Food security is the ability of a population to access and afford enough food to live a healthy life (Olanrewaju et al., 2022). Feeding the growing world population is one of the major challenges for agriculture. In Benin, soils are weakened and subject to deep disturbances, such as physical and chemical degradation, low microbial activity and this has resulted to the decline in the soil fertility with negative consequent to low productivity (Igué et al., 2013). For decades, the application of chemical fertilizers have played a crucial role worldwide to increase growth, crop yield and maintain an adequate food supply (Meena et al., 2017; Chaudhary et al., 2020). Several authors studied the long-term use of chemical fertilizers and their impacts on the agroecosystem (Chaudhary et al., 2017; Bishnoi, 2018). Their applications provide nutrients in high concentrations but with many drawbacks on soil health, water quality and safe environment (Vejan et al., 2016). The use of mineral fertilizers improve productivity, but also leaves undetermined effects on the ecosystem (Kumar and Shastri, 2017). These numerous environmental problems include groundwater pollution, soil acidification, eutrophication, low soil fertility, loss of biodiversity, high energy consumption in synthesis processes, and contamination of crop products (Agbodjato et al., 2016; Tomer et al., 2016; Mahanty et al., 2017; Ilangumaran and Smith, 2017; Kourgialas et al., 2017). To increase crop productivity in an environmentally friendly manner, the use of biostimulants, such as plant growth-promoting microorganisms remain the the most promising ways (De Pascale et al., 2017).

In the last decade, great efforts have been made to substitute chemical fertilizers with environmentally friendly biostimulants (Kamilova et al., 2015; Liu et al., 2018; Thomas and Singh, 2019; Amogou et al., 2021). The response to microbial biostimulants inoculation on different crops has been widely evaluated, thus showing significant increase in the growth and yields of agricultural crops (Babalola et al., 2020; Aguégué et al., 2021b; Adoko et al., 2021a).

Plant growth-promoting microorganisms play an important role in regulating the dynamics of various ecological processes, such as decomposition of organic matter and accessibility of different plant nutrients, such as iron magnesium, nitrogen, phosphorus and potassium (Priyanka et al., 2020). Microbial biostimulants are the main component of integrated nutrient management, thus leading to their sustainability. In addition, these biostimulants can be used as cost-effective biological inputs to increase crop productivity while reducing mineral fertilizer rates and ultimately harvesting more nutrients from the soil (Aguégué et al., 2021a). Biostimulants are sometimes composed of plant growth-promoting rhizobacteria (PGPR), a group of bacteria that actively colonise plant roots, that support plant growth and suppress plant pathogens (Khan et al., 2018). PGPR produce plant hormones (auxin, gibberellin and cytokinin), promote phosphate solubilisation, potassium mineralization and nitrogen fixation, which are important natural organic biostimulants (Rosier et al., 2018). PGPR based biostimulants, with their natures, can play important roles in maintaining soil fertility (Gamez et al., 2019).

Maize is a prevalent crop in Benin’s cropping systems (Gogan et al., 2018). It is very sensitive to low availability of phosphorus and other mineral elements for growth (Postma and Lynch, 2011) and has been shown to be amenable to application of PGPR-based biostimulants (Agbodjato et al., 2021a). Over the last decades in Benin, a lot of work has been done on the use of different biostimulants on maize productivity These studies were carried out on the identification, biochemical characterization, formulation, inoculation and application of PGPR-based biostimulants to increase maize growth and yield (Adjanohoun et al., 2012; Agbodjato et al., 2021b; Adoko et al., 2021b). Nevertheless, studies on the PGPR-based biostimulant-coated maize seed in Benin are less documented. Therefore, the aim of this study was to compare the effect of biostimulant-coated maize seed and biostimulant application on growth, yield and nutritional status of maize in Benin.

