Impact of Rhizobium Inoculation on the Growth and Yield of Soybean Varieties in Sudan Savanna, Nigeria

Impact of Rhizobium Inoculation on the Growth and Yield of Soybean Varieties in Sudan Savanna, Nigeria

R.T., Rabiu^1,4 , A.M., Sa'ad¹ , A. Muhammad¹ , H.S Hamisu³ , M.S. Jibrin²

¹Department of Crop Science, faculty of agriculture, Aliko Dangote university of science and technology, Wudil Kano

²Crop Science Department, Saadu Zungur University, Bauchi State

³National Horticultural Research Institute, Bagauda Station, P.M.B 3390, Kano State

⁴Flour Milling Association of Nigeria

Corresponding Author Email: rabiutijjani2020@gmail.com

DOI : https://doi.org/10.51470/JOD.2025.4.1.52

Abstract

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Introduction

Soybean (Glycine max) is a valuable legume crop in Sub-Saharan Africa that offers nutritional benefits and income opportunities for farmers. It provides about 40% protein and 20% oil for human food and animal feed [9]. It is the chief oil seed in the world at present and is used mainly for edible oil extraction (Large-scale solvent extraction) and meal production for livestock feed, [10].  Inoculating soybean seeds with the Rhizobium strain enhances nitrogen fixation regardless of whether the cultivar is promiscuous. Several studies have reported that inoculating soybean with suitable bacteria before sowing results in significant yield increases [10-12]. The efficiency of nitrogen fixation is primarily influenced by the native soil rhizobium population and its compatibility with soybean plants. [20] documented the responses of five promiscuous nodulating soybean varieties to selected Bradyrhizobial strains and concluded that all the tested soybean cultivars exhibited beneficial nodulation effects, particularly in soils with low indigenous rhizobia populations. The application of micronutrients, along with nitrogen (N), phosphorus (P), and potassium (K), has been demonstrated to improve soybean yield. This practice may also help reduce poverty in Sub-Saharan Africa [18]. According to [6], soybeans can fixate 175 kg of nitrogen per year in irrigated areas, whereas in dry areas, they can fixate up to 100 kg of nitrogen per year. The plants meet their nitrogen requirements either through soil mineral nitrogen or symbiotic nitrogen fixation. Rhizobia can live as saprophytes in plant residues, as endophytes within plants, or in close association with plant root rhizobacteria [15]. The study of [1] indicates that the number of nodules formed is higher if the soil is inoculated with Rhizobium. The interactions between root nodules and symbiotic bacteria have been examined using proteomics during signal exchange and symbiotic growth [24]. Crop production in Sub-Saharan Africa (SSA) faces various challenges, including abiotic and socio-economic factors, which lead to differences in production across regions. The predominant causes of low soybean yields are poor and declining soil fertility, soil acidity, inefficient management practices, and limited use of agricultural inputs [11], [12], [19], and [17]. Numerous studies conducted throughout Africa have demonstrated that indigenous rhizobia in many areas are either ineffectual or insufficient to meet the nitrogen requirements of promiscuous varieties [22]. This indicates that inoculation is a more reliable option than relying on expensive commercial fertilizers or indigenous rhizobia with uncertain efficacy [25]. In sub-Saharan Africa (SSA), more than 80% of the soil is deficient in nitrogen, and over 39% of children under the age of five suffer from malnutrition and stunting. This issue has been linked to a deficiency in essential nutrients, particularly proteins, in many diets, which resulted in over one-third of child mortality cases [15]. Soybeans are less expensive compared to other protein-rich foods like fish, eggs, and meat. Despite its potential as a source of protein, feed and income for farmers, soybean production is insufficient due to low yields, creating a gap between current and needed output [14]. Using high nitrogen-fixing soybean varieties and rhizobia inoculants can reduce the need for mineral N application [14], [26], [21]. There is limited information on the impact of rhizobium inoculation on the growth and yield characteristics of soybeans in the Sudan Savanna region of Nigeria. Therefore, the study was conducted to assess the impact of Rhizobium inoculation on the growth and yield of soybeans varieties in the Sudan Savanna region of Nigeria.

