Layered double hydroxides intercalated with borate: effect of fertilization on boron leaching and successive sunflower cultivations

Abstract

Boron (B) can easily leach into the soil when added in the form of a soluble fertilizer such as borax or boric acid (H₃BO₃); however, large quantities of B can cause toxicity in plants. The use of a slow release source of B such as layered double hydroxides intercalated with borate may minimize leaching/toxicity of B. The objectives of this study are to evaluate the availability and leaching of B from magnesium–aluminium layered double hydroxides intercalated with borate anions (Mg₂Al-B-LDH) and H₃BO₃ in a sandy soil, and the B bioavailability of these two sources in consecutive cultivations of sunflower. Mg₂Al-B-LDH and H₃BO₃ at two rates (10 and 20 mg dm⁻³ of B) were incubated for 1, 2, 3, 5, 10, 20 and 40 days. After incubation, the soil B availability was evaluated using the hot-water extraction method. For the leaching study, 20 mg dm⁻³ of B from the two sources was incorporated into the top 0.5 cm of soil and incubated for 1, 5, 10, 15, 20, 25 and 30 days before leaching with water volume equivalent to the total soil-pore space. Sunflower plants were cultivated for two consecutive seasons in greenhouse using Mg₂Al-B-LDH and H₃BO₃ and six rates (0, 0.5, 1, 2, 3 and 5 mg dm⁻³) in a factorial 2 × 6, with four replicates. Plants received a single application of B before sowing at the first cultivation. H₃BO₃ had greater availability of B in the soil than Mg₂Al-B-LDH regardless of the applied rate or time of incubation. The slow release of B by Mg₂Al-B-LDH resulted in a significant reduction in B leached compared to H₃BO₃. There was a quadratic and linear response of sunflower aboveground biomass and B accumulation with increasing rates of H₃BO₃ and Mg₂Al-B-LDH, respectively, in the second cultivation only. A boron rate of 5 mg dm⁻³ applied as H₃BO₃ resulted in plant toxicity, while Mg₂Al-B-LDH promoted a slow release of B to the plants throughout the cultivation period.