Nickel (Ni) is a trace element beneficial for plant growth
and
development and could improve crop yield by stimulating urea decomposition
and nitrogen-fixing enzyme activity. A full life cycle study was conducted
to compare the long-term effects of soil-applied NiO nanoparticles
(n-NiO), NiO bulk (b-NiO), and NiSO4 at 10–200 mg
kg–1 on plant growth and nutritional content of
soybean. n-NiO at 50 mg kg–1 significantly promoted
the seed yield by 39%. Only 50 mg kg–1 n-NiO promoted
total fatty acid content and starch content by 28 and 19%, respectively.
The increased yield and nutrition could be attributed to the regulatory
effects of n-NiO, including photosynthesis, mineral homeostasis, phytohormone,
and nitrogen metabolism. Furthermore, n-NiO maintained a Ni2+ supply for more extended periods than NiSO4, reducing
potential phytotoxicity concerns. Single-particle inductively coupled
plasma mass spectrometry (sp-ICP-MS) for the first time confirmed
that the majority of the Ni in seeds is in ionic form, with only 28–34%
as n-NiO. These findings deepen our understanding of the potential
of nanoscale and non-nanoscale Ni to accumulate and translocate in
soybean, as well as the long-term fate of these materials in agricultural
soils as a strategy for nanoenabled agriculture.