Which one of the following bacteria helps in improving the soil fertility ?

Rhizobium is a genus of bacteria that plays a critical role in improving soil fertility through biological nitrogen fixation [1][t1]. These bacteria form a symbiotic relationship with the root nodules of leguminous plants, such as beans and peas, where they convert atmospheric nitrogen (N2) into ammonium (NH4), a form that plants can readily absorb [c1][t4]. This process significantly enhances soil nitrogen levels, reducing the need for synthetic chemical fertilizers and promoting sustainable agriculture [t2][t3]. While Clostridium is also a nitrogen-fixing bacterium, it is typically free-living and contributes less significantly to agricultural soil fertility compared to the symbiotic Rhizobium [c2][t5]. In contrast, Salmonella and Staphylococcus are primarily known as human pathogens and do not contribute to soil nutrient enhancement [t7]. Therefore, Rhizobium is the most effective agent for improving soil fertility among the given options [t6][t8].

Sources

1. [1] FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45