Materials and methods

The experiments were conducted during the 2021 cropping season at the University Teaching and Research Farm of Aliko Dangote University of Science and Technology Wudil in Gaya Latitude: 11.9331° N, Longitude: 8.5216° E and Bayero University Kano (BUK) teaching and research farm, Kano, which was located at the Latitude: 12.0027° N, Longitude: 8.5914° E with an elevation of 415m above sea level. Both sites were in Nigeria’s Sudan savanna zone. The experiment comprised two soybean varieties, TGX1447-2E and TGX1885-10E, with two Rhizobium treatment levels: un-inoculated and inoculated. The experiments were conducted using a Randomized Complete Block Design (RCBD) with three replications. Plot size was 3 m x 3m consisting of four ridges and 4 plots per replication, having a total of 12 plots. A distance of 0.5 meters was maintained between plots, and a 1-meter distance between replications, to ensure ease of movement within the experimental field. The data collected were number of leaves per plant, number of branches per plant, plant height (cm), days to 50% flowering, number of effective nodules, number of ineffective nodules, fresh weight of nodules, dry weight of nodules, number of pods per plant, pod weight per plant (g), shelling percentage per plot, 100 seed weight, yield per plant, and yield per hectare. The data were analyzed using analysis of variance, and the means were compared using the Duncan Multiple Range Test (DMRT). 

Soil analysis

Soil samples were randomly collected from various points in the experimental fields at a depth of 0-30 cm. The samples were combined in a bucket, after which a portion of the aggregated soil was collected, placed into a labelled plastic bag, and transported to the laboratory for analysis. The soil was allowed to air-dry at ambient room temperature and later crushed gently to facilitate the separation of gravel and roots from the mineral soil. The soil was sieved through 2mm and 0.5mm sieves to separate the gravel and roots, which were kept in the sieve. The processed soil was then stored in a plastic bag in a cool, dry place. The soil analysis was then conducted, with the results presented in Table 1 below.

RESULT

The results of soil analysis for the two sites are presented in Table 1. The soil samples were analyzed at the soil laboratory of the department of soil science, Bayero University, Kano. The results shown that at the experimental site of Bayero University, Kano was sandy loam while loamy sand was observed at Gaya. The pH (H₂O) of the soil was 5.9 and 6.1 at BUK and Gaya, respectively. The organic matter (OM) content of BUK and Gaya were 0.43 and 4.5gkg^-1,respectively.

Source: Soil Lab, Department of Soil Science, Bayero University, Kano

Fresh and dry weight (DW) of nodules and number of pods per plant

The results indicated substantial differences between the treatments at both the Gaya and BUK locations, as shown in Table 2. The effect of inoculum at both locations showed that the inoculated recorded the highest values as compared to non-inoculated for fresh weight, dry weight and number of pods per plant. The effect of variety showed that variety TGX 1885-10E had more fresh weight, dry weight and number of pods per plant also compared to TGX 1448-2E. At the BUK location, no significant differences were noted among the varieties in terms of fresh weight (Table 2). Variety TGX 1448-2E had more dry weight value (0.35) than variety TGX 1885-10E with a value of 0.29. TGX 1448-2E recorded 68.58 pods per plant, while TGX 1885-10E recorded 52.04 pods per plant.

Means followed by the same letters within the same column are not significantly different at 5 % level of probability using Duncan’s Multiple Range Test, * = Significant at 5%, NS = Not significant, I = Inoculum, V = Variety. WAP = Weeks after planting and SE = Standard error.

One hundred Seed Weight, pod weight per plant and Grain yield per plant

Table 3 shows impact of seed inoculant which significantly affected one hundred seed weight, pod weight, and grain per plant in both locations. Inoculated seed significantly produces the weightiest 100 seed weight (13.67g and 11.35g), pod weight per plant (56.15g and 35.36g), and grain yield/plant (47.36g and 29.16g) in both locations, respectively. TGX1885-10E demonstrated outstanding performance, yielding the heaviest seeds, highest pod count, and seed yield per plant across the locations, except one hundred seed weight at BUK.

Means with the same letters in a column are not significantly different at a 5% probability level using Duncan’s Multiple Range Test. * = Significant at 5%, NS = Not significant, I = Inoculum, V = Variety, WAP = Weeks after planting, SE = Standard error.

Grain Yield per hectare and Shelling Percentage

Table 4 shows how inoculant and variety affect yield and shelling percentage at both locations. Inoculant significantly affected grain yield and shelling percentage at Gaya and BUK. The results showed that the inoculated seed had the highest grain yield and shelling percentage at Gaya, except for the shelling percentage, which did not show a significant difference between inoculated and non-inoculated seeds.

