Effects of Biofertilizers on Growth and Yield of Cucumber (Cucumis sativus L.) Production: A Species-Level Comparison

Cucumbers (Cucumis sativus L.) are a widely cultivated vegetable crop, known for their nutritional value and economic importance (Peyvest, 2009), especially in sub-Saharan Africa and parts of Asia. In countries like Nigeria, cucumber cultivation has seen rapid growth due to its short growth cycle and high market demand. Enhancing cucumber yield and quality through sustainable practices is vital for both farmers and consumers. Biofertilizers, through mechanisms such as nitrogen fixation, phosphate solubilization, and production of growth-promoting substances, can play a significant role in improving cucumber cultivation (Khan, 2020). Cucumber production faces challenges such as soil nutrient depletion, poor soil management, water stress, and susceptibility to a variety of pests and diseases (Pawar et al., 2020). Given these constraints, there is a growing need to identify sustainable approach that improves the yield and quality of cucumber. Biofertilizers enhance nutrient uptake, improves soil microbial diversity, and promotes plant resilience. This has shown considerable promise in improving both yield and quality in various crops, including cucumbers (Liao et al., 2015). Biofertilizers have attracted widespread interest due to their potential to promote plant growth, improve soil health, and reduce the incidence of soil-borne diseases. These microorganisms include bacteria, fungi, and algae, with each group contributing uniquely to the soil-plant system. The role of biofertilizers in promoting plant growth is diverse as they improve the structure of the soil, fix nitrogen, solubilize phosphorus, decompose organic matter, and enhance the availability of essential nutrients (Verma et al., 2001). Biofertilizers can act as biocontrol agents by suppressing plant pathogens and reducing the need for chemical pesticides (Bashan et al., 2014). Biofertilizers represents an essential component of integrated soil fertility management, especially in crops like cucumber (Cucumis sativus L.), which is widely grown for its nutritional value and commercial importance in many parts of the world. Among the diverse microorganisms used in biofertilizers, fungi and bacteria are the most common. Fungal species such as Trichoderma harzianum and Penicillium menorum have been shown to act as effective biocontrol agents by inhibiting pathogenic fungi and promoting plant growth through mechanisms such as the production of plant growth hormones (Sharma et al., 2017). Trichoderma harzianum, in particular, is known for its ability to degrade organic matter, improve soil structure, and enhance nutrient cycling in soils, which leads to better growth conditions for plants. Additionally, Penicillium menorum has been reported to produce various enzymes that aid in the breakdown of soil organic matter and support plant growth by enhancing nutrient availability (Singh et al., 2013). Bacterial biofertilizers, such as Bacillus subtilis, Rhizobacteria, and Pseudomonas spp., have also been extensively studied for their roles in promoting plant growth and improving soil health. These microorganisms function through several mechanisms, including nitrogen fixation, phosphorus solubilization, and the production of plant growth-promoting substances like auxins and cytokinins (Mishra and Kaur, 2015). Bacillus subtilis, has been shown to improve the yield and disease resistance of cucumbers by enhancing root growth and reducing the severity of fungal infections (Wang et al., 2020). Similarly, Rhizobacteria are well known for their ability to colonize the rhizosphere, where they facilitate nutrient uptake and enhance plant growth through both direct and indirect mechanisms (Choudhury et al., 2017). The response of cucumber varieties to biofertilizer treatments is a crucial aspect of understanding the potential benefits of bio-inoculation. Different cucumber varieties may exhibit varying responses to biofertilizers due to genetic differences in growth characteristics, disease resistance, and nutrient uptake efficiency (Ali et al., 2019). Varieties such as Greengo and Lily F1 are commercially grown in different regions, and they may respond differently to inoculation with fungal or bacterial biofertilizers. Understanding how these varieties interact with specific microbial inoculants is vital for optimizing biofertilizer use in cucumber cultivation. Soil health is another critical factor that influences plant growth and productivity. The rhizosphere soil, where plant roots interact with soil microorganisms is a dynamic environment that plays a central role in nutrient cycling, disease suppression and plant growth promotion (Schreiter et al., 2014). A healthy and diverse microbial community in the soil can significantly enhance the effectiveness of biofertilizers by improving nutrient availability and reducing soil- borne pathogens. Microbial enumeration and analysis of the soil before and after inoculation with biofertilizers can provide valuable insights into the dynamics of microbial communities and their impact on plant health. In improving cucumber yield, biofertilizers can also enhance the nutritional quality of cucumbers. Proximate analysis (nutrient composition) which includes the determination of key nutrients such as moisture, protein, fat, carbohydrates, and minerals, is essential for assessing the nutritional content of cucumbers. The use of biofertilizers may result in improvements not only in yield but also in the overall nutritional profile of the cucumber, thus contributing to better food security and health (Akinmoladun et al., 2015). The present study therefore seeks to examine the effects of biofertilizer inoculation on cucumber yield and quality, comparing two species to provide insights into their distinct responses under five biofertilizer treatments, which includes two fungal biofertilizers (Trichoderma harzianum and Penicillium menorum) and two bacterial biofertilizers (Bacillus subtilis and Rhizobacteria), alongside a control. Additionally, this study will investigate the physicochemical properties of soil before and after biofertilizer application.