degrees C for 15-20 days, and filtering obtained product to obtain filtrate and residue, (b) subjecting the residue to microwave treatment at 230-250 W for 5-8 minutes, (c) mixing product obtained in step (b) with the biogas residue and zeolite powder to obtain mixture, diluting microbial agent using water, spraying diluted mixture on the mixture, controlling water content of the mixture at 60%, uniformly mixing and stacking mixture, and fermenting the mixture for 6-8 days, and (d) crushing fermented product, uniformly mixing with the additive, adding magnesium sulfate, monoammonium phosphate and potassium humate, mixing obtained mixture with suitable amount of water, controlling water content of the mixture at 20%. and granulating obtained product.