African Journal of
Agricultural Research

  • Abbreviation: Afr. J. Agric. Res.
  • Language: English
  • ISSN: 1991-637X
  • DOI: 10.5897/AJAR
  • Start Year: 2006
  • Published Articles: 6578

Full Length Research Paper

Yield response and economic benefits of groundnut to phosphorus fertilization and inoculant rates in Northern Ghana

Richard Yaro Naabe
  • Richard Yaro Naabe
  • Department of Agronomy, Faculty of Agriculture, University for Development Studies, Ghana.
  • Google Scholar
Albert Berdjour
  • Albert Berdjour
  • International Institute of Tropical Agriculture (IITA), Ghana.
  • Google Scholar
Daniel Asomaning Odoom
  • Daniel Asomaning Odoom
  • Department of Agronomy, Faculty of Agriculture, University for Development Studies, Ghana.
  • Google Scholar
Haruna Alhassan Yemyoliya
  • Haruna Alhassan Yemyoliya
  • Savanna Agricultural Research Institute (SARI), Ghana
  • Google Scholar

  •  Received: 06 November 2020
  •  Accepted: 05 January 2021
  •  Published: 28 February 2021


Groundnut (Arachis hypogea L.) is a major source of dietary protein, cultivated for both human and animal consumption. However, in West Africa, the yields are low, renewing the interest to evaluate groundnut response to P fertilizer (P) and rhizobium inoculant (IR) application. A study was conducted on the experimental field of the University for Development Studies, Nyankpala in the Northern region of Ghana to evaluate the interactive effect of three P rates (0, 30 and 60 kg P2O5/ha) and three IR rates (0, 3 and 6 g/kg seed) on groundnut yield and to assess the economic viability of these technologies to farmers. The study was conducted using a 3 × 3 factorial laid out in a randomized complete block design with three replications. Nodule count and pod number per plant were significantly affected by P fertilizer rates (PR) and rhizobium inoculant rates (IR) interaction. The effects of PR and IR significantly increased grain yield of groundnut, with 60 kg P2O5/ha and 6g inoculant/kg seed recording the highest grain yield of 2708.3 and 2376.6 kg/ha respectively. Correlation analysis suggested that major determinants of groundnut grain yield were nodule count, effective nodule count, pod number and pod weight. Gross benefits were higher in treatment with P fertilizer and/or inoculant application. Estimated B/C ratios also indicated that, compared to the control, all the treatments are attractive. Therefore, cultivating groundnut by using P fertilizer and/or inoculant may provide the most economically viable and low-risk options for increasing groundnut yield in northern Ghana.

Key words: Phosphorus, rhizobium inoculant, gross benefit, groundnut, grain yield.


Groundnut (Arachis hypogea L.) is a major grain legume in the world, cultivated for both human and animal consumption (Dapaah et al., 2014). Its seed is a major source of protein (12-30%) and oil (36-54%) for both rural and urban settlers  in  Sub-Saharan  Africa  (Naab  et  al., 2009). According to the Food and Agriculture Organization (FAO) estimate for 2018, 28.5 million hectares of peanut were harvested worldwide of which West African sub-region harvested 7.1 million ha ( Despite its importance, the average yield of  groundnut in  West Africa is estimated to be 1.1 t/ha. Several biophysical and socio-economic factors; including low and declining soil fertility, high cost and/or unavailability of inputs (seed, fertilizer, inoculant) and use of low yielding varieties are often cited as the major causes of the low yield of groundnut.

Low and declining soil fertility, especially phosphorus (P) deficiency, in smallholder groundnut farms has been described as the fundamental biophysical factor responsible for the declining yield in Sub-Saharan Africa (Naab et al., 2009). Although groundnut can fix their own nitrogen, they often need P for enhanced seed formation (Asiedu et al., 2000). Some authors (Naab et al. 2005; Kamanga 2010) have reported a significant yield response of groundnut to P application. Despite, these benefits, results from various studies on the optimum application rate of P to enhance groundnut yield proves to be inconsistent. For instance, studies by Mouri et al. (2018) reported higher yields with P rate at 60 kg P2O5/ha whiles Taruvinga (2014) found no significant effect when P rate was increased beyond 45 kg P2O5/ha. Therefore, this has renewed the interest for further studies.

