Effects of phosphate loaded LDH-biochar/hydrochar on maize dry matter and P uptake in a calcareous soil

Novel adsorbents that remove P from contaminated waters can be potentially used as slow release P-fertilizers. In this study, Mg-Al layered double hydroxide (Mg-Al-LDH) and Mg-Al-LDH functionalized apple wood biochar and hydrochar were prepared to remove phosphate from aqueous solutions and then P-loaded LDH-biochar/hydrochar composites used as fertilizers for maize production in calcareous soils under controlled conditions. After five successive desorption cycles, the LDH, LDH-biochar, and LDH-hydrochar desorbed 18, 22, and 27% of adsorbed-P into a 0.03 M KCl solution, respectively, while, these adsorbents desorbed 52, 63, and 66% of adsorbed-P into a 0.1 M Na₂CO₃ solution, respectively. Additionally, increasing solution pH from 3.0 to 10 increased P desorption. The results revealed that the P-loaded LDH-biochar and LDH-hydrochar significantly increased available-P, maize shoot and root dry matters, and P uptake as compared with control. The integration of monocalcium phosphate fertilizer with ‎biochar, hydrochar, LDH-biochar, and LDH-hydrochar increased available-P, ‎maize shoot and root dry matters, and P uptake; while P integration with P-loaded LDH-biochar/hydrochar decreased shoot dry matter. Therefore, the P-loaded LDH-biochar/hydrochar can be added to soil as P-fertilizers without any chemical P-fertilizer. Application of biochar, hydrochar, and LDH-biochar/hydrochar accompany with chemical P-fertilizers is recommended to increase available-P and maize growth.