The use of microbial biostimulants in agriculture to increase productivity is a natural and environmentally friendly alternative. Results of the initial chemical properties of experimental soils showed that they were slightly acidic. In addition, soils of different R-D sites had a low level of fertility characterised by a high C/N ratio in topsoil. Interaction between different chemical characteristics of soil, which leads to soil fertility classification, reveals that majority of soils in Benin have lost their agricultural potential (Igué et al., 2013). This might be due to very low nitrogen, phosphorus, potassium and cation exchange capacity in the soils. The pH of soil should be neutral to slightly acidic to favour assimilation of mineral elements. Only cation exchange capacity in all soils appears to be a severe to medium limitation regardless of farming system (Igué et al., 2013).

The best performance in height was obtained by coating the seeds with biostimulant, followed by the application of the biostimulant. Statistical analysis revealed in some R-D sites a significant difference in plant height between application and coating of the biostimulant. The difference between the biostimulant treatments can be explained by the seed coating carried out on the day one before sowing to allow a good adhesion of the PGPR contained in the formulation, which can be favourable to the height growth of the maize plants. It makes more PGPR and nutrients available to the plant for better height growth (Neufeld et al., 2017). An increase of 29.43% in the height of wheat plants was observed after the use of the biostimulant Pseudomonas fluorescens RRb-11 and talc (Jambhulkar and Sharma, 2013).

In all the study R-D sites, there was no significant difference between treatments on stem diameter of maize plants. However, from one site to another, the differences were significant. The same phenomenon was observed on the leaf area of maize plants in one South R-D site (Eglimey), in all Center R-D sites and in two North R-D sites. In the other two South R-D sites (Adakplamè and Saharo-Nagot) and the North (Soaodou) a significant difference was observed between treatments. These results were related to soil types (Bishnoi, 2015; Adoko et al., 2020; Agbodjato et al.,2021a) and also to maize varieties. Indeed, ferrallitic soils of South had a higher assimilable phosphorus rate (9-14) than ferruginous soils of Center (4-5) and North (5.03-12.6). In South, the 2000 SYNEE-W BENIN variety was used, in Center and North, the TZL COMP 4-W BENIN variety was used during the experiment. Similar results were recorded by Lin et al. (2019) who reported an increase in nitrogen and chlorophyll content throughout the growth stages of the plant that received the biostimulant in combination with mineral fertiliser. The biostimulant applied or coated to the seed makes more nitrogen available to the plant to achieve good photosynthesis for growth. Biostimulants were able to increase yield of cereals. Hassan and Bano (2015) shown that wheat yield was improved by 15-25% over controls with the use of P. moraviensis and B. cereus.

In all southern R-D sites, the highest maize grains yields were obtained with the application of biostimulant + ½ NPK-Urea, followed by the coating of maize seeds with biostimulant + ½ NPK-Urea. Farming practice gave the lowest yields in all R-D sites. In the majority of these sites, no significant difference was recorded between the application + ½ NPK-Urea and seed coating + ½ NPK-Urea. However, in very few R-D sites, there was a significant difference between the two biostimulant treatments (T₂ and T₃) and the farmers’ practice. From one R-D site to another, the differences were significant. The results can be explained by the stimulating effect of a good yield of the rhizobacteria P. putida contained in the biostimulant used. This strain was able to produce indole acetic acid (IAA), solubilise certain nutrients, such as phosphate, potassium, make nitrogen (ammonia) and other micronutrients necessary for plant growth and yield enhancement (Noumavo et al., 2015; Agbodjato et al., 2018).

In the Southern R-D sites, maize grains from the application + ½ NPK-Urea had a higher weight than the other treatments. The highest weight of 1000 grains obtained was observed in Saharo-Nagot (324.60 g) with an increase of 18.44% compared to the farmers’ practice. In the Center, there was no significant difference between treatments. In the North, the application + ½ NPK-Urea was also better. The ANOVA showed a significant difference between treatment T₂ and the others (T₁ and T₃) but there was no significant difference between treatments the farmers’ practice (T₁) and the coating of maize seeds with biostimulant + ½ NPK-Urea (T₃). Across R-D sites, the differences were also significant. This effect can be due to the soil types, maize varieties and variation in the degree of fertility from one R-D site to another. The amount of biostimulant used for the application (2 g per hole) far exceeds that used for coating two maize seeds (0.1 g). These quantitative differences between application and coating can be the basis of our results. As the amount of biostimulant increases, there was more PGPR and binder (clay) available to the plant, which is favourable for good growth and grains yield and 1000 grains weight.

