Emphasis on sustainable cassava production is increasing, with aims to increase the net income of cassava farmers in an ecologically friendly way. This study examined the optimization of soil fertilizer management at two research locations (Nampong and Seungsang) in northeastern Thailand. The experiment was conducted as a randomized complete block design with five replications. Eight different fertilizer management protocols consisted of (1) no fertilizer application (control), (2) the recommended dosage of chemical fertilizer (RDCF), (3) 3.12 t ha⁻¹ of chicken manure (CM), (4) 937.5 L ha⁻¹ of swine manure extract (SME), (5) CM + SME, (6) ½ RDCF + ½ CM, (7) ½ RDCF + ½ SME, and (8) CM + PGPR (stake soaking with PGPR solution). At the Nampong site, the application of CM + PGPR has the most potential for increasing the cassava yield in terms of the fresh tuber yield when compared with no fertilizer and RDCF applications. At the Seungsang site, the application of CM gave the high fresh tuber yield, without significant differences from RDCF applications. Furthermore, compared to the RDCF treatment, both soil fertilizer management protocols produced positive marginal rate of return values, showing clear potential for contributing to sustainable cassava production.