Impacts of chemical and organic fertilizers along with silicon on agronomic traits, yield and nutrient content in rice under plant growth-promoting bacteria

The application of biochar and plant growth-promoting bacteria (PGPB) with silicon (Si) can help to improve the yield and grain enrichment of rice. Hence, we investigated the impacts of NPK and biochar fertilizers along with Si sources on agronomic traits, grain yield and nutrient uptake in rice grain under PGPB. The experiment was conducted as a split-split-plot in a randomized complete block design with three replications during two crop years of 2022 and 2023. The experimental treatments included the main plot assigned to fertilizer application (control, NPK and biochar), the sub-plot assigned to Si sources (calcium silicate, potassium silicate and nano-Si), and the sub-sub-plot assigned to bacteria application (azospirilum and azotobacter). The results indicated that there was no significant difference between the PGPB in terms of the studied traits. The addition of both fertilizers (NPK or biochar) to the soil significantly enhanced the agronomic traits, grain yield and nutrient uptake in rice grains when compared with control plants. However, the plants treated with biochar showed higher grain yield (4845.83 kg ha^–1) and greater nutrients uptake like N (1.72%) and Si (7.26%) compared with NPK fertilizer. Among the different Si sources, the nano-Si-treated plants had greater N (1.61%), P (6.90%) and Si (7.08%) concentrations than other Si sources. When the plants were sprayed by potassium silicate (1.41%), the grain K concentration significantly increased compared with calcium silicate (1.30%) and nano-Si (1.36%). Application of both potassium silicate (4465.97 kg ha^–1) and nano-Si (4570.28 kg ha^–1) resulted in higher grain yield, whereas the lower grain yield (4315.28 kg ha^–1) was observed in calcium silicate treatment. Overall, our results suggest that the application of biochar + nano-Si has a great potential to increasing grain yield and improving nutrients uptake in rice grains, thus the application of this combination can be an ideal option to reduce or supplement NPK fertilizers in paddy soils. However, there is a need for further studies on the long-term effects of biochar and nanoparticles on plants and soil, as well as their impacts on different soil textures.