Annual production of the crop straw has been ever-increasing under intensive agriculture in China. Composting can be expected to serve as the major pathway for straw utilization. The lignocellulosic residues can be converted into humified organic matter. However, its practical application is often constrained by slow degradation rates and suboptimal compost quality. Straw-decomposing inoculants (SDIs) have been proposed to accelerate the straw transformation for compost maturity. It is often required to clarify their actual performance under different composting conditions. This study aims to systematically quantify the overall effects of the SDIs on the straw degradation efficiency and compost maturation, with emphasis on their responses to different measures. A meta-analysis was conducted using 647 composting experiments in China. A systematic investigation was implemented to examine the influences of the composting site, environmental conditions, and practices. The results showed that the SDIs significantly enhanced the straw degradation rate and compost maturity, with the increase ranging from 36.57% to 53.13% and from 5.32% to 22.56%, respectively (P<0.05). Notably, the efficient straw decomposition and high-quality compost maturation also followed the regulatory pathways. At the decomposition level, the SDIs markedly accelerated the straw breakdown, where their effectiveness depended primarily on the inoculant type, straw species, and composting volume. Fungal inoculants also showed the strongest promoting effect, due to their superior lignocellulose-degrading capacity, particularly for the rice straw. Moreover, the composting volume over 500 L significantly enhanced the decomposition efficiency (P<0.05). At the maturation level, the initial composting temperature also emerged as a key driving factor, with an optimal range of (30~40 °C) for compost maturity. Co-composting with the manure was used to steer the maturation and optimize the initial Carbon-to-Nitrogen (C/N) ratio and metabolic pathways. Once the composting cycles exceeded 45 days, the effectiveness of the SDIs was significantly diminished (P<0.05) for the maturity at the thermophilic phase, indicating a decreasing trend with the prolonged composting time. Optimization strategies were proposed to tailor to the rice and maize straw. The fungal SDIs were recommended to combine with the manure at a mass ratio greater than 5:4, an initial C/N ratio below 30, an initial composting temperature of 30~40°C, and a composting volume exceeding 500 L. In wheat straw, more suitable composite inoculants were also recommended with a manure-to-straw ratio above 5:4. The optimal initial temperature and composting volume can be expected for the straw transformation.

The returning straw directly to the field is the most widely adopted approach of straw utilization. Anhui is an important agricultural province with abundant main grain crop straw resources. In recent years, the direct straw return was actively promoted and a series of relative research were conducted in Anhui Province. In order to provide reference for the development of more in-depth research and promote the efficient utilization of straw resources, the recent important advances in straw direct returning technology and the effects of straw incorporation on soil fertility, crop production and agricultural eco-environment in Anhui Province were reviewed in this paper. The research progress of direct straw return in Anhui Province over the last decade were mainly embodied in the following aspects. (1) The technology of straw direct returning was optimized from manner of straw returning and combined application of chemical fertilizers. (2) The introduction of chemical structure of soil organic matter and soil microbial community structure broadened the research field concerning the effects of direct straw return on soil physical, chemical and biological properties. (3) The impact of straw incorporation on crop diseases, insect pests and weeds was beginning to be explored, and the increasingly attention was being paid to the environmental effects of straw return on nitrogen and phosphorus loss and greenhouse gas emission. Therefore, it could be concluded that the research on direct straw return in Anhui Province presented the transformation from a focus on crop production to more attention on eco-environmental effects. In the future, the study on straw directly returning to the field in Anhui Province should be strengthened from the following aspects: improving regional weak links, expanding research contents, clarifying environmental effects, and deepening mechanism exploration.