Interaction of liming, mineral nitrogen fertilization, and Rhizobium inoculation in biomass partitioning and production of cowpea

Cowpea has great capacity of biological fixation of nitrogen (BFN) in association with Rhizobium. However, it is not known whether the interaction of liming, mineral N fertilization, and Rhizobium-inoculated seeds can modify the efficiency of BFN, and still, result in gains in biomass production and yield in cowpea. This study evaluated the use of liming associated to Rhizobium-inoculated seeds and supplemental mineral N fertilization on the nodulation improvement, biomass production, and on the increase of cowpea grain production. Two experiments were conducted under field conditions in two consecutive years, using the same treatments and experimental design. The treatments were conditioned in a split-plot scheme in randomized blocks with four replications in a 2 × 6 factorial, the first factor being two cowpea cultivars (BRS Tapaihum and BRS Marataoã) and the second factor was considered six conditions of corrective practice and N supply [no N supply and no liming (T1), liming + rhizobium (T2), rhizobium (T3), liming + mineral N (T4), liming (T5), and liming + mineral N + rhizobium (T6)]. Nitrogen concentration and accumulation in the leaves increased with liming and N supply (T2, T4, and T6) and increased dry matter (DM) accumulation in the stem, leaves, shoots, and total DM. The absence of liming limited root length growth, decreased root DM, and the number and DM of nodules thus limiting grain production. Additionally, N fertilization supplemented with Rhizobium-inoculated seeds did not increase grain production. However, the use of liming and the inoculation of seeds with Rhizobium increased plant performance and improved grain yield of both cowpea cultivars.