Nano fertilization is a precision approach to sustain economically viable
and environmentally compatible crop production. The objective of our
study was to evaluate the effects of different sources and rates of iron (Fe)
fertilization as an essential micronutrient on the growth, physiological
processes, and yield of greenhouse-grown tomatoes (Solanum lycopersicum
cv. Bigdena F1). A factorial experiment in randomized complete block
design with four replications was conducted using three sources
(Conventional, FeCl3.6H2O [Conv-Fe]; Chelated with 6% Fe [Che-Fe]; and
Nano Fe2O3 [Nano-Fe], alpha, 99%, 30–50 nm) and rates of Fe (0, 50, and
100 mg/kg soil) during 2015 and 2016 growing seasons. Averaged across
Fe rates, the Nano-Fe significantly increased plant height, leaf number and
area, shoot and root fresh and dry weights, and Soil Plant Analysis
Development (SPAD) readings. Nano-Fe at 100mg/kg significantly
increased plant height, leaf number and area, fresh and dry weights of
shoot and roots, gas exchange parameters i.e., photosynthesis (Pn), stomatal
conductance (gs) and transpiration (E) rates, total yield, and yield components
of tomatoes in comparison to the other rates. While there were
no significant simple and interactions of Fe on plant physiological processes,
the Nano-Fe had the highest Pn with an associated decrease in E
and an increase in gs. Nano-Fe, when applied at 100mg/kg, produced the
highest fruit diameter, fruit numbers/plant, total fruit weight/plant, mean
fruit weight/plant, total fruit numbers/ha, and total fruit weight/ha, followed
by Nano-Fe at 50mg kg as compared with other Fe sources and
rates. In conclusion, Nano-Fe fertilization is more effective than Conv-Fe
and Che-Fe fertilizations across growing seasons to improve growth characteristics
and metabolic processes of tomato plants, as Fe plays an
important role in photosynthates accumulation and translocation. Nano-Fe
increased tomato yield by 11% compared to Conv-Fe and Che-Fe fertilizers
and will greatly improve farmers’ profitability.