Influence of organic, synthetic and biofertilizers on the diversity of cassava rhizosphere microbiome in Northeastern Thailand

Cassava, one of Thailand's main economic crops, is capable of growing in nearly all soil types. However, continuous monocropping depletes soil nutrients over time. Adopting good agricultural practices can help farmers reduce costs while improving soil fertility. The aim of this study was to compare cassava rhizosphere microbial communities resulting from cultivation under eight different fertilizer treatments, including synthetic, organic, and biological fertilizers, and to identify beneficial microbes that promote cassava growth and yield. The study was conducted at two sites in Northeastern Thailand. Results show that bacterial abundance and species richness (alpha diversity) peaked at 5 months after planting (MAP), showing a significant increase compared to 2 MAP. However, by 10 MAP, alpha diversity began to decline at both sites, Nampong and Seungsang. Among the treatments, the most notable differences in alpha diversity were observed at 5 MAP. At the Nampong site, experimental treatments with chicken manure (T3) and chicken manure combined with other fertilizers (T5, T6, and T8) exhibited significantly higher alpha diversity than did the control (without fertilizer, T1). At the Seungsang site, sole treatment with the full recommended rate of chicken manure (T3), and half of the recommended dose of synthetic fertilizer combined with half the recommended dose of chicken manure (T6) resulted in greater alpha diversity than did swine manure extract application (T4), half of the recommended dose of synthetic fertilizer combined with half of the recommended dose of swine manure extract (T7), and chicken manure application combined with stalk inoculation with plant growth-promoting rhizobacteria (PGPRs) (T8). Since T3 and T8 had the most significant impact on microbial abundance and diversity, as well as cassava growth and yield, the predominant bacteria in these treatments were identified as key targets. A total of eight target bacterial genera were identified: <i>Pseudomonas</i>, <i>Tumebacillus</i>, <i>Lysinibacillus</i>, <i>Paenibacillus</i>, <i>Dongia</i>, <i>Acidibacter</i>, <i>Sphingomonas</i>, and <i>Bacillus</i>. Among them, <i>Tumebacillus</i> was the most notable, as it showed a significant correlation with fresh tuber yield. These beneficial bacteria may serve as key candidates for future biofertilizer production.