Combined controlled-release urea and organic fertilizer boost sustainable sugarcane productivity by optimizing soil C–N properties and microbial communities

Long-term monocropping and excessive nitrogen (N) fertilization drive soil degradation, biodiversity loss, and low N use efficiency in Chinese sugarcane (Saccharum officinarum L.) production. Organic substitution, while proposed to improve soil quality, faces trade-offs between short-term yield and soil quality due to slow mineralization. Controlled-release urea (CRU) provides sustained and stable N supply. It was hypothesized that integrating CRU and organic fertilizer will synergistically enhance crop productivity and soil multifunctionality (SMF) compared with single fertilization practices, thereby achieving sustainable productivity. Therefore, a two-year field experiment was conducted in an intensive sugarcane cropping system to evaluate five N management strategies: FP (conventional practice; 560 kg N ha−1), U (reduced urea-N; 300 kg N ha−1), CU (based on U, a 1:2 ratio of urea-N and controlled-release urea-N), MU (based on U, 30 % organic-N substitution), and MCU (integrated MU and CU). The effects on soil properties, microbial community characteristics, and microbial functions in rhizosphere and bulk soil were systematically evaluated. MCU optimized fertilizer C-N characteristics, reducing N input by 46.4 % while achieving the highest sugar yield (17.7 t ha⁻¹) and SMF. MCU produced greater improvements in soil C-N-P nutrients, enzyme activities, and 16 s/ITS-quantity. Regarding microbial community characteristics, MCU exhibited the highest bacterial ACE and network complexity, and enriched beneficial core species such as Bacillus and Mortierella. Regarding microbial functions, MCU enhanced bacterial C-N-P cycling genes (e.g., aerobic respiration, C-fixation, ammonification, N-fixation, organic-P mineralization) and reduced fungal pathogens. SEM identified soil properties and microbial functions as the primary and secondary drivers of both yield and SMF. Economically, MCU maintained net benefits comparable to FP and U, exceeded MU by 43.87 %, and although lower than CU, achieved optimal productivity and SMF. Overall, the MCU strategy offers an evidence-based approach for sustainable production of sugarcane in tropical and subtropical regions.