Agrotechnology

Abstract

Influence of Rhizobacteria Inoculant Application Methods and Phosphate Fertilizer Rates on Dry Matter Accumulation, Yield of Bambara Groundnut [Vigna subterranea (L.) Verdc] and Soil Total Nitrogen Content in a Degraded Ultisol in Southeast Nigeria

Ikenganyia EE, Anikwe MAN and Ngwu OE

Bacterial inoculants contribute to increased agronomic efficiency in the rhizosphere via its effects on biological nitrogen fixation, phosphate solubilization and other plant growth promotion (PGP) traits. This study evaluates the influence of rhizobacteria inoculant application methods and phosphate fertilizer rates on dry matter accumulation, nodulation, yield of Bambara groundnut [Vigna subterranea (L.) Verdc] and post-harvest soil total nitrogen content in a Typic Paleudult in Southeast Nigeria (6° 29′ N; 7° 54′ E). Field trials were conducted in 2015 and 2016 cropping seasons in a 2 × 4 factorial in a randomized complete block design with three replications. The treatments were four rates of single super phosphate fertilizer (0 kg P ha-1, 25 kg P ha-1, 50 kg P ha-1 and 75 kg P ha-1) and two rhizobacteria inoculant application methods (seed applied method and soil applied method). The results from the study showed that soil applied rhizobacteria inoculant increased leaf, stem and root dry weight of Bambara groundnut significantly (P<0.05) by between 19%-25% when compared with seed applied rhizobacteria inoculants. Similarly, soil applied rhizobacteria inoculant increased number of root nodules, fresh pods of Bambara groundnut and soil total nitrogen content at 90 days after planting (DAP) significantly (P<0.05) by 29%, 22% and 19% respectively when compared with seed applied rhizobacteria inoculants. Soils fertilized with 75 kg P ha-1 produced the highest dry matter (above and below) yield of Bambara groundnut (97.37 g plant) and this was significantly higher than when P was applied at 0 kg P ha-1, 25 kg P ha-1 and 50 kg P ha-1 by 54%, 32% and 15% respectively for the two cropping seasons. The interaction effect showed that soils fertilized with 75 kg P ha-1 combined with soil application method of rhizobacteria inoculation produced the highest fresh pod yield of Bambara groundnut (178.4 g plant) and postharvest soil total N content (0.29%) and this was significantly higher in plots without P in seed applied rhizobacteria plots by 52% and 88% for the two cropping seasons. The results of our study showed that the inoculation method plays an important role in determining the success of microbial inoculation. Soil inoculation rather than seed application of exogenous rhizobacteria and up to 75 Kg P ha-1 is recommended that for optimal dry matter yield and increment in postharvest soil total nitrogen content for cultivation of Bambara groundnut in degraded Ultisols and soils with similar edaphic conditions.