Biochar and Bioorganic Fertilizer Amendment Improved Soil Qualities and Altered Bacterial Communities in Quinoa Rhizosphere Soils of the Yellow River Delta

The application of biochar and bioorganic fertilizer (BOF) in agricultural systems has garnered increasing attention in recent years. Nevertheless, research remains scarce on the impacts of biochar and BOF on the rhizosphere microecological characteristics of saline-alkali soils. This research involved the execution and analysis of 16S rRNA sequencing using Illumina technology to explore how biochar, whether used alone or in conjunction with BOF, along with varying application rates, impacts the microbial community in the saline-alkali rhizosphere soil during quinoa cultivation. In the conducted field trial, sole BOF application, sole biochar application, and their combined application (referred to as BOFB) led to a substantial enhancement of 23.88%, 74.08–97.00%, and 188.88–220.59% in quinoa aerial biomass, respectively. Meanwhile, sole biochar application or biochar combined with BOF reduced soil electrical conductivity (EC) by 26.42–39.81%. Biochar and BOF significantly improved most soil parameters, with the exception of total phosphorus (TP). In comparison to the control (CK), the relative abundances of Pseudomonas, Arthrobacter, Skermanella, and Bacillus were elevated in the biochar and BOFB treatments, while Sphingomonas was more abundant in the BOF treatment. In addition, Skermanella exhibited a significant positive correlation with EC and available potassium (AK). Biochar exerted a stronger effect on soil bacterial community structure than BOF. Furthermore, the complexity of the bacterial community in biochar and BOFB treatments far exceeded that in the BOF and CK treatments. Overall, the application of biochar effectively reduced soil EC and improved soil fertility, enhanced bacterial community stability, and optimized bacterial community structure, thereby increasing quinoa aerial biomass. Under the conditions of this study, the optimal application rate for biochar was 15 t/ha, and the combined application of biochar and BOF produced superior effects relative to either amendment alone.