Rice (Oryza sativa L.) is an important grain that is consume by over half of the world population. (Maclean et al., 2002). In African, it is the second most consumed food after maize (Ajala and Gana, 2015) and accounts up a large component of the food consumed in most Nigerian families (Ikhajiagbe and Musa, 2020). It is a significant starchy grain for human consumption since it supplies 23% of world human per capita calories and 16% of global human per capita protein (Ojo and Adebayo, 2012). Additionally, it increases national income. Rice consumption per capita in Nigeria is predicted to be more than 100 kg per year (Udemezue, 2018). Rice demand is rising, and more production is required to feed more people while reducing costly imports. Rice production in southern Nigeria has been severely hampered since the 1970s. High soil pH, low nitrogen, phosphorus deficiency, leading to a ferruginous conditions are some of the variables that have been related to this (Doyou et al., 2017). Unfortunately, the majority of soils in southern Nigeria, particularly in Edo State, are ferruginous (Daramola, 2005; Obayelu, 2015). According to Musa and Ikhajiagbe (2021), iron toxicity leading to phosphorus deficiency and acidic pH has been linked to reasons why ferruginous soils are not supporting rice growth. To sustainably improve rice productivity in these P-deficient soils, there is need to consider the use of biological agents such as microorganisms as inoculant, as against the widely used chemical fertilizers (Adnan et al., 2018; Joshis et al., 2007).
Ferruginous soil also known as red soil are iron-rich soil. This kind of soil is usually observed in warm and humid climates (Yu et al., 2016), or in some tropical regions as seen in some parts of Africa (Zhao, 2014). Ferruginous soils have been documented to account for about the average percentage (45.2%) of the Earth’s landscape. In Nigeria for instance, it is transcendent in some southern States, for example, Edo state, possessing several regions, including northern region and Benin central (Doyou et al., 2017). Ferruginous soils are known for its unique properties such as high iron levels; which creates complexes with soil phosphate and making it low available for plant use (Gyaneshwar et al., 2002). Consequently, this condition now brings about low biotic and abiotic properties needed for plant growth (Wang et al., 2014). Hence to enhance soil fertility, some local farmers have tried to use synthetic chemicals which had negative influence on the soil and plants as a results of insufficient beneficial microorganisms to fuel the nutrient cycling and release important metabolites that can improve the soil properties and plant growth (Sharma et al., 2013). Musa and Ikhajiagbe 2021 following 16S rRNA gene sequencing successfully isolated and identified Bacillus cereus strain GGBSU-1, Klebsiella variicola strain AUH-KAM-9 and Proteus mirabilis strain TL14-1 as efficient in solubilizing insoluble phosphate in soils (Musa and Ikhajiagbe, 2020b; Plate 1, 2 and Supplementary table 1). These isolates have significantly improved germination and yield parameters in rice in in vitro setup. In a bid to investigate the efficacy of these isolates to influence the iron-phosphate flux in soil and as biofertilizer, there is need to consider a field experiment. According to Saneya and Muhammad (2017), confirmation of efficacy in vivo is very important because in vitro studies may not necessarily give the real situation when introduced to the ecosystem or may not consider the real environmental conditions. This research considered rhizo-inoculation of rice seedlings with PSB strains in ferruginous ultisol conditions.
Rhizo-inoculation involves introduction of microorganism into the root region of plants to stimulate growth (Ikhajiagbe and Edokpolor, 2019). Rhizo-inoculation of PGPs are known to enhance plants’ survival by releasing important plant nutrients as well as plant growth hormones (Glick, 1995). Gupta et al. (2000) and Biswas et al. (2000) have reported significant enhancement in growth and yield of important crops in response to rhizo-inoculation with PGPR. Previous research by Musa and Ikhajiagbe (2021) confirmed the use of PSB with PGP to improve the growth parameters of rice seeds. Increase in physiological parameters of sweet pepper (Capsicum annum) as response to rhizo-inoculation with PGP have been severally reported by Backer et al. (2018; 2017). Therefore, the present study aim to investigate the possibilities of these PSBs (Bacillus cereus strain GGBSU-1, Klebsiella variicola strain AUH-KAM-9 and Proteus mirabilis strain TL14-1.) that were previously obtained from FU soils and a control soil to improve the growth parameters of rice plant under FU conditions. The current study will bring about another sustainable strategy of improve agricultural productivity and food security.