The effect of variety revealed that TGX1885-10E had higher grain weight and shelling percentage as compared to TGX1447-2E at Gaya. However, TGX 1447-2E produced a higher grain yield than TGX1885-10E at BUK. The shelling percentage showed no significant variation attributable to the variety at the same location.

Means with identical letters in the same column do not differ significantly at a 5% probability using Duncan’s Multiple Range Test. * = Significant at 5%, NS = Not significant, I = Inoculum, F = Inorganic fertilizer, V = Variety, WAP = Weeks after planting, SE = Standard error.

DISCUSSION

Rhizobium is a group of nitrogen-fixing bacteria that form a symbiotic relationship with leguminous plants, such as soybean. These bacteria colonize the root nodules of the host plants, facilitating the conversion of atmospheric nitrogen into forms that can be readily assimilated by the plants, thereby enhancing their nitrogen nutrition. The study results showed that most of the observed growth and yield traits responded positively to rhizobium inoculation. Rhizobium inoculation significantly impacted the growth and yield traits of soybean, increasing plant height, number of leaves, and number of branches. This might be explained by the ability of rhizobium bacteria to increase nitrogen fixation. Rhizobium inoculation significantly enhances nitrogen fixation in soybean plants with a substantial amount of fixed nitrogen, which is essential for various physiological processes. This increased nitrogen availability promotes vegetative growth and overall plant development. A study [7] examined the impact of rhizobium inoculation on soybean yield and nitrogen fixation. The findings indicated that inoculated soybean plants exhibited an increased number of nodules, higher nodule dry weight, and enhanced nitrogenase activity. These factors contributed to improved nitrogen fixation capacity, which in turn led to increased soybean growth and yield.  The enhanced availability of fixed nitrogen supports the development of leaves, stems, and roots resulting in increased plant height, leaf area, and overall biomass. A study by [23] examined the effects of rhizobium inoculation on soybean growth and yield. The study found that inoculated plants exhibited substantially greater plant height, leaf area, and dry matter production than their non-inoculated counterparts. There was a significant increase in a number of nodules and effective nodules could be due to rhizobium inoculation which stimulates nodulation in soybeans, leading to the formation of more and healthier nodules. Increased nodulation ensures a greater nitrogen-fixing capacity, providing a continuous supply of nitrogen to the plant throughout its growth stages. [5] investigated the effect of rhizobium inoculation on soybean nodulation and growth, the findings have shown that inoculated soybean plants exhibited increased nodule number, nodules fresh weight, and nodule efficiency compared to non-inoculated plants, thereby promoting better nitrogen fixation and subsequent growth. The results revealed a significant effect of rhizobium on growth and yield characteristics. Rhizobium inoculation has a significant positive impact on soybean yield by improving nitrogen availability and promoting plant growth, rhizobium symbiosis contributes to higher crop productivity and increased yield. A meta-analysis conducted by [27] analyzed various studies on rhizobium inoculation in soybeans. The results revealed that inoculated soybean plants had significantly higher grain yield compared to non-inoculated plants, with an average yield increase of approximately 15 %.

This study indicates that the response of soybean varieties to most of the growth characters evaluated was significant at Gaya. This might be attributed to the interaction between the varieties and rhizobium inoculation, which enhances nitrogen fixation and thereby improves growth potential. Variations observed for growth and yield characteristics among the soybean varieties were due to their genetic constitution, which affects their response to rhizobium inoculation. These variations could also result from selection by plant breeders who choose varieties based on traits like responsiveness to inoculation. It should be noted that the varieties involved in this study had diverse origins and different breeding histories, which likely contributed to their varied responses to the inoculant. However, at BUK, the response of most of the varieties to rhizobium inoculation was not significant. This might be due to the adaptability of the varieties to the specific environmental conditions, which could have influenced the effectiveness of the inoculation.

CONCLUSION

The study’s findings indicated that the growth and yield characteristics of soybean varieties were significantly impacted by the application of rhizobium inoculation in the study areas. All growth and yield characters increased with rhizobium inoculation at both locations. The result also revealed that TGX 1448-2E had a significant advantage over TGX 1885-10E at BUK, while at Gaya TGX 1885-10E performed better.

Conflict of Interest

We declare no conflict of interest in this publication.

Artificial Intelligence

Artificial intelligence tools were not used to make this manuscript.

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