ReviewSetting good practices to assess the efficiency of iron fertilizers
Highlights
► Iron deficiency chlorosis is a major constraint in fruit crops grown in high pH soils. ► Iron fertilizers must be assessed for efficiency using sound practices. ► This review outlines adequate procedures and discusses common errors. ► The review includes real examples of practical studies.
Introduction
The most prevalent nutritional disorder in fruit tree crops growing in calcareous soils is Fe deficiency (see reviews in [1], [2]). The main symptom of Fe deficiency in plants is leaf yellowing, which is usually called leaf chlorosis; this occurs both in growth chamber and field-grown plants (e.g., in sugar beet and peach trees, respectively; Fig. 1). In field conditions, chlorosis in the orchards is often heterogeneous, with individual trees affected to different extents. Images of fruit tree field orchards affected by Fe-chlorosis are shown in Fig. 2 (A: peach tree orchard; B: pear tree orchard). Iron-deficient, chlorotic tree orchards are usually fertilized with Fe every year, because chlorosis causes decreases in tree vegetative growth, a shortening of the orchard lifespan as well as losses in fruit yield [2] and changes in fruit quality [3], [4]. The diagnosis of Fe deficiency, conversely to what happens with other nutrient disorders, cannot be adequately assessed using leaf elemental composition, because Fe-deficient field-grown leaves often have Fe concentrations as high as that of Fe-sufficient ones (the “chlorosis paradox”; [5]). This is possibly associated to an accumulation of Fe in or near the vascular system [6], [7]. Therefore, leaf chlorophyll (Chl) concentrations (generally monitored using a hand-held device) are used most of the times to assess the Fe nutritional status.
Iron fertilization in trees can be carried out in several ways, including the addition to the soil or irrigation water of Fe-containing compounds [8], as well as providing Fe directly to the plant by spraying tree canopies or injecting trunks or branches with Fe-compounds in solid or liquid forms [1]. There is a very large number (several hundred) of Fe-containing fertilizers, many of them containing the same active principles and others consisting of a mixture of Fe-compounds [8], [9]. These Fe-fertilizers often have different degrees of effectiveness due to many different factors [1], [8], [10]. Therefore, it is necessary to compare the efficiencies of Fe-fertilizers, and many studies are published every year assessing and comparing Fe-containing products (e.g., see [11], [12]). In particular, any new Fe-fertilizer must be assessed using this type of studies. The recovery after Fe-fertilization is generally monitored using the leaf Chl concentration, for the reasons explained above, although leaf Fe concentrations are still sometimes used. However, divergences in specific methodological details could be found in the literature, and this could make difficult the comparison of results obtained in different experiments.
This paper proposes good practices to assess the efficiency of Fe-fertilizers, by examining a number of factors that are crucial in this type of assessment studies. The rationale for most of them is provided by the current knowledge on plant physiology and biochemistry [13], which is not always taken into account in Fe-fertilizer efficiency agronomical studies.
Section snippets
Design of iron fertilization experiments
Iron fertilizers should be first tested for stability of the Fe-containing active agent in the conditions prevailing in the media to be used (e.g., spray solutions, nutrient solutions, soils, etc.) [14]. Many factors (light, pH, etc.) can affect its stability and availability for plants. Once the possible usefulness of a Fe-fertilizer is predicted, controlled conditions or field experiments must be designed for assessing efficiency.
Assessment of chlorosis recovery upon iron fertilization
The most appropriate way to assess the efficiency of Fe-fertilizers is to follow the evolution of leaf Chl after Fe-fertilization. This has been carried out traditionally by using visual scale ratings [21], [22], [23]. In the last two decades, however, hand-held apparatus, such as the SPAD (Soil and Plant Analyzer Development) from Minolta and others, have become popular for the diagnosis of plant nutrient status (of Fe and other elements; [24], [25], [26], [27], [28]). These devices measure
Analysis of the plant responses upon iron fertilization
Besides assessing the effectiveness of Fe-fertilizers in chlorosis recovery, the evaluation of their effects on crop yield and quality will be also desirable. However, the normalization of the tree Fe-status via corrective Fe-fertilization is likely to have major fruit quality effects only in the following growth season, and not in the season when corrective fertilization is carried out. The most likely explanation for this fact is that the recovery of the tree physiological processes after
Concluding remarks
When assessing the effectiveness of Fe-fertilizers, it is necessary to use sound practices based in the state-of-the art knowledge on the physiology and biochemistry of Fe deficiency [13]. This includes using appropriate choosing of experimental orchards and individuals (taking special care in assuring the presence of Fe deficiency and the homogeneity of chlorosis) as well as an adequate methodology to measure leaf Chl concentrations. It should be always taken into account that the
Acknowledgements
Study supported by the Spanish Ministry of Science and Innovation (MICINN; projects AGL2007-61948 and AGL2009-09018, co-financed with FEDER), the European Commission (Thematic Priority 5–Food Quality and Safety, 6th Framework RTD Programme, Contract no. FP6-FOOD–CT-2006-016279), the trilateral Project Hot Iron (ERA-NET Plant Genome Research KKBE; MICINN EUI2008-03618), and the Aragón Government (group A03). HEJ and JCM were supported by a FPI-MICINN grant and a JAE-CSIC postdoctoral contract,
References (51)
- et al.
