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Alkaline pretreatment can effectively remove lignin and significantly increase enzymatic hydrolysis efficiency of lignocellulosic biomass. Sodium hydroxide (NaOH) is the common alkali for treating lignocellulose. However, a large quantity of liquid waste (LW) generated in the NaOH pretreatment process is hard to be removed. In this context, this work employed KOH together with urea for treating corn stover (CS) and explored the feasibility of recovering LW for plant fertilization due to the existence of potassium (K) and nitrogen (N) elements in LW. With response surface methodology, an optimum pretreatment condition, which was 1:1 (2% w/v) Urea/KOH (UK) at 30 °C for 2 h was achieved. Enzymatic digestibility of UK-treated CS could attain 75.49%, which was 12.55% higher than that of KOH-treated CS under the same conditions. The glucose yield could be further increased to 83.1% with the addition of 1% Tween-80. Meanwhile, the LW showed significant enhancement in the length and biomass yield of two cereal and three vegetable crops. UK pretreatment is a promising greenway for cellulosic ethanol production by recycling LW as value-added fertilizer. Image 1 • The Urea/KOH (UK) pretreatment of Corn straw (CS) at 30 °C was achieved. • It increased Cellulose content and reduced Lignin level with limited water wash. • Liquid waste (LW) of the pretreatment were recovered as fertilizer to realize zero waste emission. [ABSTRACT FROM AUTHOR]