Nitrate leaching from layered double hydroxides in tropical and temperate soils

We evaluate layered double hydroxide (LDH) as a potential alternative for nitrate slow release fertilizer. Synthesized Mg-Fe-NO3 LDH particles with Mg:Fe (2:1) were synthesized by coprecipitation and characterized by ICP-OES, XRD, FTIR and TGA analyses. Batch experiments with LDH particles containing 0.5, 0.1 or 0.01 M of KCl, K2SO4 or CaCl2 showed that 60 to 100% of intercalated nitrate is exchanged by anions within a few hours. Soil column studies with soils from temperate (Denmark) and tropical (Brazil) regions confirmed rapid release of nitrate from LDH. A reduction of 22% in nitrate leaching was the best result obtained for LDH applied to the Danish soils. The highest X-ray fluorescence spectroscopy (XRF) intensities of Fe and Mg were recorded at the top 0.5 cm of tropical soil columns, showing the high retention of LDH residues at soil surface. Application of LDH to a soil profile with bulk density of 1300 kgm(-3), 0.3 m rooting depth and a typical rate of field nitrogen application (120 kg ha(-1)) caused accumulation of 400 to 1050 kg Mg and 230 to 478 kg of Fe or Al depending on type of LDH. This high load of residual metals may restrain the use of the LDH as slow release nitrate source.