Abstract: In order to understand the effects of different bulking agents on straw biogas residue composting, straw biogas residue was used as raw material, and seven bulking agents of sawdust, peanut straw, corn straw, wheat straw, soybean straw, reed straw and rice straw were introduced and mixed homogeneously with straw biogas residue at the ratio of 1∶5 (wet weight) in this experiment with 30 days of aerobic composting, respectively. The physical, chemical and biological characteristics were studied during the composting. Results indicated that all the test bulking agents could be used as the bulking agent for straw biogas residue composting, which could promote the piles produce a great deal of heat rapidly, make compost products harmless and sanitary. The thermophilic phase (≥55 ℃) duration of treatments with straws as bulking agent was longer than the that of the treatment with sawdust as bulking agent. The electrical conductivity (EC) was the lowest in the treatment with sawdust as bulking agent. The highest temperature reached 68 ℃ when soybean straw was used as the bulking agent. Under this treatment, the polyphenol oxidase activity was more active and helpful to promote the formation of humus. Rice straw could decrease pH, enhance nitrate nitrogen (NO3--N) content and cellulase activity, and promote the degradation of cellulose during straw biogas residue composting. The germination index reached 137.06% and 138.26% in treatment with soybean straw or rice straw as the bulking agent, respectively, which indicated that soybean and rice straw could promote root growth of seeds, and improve the quality of compost products.

Key words: bulking agent, straw biogas residue, compost, decomposition