Root nodules are stronger sinks for phosphorus compared to other plant parts; this emphasizes the crucial role phosphorus plays in plant growth. This study determined the influence of phosphorus on high-haulm-producing groundnut for growth and nodulation parameters in a pot experiment. The experiment was a 2 x 8 factorial design in a completely randomized design (CRD). Two groundnut varieties (NkatieSARI and Chinese) and 8 levels of phosphorus were applied with three the replicates. Plants were top-dressed with urea at 21 days after planting. Shoots were harvested twice during the growth period (R3 and R6). Results showed that shoot biomass produced at R6 was 21% and 42% higher than at R3 for both varieties. Root biomass significantly (p = 0.045) increased at 41.2 mg P kg⁻¹ soil compared to the control and Chinese, while NkatieSARI had an increase in root weight at ≥ 30.9 mg P kg⁻¹ soil. Phosphorus at ≥ 20.6 mg P kg⁻¹ soil significantly (p = 0.039) increased the number of nodules produced by NkatieSARI from an average of 37 (control) to 86.8 nodules at 51.5 mg P kg⁻¹ soil. Irrespective of the phosphorus rates, Chinese produced few but heavy nodules, while NkatieSARI produced more but light nodules.

Keywords: Effective nodules, fodder, groundnut, phosphorus, root density, shoot biomass.