How does Ni fertilization affect a responsive soybean genotype? A dose study

Abstract

Background and aims: Nickel affects a wide range of physiological processes in plants, which may result in higher growth and yield. Recent studies demonstrate that soybean genotypes show positive, but differential, responsiveness to Ni-fertilization. Thus, this study investigated the impact of supplying this micronutrient to a soybean genotype previously known to be responsive to Ni-fertilization, with the aim of identifying a suitable range of Ni for the adequate development of this crop plant.

Methods: We tested, under greenhouse conditions, the effect of applying six Ni doses (0.00, 0.25, 0.50, 1.00, 3.00, and 9.00 mg kg−1) via soil to a commonly-grown soybean genotype. Soybean plants were evaluated for nutrition, physiology, growth, N-urea metabolism, and efficiency of the N2 fixation process.

Results: Nickel supply positively affected the physiology and growth of the genotype, indicating a deficiency of this micronutrient. Ni-application also led to an increased N metabolism; in particular, nodules had a higher nitrogenase activity associated with greater Ni-concentrations in areas of highest metabolic activity. By exploiting the data acquired in a growth response curve (grain yield x Ni concentration), the greatest beneficial effects were observed following an application of 3.35 mg of Ni kg−1. A supply of more than 4.25 mg of Ni kg−1 was toxic to the plants.

Conclusions: Ni-fertilization improved the N-mineral and N-biological assimilation pathways of soybean, optimizing the overall development of the plants. Through this study, we defined a reliable and adequate Ni-range for both plants and soil, which can be used as a basis for agricultural practice. Moreover, supplying plants with Ni at the recommended doses was revealed to be safe for in natura human consumption of soybean grains; however, more studies are required to establish the appropriate safety limit standards for soybean-based food products.