Efeito do níquel na fixação biológica de nitrogênio e no desenvolvimento do feijão-caupi

Abstract

The application of nickel in cowpea has significant and direct effects on biological nitrogen fixation and crop growth, playing an essential role in nodulation and nitrogen metabolism. In this context, the objective of the present study was to evaluate the effect of increasing doses of Ni on biological nitrogen fixation in two cowpea cultivars. The experiment was conducted in a completely randomized design in a 4 x 2 factorial scheme, corresponding to four Ni doses (0; 0.5; 1.5; and 3.0 mg Ni kg⁻¹) and two cowpea cultivars (BRS Tumucumaque and BRS Xique-xique), with four replications, using nickel sulfate applied to the soil. At 38 days after emergence, the following parameters were evaluated: number of nodules per plant, nodule dry mass, number of viable nodules, plant height, shoot dry mass, and root dry mass. The results indicated that moderate doses of Ni promoted growth and nodulation, with the optimal dose varying between cultivars. The Tumucumaque cultivar exhibited higher nodulation at the dose of 2.0 mg Ni kg⁻¹, while the Xique-xique cultivar showed a lower response to the element. However, high doses of Ni caused reductions in shoot biomass and nodulation, indicating toxicity. The data confirm that proper Ni management can optimize biological nitrogen fixation in cowpea, contributing to sustainable agricultural systems and reducing the use of nitrogen fertilizers. The application of Ni at a dose of 1.0 mg Ni kg⁻¹ promoted greater nodulation in the Tumucumaque cultivar without reducing its biomass accumulation