The coupling of straw, manure and chemical fertilizer improved soil salinity management and microbial communities for saline farmland in Hetao Irrigation District, China.

Organic amendments are fundamental strategies for the sustainable reclamation of saline-alkaline soils. However, the mechanisms underlying the effects of different fertilization regimes, applied individually or in combination, on biotic and abiotic factors remain inadequately understood. This study conducted an 8-year (2016-2023) field experiment in the Hetao Irrigation District of China to evaluate the effects of five fertilization regimes on soil salinity-alkalinity, nutrient dynamics, microbial communities, and sunflower yield. Five fertilization treatments, namely a non-fertilization control (CK), chemical fertilization alone (CF), chemical fertilization with straw return (CFS), chemical fertilization with manure (CFM), and chemical fertilization with both straw return and manure (CFSM) were conducted. The results showed that the CFSM treatment outperformed other regimes by significantly reducing soil pH (0.27), total salt content (26.1%), and alkalinity (14.5%) while increasing soil organic carbon (6.2%), total nitrogen (17.4%), available nitrogen (80.3%), phosphorus (136.0%), and potassium (31.6%). The CFSM treatment also optimized the microbial community, enriching carbon-loving microbial populations (e.g., MND1, Lysobacter, and Gemmatimonas) and reducing soil-borne fungal pathogen (e.g., Fusarium, Plectosphaerella, Metarhizium, and Alternaria). After 8 years, sunflower yield under CFSM increased by 49.4% compared to CK. Pathway analysis revealed that the CF strategy showed limited efficacy, as soil salinity and alkalinity suppressed NPK levels, negatively impacting fungal communities and crop yield. The CFS and CFM strategies mitigated the negative effects of salinity and alkalinity to varying degrees, with CFM exhibiting a more pronounced positive impact on fungal communities through SOC-mediated regulation of NPK. The CFSM strategy demonstrated the most significant multi-factor synergistic effects, mitigating the inhibitory effects of salinity and alkalinity while enhancing the regulation of NPK by SOC, resulting in improved fungal community structure and nutrient availability, ultimately maximizing sunflower yield. This study highlights the importance of integrating straw, manure, and chemical fertilizers for sustainable saline soil management and productivity.