Behavior of zinc from six organic fertilizers applied to a navy bean crop grown in a calcareous soil

A new glance on root-to-shoot in vivo zinc transport and time-dependent physiological effects of ZnSO4 and ZnO nanoparticles on plants

Understanding nanoparticle root uptake and root-to-shoot transport might contribute to the use of nanotechnology in plant nutrition. This study performed time resolved experiments to probe Zn uptake, biotransformation and physiological effects on Phaseolus vulgaris (L.). Plants roots were exposed to ZnO nanoparticles (40 and 300 nm) dispersions and ZnSO_4(aq) (100 and 1000 mg Zn L⁻¹) for 48 h. Near edge X-ray absorption spectroscopy showed that 40 nm ZnO was more easily dissolved by roots than 300 nm ZnO. It also showed that in the leaves Zn was found as a mixture Zn₃(PO₄)₂ and Zn-histidine complex. X-ray fluorescence spectroscopy showed that root-to-shoot Zn-translocation presented a decreasing gradient of concentration and velocity, it seems radial Zn movement occurs simultaneously to the axial xylem transport. Below 100 mg Zn L⁻¹, the lower stem tissue section served as a buffer preventing Zn from reaching the leaves. Conversely, it was not observed for 1000 mg Zn L⁻¹ ZnSO_4(aq). Transcriptional analysis of genes encoding metal carriers indicated higher expression levels of tonoplast-localized transporters, suggesting that the mechanism trend to accumulate Zn in the lower tissues may be associated with an enhanced of Zn compartmentalization in vacuoles. The photosynthetic rate, transpiration, and water conductance were impaired by treatments.

Effects of ZnSO4 and Zn-EDTA broadcast or banded to soil on Zn bioavailability in wheat (Triticum aestivum L.) and Zn fractions in soil

Human Zn deficiency is prevalent in developing countries, and staple grains are commonly bio-fortified to increase their Zn contents. We measured Zn content, distribution, and bioavailability in calcareous soil and in wheat plants (Triticum aestivum L.) in Shaanxi Province, China, when either an organic Zn-ethylenediaminetetraacetate (Zn-EDTA) or an inorganic zinc sulfate heptahydrate (ZnSO₄·7H₂O) Zn source was banded below the seedbed or broadcasted into soil. Compared with ZnSO₄·7H₂O, Zn-EDTA fertilization produced higher Zn concentration and uptake in wheat plants. However, Zn bioavailability in grain remained low, with [phytate]/[Zn] ratio >15 and the resulting estimated dietary total absorbed zinc (TAZ) < 3 mg Zn/d. ZnSO₄ banded into soil had little short-term effect on grain Zn concentration but had a high residual effect and promoted the maintenance of a high concentration of the Zn fraction bound to loose organic matter (LOM-Zn) in rhizosphere soil. Both ZnSO₄ and Zn-EDTA were more efficient if uniformly mixed through the soil than if banded to soil. Both ZnSO₄ and Zn-EDTA had limited effects on Zn bioavailability in wheat plants due to the high rate of Zn fixation in this calcareous soil.

Layered Double Hydroxides: Potential Release-on-Demand Fertilizers for Plant Zinc Nutrition

A novel zinc (Zn) fertilizer concept based on Zn-doped layered double hydroxides (Zn-doped Mg-Fe-LDHs) has been investigated. Zn-doped Mg-Fe-LDHs were synthesized, their chemical composition was analyzed, and their nutrient release was studied in buffered solutions with different pH values. Uptake of Zn by barley (Hordeum vulgare cv. Antonia) was evaluated in short- (8 weeks), medium- (11 weeks), and long-term (28 weeks) experiments in quartz sand and in a calcareous soil enriched with Zn-doped Mg-Fe-LDHs. The Zn release rate of the Zn-doped Mg-Fe-LDHs was described by a first-order kinetics equation showing maximum release at pH 5.2, reaching approximately 45% of the total Zn content. The Zn concentrations in the plants receiving the LDHs were between 2- and 9.5-fold higher than those in plants without Zn addition. A positive effect of the LDHs was also found in soil. This work documents the long-term Zn release capacity of LDHs complying with a release-on-demand behavior and serves as proof-of-concept that Zn-doped Mg-Fe-LDHs can be used as Zn fertilizers.

