Foliar Application of Humic Acid with Fe Supplement Improved Rice, Soybean, and Lettuce Iron Fortification

Abstract

Iron (Fe) deficiency in humans, particularly in pregnant women and children, is caused by inadequate dietary Fe intake and is a global nutritional problem. Foliar fertilization is a cost-effective agronomic approach to increase Fe bioavailability in the human diet. We evaluated the effects of different Fe formulations (Fe-citrate, Fe-EDTA, FePO4, nano-Fe oxide, and humic acid (HA) with and without Fe) on growth, yield, and Fe accumulation in the edible parts of rice, soybean, and lettuce crops. Rice and soybean received multiple sprays at different growth stages, i.e., tillering, anthesis, and grain filling in rice as well as flowering and pod filling in soybean, while lettuce received a single foliar spray. In rice and soybean, the seed Fe accumulation increased proportionally as the number of foliar sprays increased; however, the grain yield did not show this relationship. Among Fe treatments, HA+Fe was identified as the best treatment in terms of improving overall plant growth, yield, and Fe accumulation in the edible parts of all three crops. We found a significant positive correlation between the shoot/stover Fe content and the grain Fe content, but HA+Fe showed an opposite trend, i.e., minimal Fe retention in shoots/stovers and maximal increases in the seed Fe contents in both crops, suggesting better Fe mobilization efficiency from shoots to developing seeds. We strongly recommend that HA with Fe can be used as a foliar Fe fertilizer to improve the growth, yield, and Fe status in different crops.

Effects of Citric Acid and Humic-like Substances on Yield, Enzyme Activities, and Expression of Genes Involved in Iron Uptake in Tomato Plants

“…Previous studies have found that the application of CA [39] and leonardite-derived compounds [21] improved the growth and yield of tomatoes grown in calcareous soil, probably via plant stimulation [40,41] and punctually by increasing photosynthetic parameters [42]. Similarly, the use of humic-Fe materials in soybean may be a suitable strategy for the management of Fe nutrition in calcareous soil [43], consequently leading to a reduction in Fe deficiency and an improvement in plant growth, development, and productivity.…”

“…Similarly, the use of humic-Fe materials in soybean may be a suitable strategy for the management of Fe nutrition in calcareous soil [43], consequently leading to a reduction in Fe deficiency and an improvement in plant growth, development, and productivity. This is because the addition of Fe together with humic complexes act as "organic chelators" that boost plant growth [41]. CA and leonardite-derived complexes exhibit various levels of complexation with Fe, promoting plant growth by inducing a physiological response [44].…”

“…In addition, CA can reduce abiotic stress resulting from phosphorus deficiency in plants grown in calcareous soils [45][46][47]. Likewise, it has been described that the use of humic substances in calcareous soils promotes nutrient bioavailability by generating soluble complexes with minerals [23,48] and increasing nutrient uptake [40,41], and that their combination with chelate Fe (Fe-EDDHA) can increase the yield and nutrient content of plants [49].…”

“…This may also have been due to feedback control mechanisms and the concentration of NO 3 − in the medium [55]. In contrast, the increase in the activity of this enzyme in leaf tissue (at 49 DAT) could be a consequence of the biostimulation (promoting a redistribution of nutrients) induced by HLS and CA [40,41]. In addition, CA is associated with the energy metabolism of the plant [44]; thus, H + -ATPase activity would be necessary to generate gradients in the different cellular compartments of the leaf.…”

Novel bio-inorganic iron chelate from coffee by-products for agronomic purpose

“…longifolia one of the most popular varieties (Giordano et al, 2019) and can be an optimal target for Fe bioforti cation (Mou 2009). The bioforti cation of lettuce with Fe would also provide an urgent and easy way to alleviate human Fe de ciency (Sharma et al, 2023).…”