Inoculation using Rhizobia strains has been identified as one of the most successful strategies employed to enhance symbiotic N-fixation by legume (Amba et al., 2013). It has been reported that, leguminous plant with symbiotic nitrogen fixing bacteria are able to fix about 15 - 210 kg/ha of nitrogen per season (Dakora and Keya, 1997). Thus, the inoculation of peanut with appropriate rate of rhizobium inoculant can be a beneficial strategy to improve peanut productivity. However, peanut response to inoculation has been inconsistent (Sharma et al., 2011), as survival and effective functioning of rhizobia population are reduced by high soil temperature, salt, soil acidity and nutrient deficiency (Zahran, 1999). Therefore, the full potential of the symbiotic system may be realized by increasing the number of effective rhizobia. Consequently, Deaker et al. (2004) demonstrated that, increasing number of effective rhizobia per seed application of inoculants improves nodulation and yield.

Previous studies on groundnut with P rate and rhizobium inoculant application only covered information on yield components and yield with little or no data on their economic viability. The objective of this study was therefore to evaluate the interactive effect of phosphorus and rhizobium inoculant rates on the performance of groundnut and assess the economic viability of P and inoculant application to guide farmer’s adoption.


Study site description

Field experiment was conducted during the 2018 cropping season at the University for Development Studies experimental field at Nyankpala in the Northern Region of Ghana, located at latitude 9.40980° N; longitude 0.98654° W at altitude 183 m above sea level. The area experiences a  unimodal  annual  rainfall  of  800  to 1200 mm which occurs from May to October. The mean monthly minimum and maximum temperature ranges between 21 and 34.1°C respectively.

Experimental design and treatment

The study was a 3 × 3 factorial experiment laid in a randomized complete block design with three replications. The treatments included three P application rates (0, 30 and 60 kg P205/ha) and three rhizobium inoculation rates (0, 3 and 6 g/kg seed). The unapplied treatment plots (0 kg P205/ha and 0 g/kg seed) served as the control treatments for P rate and rhizobium inoculant rate respectively.

Agronomic procedures

Each treatment plot consisted of six rows of 4 m in length, 0.40 m inter-row spacing and 0.2 m intra-row spacing. The groundnut variety: Nkatie SARI, an erect bunch habit with 110 days maturity duration and resistant to early and late leafspot infections was used in the study. Commercial rhizobium inoculant product: Nodumax (strain USDA 110) was obtained from Savannah Agricultural Research Institute, Tamale, Ghana for the experiment.

Seed inoculation was performed just before planting by weighing 1 kg of seed into a plastic container and adding 10 ml of dissolved gum Arabic solution as sticker. The seeds and gum Arabic solution were mixed thoroughly and 10 g of Nodumax inoculant was applied to the seed and mixed thoroughly to ensure that all the seed were effectively covered with the inoculant.  The groundnut was then planted at 1 seed/hill. Weed was controlled manually at 3 and 6 weeks after sowing (WAS) to avoid weeds build up to critical infestations levels as suggested by Priya et al. (2013).

Data collection

Growth, yield components and yield

Plant height and nodulation assessment were determined 8 weeks after sowing. For nodulation assessment, 5 plants outside the two centre rows were randomly uprooted from each plot. The roots were carefully washed with water inside a bowl to loosen adhering soil. The nodules were then removed, counted and dissected to determine nodule number and effective nodule number. At physiological maturity, 5 plants from the two centre rows of each plot were randomly selected for pod weight and count. The total weight and average number of pods were then calculated for each plot. The grain yield was measured from the two centre rows of each plot (3.2 m2). The pods were stripped, sun dried and shelled to measure grain yield.

