With the continuous development of food industry and processing industry, a large number of agricultural by-products were produced, including watermelon rind, broad bean pod and beer lees, which caused serious environmental pollution. In order to improve the feeding degree of agricultural by-products and wheat straw and to reduce environmental pressure, in this study, the effects of additives on the fermentation quality of agricultural by-products (watermelon rind, broad bean pod and beer lees) mixed with wheat straw were investigated.

The mixture of agricultural by-products (watermelon rind∶broad bean pod∶beer lees = 1∶3∶4) and wheat straw, as raw materials, were mixed in ratios at fresh weight of 100%∶0 (MW), 25%∶75% (X25), 50%∶50% (X50) and 25%∶75% (X75), and the mixed silages were treated with additives: 1×10⁶ cfu·g^-1Lactobacillus buchneri (B), 0.2% FW cellulase (C), and 1×10⁶ cfu·g^-1Lactobacillus rhamnosus (R), and without additives (CON) as the control. The 200 g of raw materials treated with different additives were put into 250 mL polyethylene plastic bottles. After ensiling for 60 days at room temperature, the silos were opened to analyze the fermentation quality and nutrient composition. The treated silages and raw materials were filtered by two layers of gauze and qualitative filter paper, and the extract was used for measuring the pH value. The raw materials and silage were dried to a constant weight and the dry matter (DM) was measured. The crude protein (CP) was determined by Kjeldahl nitrogen determination method. The contents of neutral detergent fiber (NDF) and acid detergent fiber (ADF) were determined by the method of Van's fiber determination. The water-soluble carbohydrates (WSC) content was determined via the modified phenol-sulfuric acid method. The microorganisms were cultured and counted in the culture medium respectively. The organic acids were analyzed using high performance liquid chromatography. The ammonia nitrogen (NH₃-N) content was determined by the phenol-hypochlorite reaction method.

Compared with MW-treated silage, NH₃-N content was notably decreased in X25-treated silage (P<0.05); pH and NH₃-N content were decreased in X50-treated silage, significantly (P<0.05); pH and NH₃-N content were notably decreased and the ratio of lactic acid to acetic acid (LA/AA) was notably increased in X75-treated silage, respectively (P<0.05). In addition, compared with the MW-treated silage, the butyric acid content was reduced in X25-, X50- and X75-treated silage, notably (P<0.05). In MW-treated silage, compared with the control, adding C significantly decreased the pH and NH₃-N content (P<0.05), and increased the lactic acid (LA) content and LA/AA (P<0.05). In X25-treated silage, compared with the control, adding C decreased the pH and increased the LA content, significantly (P<0.05); adding B decreased the NH₃-N content, notably (P<0.05). In X75-treated silage, compared with the control, adding C decreased the pH and increased the lactic acid content, significantly (P<0.05). As the increase of wheat straw mixing ratio, the contents of DM, NDF and ADF was increased, significantly (P<0.05). In contrast, the CP content was decreased, significantly (P<0.05). Compared with MW-treated silage, X25-, X50- and X75-treated silage increased WSC content, notably (P<0.05). In X25-treated silage, compared with the control, the addition of C significantly reduced the contents of NDF and ADF (P<0.05). In X50-treated silage, the addition of B and C significantly reduced the NDF content (P<0.05). In X75-treated silage, compared with the control, the addition of B, C and R reduced the contents of NDF and ADF, notably (P<0.05).

The fermentation quality of mixed agricultural by-products (watermelon skin∶broad bean pod∶beer bad = 1∶3∶4) was poor. The mixed silage of agricultural by-products and wheat straw could improve the fermentation quality, and the best mixture ratios of wheat straw and agricultural by-products (watermelon rind∶broad bean pod∶beer lees = 1∶3∶4) were 50%∶50% and 75%∶25%. In terms of nutrition quality, X25 and X50 were the best mixture ratios of wheat straw and agricultural by-products (watermelon rind∶broad bean pod∶beer lees = 1∶3∶4) were 25%∶75% and 50%∶50%. Comprehensively considered the fermentation quality and nutritive value, the optimum mixing ratio of agricultural by-products (watermelon rind∶broad bean pod∶beer lees = 1∶3∶4) and wheat straw was 50%∶50%, and the addition of cellulose could further enhance the fermentation quality and improve the nutritional composition.