RE-GREENING OF LYCHEE (LITCHI CHINENSISSONN.) LEAVES WITH FOLIAR APPLICATIONS OF IRON SULFATE AND WEAK ACIDS

Abstract

2 Lychee (Litchi chinensis Sonn. cv. 'Mauritius') trees growing in calcareous soils are prone to iron (Fe) deficiency, typically prevented by soil application of chelated Fe, which is very expensive compared to iron sulfate (FeSO 4 ). Therefore, the effects of foliar applications of weak acids (ascorbic or dilute sulfuric acid), weak acids plus FeSO 4 , or a soil drench of chelated iron (Fe-EDDHA) on leaf chlorophyll index, leaf ferrous iron (Fe 2+ ) and total Fe concentrations, leaf gas exchange and plant dry weight were determined for 2-year-old lychee trees growing in calcareous soil in containers. Treatments were: foliar applications of ascorbic acid in deionized (DI) water plus surfactant, sulfuric acid in DI water plus surfactant, ascorbic acid in DI water plus FeSO 4 plus surfactant, sulfuric acid in DI water plus FeSO 4 plus surfactant, FeSO 4 in DI water plus surfactant, FeSO 4 in DI water with no surfactant, FeSO 4 in well water plus surfactant, sulfuric acid plus FeSO 4 in well water plus surfactant, surfactant in DI water. An additional treatment was chelated iron (Fe-EDDHA) applied to the soil. The organosilicone compound Freeway R was used as the surfactant. Well water was used instead of DI water in two treatments because fertilizers are often mixed with water from a well that typically has a pH much higher than that of DI water. Foliar treatments were applied at 4-week intervals for 24 weeks and chelated iron was applied to the soil at the time of first foliar treatments and 8 and 16 weeks later. There was generally no difference in leaf chlorophyll index among plants receiving chelated iron as a soil drench or foliar treatments containing FeSO 4 plus surfactant with or without organic acid. Foliar applications of acid with no FeSO 4 resulted in a lower leaf chlorophyll index than soil-applied Fe-EDDHA or any of the foliar treatments containing FeSO 4 plus surfactant. Leaf total Fe and Fe 2+ concentrations were generally highest for plants in the soil-applied Fe-EDDHA treatment and all foliar application treatments containing FeSO 4 plus surfactant. Net CO 2 assimilation (A net ), stomatal conductance (g s ), transpiration (Tr) and leaf, stem, root and total plant dry weights were highest for plants treated with soil-applied Fe-EDDHA or foliarly applied FeSO 4 with no surfactant. Further studies indicated that the surfactant Freeway R inhibits leaf gas exchange and plant growth. The results indicate that foliar applications of FeSO 4 are almost as effective as soil applications of chelated Fe for eliminating or preventing Fe deficiency symptoms of lychee trees growing in calcareous soil. While the addition of a surfactant to the foliar spray mixture appears to be necessary for preventing Fe deficiency, care must be taken when selecting a surfactant for foliar applications of FeSO 4 to be sure that there are no negative effects on leaf gas exchange and plant growth.

Comparison of foliar and soil applications for correction of iron deficiency in peanut (Arachis hypogaea L.)

“…In lychee leaves, foliar application of FeSO 4 either alone or in combination with acid and surfactant as well as with soil applied Fe-EDDHA leads to high leaf Fe 2+ concentration. Total Fe concentration was higher than 110mg/kg DW in lychee plants with foliar application of FeSO 4 (Schaffer et al, 2011).…”

“…All plants in foliar application of FeSO 4 were greener (Schaffer et al, 2011). Likewise, foliar application of FeSO 4 to pear trees improved the leaf chlorophyll content either due to the better activity of enzyme ferric chelate reductase after oxidation of foliarly applied Fe 3+ to Fe 2+ or the direct uptake of Fe 2+ (Álvarez-Fernández et al, 2004).…”

“…Combination of ferrous sulphate or other solutions with additional products may result in sustaining the added Fe source in accessible form for a long period of time (Kumawat et al, 2006). Though, there are many disadvantages, still foliar sprays are commonly used to rectify the problem of Fe deficiency in plants (Roosta & Mohsenian, 2012;Schaffer et al, 2011;Tagliavini et al, 2000). The foliar applications are used for treatment of abiotic stress in plants as they are cost effective (Noreen et al, 2018).…”

Synthesis of iron chelates for remediation of iron deficiency in an alkaline and calcareous soil

“…Natural amino acids are very small molecules that chelate with micronutrients are quickly absorbed, translocated and metabolized by plants. The merits of amino acid chelates are that the amino acid ligand frame and defend the micronutrients from adverse relations usually take place in soil solution, in the presence of soil or on leaf surfaces (Schaffer et al, 2011). Various examinations have demonstrated that the likely limit of iron compounds to address iron lacks in plants developed in alkaline and calcareous soils relies upon two fundamental features (Chaney and Bell, 1987) viz.…”

Synthesis of organic iron chelates and evaluation of their efficiency in improving the growth and yield of Blackgram

“…These amino acid chelated micronutrients are exactly used for foliar spraying and soil application. Schaffer et al (2011) [16] examined that the natural amino acids are very small molecules they chelated with micronutrients therefore they are quickly absorbed, translocated and metabolized by plants. The merits of amino acid chelates are that the amino acid ligand frame and defend the micronutrients from adverse relations usually those take place in soil solution, in the presence of soil or on leaf surfaces.…”