Economic benefits

Data on cost of production and price of the grain after harvest were collected to estimate the total income of the output. The total cost of production constituted cost of land preparation, seed, fertilizer, inoculant and labour. Price of groundnut seed, P fertilizer and inoculant were as purchased in the study area. Cost of ploughing and harrowing were as charge by operators in the area while labour payment was valued at the daily wage rate of hired farm labourers. Grain yield price was determined by the market price at the nearest market (Tamale) during harvest (2018).The profit or marginal net return (MNR) was computed for each treatment as follows:

MNR = Y x P – TVC                                                          (1)

Where Y is grain yield of groundnut (kg/ha), P is selling price of groundnut grain at harvest and TVC is the cost of inputs related to the treatment. The marginal rate of return (MRR) for each treatment was calculated as follows:

MRR = MNR/TVC                                                             (2)

Data analysis

The General Linear Model of the Statistix 10 Analytical Package (2013) for windows was used to analyse data on growth, yield components and yield. Duncan Multiple Range Test was used to separate treatment means of significance level at 5% probability level. However, the economic benefit of groundnut production was not statistically analysed. Correlation analysis was performed to determine relationship among growth, nodulation, podding   capacity   and    grain    yield.    Parameters   with correlation values of 0.50 and above were considered to be best fitted and less than 0.50 considered non-best fit. Linear regression was used to determine predictive equations among correlated variables.


Growth, yield components and yield

The PR x IR interaction was not significant on plant height at 8 WAS, however, the effects of PR and IR did influence plant height significantly, such that plant height at 30 kg P2O5/ha and inoculant at 6 g/kg seed increased significantly compared with their respective control (Table 1). Nodule count was significantly affected by PR x IR application rates. P rate at 60 kg P2O5/ha and inoculant rate  at  6 g/kg  seed  combined  to  give higher (P < 0.001) nodule count than the control (Figure 1). Conversely, effective nodule number was influenced by the effects of PR and IR with P rate at 60 kg P2O5/ha and inoculant rate at 6 g/kg seed recording the highest number than their respective controls (Table 1). The PR x IR interaction was significant on pod number, likewise the effects of PR and IR. Pod number of P at 60 kg P2O5/ha combined with inoculation at 6 g/kg seed increased significantly compared with the control (Figure 2). The weight of pods produced by groundnut in response to application rates of P and inoculant are shown in Table 1. Statistically, the lowest pod weight was observed under the control of both PR and IR. The PR x IR interaction was not significant on grain yield, however the effects of PR and IR affected grain yield significantly. Groundnut  grain  yields of P at 60 kg P2O5/ha and inoculation at 6 g/kg seed increased significantly compared with their respective controls (Table 1). Groundnut grain yield (GGY) was positively correlated with nodule count (NC), effective nodule count pod number (PN) and pod weight (PW). This indicates that when NC, ENN, PN and PW increase GGY also increases. This relationship could be predicted from the general linear regression model:

YGGY = - 2275.03 + 25.72NC + 121.73ENC + 168.00PN + 0.26PW, r2 = 0.75                                                           (3)



Economic benefits

Table 2 depicts the total variable cost, gross benefits, net benefits   and   benefit: cost   (B/C)   ratio   for   groundnut production for the different technologies. The cost of producing groundnut by applying P alone at either 30 or 60 kg P2O5/ha was 57.5% (USD 381/ha) and 77.8% (432 USD/ha) higher respectively than the control (249 USD/ha). Similarly, applying inoculant alone at either 3 or 6 g/kg seed increased the production cost by 18% (331 USD/ha) and 28.5% (320 USD/ha) respectively above the control. Substituting 30 kg P2O5/ha  with   60   kg  P2O5/ha    increased    the production cost by 12.9% whiles replacing 3 g/kg seed with 6 g/kg seed inoculant raised the production cost by 8.1%. However, increasing rate of P from 30 to 60 kg P2O5 and inoculant from 3 to 6 g/kg seed, which added to the cost of production, did not significantly enhanced grain yield. The application of 60 kg P2O5/ha with inoculant at 3 or 6 g/kg seed yielded higher net benefit than all the treatments. Furthermore, compared  to  the  control,  the B/C  ratios  for  the other treatments were all greater than 1.



The significant effect of P and rhizobium inoculant on plant height could possibly be attributed to the stimulation of vegetative growth by the application of P and inoculant. The increase in vegetative growth in response to  phosphorus  and  inoculant application has been reported by several authors (Kwari, 2005; Hasan and Sahid, 2016).

