| Summary: | This study aimed to verify the effect of Plant Growth-Promoting Rhizobacteria (PGPR) and humic acid amendment with different N-fertilizer rates on sweet potato. The results showed that inoculation of UPMRB9 in combination with 50% fertilizer-N produced significantly higher dry matter (DM) in leaves, storage, and fibrous roots, and in the whole plant. Similar trends were observed for nitrogen use efficiency (NUE), in which 75% N+UPMB10 and 50% N+UPMRB9 treatments significantly produced higher efficiency by 44.89% and 40%, respectively. In addition, the highest OD of β-carotene, 0.71 and 0.68 mg g-1, were observed in 50% N+UPMRB9 and 75% N+UPMB10, respectively. Sweet potato plants obtained greater NUE and N uptake when lower rates of N were used with the microbial inoculations. These findings show the ability of PGPR-HA to fix nitrogen and thereby increase N availability of soils, reducing the need to provide mineral nitrogen to crops. Thus, applying biofertilizer containing PGPR amended with humic acid could be a sustainable approach to improving the NUE and total N concentration of sweet potato plants. Higher N use efficiency will lead to savings in the amount of N fertilizer needed, thus reducing costs and promoting an eco-friendly approach at the same time. © 2023, Malaysian Society of Soil Science. All rights reserved.
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