Synthesis, characterization and agronomic use of alginate microspheres containing layered double hydroxides intercalated with borate

Abstract

Boron (B) is generally present in soil as boric acid (H₃BO₃), a non-ionized molecule with weak retention in the soil and very leachable. Boron leaching may occur especially when soluble sources are applied in sandy soils in high-rainfall environments. Slow release fertilizers are important for the management of B fertilization and to obtain a desirable residual effect. We produced and evaluated the performance of a new slow release fertilizer made from alginate microspheres containing magnesium–aluminum layered double hydroxide intercalated with borate (LDH-B-ALG). LDH-B-ALG microspheres and alginate microspheres containing H₃BO₃ (BA-ALG) were produced using the modified complex coacervation method. The fertilizers were characterized by X-ray diffraction, attenuated total reflectance Fourier transform infrared spectroscopy, and scanning electronic microscopy. The B release test and leaching in soil columns were performed for synthetized fertilizers, H₃BO₃, and Ulexite. A greenhouse experiment with two responsive species (sunflower and cotton) was carried out using a factorial 2 × (4 + 1) with two soil pH (6.5 and 7.5), four sources of B (LDH-B-ALG, BA-ALG, H₃BO₃, and Ulexite), and a treatment control, without the application of B. The chemical characterization of LDH-B-ALG showed that LDH (powder) was successfully incorporated into the alginate polymer. The B release and leaching were much lower from LDH-B-ALG compared to conventional B sources. LDH-B-ALG was solubilized into the soil similarly to the other B sources in the greenhouse experiment. The lower release and leaching from LDH-B-ALG improved the accumulation of B in the root zone, consequently increasing the fertilizer efficiency and plant's B uptake. The new fertilizer showed be a suitable source in high-rainfall areas, especially for sandy soils, supplying B in a more adjusted way and reducing leaching losses.