Alginate beads containing layered double hydroxide intercalated with borate: a potential slow-release boron fertilizer for application in sandy soils

Abstract

Boron (B) is very soluble and mobile in soil, and for this reason, it can be easily leached when applied as boric acid (H₃BO₃), particularly in sandy soils. High application rates of B may be toxic to plants. Alginate beads containing layered double hydroxides intercalated with borate (LDH-B-ALG) can potentially minimize the B leaching in soils and reduce the toxicity to plants. The aims of this work were to evaluate the leaching of B in sandy soils from different B sources such as H₃BO₃, Ulexite, and alginate beads containing H₃BO₃ (BA-ALG), and LDH-B-ALG, and investigate the bioavailability of B from these sources in consecutive cultivations of plants. The LDH-B-ALG was synthesized, characterized, and evaluated through the B leaching test in sandy soil. For the leaching column study, the B sources were homogenized with the soil, and incubated before leaching. Sunflower and cotton were cultivated for two seasons in a greenhouse experiment without leaching. Additionally, a greenhouse experiment with leaching was carried out, in which sunflower and cotton were sequentially cultivated after B leaching. In the leaching tests, throughout the incubation time, the percentage of B leached from LDH-B-ALG was significantly lower compared to other B commercial sources. In a greenhouse experiment with leaching, the residual concentration of B in the soil after first cultivation was 1.57, 0.73, 0.66, and 0.61 mg dm⁻³ of B for LDH-B-ALG, Ulexite, H₃BO₃, and BA-ALG treatments, respectively. The residual B in the soil was significantly higher for LDH-B-ALG compared to the other B sources after first cultivation, and, resulted in a higher B uptake in shoots and total (shoots and roots) for the cotton (second cultivation) and for the sum of sunflower and cotton (total cultivation). These results suggest that LDH-B-ALG can improve the B accumulation in topsoil, the fertilizer efficiency, and also B uptake by plants.