Effects of moderate and severe iron deficiency chlorosis on (Pyrus communis L.) and peach (Prunus persica (L.) Batsch)
Environ. Exp. Bot.
(2011) - et al.
Foliar fertilization of peach (Prunus persica (L.) Batsch) with different iron formulations: effects on re-greening, iron concentration and mineral composition in treated and untreated leaf surfaces
Sci. Hortic.
(2008) - et al.
Selection of olive varieties for tolerance to iron chlorosis
J. Plant Physiol.
(2003) - et al.
Effects of branch solid Fe sulphate implants on xylem sap composition in field-grown peach and pear: changes in Fe, organic anions and pH
J. Plant Physiol.
(2003) - et al.
Technologies for the diagnosis and remediation of Fe deficiency
Soil Sci. Plant Nutr.
(2004) - et al.
Iron nutrition of fruit tree crops
- et al.
Iron deficiency, fruit yield and quality
- et al.
Iron chlorosis paradox in fruit trees
J. Plant Nutr.
(1998) - et al.
Elemental 2-D mapping and changes in leaf iron and chlorophyll in response to iron re-supply in iron deficient GF 677 peach-almond hybrid
Plant Soil
(2009) - et al.
Micro-analytical, physiological and molecular aspects of Fe acquisition in leaves of Fe-deficient tomato plants re-supplied with natural Fe complexes in nutrient solution
Plant Soil
(2009)
Synthetic iron chelates to correct iron deficiency in plants
Analytical technologies to study the biological and environmental implications of iron-fertilisation using synthetic ferric chelates: the case of Fe(III)-EDDHA - a review
J. Hortic. Sci. Biotech.
Foliar iron-fertilisation of fruit trees: present knowledge and future perspectives - a review
J. Hortic. Sci. Biotech.
Effectiveness of N, N′-bis(2-hydroxy-5-methylbenzyl) ethylenediamine-N, N′-diacetic acid (HJB) to supply iron to dicot plants
Plant Soil
Comparison of iron chelates and complexes supplied as foliar sprays and in nutrient solution to correct iron chlorosis of soybean
J. Plant Nutr. Soil Sci.
Chemical evaluation of HBED/Fe3+ and the novel HJB/Fe3+ chelates as fertilizers to alleviate iron chlorosis
J. Agric. Food Chem.
Growth and iron-manganese relationships in dry bean as affected by foliar and soil applications of iron manganese in a calcareous soil
J. Plant Nutr.
Iron deficiency-induced changes in the photosynthetic pigment composition of field-grown pear (Pyrus communis L) leaves
Plant Cell Environ.
Increasing iron availability to crops: fertilizers, organo fertilizers, and biological approaches
Soil Sci. Plant Nutr.
Immobilized EDDHA and DFOB as iron carriers to cucumber plants
J. Plant Nutr.
Response of cucumber plants to low doses of different synthetic iron chelates in hydroponics
J. Plant Nutr.
Characterization of the tolerance to iron chlorosis in different peach rootstocks grown in nutrient solution
Plant Soil
Diagnosis and correction of iron chlorosis in fruit trees: a review
J. Food Agric. Environ.
Diagnóstico visual de la clorosis férrica
ITEA-Inf. Tec. Econ. Ag.
Cited by (38)
A framework for good practices to assess abiotic mineral resource depletion in Life Cycle Assessment
2021, Journal of Cleaner ProductionNeodymium recovery from scrap magnet using ammonium persulfate
2019, HydrometallurgyCitation Excerpt :Thus, the obtained by-products in the solid state show the absence of toxic or harmful salts. Furthermore, the amounts of metals could be eventually implemented as iron precursors for technological fields based on pigments and fertilizers (El-jendoubi et al., 2011; Tolinski, 2015; Xue et al., 2017). The recovery of neodymium from scrap Nd-Fe-B magnets was developed using a novel eco-friendly alternative with ammonium persulfate.
Role of Carbonates in the Physical Stabilization of Soil Organic Matter in Agricultural Mediterranean Soils
2018, Soil Management and Climate Change: Effects on Organic Carbon, Nitrogen Dynamics, and Greenhouse Gas EmissionsResponse of soybean plants to the application of synthetic and biodegradable Fe chelates and Fe complexes
2017, Plant Physiology and BiochemistryCitation Excerpt :The reciprocal ratio of 690 and 735 nm steady-state Chl a fluorescence correlates to Chl content (linear correlation) (Hák et al., 1990). SPAD index is related with the chlorophyll content in leaves and is normally used to assess the efficacy of Fe fertilizers (El-Jendoubi et al., 2011). The C –Fe treatment caused a strong decrease in the PSII activity but all recovery treatments regenerated it.
Role of Carbonates in the Physical Stabilization of Soil Organic Matter in Agricultural Mediterranean Soils
2017, Soil Management and Climate Change: Effects on Organic Carbon, Nitrogen Dynamics, and Greenhouse Gas Emissions
- 1
Current address: Citrus Center, Texas A&M University-Kingsville, 312 N International Blvd., Weslaco, TX 78596, USA.