Nodulation plays important role in nitrogen (N) fixation by leguminous crop. In this study, the significant interaction effect of PR x IR on nodule count could possibly be due to the effectiveness of the P fertilizer rate in providing energy source (ATP) for rhizobium to enhance its nodule formation activity. This result concurs with earlier reports that P applied in combination with rhizobium inoculant increases nodule number per plant (Badar et al., 2015). Similarly, the number of effective nodules was significantly influenced by PR and IR effects. This finding indicates that the ability of peanut to nodulate and further produce effective nodules can also be influenced by the application of either P fertilizer rates or rhizobium inoculant rates.

The significant effect of PR x IR interaction on pod number could be attributed to the synergistic effect of PR and IR on pod formation. The increase in pod number with PR and IR application supports earlier reports that integrated application of P fertilizer and rhizobium inoculant result in improved soil productivity because of the supply of P for improved N fixation by the bacteria. Conversely, in spite of the increased number of pods, pod weight was not significantly affected by PR x IR interaction. The failure of higher pod number to translate into pod weight could be due to poor pod filling, encountered as a result of drought during the pod filling stage. Pod filling in legumes tends to be ineffective under extreme drought conditions (Schulz and Thelen, 2008).

Although the interactive effect of PR x IR was not significant on grain yield, the effects of PR and IR significantly contributed to grain yield. This result suggests that the use of either P fertilizer or rhizobium inoculant is very important for groundnut production. This finding is in agreement with earlier observations made by Ikenganyia et al. (2017) that phosphorus and rhizobium inoculant impact positively on grain yield.

The expected profitability of a technology is a prerequisite for adoption by smallholder farmers (Morris et al., 1999). This study has revealed that groundnut production can be very profitable with the application of P fertilizer and/or rhizobium inoculant. Accordingly, gross benefits were much higher in treatments with P fertilizer and/or rhizobium inoculant than the control. Similar economic benefits with P and inoculant application have been reported by several authors (Naab et al., 2009; Ahiabor et al., 2014). Although the application of inoculant alone increased grain yield and gross benefits per hectare relative to its’ control, these were nevertheless lower when compared with P fertilizer alone or its combination with rhizobium inoculant. This result indicates that phosphorus is the main deficient factor for groundnut production in the study area. This finding corroborates study by Adjei-Nsiah et al. (2018). The estimated B/C ratios for plots with P fertilizer and rhizobium inoculant applications, shows the attractiveness of the  treatments. A  farmer  could  adopt  the  combined application of P fertilizer at 30 kg P2O5/ha and inoculant at 6 g/kg seed, as it gives a high return to investment at a relatively lower production cost and higher net benefit. However, according to Morris et al. (1999), in reality the uptake of agricultural technology is more likely to proceed erratically as individual farmers learn to adapt the technology to their own socio-economic circumstances. Therefore, depending on resource availability (P fertilizer and inoculant), small-scale groundnut farmers with low resource endowment could either adopt the application of P alone at either 30 kg P2O5/ha or inoculation alone at 6 g/kg seed whiles those with more resource endowment could use P fertilizer at 60 kgP2O5/ha alone or in combination with rhizobium inoculant at either 3 or 6 g/kg seed.


Results show that P fertilizer rates combined with rhizobium inoculant rates has a significant influence on nodule number and pod number. P rate at 60 kgP2O5/ha and rhizobium inoculant rate at 6 g/kg seed combined to promote the best nodule and pod number. The application of either P fertilizer or inoculant affected groundnut grain yield significantly. Higher grain yields were observed in groundnut sown with either 60 kg P2O5/ha or 6 g/kg seed. Gross and net benefits were all higher in treatment with P fertilizer and/or inoculant application. Estimated B/C ratios also indicated that, compared to the control, all the treatments are attractive. Therefore, cultivating groundnut by using P fertilizer and/or inoculant may provide economically viable and low-risk options for increasing groundnut yield in northern Ghana.


The authors have not declared any conflict of interests.


Collaborative staff, field and data collection support from the Department of Agronomy, University for Development Studies is greatly appreciated.


Adjei-Nsiah S, Alabi BU, Ahiakpa JK, Kanampiu F (2018). Response of grain legumes to phosphorus application in the Guinea Savanna agro-ecological zone of Ghana. Agronomy Journal 110(3):1089-1096. 


Ahiabor BDK, Lamptey S, Yeboah S, Bahari V (2014). Application of phosphorus fertilizer on soybean (Glycine max L.) inoculated withrhizobium and its economic implication to farmers. American Journal of Experimental Agriculture 4(11):1420-1434.


