Table 3 The observed positive effects of iron/iron oxide NPs on plants

Arachis hypogaea

γ-Fe₂O₃, 20 nm

2, 10, 50, 250, 1000 mg kg⁻¹ of soil

Fe₂O₃ NPs were applied into soil and compared with a chelated-Fe fertilizer

Fe₂O₃ NPs increased root length, plant height, biomass, and SPAD values of peanut plants. Fe₂O₃ NPs adsorbed onto sandy soil and improved the availability of Fe to the plants. Fe₂O₃ NPs can replace traditional Fe fertilizers in the cultivation of peanut plants

[77]

Vigna radiata

FeNPs 2–6 nm

+0.2% gum, +0.4% gum

1 mM Fe²⁺ions

Natural biopolymer gum kondagogu as reducing and capping agent was used

The radical length and biomass was increased in seeds exposed to Fe NPs in comparison to Fe²⁺ ions. The α-amylase activity was increased in the seeds exposed to Fe NPs

[78]

Spinacea oleracea

α-Fe₂O₃ 50 nm

100, 150, 200 mg kg⁻¹ of soil

Experiments were performed in a solid hydroponic medium consisting of sawdust and coco peat and adequate amounts of water

Positive effects on spinach plant due to uptake of Fe₂O₃ nanoparticles such as increase in stem and root lengths, biomass production and magnetic properties were observed

[19]

Lactuca sativa

Core–shell NPs Fe/Fe₃O₄ 13/9 nm

10, 20 mg L⁻¹

15-days treatment of hydroponically grown lettuce

The nano-Fe/Fe₃O₄ at 10 and 20 mg L⁻¹ and FeSO₄·7H₂O at 10 mg L⁻¹ did not affect lettuce growth and chlorophyll content

[71]

Vigna unguiculata

<100 nm

25, 500 mg L⁻¹

The elements were applied 56 and 72 days after sowing over the leaves, and data was collected after day 85

Iron had significant effect on yield, leaf Fe content, stem Mg content, plasma membrane stability, and chlorophyll content, probably as a result of more efficient photosynthesis

[79]

Glycine max

γ-Fe₂O₃ (IONPS) and citrate coated IONPs 6 nm

500, 1000 mg L⁻¹

Plant physiological performance was assessed after foliar and soil IONPs fertilization

IONPs produced a significant positive effect on root elongation. IONPs-Cit significantly enhanced photosynthetic parameters when sprayed foliarly. More pronounced positive effects of IONPs via foliar application than by soil treatment was observed

[20]

Glycine max

Superparamagnetic iron oxide NPs (SPIONs) 8–12 nm

200, 400, 1000 and 2000 mg L⁻¹

Seed germination of soybean exposed to SPIONs was investigated

SPIONs, which were entered and translocated in the soybean, increased chlorophyll levels, with no trace of toxicity

[80]