A review of research progress in the compaction of major crop waste by mechanical equipment

Under the premise of ensuring food supply, high crop yields are accompanied by high crop waste production. Crop waste is being used in many ways to increase the comprehensive utilization efficiency of land and biomass resources, such as raw materials for energy, feed, fertilizer, materials, and substrates. The use of mechanical equipment to compress and densify crop waste can improve the overall density of material groups, further enhance the efficiency of harvesting, storage, and transportation, and reduce costs. In this paper, the research progress of compressing and densification of major crop waste by mechanical equipment was reviewed, and a foundational framework for this field was established. First, we extracted the first four crops of the world's total output in 2022, as well as several other typical crops of densification application obtained from the literature, and analyzed their utilization paths, composition characteristics, and densification application scenarios. Then, the densification process was investigated at three different material levels: tissue and fiber, crop and stalk, straw bale and wrap. Following that, the process, influencing factors and model interpretation of uniaxial compression were systematically summarized. Finally, the challenges facing the research and application of mechanized crop waste densification were discussed, along with some recommendations for further research. In the future, it is essential to conduct research aimed at enhancing the level of engineering application and improving the energy efficiency of mechanical compaction, following this research framework and the proposed macro-level recommendations, thereby enriching the theoretical system of compaction and densification.