Amba AA, Agbo EB, Garba A (2013). Effect of nitrogen and phosphorus fertilizers on nodulation of selected grain legumes at Bauchi, Northern Guinea Savanna of Nigeria. Journal of Biosciences 3(10):1-7.


Asiedu EA, Vangastel AJG, Gregg BR (2000). Extension agent's technical crop guidelines for assisting seed producers in Ghana.


Badar R, Nisa Z, Ibrahim S (2015). Supplementation of phosphorus with rhizobia inoculants to improve growth of peanut plants. International Journal of Applied Research 1(4):19-23.


Dakora FD, Keya SO (1997). Contribution of legume nitrogen fixation to sustainable agriculture in Sub-Saharan Africa. Soil Biology and Biochemistry 29(5-6): 809-817.


Dapaah HK, Mohammed I, Awuah RT (2014). Growth and Yield Performance of Groundnuts (Arachis hypogaea L.) in Response to Plant Density. International Journal of Plant and Soil Science 3(9):1069-1082.


Deaker R, Roughley RJ, Kennedy IR (2004). Legume seed inoculation technology: a review. Soil Biology and Biochemistry 36(8):1275-1288.


Food and Agriculture Organization (FAO) (2018). FAO Agricultural Statistics.



Hasan M, Sahid BI (2016). Evaluation of Rhizobium inoculation in combination with phosphorus and nitrogen fertilization on groundnut growth and yield. Journal of Agronomy 15(3):142-146.


Ikenganyia EE, Anikwe MAN, Nguwu OE (2017). Influence of Rhizobacteria inoculant application methods and phosphate fertilizer rate on dry matter accumulation, yield of Bambara groundnut (Vigna subterranean (L.) verdc) and soil total nitrogen content in a degraded Utisol in Southeast Nigeria. Agrotechnology 6(165):2. 


Kamanga BCG, Whitbread A, Wall P, Waddington SR, Almekinders C, Giller KE (2010). Farmer evaluation of P-fertilizer application to annual legumes in Chisepo, Central Malawi. African Journal of Agriculture Research 5(8):668-680.


Kwari JD (2005). Soil fertility status in some communities of southern Borno. Final report to PROSAB Project. Maiduguri, Nigeria P 21.


Morris M.L, Tripp R, Dankyi AA (1999). Adoption and Impacts of Improved Maize Production Technology: A Case Study of the Ghana Grains Development Project. Economics Program Paper 99-01. Mexico, DF: CIMMYT.


Mouri SJ, Sarkar MAR, Uddin MR, Sarker UK, Kaysar MS, Hoque MMI (2018). Effect of variety and phosphorus on the yield components and yield of groundnut. Progressive Agriculture 29(2):117-126.


Naab JB, Seini SS, Gyasi KO, Mahama GY, Prasad PVV, Boote KJ, Jones JW (2009). Groundnut Yield Response and Economic Benefits of Fungicide and Phosphorus Application in Farmer-Managed Trials in Northern Ghana. Experimental Agriculture 45(4):385-399.


Naab JB, Tsigbey FK, Prasad PVV, Boote KJ, Bailey JE, Bradenburg RL (2005). Effects of sowing date and fungicide application on yield of early and late maturing peanut cultivars grown under rainfed conditions in Ghana. Crop Protection 24(4):325-332.


Schulz TJ, Thelen KD (2008). Soybean seed inoculant and fungicidal seed treatment effects on soybean. Crop Science 48(5):1975-1983. 


Sharma UC, Datta M, Sharma V (2011). Effect of applied phosphorus on the yield and nutrient uptake by soybean cultivars on acidic hill soil. Journal of Soil Science 1(2):45-48.


Statistix 10 Analytical Software (2013). Analytical Software, Tallahasee, FL.


Taruvinga B (2014). Nutritional and soil fertility benefits: Influence of fertilizers on groundnut (Arachis hypogea L.) yield and soil nitrogen contribution for smallholder farmers in Uganda. Thesis submitted to Wageningen University.


Zahran HH (1999). Rhizobium- legume symbiosis and nitrogen fixation under severe conditions and in an arid climate. Microbiology and Molecular Biology Reviews 63(4):968-989.