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Reactivity and effectiveness of traditional and novel ligands for multi-micronutrient fertilization in a calcareous soil.

López-Rayo S, Nadal P, Lucena JJ - Front Plant Sci (2015)

Bottom Line: The application of traditional or novel ligands in formulations did not result in sufficient plant Mn concentrations, which was related to the low Mn stability observed for all formulations under moderate oxidation conditions.The results highlight the need to consider the effect of metals and ligands interactions in multi-nutrient fertilization and the potential of S,S-EDDS to be used for Zn fertilization.Furthermore, it is necessary to explore new sources of Mn fertilization for calcareous soils that have greater stability and efficiency, or instead to use foliar fertilization.

View Article: PubMed Central - PubMed

Affiliation: Department of Agricultural and Food Chemistry, Faculty of Science, Autonomous University of Madrid Madrid, Spain.

ABSTRACT
This study compares the effectiveness of multi-micronutrient formulations containing iron (Fe), manganese (Mn), and zinc (Zn) with traditional (EDTA, DTPA, HEEDTA, and EDDHAm) or novel chelates (o,p-EDDHA, S,S-EDDS, and IDHA) and natural complexing agents (gluconate and lignosulfonate). The stability and reactivity of the formulations were studied on batch experiments with calcareous soil and by speciation modeling. Formulations containing traditional ligands maintained higher Mn but lower Zn concentration in soil solution than the novel ligands. The gluconate and lignosulfonate maintained low concentrations of both Mn and Zn in soil solution. Selected formulations were applied into calcareous soil and their efficacy was evaluated in a pot experiment with soybean. The formulation containing DTPA led to the highest Zn concentration in plants, as well as the formulation containing S,S-EDDS in the short-term, which correlated with its biodegradability. The application of traditional or novel ligands in formulations did not result in sufficient plant Mn concentrations, which was related to the low Mn stability observed for all formulations under moderate oxidation conditions. The results highlight the need to consider the effect of metals and ligands interactions in multi-nutrient fertilization and the potential of S,S-EDDS to be used for Zn fertilization. Furthermore, it is necessary to explore new sources of Mn fertilization for calcareous soils that have greater stability and efficiency, or instead to use foliar fertilization.

No MeSH data available.


Proposed mechanisms of metal chelates interaction in soils and in nutrient solution, and plant uptake. See explanation in the text.
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Figure 4: Proposed mechanisms of metal chelates interaction in soils and in nutrient solution, and plant uptake. See explanation in the text.

Mentions: According to the free ion activity model (FIAM) and the biotic ligand model (BLM), cells in general take up metals such as Zn and Mn from the soil solution only if they are present as free ions and not in the form of metal–organic complexes (Hassler et al., 2004). The Fe uptake in all higher plants except for graminaceous (Strategy-I plants) is performed, in contrast, by the Fe chelate reductase enzyme (FCR); which activity requires the presence of Fe in soil solution as a Fe chelate for further reduction and uptake on the root surface (Römheld and Marschner, 1986). Thus, different biochemical processes are involved in the mechanisms for micronutrient uptake, which also differs when soil or hydroponic solutions are considered. In Figure 4, a schematic explanation of these processes is shown. When the chelate mixes are added to the system, chemical reactions limit their permanence in the nutrient/soil solution. In all cases, competition between the chelating agents and metals occurs. While metal substitution is slow in nutrient solution, the process is faster in soil (Figure 1). The addition of individual chelates with a high affinity ligand:metal can avoid competition between metals. In soil conditions, surface processes may decrease the presence of chelates in the soil solution, even if high affinity chelates are chosen. As mentioned above, Fe chelates are directly reduced by dicot plant roots due to the action of FCR, therefore, Fe uptake is in both cases (hydroponics and soil) favored by the more stable chelates in the corresponding conditions. It is also important to consider the reoxidation of tFe, degradation of chelates and complexation of Fe(II) (Lucena, 2006). The use of chelating agents forming stable chelates with Fe(II) such as EDTA also reduce Fe uptake due to ligand–root competition for the metal. The ligand–root competition for the metal is the key factor in understanding the different behaviors between hydroponics and soil systems for Zn and Mn. The uptake of the Zn2+ and Mn2+ mentioned in the FIAM and BLM models requires the dissociation of the metal chelates at the root surface (Degryse et al., 2006; Wang et al., 2009) which increase the concentration of free ligand and then decrease the free ion activity:


Reactivity and effectiveness of traditional and novel ligands for multi-micronutrient fertilization in a calcareous soil.

