Evaluation of Rhizobial Strains for Improving Biological Nitrogen Fixation and Yield in Rabi-Summer Groundnut (Arachis hypogaea L.)

Abstract

Rhizobium inoculation has been widely reported to have a positive impact on various growth parameters and yield attributes in groundnut. Moreover, the combined application of Rhizobium inoculants with chemical fertilizers has shown synergistic effects in improving pod yield and other agronomic traits. A field experiment was conducted during the rabi–summer seasons of 2022–23, 2023–24, and 2024–25 at the Agricultural Research Station, Kadiri, with the objective of evaluating different rhizobial strains for their effectiveness in improving biological nitrogen fixation and enhancing the yield of rabi–summer groundnut. The experiment was laid out in a Randomized Block Design (RBD) with three replications and eight treatments, each representing a different rhizobial strain. The study focused on assessing various yield attributes, including the number of pods per plant, 100-pod weight, 100-kernel weight, shelling percentage, and sound mature kernel percentage. The results revealed that these yield parameters were not significantly influenced by the application of different rhizobial strains, indicating that the strains had a limited direct effect on these specific yield components under the given conditions. However, significant differences were observed in terms of nodulation, overall pod yield, and economic returns. Among the tested treatments, Rhizo-7 (IGR-6) and Rhizo-5 (DGR-35) emerged as the most promising and effective strains. Among the treatments, Rhizo-7 (IGR-6) recorded the highest pod yield (2739 kg ha⁻¹) whereas, Rhizo-5 (DGR-35) recorded the higher halum yield (6518 kg ha⁻¹). Rhizo-1 (DGR-23) and Rhizo-3 (DGR-25) consistently exhibited the lowest values for several key parameters, often performing even below or on par with the uninoculated control. The study highlights the importance of selecting efficient rhizobial strains to optimize nitrogen fixation and improve productivity and profitability in groundnut cultivation under specific seasonal conditions.