Nodulation and Agronomic Performance of Legumes in an Input-omission Trial in Southeastern Nigeria

Abstract

This study evaluated the nodulation capacity and agronomic performance of soybean and groundnut under an input-omission trial in southeastern Nigeria. A field experiment was conducted in 2025 using a randomized complete block design with Rhizobium inoculant, phosphorus (P), and potassium (K) applied singly and in combinations. Plant height and number of leaves were assessed at 40 days after planting, nodulation characteristics were evaluated during crop growth, and yield was determined at 90 days after planting. Post-harvest soil samples were analyzed for residual nitrogen forms, and treatment effects were assessed by analysis of variance. The combined application of inoculant, P, and K produced the highest growth and yield values for both legumes. Soybean yield increased from 1.000 to 2.200 t ha⁻¹, while groundnut yield increased from 1.617 to 3.043 t ha⁻¹ between the control and the treatment receiving all three inputs. Inoculation and P application were particularly associated with improved nodulation characteristics. Groundnut recorded a higher mean number of nodules, whereas soybean recorded higher mean nodule weight and viability. Residual nitrogen forms were generally higher in soybean-grown plots than in groundnut-grown plots. These findings indicate that combined inoculation and nutrient application supported legume productivity, while inoculation with phosphorus was particularly favorable for nodulation under the study conditions.