Straw humification coefficient and its relation to soil carbon and nitrogen status

Straw return is one of the crucial practices available for enhancing soil organic carbon and nitrogen, biological activity, and nutrient availability. While the impact of straw return on soil organic carbon has been extensively studied, it remains unclear how soil organic carbon (C) and nitrogen (N) status contributes to straw decomposition in different climatic regions. We conducted a meta-analysis of 464 comparison data sets from 126 peer-reviewed publications to explore the decomposition characteristics of straw in different climatic regions of China. The average humification coefficient of straw is 0.36 across farmlands in China, and it is 0.39, 0.36, and 0.32 in the medium temperature, subtropical, and warm temperate zones respectively, the larger the humification coefficient, the slower the straw decomposition, indicating that the decomposition rate of straw is highest in the warm temperate region (i.e., 68 % of straw biomass could be composed annually). While annual temperature and rainfall were the dominant contributors (32.6 %) to humification coefficient variability, soil conditions, particularly soil organic carbon (11.9 %) and C to N ratio (11.8 %), played pivotal roles in modulating decomposition rates. The SOC content displayed contrasting effects across regions: high SOC suppressed decomposition in medium and warm temperate zones, but enhanced it in subtropical soils. Soil C:N ratios further influenced decomposition pathways, with lower ratios accelerating decomposition in medium temperate soils but inhibiting it in subtropical regions, highlighting the need for region-specific nutrient balancing. The interaction between N fertilizer and SOC revealed nuanced patterns: in medium temperate zones, high N application reduced humification coefficient in soils (SOC >18 g kg^-1) but increased humification coefficient in soils (SOC <9 g kg^-1), emphasizing the importance of tailored N management. In subtropical regions, high N inputs effectively lowered humification coefficient in low-moderate SOC soils (<15 g kg^-1), promoting decomposition. Overall, by aligning straw return practices with regional agroecological conditions, this study advances strategies for enhancing soil health, nutrient cycling, and sustainable agricultural productivity.