TECHNOLOGY FOCUS - AGRICULTURE - Preferred Method: The method comprises boiling the stalks of the fiber plant at a temperature not lower than 100 degrees C for 0.5-2 hours in the water containing 25% ammonia liquor added in an amount of 5-15 dm3 per 1000 kg of stalks, and cooling at a temperature of 28 degrees C and treating with acid whey (80-120 dm3 per 1000 kg), and adding water to the ensilage at a temperature not lower than 110 degrees C for 0.5-2 hours, and cooling to a temperature as required for a liquefying enzyme, preferably an alpha -amylase, which is added to whole mixture. The whole mixture is further cooled to a temperature as required for a saccharifying enzyme, preferably a glucoamylase, which is added to it, and the whole mixture is separated and the solution undergoes the alcoholic fermentation and/or yeast fermentation processes, and the pre-processed stalks undergo the delignification process. The delignification process is carried out as a multistage process, preferably, as a three stage process. The digesting liquor flows through subsequent stages in a continuous system, and the fresh digesting liquor contacts the fiber plant stalks during the last stage, the fresh fiber plant stalks contacts the most spent digesting liquor, and after the first step of the delignification process, the content of the carbohydrates soluble in the digesting liquor is 10-15% (mass fraction), and after the last step of the delignification process, this content is 30-35%. The method comprises removing lignin from the cellulose with the use of sodium and/or potassium bisulfate (VI) solution, and after the cellulose pulp has been water-washed, it is again washed using a sodium and/or potassium bisulfate (IV) solution (30-50% mass concentration), whereas the solution contains Mg2+ ions (0.1-0.3% (mass fraction)), and then, the cellulose pulp is water-washed again. The spent digesting liquor is purifying with a mixture of calcium oxide and magnesium oxide, and saturated with a carbon dioxide to a pH value of 7.0 plus minus 0.5, the precipitated calcium carbonate deposit is removed and a clear solution is concentrated to a concentration level of at least 35%, and the crystals of sodium hydrogen carbonate are isolated, and the solution undergoes the alcoholic fermentation and/or the yeast fermentation processes. The method comprises isolating the yeast from the solution, and adding the whitewash to the solution in order to increase the pH value to a level above 8.5, then, the deposit precipitated is removed and added to the yeast pulp, and the clear fluid is saturated with a carbon dioxide, the calcium carbonate precipitated during the on going process is isolated, and the clear fluid is utilized in many ways to prepare digesting liquor, in the cellulose delignification process, the cellulose is washed to obtain the fiber plant stalks.