López-Rayo S, Nadal P, Lucena JJ - Front Plant Sci (2015)

Proposed mechanisms of metal chelates interaction in soils and in nutrient solution, and plant uptake. See explanation in the text.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585085&req=5

Figure 4: Proposed mechanisms of metal chelates interaction in soils and in nutrient solution, and plant uptake. See explanation in the text.
Mentions: According to the free ion activity model (FIAM) and the biotic ligand model (BLM), cells in general take up metals such as Zn and Mn from the soil solution only if they are present as free ions and not in the form of metal–organic complexes (Hassler et al., 2004). The Fe uptake in all higher plants except for graminaceous (Strategy-I plants) is performed, in contrast, by the Fe chelate reductase enzyme (FCR); which activity requires the presence of Fe in soil solution as a Fe chelate for further reduction and uptake on the root surface (Römheld and Marschner, 1986). Thus, different biochemical processes are involved in the mechanisms for micronutrient uptake, which also differs when soil or hydroponic solutions are considered. In Figure 4, a schematic explanation of these processes is shown. When the chelate mixes are added to the system, chemical reactions limit their permanence in the nutrient/soil solution. In all cases, competition between the chelating agents and metals occurs. While metal substitution is slow in nutrient solution, the process is faster in soil (Figure 1). The addition of individual chelates with a high affinity ligand:metal can avoid competition between metals. In soil conditions, surface processes may decrease the presence of chelates in the soil solution, even if high affinity chelates are chosen. As mentioned above, Fe chelates are directly reduced by dicot plant roots due to the action of FCR, therefore, Fe uptake is in both cases (hydroponics and soil) favored by the more stable chelates in the corresponding conditions. It is also important to consider the reoxidation of tFe, degradation of chelates and complexation of Fe(II) (Lucena, 2006). The use of chelating agents forming stable chelates with Fe(II) such as EDTA also reduce Fe uptake due to ligand–root competition for the metal. The ligand–root competition for the metal is the key factor in understanding the different behaviors between hydroponics and soil systems for Zn and Mn. The uptake of the Zn2+ and Mn2+ mentioned in the FIAM and BLM models requires the dissociation of the metal chelates at the root surface (Degryse et al., 2006; Wang et al., 2009) which increase the concentration of free ligand and then decrease the free ion activity:

Bottom Line: The application of traditional or novel ligands in formulations did not result in sufficient plant Mn concentrations, which was related to the low Mn stability observed for all formulations under moderate oxidation conditions.The results highlight the need to consider the effect of metals and ligands interactions in multi-nutrient fertilization and the potential of S,S-EDDS to be used for Zn fertilization.Furthermore, it is necessary to explore new sources of Mn fertilization for calcareous soils that have greater stability and efficiency, or instead to use foliar fertilization.

View Article: PubMed Central - PubMed

Affiliation: Department of Agricultural and Food Chemistry, Faculty of Science, Autonomous University of Madrid Madrid, Spain.

ABSTRACT
This study compares the effectiveness of multi-micronutrient formulations containing iron (Fe), manganese (Mn), and zinc (Zn) with traditional (EDTA, DTPA, HEEDTA, and EDDHAm) or novel chelates (o,p-EDDHA, S,S-EDDS, and IDHA) and natural complexing agents (gluconate and lignosulfonate). The stability and reactivity of the formulations were studied on batch experiments with calcareous soil and by speciation modeling. Formulations containing traditional ligands maintained higher Mn but lower Zn concentration in soil solution than the novel ligands. The gluconate and lignosulfonate maintained low concentrations of both Mn and Zn in soil solution. Selected formulations were applied into calcareous soil and their efficacy was evaluated in a pot experiment with soybean. The formulation containing DTPA led to the highest Zn concentration in plants, as well as the formulation containing S,S-EDDS in the short-term, which correlated with its biodegradability. The application of traditional or novel ligands in formulations did not result in sufficient plant Mn concentrations, which was related to the low Mn stability observed for all formulations under moderate oxidation conditions. The results highlight the need to consider the effect of metals and ligands interactions in multi-nutrient fertilization and the potential of S,S-EDDS to be used for Zn fertilization. Furthermore, it is necessary to explore new sources of Mn fertilization for calcareous soils that have greater stability and efficiency, or instead to use foliar fertilization.

No MeSH data available.