Effects of decomposing agent applications on the lignocellulose aegradation efficiency and compost maturity of composted straw

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.