Composites of Biopolymers and ZnO NPs for Controlled Release of Zinc in Agricultural Soils and Timed Delivery for Maize


Zinc (Zn) micronutrient deficiency is a widespread problem affecting crops worldwide. Unlike conventional ionic fertilizers (Zn as salt or chelated forms), Zn-based engineered nanomaterials (ENMs) have the potential to release Zn in a controlled manner, reducing Zn losses through leaching upon application to soil. In this work, composites made of biopolymers (microcrystalline cellulose, chitosan, and alginate) and ZnO nanoparticles [NPs; 4-65% (w/w) Zn] were prepared. Their potential for Zn controlled release was tested in four agricultural soils of distinct pH and organic matter content over 30 days. While conventionally used Zn salts leached from the soil resulting in very low CaCl2-extractable Zn concentration, Zn in ZnO NPs was less labile, and ZnO biopolymers maintained a better constant supply of CaCl2-extractable Zn than all other treatments. ZnO NPs/alginate beads prepared by cross-linking with CaCl2 presented the slowest Zn release kinetics. As assessed with maize plants grown in poor Zn acidic soil (LUFA 2.1, pH 5.2), this constant Zn release from ZnO NPs/alginate beads resulted in a steadier Zn concentration in soil pore water over time. Results further indicated that ZnO NPs/alginate beads could meet the maize Zn needs while avoiding the early stage Zn toxicity induced by conventional Zn supplies, demonstrating that these ENMs are a sustainable way to supply Zn in a controlled manner in acidic soils. The impact of plant exudates on Zn bioavailability in the soil under maize-root influence (rhizosphere) is also discussed, underlying the need to study the fate of micronutrients in the rhizosphere to better predict its long-term bioavailability in bulk soils.




Science & Technology - Other Topics; Materials Science


Martins, NCT; Avellan, A; Rodrigues, S; Salvador, D; Rodrigues, SM; Trindade, T

nossos autores


Thanks are due to FCT/MCTES for the financial support to CESAM (UID/AMB/50017/2019), through national funds, and to cofunding by FEDER, within the PT2020 Partnership Agreement and Compete 2020, under Project NanoFertil (POCI-01-0145-FEDER-016749 and PTDC/AGR-PRO/6262/2014) for financial support. S.M.R. also acknowledges financial support from FCT (Project IF/01637/2013). T.T. and N.C.T.M. thank the CICECO-Aveiro Institute of Materials (FCT UID/CTM/50011/2019), financed by na-tional funds through the FCT/MEC and, when appropriate, cofinanced by FEDER under the PT2020 Partnership Agreement. N.C.T.M. is funded by national funds (OE), through FCT-Fundacao para a Ciencia e Tecnologia, I.P., in the scope of the framework contract foreseen in numbers 4-6 of article 23, of the Decree-Law 57/2016, of August 29, changed by the law 57/2017, of July 19.

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