A Critical Review of Methodologies for Evaluating Iron Fertilizers Based on Iron Reduction and Uptake by Strategy I Plants.

Under iron (Fe)-limited conditions, plants have developed strategies for acquiring this essential micronutrient. Several Fe sources have been studied as potential fertilizers, with Fe synthetic chelates being the most used to prevent and correct Fe chlorosis in crops. The determination of the activity of the Fe chelate reductase (FCR) enzyme has long been described in the literature to understand the efficiency of Strategy I plants in acquiring Fe from fertilizers under deficient conditions. Other experiments have focused on the translocation of Fe to the plant to define the effectiveness of Fe fertilizers. Yet, both assays are relevant in knowing the capacity of a novel Fe source and other compounds alleviating Fe chlorosis in Strategy I plants. This work reviews the methodologies that are used in FCR assays to evaluate novel Fe fertilizers, including the factors modulating the results obtained for FCR assay activity, such as the Fe substrate, the Fe level during the growing period and during the FCR assay, the pH, the choice of an in vivo or in vitro method, and the plant species. A discussion of the benefits of the concurrence of FCR and Fe uptake assays is then presented alongside a proposed methodology for assessing the effectiveness of Fe fertilizers, emphasizing the importance of understanding chemical and physiological plant interactions. This methodology unifies key factors that modify FCR activity and combines these with the use of the 57Fe tracer to enhance our comprehension of the efficacy of Fe-based fertilizers' effectiveness in alleviating Fe chlorosis. This comprehensive approach not only contributes to the fundamental understanding of Fe-deficient Strategy I plants but also establishes a robust method for determining the efficiency of novel sources for correcting Fe deficiency in plants.

Response of soybean plants to the application of synthetic and biodegradable Fe chelates and Fe complexes.

The growing concern over the environmental risk of synthetic chelate application promotes the search for alternatives in Fe fertilization, such as biodegradable chelating agents and natural complexing agents. In this work, plant responses to the application of several Fe treatments (chelates and complexes) was analyzed to study their potential use in Fe fertilization under calcareous conditions. Thus, the root ferric chelate reductase (FCR) activity of soybean (Glycine max cv. Klaxon) plants was determined, and the effectiveness of the Fe chelates and complexes assessed in a pot experiment, by SPAD and fluorescence induction measurements, and the determination of Fe distribution in plant and soil. Additionally, 57Fe Mössbauer spectroscopy was conducted to identify the Fe forms present in the soybean roots. The highest FCR activity was observed for the chelates EDDS/Fe3+ and IDHA/Fe3+; while no activity was observed when using complexes as Fe substrates. In contrast to the FCR data, the pot experiment confirmed that the o,oEDDHA/Fe3+ is the most effective treatment, and the complexes LS/Fe3+ and GA/Fe3+ are able to alleviate Fe chlorosis, also indicated by SPAD data and the maximal quantum efficiency of photosystem II reaction centers as vitality parameters, and the enhanced plant uptake of Fe from natural sources.

The use of spent mushroom compost to enhance the ability of Atriplex halimus to phytoremediate contaminated mine soils.

The mushroom cultivation industry produces a huge amount of spent mushroom compost (SMC), a wide world agricultural organic waste which causes serious environmental problems. However, this cheap organic waste could be useful in the remediation of contaminated soils. The aim of this work was to assess the potential of SMC in combination with the native shrub Atriplex halimus, to phytoremediate two mine soils contaminated with Cd, Pb and Cu. Firstly, to minimize metal availability in the soil, the optimal doses of SMC were determined. Secondly, a phytoremediation assay in greenhouse conditions was carried out to test the effects of A. halimus in combination with SMC at different doses. The results showed the ability of SMC to reduce soil acidity, the mobility of the metals and the enhancement of A. halimus growth. SMC promoted metal immobilization in the root of A. halimus and decreased the translocation from the roots to the shoots. The combination of SMC amendment and A. halimus produced phytostabilization of the metals in the mine soils assayed. In conclusion, SMC represents an adequate organic solid waste which in combination with A. halimus can reduce the adverse impact caused by the high mobility of metals in acid mine soils.

Wheat (Triticum aestivum L.) response to a zinc fertilizer applied as zinc lignosulfonate adhered to a NPK fertilizer.

The efficacy as Zn fertilizers for wheat of zinc lignosulfonate (ZnLS) products adhered to NPK was evaluated by three plant experimental designs. In the first and second assays, wheat plants were grown under controlled conditions with perlite and a calcareous soil as substrate, respectively. Shoot dry matter and Zn concentration showed that NPK + ZnLS was a better Zn source for wheat than NPK + ZnSO(4) under our experimental conditions. A third experiment was conducted under field conditions on a calcareous soil with a low Zn level. Wheat samples were taken at five growth stages of the crop. Although at early stages NPK + ZnLS was the most efficient source of Zn, at harvest no significant differences among treatments were found. Despite that, NPK + ZnLS showed evidence of being a useful Zn source for wheat crop under calcareous conditions.

Efficiency of a NPK fertilizer with adhered zinc lignosulfonate as a zinc source for maize (Zea mays L.).

The aim of this work was to evaluate the efficiency of a NPK fertilizer (8:15:15) with a Zn lignosulfonate (ZnLS) adhered as Zn source for maize plants. This product was compared in three experimental designs with the same NPK fertilizer with ZnSO(4) adhered and with no Zn adhered. The first and the second assays were carried out in a growth chamber by using perlite and a calcareous soil as substrate and the third experiment was raised in two calcareous fields. In general, growth chamber experiments showed that plants treated with NPK + ZnLS presented the highest dry weight and Zn concentrations in shoots. Also at field experiments, the Zn concentration in shoots was significantly high in plants treated with NPK + ZnLS. The grain harvested showed that this treatment gave the highest values in one location, but in the other no significant differences were observed. Although further research is required, we can conclude that NPK + ZnLS product could be a suitable source of Zn for maize crops.

Efficiency of a zinc lignosulfonate as Zn source for wheat (Triticum aestivum L.) and corn (Zea mays L.) under hydroponic culture conditions.

The objective of this study was to evaluate the efficiency of a zinc lignosulfonate (ZnLS) as Zn source for wheat and corn plants under hydroponic conditions. The Zn-complexing capacity of three commercial lignosulfonates (byproducts of the paper and pulp industry) was tested, and a LS-NH4, from spruce wood, was selected. Its efficacy as Zn fertilizer for wheat and corn plants was assessed at different pH values (7.0 and 8.0) in comparison with a chelate (ZnEDTA) and an inorganic salt (ZnSO4). For wheat at pH 7.0, it was concluded that the efficacy of the Zn fertilizers followed the sequence Zn-EDTA > Zn-LS approximately ZnSO4 > zero-Zn; and for wheat and corn at pH 8.0, similar results were obtained: Zn-LS > ZnSO4 approximately 0 Zn. These data give evidence that ZnLS could be used as Zn source to the roots of wheat and corn and seems to be more efficient than ZnSO4 to correct Zn deficiency in both plants.