Understanding the bioavailability and sequestration of different metal cations in the presence of a biodegradable chelant S,S-EDDS in biological fluids and natural waters

Ethylenediamine-N,N'-disuccinic acid is a biodegradable alternative to EDTA, therefore its use for the sequestration of Ca(2+), Sn(2+), Cu(2+), Zn(2+) and Fe(3+) is analyzed. New data on its binding ability towards these cations were obtained with potentiometric, voltammetric and calorimetric measurements at different ionic strengths and at T = 298.15 K. Real multi-component fluids, namely fresh water, urine, sea water, saliva and blood plasma were chosen as case studies to evaluate the sequestering ability of EDDS in comparison with EDTA. Speciation diagrams were drawn in selected conditions, considering all interactions among the "natural" components of the fluid and those studied in this work, EDDS and EDTA (cL = 1 mmol dm(-3)) as sequestering agents and the cited metal cations (cM ∼ 10(-5) mol dm(-3)). The comparison of the sequestering ability of EDDS and EDTA is done using pM and pL0.5. In blood plasma the plasma mobilizing index was adopted. It was found that EDDS is a good alternative to EDTA, which tends to bind Ca(2+) and Mg(2+) more than EDDS. In particular, EDTA cannot be used as a sequestrant for Sn(2+) when cCa > cEDTA. EDDS is more efficient than EDTA at pH < 8, particularly in urine, where carbonate is absent. In sea water, the sequestering ability of EDDS towards Fe(3+) is higher than that of EDTA. In blood plasma, the PMI of EDDS towards Cu(2+) is higher than that of EDTA. Thermodynamic information, in terms of ΔH and ΔS, for the protonation and metal complex formation reactions are reported.

Review: The potential of the common bean (Phaseolus vulgaris) as a vehicle for iron biofortification

Common beans are a staple food and the major source of iron for populations in Eastern Africa and Latin America. Bean iron concentration is high and can be further increased by biofortification. A major constraint to bean iron biofortification is low iron absorption, attributed to inhibitory compounds such as phytic acid (PA) and polyphenol(s) (PP). We have evaluated the usefulness of the common bean as a vehicle for iron biofortification. High iron concentrations and wide genetic variability have enabled plant breeders to develop high iron bean varieties (up to 10 mg/100 g). PA concentrations in beans are high and tend to increase with iron biofortification. Short-term human isotope studies indicate that iron absorption from beans is low, PA is the major inhibitor, and bean PP play a minor role. Multiple composite meal studies indicate that decreasing the PA level in the biofortified varieties substantially increases iron absorption. Fractional iron absorption from composite meals was 4%–7% in iron deficient women; thus the consumption of 100 g biofortified beans/day would provide about 30%–50% of their daily iron requirement. Beans are a good vehicle for iron biofortification, and regular high consumption would be expected to help combat iron deficiency (ID).

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

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.

Leaching and efficiency of six organic zinc fertilizers applied to navy bean crop grown in a weakly acidic soil of Spain

Zinc contamination of groundwater from fertilizers applied to pulse crops is a potential problem, but the use of different types of organic chelates can minimize the contamination potential while still adequately feeding the crops. The objective of this study was to compare the leaching, distribution in fractions and availability, and relative effectiveness of Zn from six organic Zn fertilizers (zinc-ethylenediaminetetraacetate- N-2-hydroxyethylethylenediaminetriacetate (Zn-EDTA-HEDTA), Zn-HEDTA, zinc- S, S'-ethylenediaminedisuccinate (Zn- S, S-EDDS), zinc-polyhydroxyphenylcarboxylate, Zn-EDTA, and zinc-ethylenediaminedi(2-hydroxy-5-sulfophenylacetate) (Zn-EDDHSA)) applied to a navy bean ( Phaseolus vulgaris, L.) crop cultivated by applying different Zn levels, in a weakly acidic soil under greenhouse conditions. Zinc soil behavior was evaluated by diethylenetriaminepentaacetic acid-triethanolamine (DTPA-TEA), DTPA-ammonium bicarbonate (DTPA-AB), Mehlich-3, and BaCl 2 extractions and sequential fractionation. In all the fertilizer treatments, the percentage of labile Zn that remained in the soil was high with respect to the quantity of Zn applied, with values respectively ranging from 42 to 80% for Zn-EDDHSA and Zn-EDTA sources. A positive correlation with a high level of significance existed between the micronutrient concentration in the navy bean crop (total and soluble) and labile Zn fractions, available Zn, and easily leachable Zn ( r ranged from 0.89 to 0.95, P < 0.0001). The relatively high quantity of total Zn leached by applying Zn-EDTA and Zn-S,S-EDDS sources (11.9 and 6.0%, respectively, for the rate 10 mg of Zn kg(-1) of soil) poses a potential pollution risk for neighboring waters. It would seem recommendable to apply Zn-HEDTA or Zn-EDDHSA sources, even applied at the low rate (5 mg of Zn kg(-1) of soil), because they produced available Zn concentrations in the soil that were above the critical concentration and also produced high Zn concentrations in plants (139 and 106 mg of Zn kg(-1) of dry matter, respectively).