In all R-D sites, the application and seed coating of biostimulant gave the best results on all parameters (growth, yield and nutritional status) evaluated compared to the farmer practice. This allows us to say that the biostimulant + ½ of NPK-Urea was better than the recommended dose of NPK-Urea for maize cultivation in Benin. This biostimulant provided the plant with nutrients, such as nitrogen, phosphorus and especially potassium (p< 0.001) necessary for its growth and yield. Some soil nutrients can also be better absorbed by plants if microorganisms were added. The application of biostimulants was favourable to better increase the biodiversity of the soil microbial community (Ding et al., 2016), which justifies the results obtained in this study.

At some R-D sites in Benin, application and coating of biostimulant had comparable effects. This similarity can be explained by the intrinsic characteristics of P. putida known for their roles in promoting crop growth and development. Difference observed was believed to be due to the amount of biostimulant used in the two treatments (Adoko et al., 2021a). Indeed, 2 g of biostimulants applied per hole and less than one twentieth (0.1g) were used in seed coating. PGPR in biostimulants can help the host plant produce root exudates which, in turn, recruit beneficial bacterial communities, thereby increasing dissolved nutrient levels in the soil. Soil organic matter has previously shown to be the main substrate and energy source for microorganisms (Xu et al., 2013). Treatment of wheat seeds with the formulation of P. fluorescens RRb-11 in talc resulted in a significant increase in plant growth parameters and even increased the seed germination rate by 94% compared to controls (Jambhulkar and Sharma, 2013). Similarly, Jorjani et al. (2011) reported the efficacy of P. fluorescens bioformulation on the fresh weight of sugar beets. Application of inoculated P. putida to maize seeds significantly increased the fresh and dry weight of the plants compared to the control at harvest (Khashei et al., 2020). Formulations of talc or peat and Pseudomonas spp. effectively controlled chickpea wilt disease in two field trials and increased its yield (Vidhyasekaran and Muthamilan, 1995).

Agricultural practices that reduce or eliminate chemical inputs through the use of biostimulants have been of paramount importance in recent years for sustainable and environmentally friendly agriculture. The application of biostimulants, such as PGPR in agriculture is one of the promising alternatives to combat abiotic stress and to ensure food security and environmental protection. This study revealed that the biostimulant formulated with P. putida and clay binder was effective on growth parameters, yield and nutritional status of maize in Benin. The best treatment was the application of biostimulant + ½ NPK-Urea, followed by the coating of maize seeds with biostimulant + ½ NPK-Urea. Both forms of biostimulant use combined with the recommended half-dose of mineral fertilizer were better than the recommended dose of mineral fertilizer in the majority of the Benin R-D study sites. Biostimulants formulated in Benin can be used to increase maize productivity while reducing the high use of mineral fertilizers. Coating maize seeds with the biostimulant require a small amount of biostimulant, less physical effort than applying the biostimulant, and is better than the recommended practice. However, the formulation process of the biostimulant deserves a slight improvement for a better adhesion of the biostimulant to the seed during coating. Nevertheless, the biostimulant formulated in Benin can be used as a seed coating for sustainable and environmentally friendly agriculture. It will be interesting to continue studies to see the acceptability of the technology by Beninese farmers and to evaluate its financial profitability.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

MA, AN, NaAA, OA, HS, and R.M.A, carried out the experimental work and analysis. MA, AN, NaAA, A.A., NeAA, and LB-M contributed to the designing, supervision, and interpretation of the results. MA, AN, A.A., NeAA, and LB-M, revised the final draft. LB-M, reviewed the final project. All authors contributed to the article and approved the submitted version.