Abstract:

Objective: The amount of Juglans regia (walnut) branches and leaves waste is large every year, and its arbitrary stacking is not conducive to the daily management of the orchard. This study aims to explore the suitability and feasibility of walnut branches and leaves composting, and screen suitable composting processes, so as to provide scientific basis for the resource utilization of organic waste and green ecological management of orchards. Method: Walnut branch and leaf waste and chicken manure were used as composting materials. Different composting material ratios (walnut branch and leaf waste: chicken manure ratio of 3∶7, 4∶6, and 5∶5, respectively) were set up, and effective microorganisms (EM), San'an microorganisms (SM), or no external microorganisms were added to each composting material ratio. During the composting process, the physico-chemical properties, bacterial community diversity and composition of samples from each treatment were measured, and the maturity of each composting treatment also was evaluated to ultimately determine the appropriate composting process. Result: 1) The treatment with addition of microbial agent entered the high-temperature stage earlier than the treatment without microbial agent added, and the decrease in moisture content, the EC value, total nutrient, total phosphorus, and total potassium content, as well as the total nutrient mass fraction of the heap were also higher. At the end of composting, the total nutrient content of BEM treatment reached 61.93±2.36 g·kg^–1,with an increase of 57.68% compared to the initial stage of composting, and was significantly higher than that of other treatments. 2) During the entire composting process, the relative abundance of Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes in each treatment was relatively higher. The diversity of bacterial communities showed an increasing trend at the early and late stages of composting. At the end of composting, the relative abundance of Proteobacteria and Actinobacteria treated with EM was higher; 3) There were significant differences in the bacterial genera composition among different treatments at different stages. At the early stage, the relative abundance of Luteimonas, Pusilimonas, B-42, and Georgenia was higher. In the later stage, the relative abundance of Streptomyces, Actinomadura, and Parapedobacter increased. By the end of composting, the relative abundance of Actinomadura in BEM treatment reached as high as 40.00%. 4) According to the multiple indicators of physical, chemical, and biological parameters and the national organic fertilizer standard, the composting of all treatment groups was able to mature within 45 days. The BEM treatment achieved the best composting performance. Without external microbial agents added, the nutrient content and maturity were higher when the material ratio was 3∶7. Conclusion: Walnut branch and leaf waste can be used as composting raw materials, which can be decomposed in about 45 days. The optimal composting process is a material ratio of 4∶6 and inoculation with 0.2% EM.

Key words: walnut branches and leaves waste, microbial agent, bacterial community diversity, bacterial community composition, composting maturity